Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session S1: Poster Session III (1:00pm - 4:00pm) |
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Sponsoring Units: APS Room: Hall D |
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S1.00001: POLYMERS AND SOFT MATTER II |
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S1.00002: Scaffolding of peptides using a coarse-grained representation of residues with side chain and backbone nodes Ras Pandey, Barry Farmer Monte Carlo simulations are performed to study scaffolding of peptides (KSL) on a cubic lattice. A residue is represented by three backbone nodes (C-terminal, C-alpha, N-terminal) and a side node connected to the central C-alpha node each connected by fluctuating bond. A peptide is a chain of residues. A solvent constituent is represented by a particle of the same size as that of a node. Peptides and solvent are distributed randomly in the cubic box with concentration $C_{p}$ and $C_{w}$ respectively. Each residue interacts with other residues and solvent particles via its side chain with the Lennard-Jones (LJ) potential where a knowledge-based interaction matrix is used for the residue-residue interaction. We examine local and global physical quantities such as mobility and energy of each residue, radial distribution function, and structure factor. We find that the scaffolding of peptides depends on the interaction strength and concentration of the solvent. The structure factor shows multi-scale structure of the aggregates. [Preview Abstract] |
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S1.00003: Ion tunable of rheology of supramolecular metallogels Nigel Clarke, Jonathan Steed, Marc-Oliver Piepenbrock A bis(pyridylurea) ligand forms metallogels in methanol in the presence of up to 0.5 equiv of copper(II) chloride. The addition of further copper(II) chloride gives an unusual crystalline 4:3 coordination polymer, whereas in the presence of 0.5 equiv of copper(II) nitrate, a 2:1 crystalline coordination polymer arises. The latter represents a possible model for supramolecular gelators and highlights key interactions with counteranions that suggest a means to tune gel properties using anion binding. The influence of chloride and acetate anions on the rheological properties of the copper(II) chloride metallogels are investigated [1]. The rheology of the anion-containing mixtures shows complex behavior with the gel structure evolving over time. We also observe shear-induced gelation [2], where vigorous shaking, rather than sonication, transforms a weak jelly like aggregate into a robust gel, exhibiting clear structural changes within the gel fibres. Reversible anion tuning allows these compounds to as responsive soft materials.\\[4pt] [1] Piepenbrock, M.M.; Clarke, N.; Steed, J.W.; Langmuir, 25, 8451, 2009.\\[0pt] [2] Piepenbrock, M.M.; Clarke, N.; Steed, J.W.; Soft Matter, 6, 3541, 2010. [Preview Abstract] |
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S1.00004: Amine-sulfonyl hydrogen bonding forms $\beta$-strand mimics Justin Barone, Katherine Harvey Ethyl vinyl sulfone (EVS)-substituted amino acids have the ability to form $\beta$-strand mimics that can then continue to aggregate into larger structures such as sheets. The $\beta$-strand forms from a sulfonyl-amine hydrogen bond. Here, we show that EVS-substituted lysine forms $\beta$-structures similar to protein $\beta$-structures as measured with x-ray diffraction. The $\beta$-structures can aggregate into macroscopic sheets with the ability to roll under the influence of the amino acid chirality. Microtubules form from sheets rolling left (L-lysine) or right (D-lysine). [Preview Abstract] |
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S1.00005: Relationship between Hydrophilicity of PEO-PPO-PEO Copolymers and Their Ability to Protect Liposomes from Peroxidation Jia-Yu Wang, Chi-Yuan Cheng, Song-I Han, Ka Yee Lee It is known that PEO-PPO-PEO triblock copolymers interact with lipid membranes but can have opposing effects on membrane integrity - they can behave either as membrane sealants or as permeabilizers depending on their architecture. To understand the origin of their biomedical functionality, interactions between PEO-PPO-PEO triblock copolymers and biomimetic phospholipid vesicles were investigated by evaluating the effect of hydrophilicity of the triblock copolymers on their ability to protect liposomes from oxidative stress, a stress source used to disrupt lipid vesicles. Our results show that while highly hydrophilic triblock copolymers exhibit no apparent insertion into lipid membranes, they are most effective in protecting liposomes from oxidation, indicating that the protective effect of triblock copolymers comes from their physical adsorption onto, rather than their insertion into the membrane. Gaining a better understanding of polymer-membrane interactions could lead to a better design of polymeric cell membrane sealants. [Preview Abstract] |
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S1.00006: The effect of ion beam sculpted nanopore size and shape on DNA translocation Ryan Rollings, Edward Graef, Denis Tita, Santoshi Nandivada, Mourad Benemara, Jiali Li Solid state nanopore based devices can sense single biomolecules in their native environment. Nanopore thickness plays a crucial role in the signal to noise ratio of current blockades caused by biomolecule translocation and ultimately limits the spatial resolution of the nanopore device when discriminating small features on DNA and protein molecules. Low energy ion beam irradiation can create nanometer size pores in very thin membranes 10-20 nm thick, but to date ion beam sculpted nanopores have shown current blockades smaller than predicted from pores of this thickness. We use electron energy loss spectroscopy and energy filtered transmission electron microscopy to study ion beam sculpted nanopore geometry in detail and determine its effect on conductance blockades and I-V curves. Current blockades from pores thinned by chemical etching and ion beam sputtering will also be presented. [Preview Abstract] |
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S1.00007: Detection of SPM tip-attached DNA molecules with solid state nanopores Changbae Hyun, Zhexue Lu, Bradley Ledden, Jiali Li Using an apparatus that combines solid-state nanopores with a scanning probe~microscope (SPM), we studied ionic current reduction due to the SPM tip. The experiment was performed at different KCl concentrations, SPM tip probing heights, and several bias voltages. The same experiment was also performed with DNA molecules attached to the SPM tip. The current blockage signal through solid-state nanopores with and without luDNA molecules attached to the SPM tip was analyzed. We also present the current blockage and electrical field profile simulation using finite element analysis software (Multiphysics, COMSOL Inc). [Preview Abstract] |
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S1.00008: Micro-phase assembly of active sites in a coarse-grained model of chromatin by Monte Carlo simulation Yang Zhang, Dieter Heermann, Barry Farmer, Ras Pandey A coarse-grained model is used to study the self-assembly of active sites in a DNA (chromatin) chain. The chromosome is described by a bond-fluctuating chain of two types of nodes A (interacting) and B (non-interacting), distributed randomly with concentration $C$ and $1-C$ respectively. Active nodes interact with a Lennard-Jones (\textit{LJ}) potential and execute their stochastic motion with the Metropolis algorithm. The depth of the \textit{LJ} potential ($f)$, a measure of interaction strength and the concentration ($C)$ of the active sites are varied. A number of local and global physical quantities are studied such as mobility ($M_{n})$ profile of each node, their local structural profile, root mean square (RMS) displacement ($R)$, radius of gyration ($R_{g})$, and structure factor $S(q)$. We find that the chain segments assemble into microphase of blobs which requires higher concentration of active sites at weaker interaction. These findings are consistent with that of a dynamic loop model of chromatin on global (large) scale but differ at small scales. [Preview Abstract] |
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S1.00009: Single-molecule studies of DNA self-diffusion in entangled linear and circular DNA blends Cole D. Chapman, Michael Harlander-Locke, Douglas E. Smith, Rae M. Robertson-Anderson Here, we use single-molecule fluorescence and particle-tracking to measure self-diffusion coefficients of single DNA molecules in varying blends of entangled linear and circular DNA. We have previously shown that the self-diffusion of entangled circular and linear DNA differ from each other and are strongly dependent on the topology of the background DNA. This phenomenon can be attributed in part to the tendency of linear polymers to thread their circular counterparts, leading to constraint release, as well as reptation. Previous rheological studies have shown a complex relationship between the ratio of linear to circular polymers and viscosity, however, conflicting results have been reported and the molecular dynamics that lead to this behavior remain unclear. Using single-molecule methods, we can directly measure self-diffusion coefficients for individual DNA molecules within concentrated solutions of linear and circular DNA, and thus determine for both topologies the dependence of self-diffusion on: the ratio of linear and circular species, the overall solution concentration, and the molecular length. [Preview Abstract] |
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S1.00010: Dual-Function Epi-fluorescence Optical Tweezers to Characterize Single Polymer Interactions in Complex Polymeric Fluids Kent Lee, Cole D. Chapman, Rae M. Robertson-Anderson Intermolecular interactions within entangled polymeric fluids are highly complex and not well understood. Previously, we investigated these interactions on a single-molecule level by using optical tweezers and fluorescence microscopy to measure interaction forces between DNA molecules and self-diffusion of DNA, respectively. To better characterize these interactions, we have developed an epi-fluorescence optical tweezers which combines an epi-fluorescence microscope with a dual-trap, force-measuring optical tweezers. One of the optical traps is moveable enabling different DNA lengths to be stretched across the two traps. Forces on both traps are measured allowing us to probe the force exerted on a trapped DNA molecule by surrounding entangling DNA. Fluorescence capabilities allow us to directly visualize polymer interactions and dynamics while take force measurements. By fluorescently-labeling either the trapped DNA or a select number of surrounding DNA, we can determine both the conformational changes that the measured force induces on the DNA as well as the various molecular configurations that produce each force. These studies will provide a much needed link between single-molecule dynamics and conformations and intermolecular forces in complex polymeric fluids. [Preview Abstract] |
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S1.00011: Dynamics of a linear polymer in a microchannel creeping flow Prasenjit Bose, Miron Kaufman, Petru Fodor An understanding of the dynamics of a polymer in a microchannel could be used to design the technology for high throughput molecular analysis and manipulation. We simulate the motion of a linear polymer advected by a fluid in a rectangular microchannel. We consider the creeping laminar flow, i. e. zero Reynolds number. The model polymer is made up of beads connected by elastic springs. The dynamics of this nonlinear mechanical system is studied as a function of model parameters: the spring equilibrium distance, the mass of a bead, and the spring constant. [Preview Abstract] |
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S1.00012: Glassy dynamics in thin layers of polystyrene and polyisoprene Emmanuel Urandu Mapesa, Martin Tress, Friedrich Kremer Broadband Dielectric Spectroscopy (BDS), Spectroscopic vis-Ellipsometry (SE), X-Ray Reflectometry (XRR), Alternating (ACC) and Differential Scanning Calorimetry (DSC) are combined to study glassy dynamics and the glass transition temperature in nanometric thin ($\ge $5 nm) layers of polystyrene (PS) having widely varying molecular weights (27,500 to 8,090,000 g/mol). For the dielectric measurements two sample geometries are employed, the common technique (capped) using evaporated electrodes and a recently developed approach (uncapped) taking advantage of highly-insulating silica nanostructures as spacers. \textit{All} applied methods deliver the concurring result that deviations from glassy dynamics and from the glass transition temperature of the bulk never exceed margins of $\pm $3K \textit{independent} of the layer thickness and the molecular weight, indicating that the length scale of interfacial interaction is restricted to less than 5 nm. We also show preliminary BDS results where thin layers of cis-1,4-polyisoprene (PI) are measured in both geometries; there are indications that the confinement-induced mode is absent when the layers are uncapped. [Preview Abstract] |
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S1.00013: Dynamics of Silica Particles Grafted with Polymer Brush in Polystyrene Matrix Taiki Hoshino, Moriya Kikuchi, Daiki Murakami, Koji Mitamura, Yoshiko Harada, Kiminori Ito, Yoshihito Tanaka, Sono Sasaki, Masaki Takata, Atsushi Takahara Nanoparticles (NPs) in soft materials near the glass transition temperature sometimes show fast diffusive behavior, called hyperdiffusion. In this study the dynamics of polystyrene (PS)- grafted silica NPs in PS matrix have been investigated by X-ray photon correlation spectroscopy (XPCS). XPCS system was setup at 27-m-long undulator beamline BL19LXU, SPring-8 (Japan). Detectors, a direct-illuminated CCD camera with a pixel size of 20$\times$20 $\mu$m$^2$ and a two-dimensional hybrid pixel array detector PILATUS, whose pixels were covered with a mask with $\sim$50 $\mu$m diameter holes for enhancement of the spatial resolution, were located about 3.2 m downstream of the sample. By XPCS measurements, autocorrelation functions, expressed by $g (q,t)=\exp(-2({\Gamma}t)^\beta)+1$ were obtained. At much higher temperature than the glass transition of PS matrix, g(q,t) with $\beta\leq1$ were observed, but at decreased temperature, $beta>1 $ were observed. These behaviors can originate from hyperdiffusion. The detail of the measurements and the results will be presented. [Preview Abstract] |
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S1.00014: New methods to characterize the confinement effects in epoxy nanocomposites Liyun Ren, Michael Goodman, Rahmi Ozisik Properties of epoxy can be improved/controlled via the addition of nanofillers. However, use of nanofillers leads to confinement and interfacial effects and the exact nature of these two effects on the properties are not yet clearly understood. In this study, the glass transition temperature of epoxy nanocomposites was investigated. The changes in the glass transition temperature were analyzed as a function of nanofiller content (confinement) and epoxy-nanofiller interface. In addition to these, the distribution and dispersion of nanoparticles also influences the properties. We applied two different methods to characterize the interparticle distance and compare the dependence of glass transition temperature on the nanofiller content and interparticle spacing. We found that our model provides a new understanding of the effect of interparticle spacing on glass transition phenomenon in polymeric nanocomposites. [Preview Abstract] |
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S1.00015: Defect structures and coarsening in spherical shells of asymetric block copolymer systems Nicol\'as Garc\'Ia, Leopoldo R. G\'omez, Aldo D. Pezzutti, Daniel A. Vega, Marcelo A. Villar We use a Brazovskii model to numerically investigate the defect structures and coarsening process of spherical shells of asymmetric block copolymers. It was found that the configurations of defects are dictated by the ratio between the radius of the spherical shell and the average lattice constant. For small system sizes most configurations of defects are in good agreement with the results for the Thomson problem and simply exhibit 12 well ordered disclinations. As the size of the system increases, in addition to the 12 disclinations the structure of defects is characterized by a varying number of dislocations arranged in grain boundary scars. [Preview Abstract] |
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S1.00016: Nanoconfinement Effect on Polymerization Maitri Vaddey, Sindee Simon Ring-opening metathesis polymerization of endo-dicyclopentadidene (DCPD) with second generation Grubbs catalyst is carried out under nanoscale constraint. Differential scanning calorimetry is used to study the polymerization reaction both in the bulk and in the nanopores of controlled pore glass as a function of heating rate; the Tg of the resulting reaction product is also determined. In 110 nm-diameter pores, DCPD undergoes incomplete polymerization followed by the reverse Diels-Alder reaction to form pentadiene. Decreasing the heating rate shifts both reactions towards lower temperatures but does not avert the side reaction. In the bulk unconfined case, the reverse Diels-Alder reaction only occurs in the absence of catalyst. The glass transition temperature of the nanoconfined polymerization product is 164 \r{ }C, approximately 20 \r{ }C higher than the polymer prepared under bulk conditions. Reaction kinetics in bulk and nanoconfined cases will also be discussed. [Preview Abstract] |
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S1.00017: Molecular Dynamics Simulations of Grafted Layers of Bottle-Brush Polyelectrolytes Daniel Russano, Jan-Michael Carrillo, Andrey Dobrynin Using molecular dynamics simulations, we study the effect of the brush grafting density and degree of polymerization of the side chains on conformations of brush layers made of charged bottle-brush macromolecules. The thickness of the brush layer first decreases with increasing brush grafting density; then, it saturates and remains constant in the wide interval of the brush grafting densities. The brush layers consisting of the bottle-brush macromolecules with longer side chains have a larger layer thickness. The elongation of the side chains of the bottle-brush macromolecules decreases with increasing brush grafting density. This contraction of the side chains is due to counterion condensation inside the volume occupied by bottle-brushes. Our simulations showed that counterion condensation is a multiscale process reflecting different symmetries of the bottle-brush layer. [Preview Abstract] |
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S1.00018: Influence of Ionic Strength on Chain Dimension in Polyelectrolyte Brushes at Aqueous Solution Interface Koji Mitamura, Motoyasu Kobayashi, Mayumi Terada, Norifumi L. Yamada, Atsushi Takahara Polyelectrolyte brush on a solid surface in water generally has a swollen structure and provides high lubricity on the surface. Previously, we have reported that friction force on a cationic poly(2-(methacryloyloxy)ethyltrimethyl-ammonium chloride) (PMTAC) brush in an aqueous medium increased with NaCl concentration, of which reason was not clear but probably due to a shrinkage of the swollen brush with the addition of salt. In this study, we investigated the salt concentration dependency of the chain dimension in PMTAC brush at the aqueous solution interfaces by neutron reflectometry. We also estimated how polydispersity in molecular weight of the brush influences the chain dimension. [Preview Abstract] |
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S1.00019: Densely grafted brushes of gradient copolymers: an effective Flory-Huggins parameter approach Sergey Venev, Igor Potemkin Manufacturing of gradient copolymers becomes cheaper and easier nowadays. There is a wide spectrum of experimental applications for such polymers. In this work, densely grafted gradient copolymer (monomers distribution function $g(n)$ along the chain is assumed to be a power law) brushes in a selective solvent are considered. Equilibrium thermodynamic properties of the system are investigated within the frames of a simple mean-field approach and an effective Flory-Huggins parameter $\chi_{eff}(n)$ approximation. Constructed profiles for polymer concentration demonstrate non-linear behavior, however the brush thickness varies in direct proportion to the molecular weight of copolymer. Coil-Globule transition properties in such a system are investigated as well. [Preview Abstract] |
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S1.00020: Fast Lattice Monte Carlo Simulations of Inhomogeneous Polymers Qiang Wang, Pengfei Zhang, Xinghua Zhang, Delian Yang, Baohui Li Fast lattice Monte Carlo (FLMC) simulation with multiple occupancy of lattice sites and Kronecker $\delta$-function interactions gives orders of magnitude faster/better sampling of the configurational space of multi-chain systems than conventional lattice MC simulations with self- and mutual- avoiding walks and nearest-neighbor interactions.\footnote{Q. Wang, \textbf{Soft Matter, 5}, 4564 (2009).} It also enables direct comparisons with the corresponding polymer field theories based on the same Hamiltonian (thus without any parameter-fitting) to unambiguously and quantitatively reveal the effects of fluctuations and correlations neglected or treated only approximately in the theories. Here we present our FLMC simulations of inhomogeneous polymeric systems including grafted and confined polymers, as well as the comparisons with lattice self-consistent field theory and Gaussian fluctuation theory to quantitatively reveal the consequences of approximations in these theories. [Preview Abstract] |
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S1.00021: Structure and Swelling Behavior of Weak Polyelectrolyte Brushes Chaitra Deodhar, Erick Soto-Cantu, David Uhrig, John Ankner, S. Michael Kilbey II In this work we describe the structure and swelling behavior of polyelectrolyte brushes consisting of poly(methacrylic acid) (PMAA) homopolymer brushes and random copolymer brushes made by a surface initiated copolymerization to create poly(MAA-co-2-hydroxyethyl methacrylate) brushes P(MAA-co-HEMA). To create dense polyelectrolyte brushes and alleviate problems with polymerization of the reactive electrolytic form of the monomer MAA, these brushes were made by chemical conversion of neutral, precursor brushes comprised of t-butyl methacrylate (tBMA). Neutron reflectivity (NR) was used to investigate the chemical conversion to ``deprotected'' form. Insight into the swelling behavior of PtBMA and PMAA brushes was obtained by ellipsometry and neutron reflectometry measurements. The responsive behavior of PMAA-containing brushes in different pH environments is evident from in situ ellipsometry and neutron reflectometry measurements, which in particular show significant sensitivity to the amount of water present in the layer as pH is changed. Current efforts to manipulate responsiveness through copolymerization to make P(MAA-co-HEMA) brushes will also be described. [Preview Abstract] |
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S1.00022: Molecular dynamics simulations of interactions and friction between bottle-brush layers Daniel Russano, Jan-Michael Carrillo, Andrey Dobrynin Experiments on tethered polyelectrolyte bottle-brush-like macromolecules consisting of glycoproteins display fascinatingly low friction properties of biological tissues such as cartilage. To understand the role of the electrostatic interactions in lubricating properties of brush layers we have performed MD simulations of charged and neutral bottle-brush macromolecules tethered to substrates. In the case of charged bottle-brush layers the compression force per unit area $F$ between two brush layers in salt-free solutions increases with decreasing the distance $D$ between substrates as $F\propto D^{-2}$. A stronger dependence of the compression force $F$ on the surface separation $D$ was observed for neutral bottle-brushes, $F\propto D^{-4.7}$, in the same interval of compression forces. This strong dependence of the compression force $F$ on the distance $D$ is due to excluded volume interactions between monomers belonging to two overlapping bottle-brush layers. The weaker dependence observed in polyelectrolyte bottle-brushes is due to interaction between counterion clouds surrounding the bottle-brush layers. The charged bottle-brush layers have lower friction coefficient than neutral layers at the same interval of the compression and shear forces. [Preview Abstract] |
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S1.00023: Surface Dynamics of Partially Tethered Polymer Films Jin Kuk Lee, Bulent Akgun, Zhang Jiang, Suresh Narayanan, Sushil Satija, Mark D. Foster The surface dynamics of ``partially tethered'' thin films have been studied using X-ray photon correlation spectroscopy (XPCS). Polystyrene (PS) chains have been grafted to substrates with low grafting densities, untethered deuterated PS (dPS) chains spun cast on the tethered chains and the films annealed to create layers containing both tethered and untethered chains. The extent of mixing between the tethered PS and untethered dPS chains has been measured by neutron reflectivity. The relaxation of surface height fluctuations for these films depends on the density of grafting, molecular weight of tethered chains, and extent to which tethered chains extend into the layer. When the tethered chains are able to stretch to the top surface, the relaxation time is slowed most remarkably. [Preview Abstract] |
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S1.00024: A mechanistic study of a thermo-responsive polymer in a liquid crystal solvent Timothy Bunning, Michael Mcconney, Jennifer Hurtubise, Vincent Tondiglia, Timothy White Thermo-responsive polymers are highly promising for a variety of applications including tailored drug release, gene delivery, and chromatography. Typical swelling/de-swelling polymer phase transitions involve isotropic liquids and disordered polymers. Here, we present a unique swelling/de-swelling polymer transition involving structured polymers and ordered liquids crystals. The polymers in this study have a degree of order that is imparted by polymerizing in the presence of a liquid crystal. The study focuses on helicoidal structured polymers templated by cholesteric liquid crystals because the optical properties are a simple indicator of the material structure properties. The mechanism of the swelling/de-swelling transition of this unique system were studied with differential scanning calorimetry, polarized optical microscopy, white light interferometery and visible/near-infrared spectroscopy. Differences in the dynamic optical changes with polymer structure are explored. [Preview Abstract] |
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S1.00025: Formation of Liquid Crystal Elastomer Microparticles Chanjoong Kim, Huan Yan, Souptik Mukherjee, Paul Luchette, Peter Palffy-Muhoray Liquid crystal elastomer (LCE) combines the properties of rubber elasticity and anisotropic properties of liquid crystalline materials. In particular, LCE has a potential to exhibit interesting properties like electric polarization, ferroelectricity and piezo-electricity. Thin films, fibers and even balloons of LCE using techniques such as spin coating, electro-spinning and in cells have been reported by many groups before. Using microfluidics technique followed by photo-polymerization, we produce uniform spherical LCE microspheres with diameter of 20 - 85 $\mu m$. Compression of the LCE microspheres generates a characteristic director configuration. The elastomers may also reveal interesting magnetic and electrical properties due to the intrinsically anisotropic nature of liquid crystalline materials. [Preview Abstract] |
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S1.00026: Coupling of Smectic Liquid Crystalline Order of iPP to Carbon Nanotube Alignment under Melt-Shear Georgi Georgiev, Robert Judith, Erin Gombos, Michael McIntyre, Peggy Cebe Carbon nanotubes (CNTs) exhibit liquid crystalline order and their nematic director couples to the one of low molecular weight liquid crystals. Here we explore the interactions between CNTs and the smectic liquid crystal phase of a polymer and the possibility for a similar coupling in this system. The pure iPP and iPP/CNT films were sheared in the melt state at 200\r{ }C and 1Hz. The sheared samples were analyzed using~polarized optical microscopy, Two Dimensional Microscopic Transmission Ellipsometry (2D-MTE) and Two Dimensional Wide Angle X-Ray Scattering (2D-WAXS). During shearing we detected a sudden increase of birefringence at 151\r{ }C in the samples, higher than the iPP crystallization temperature, indicating liquid crystalline ordering. We measured anisotropic 2D-WAXS patterns of the samples that contained CNTs, indicating strong ordering of the crystals. Our results indicate that CNTs couple to the smectic phase of iPP, improve its order upon shearing and the crystals created after the formation of the oriented smectic phase are strongly aligned parallel to the direction of shearing. [Preview Abstract] |
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S1.00027: Magnetic fields for the long-range ordering of amphiphilic block copolymers and surfactant mesophases Pawel Majewski, Manesh Gopinadhan, Chinedum Osuji We present a diamagnetic interactions-based approach to impose long range order in self-assembled soft materials. We discuss two chemically different systems which have been successfully aligned with the use of a magnetic field. The orientation and the degree of alignment are quantified by small-angle X-ray scattering, polarized optical microscopy and electrical impedance spectroscopy. We focus on Li ion-conducting liquid crystalline diblock copolymers. Our technique allows us to control the orientation of hexagonally packed PEO channels within a non-conducting liquid crystalline matrix that is responsive to the field. The electrical conductivity of the cylindrical samples with PEO domains aligned perpendicular to electrodes is an order of magnitude greater than for samples featuring randomly orientated domains. Our second system consists of non-ionic surfactants forming lamellar or cylindrical mesophase in water. The method which we term ``rotational annealing'', is successfully used to obtain highly ordered mesophases which can be further utilized as a template for nanomaterials synthesis. [Preview Abstract] |
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S1.00028: Morphology and Proton Conductivity of Ionic Liquid Containing Sulfonated Block Copolymers Sung Yeon Kim, Moon Jeong Park Proton exchange membrane fuel cells (PEMFC) offer the prospect of supplying clean electrical power for a wide variety of systems such as portable electronic devices and vehicles. Although, significant effort has been devoted to improvement of the transport properties of PEMs which is operated relatively lower temperature below 80$^{\circ}$C, it suffers from a CO poisoning at Pt catalysis, complexity of water and heat management in the system. Herein, we report unique block copolymer electrolyte membrane systems containing ionic liquid. Due to the nonvolatile property of ionic liquid the systems exhibit effective proton transport above 100$^{\circ}$C without humidification. In present study, sulfonated block copolymers, i.e., poly(styrenesulfonate-b-methylbuthylene) (SnMBm), are utilized for matrix materials by varying the ion contents and molecular weight. Imidazolium based ionic liquids are selectively incorporated into polystyrenesulfonate phases, which results in various morphological transitions as a function of the amount of the ionic liquid. The effect of counter ions on the observed morphologies is significant yielding concurrently different values of conductivity. Small angle x-ray scattering and transmission electron microscopy have been employed to determine various morphologies of the ionic liquid containing sulfonated block copolymer membranes and impedance spectroscopy is used for the conductivity measurements. [Preview Abstract] |
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S1.00029: The Role of Neutralizing Ion Type on the Dynamics of Sulfonated Polystyrene Ionomers Alicia Castagna, Wenqin Wang, Karen I. Winey, James Runt Sulfonated polystyrene (SPS) ionomers neutralized with Na, Cs, and Zn were investigated using scanning transmission electron microscopy (STEM), X-ray scattering, and dielectric relaxation spectroscopy. The role of the neutralizing ion on the structure and molecular dynamics will be discussed as a function of sulfonation level. STEM and X-ray scattering revealed the presence of spherical aggregates 2 nm in diameter. Successful fitting of the scattering data to the Kinning-Thomas modified hardsphere model provides additional information on aggregate size, number density and radius of closest approach. The dynamics of these materials, as revealed by DRS, are highly sensitive to the neutralizing ion, in particular, the character of the segmental relaxation, i.e. relaxation time, breadth and number of relaxations. Additionally, the relaxation time of the Maxwell-Wagner-Sillars interfacial polarization process at high temperatures is also highly dependent on neutralization and ion character. [Preview Abstract] |
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S1.00030: Mixed-salts effect on the ionic conductivity of PEO-containing block copolymers Wen-Shiue Young, Allen Schantz, Thomas Epps Salt-doped poly(ethylene oxide)-based block copolymers have attracted significant interest, as nanoscale ordered structures offer ideal platforms for the design of electrolytes for lithium battery membranes. However, the room temperature conductivities of these polymer electrolyte membranes are too low for many applications due to the crystallization of the PEO or the PEO:salt complex. In this study, a mixed-salt system, LiClO$_{4}$/LiTFSI, was adopted to decrease the crystallinity of PEO:salt complex and improve the relative conductivity at room temperature. Small-angle X-ray scattering and transmission electron microscopy were used to determine the microstructures of the copolymer electrolytes, while differential scanning calorimetry and AC impedance studies were used to examine the crystallinities of PEO:salt complexes and ionic conductivities of electrolyte membranes. Our results show that the 50{\%}-50{\%} LiClO$_{4}$/LiTFSI-doped PS-PEO with [EO]:[Li]=6:1 has no crystalline phase above room temperature and exhibits a higher conductivity than corresponding LiClO$_{4}$-doped and LiTFSI-doped PS-PEOs at low temperatures. [Preview Abstract] |
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S1.00031: Time Scales of Ion Transport in Imidazolium-based Polymers U. Hyeok Choi, Yuesheng Ye, Minjae Lee, Harry Gibson, Yossef Elabd, James Runt, Ralph Colby We synthesize and characterize ionic polymers with imidazolium cations covalently attached to the polymer chain and various ionic liquid counterions for ionic actuators. The imidazolium cations are attached to the polymers with flexible alkyl spacer chains and also have a variety of alkyl and alkyl ether termini. The anionic counterions are also varied; tetrafluoroborate (BF$_{4})$, hexafluorophosphate (PF$_{6})$ and bis(trifluoromethanesulfonyl)imide (TFSI) were mainly used in this study. Dielectric relaxation spectroscopy (DRS) is utilized to measure the dielectric constant and conductivity, as a function of temperature. The 1953 Macdonald model is applied to estimate the number density of conducting ions and their mobility, from electrode polarization at low frequencies in DRS. The 1988 Dyre model is used to determine ion hopping times from the frequency-dependent conductivity at higher frequencies. The consequence of polymer structural variations will be elucidated for these vital characteristics. [Preview Abstract] |
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S1.00032: Ionic Aggregation and Microphase Separation in Sulfonated Polyester Multiblock Copolymers and Ionomers Michael O'Reilly, Gregory Tudryn, Ralph Colby, Karen Winey Polyethylene oxide (PEO) has been copolymerized with polytetramethylene oxide (PTMO) using a sulfonated phthalate ionic linker between blocks. The product is a linear multiblock copolymer, which is neutralized with lithium and sodium. We used X-ray scattering to investigate the morphology from 25\r{ }C to 200\r{ }C. The results show that this copolymer exhibits three distinct morphology characteristics. First, microphase separation exists between the PEO and PTMO phases. Second, ionic aggregates occur in the PEO microdomains. Finally, the appearance of better defined ionic aggregates occurs in the PTMO microdomains. Ion aggregation and microphase separation are studied as functions of temperature and copolymer molar composition. DRS analysis confirms that ionic aggregation is independent of copolymer composition. [Preview Abstract] |
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S1.00033: Ion Conduction in Perfectly Aligned Block Copolymer-Ionic Liquid Mixtures Jae-Hong Choi, Yossef A. Elabd, Karen I. Winey Our earlier work to correlate the transport measurements in diblock copolymer-ionic liquid mixtures was limited by our bulk samples that have only partial alignment. Here, thin films with perfect alignment of lamellar microdomains from mixtures of a poly(methyl methacrylate-$b$-styrene) diblock copolymer and an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, have been studied. The morphologies will be characterized by cross-sectional transmission electron microscopy. Ion conduction will be presented within and through the thin film. [Preview Abstract] |
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S1.00034: Modification of Aqueous Peptide-based Block Copolymer Morphologies through Addition of Ionic Liquid Ashley Johnson, Jacob Ray, Sandeep Naik, Laura Bullock, Daniel Savin The self assembly of block copolymers in aqueous solution is a synthetically tunable behavior. Varying composition and the size of the block lengths, a range of morphological structures can be obtained each having diverse characteristics. Polypeptide blocks incorporate pH responsiveness due in part to the helix-coil transition. In these studies, we use light scattering to explore the morphology and pH responsiveness of PPO-P(Lys) diblock and triblock copolymers. While these materials have limited solubility for pH$>$8, the addition of a small amount of ionic liquid extends the phase range to pH above 10. Similar behavior is observed in Pluronic copolymers, which are solubilized in the presence of ionic liquid. Through use of dynamic light scattering (DLS), transmission electron microscopy (TEM), circular dichroism (CD), and Fourier Transform IR (FTIR), we seek to obtain a molecular-level understanding of the peptide interactions in water/ionic liquid solutions and how this translates to pH responsiveness. [Preview Abstract] |
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S1.00035: Phase behavior of the blend of rod-coil block copolymer with the corresponding coil homopolymer Chia-Sheng Lai, Chun-Chih Ho, Wei-Fang su, Hsin-Lung Chen We investigated the self-assembly behavior of the blends of a rod-coil block copolymer DEH-PPV-$b$-PMMA with the PMMA homopolymers (h-PMMA) with various molecular weights to clarify how the rigidity and self-organization of the rod block would affect the morphologies and the phase behavior comparing with those of coil-coil block copolymer blending. SAXS/WAXS along with TEM were used to reveal the nanostructure in detail. In the case of the blends with h-PMMA with lower molecular weight, the morphology was strongly dependent on the interplay between microphase separation and nematic interaction. The h-PMMA tended to localize into the middle of PMMA nanodomain and formed a lamellar structure irrespective of the volume fraction of h-PMMA. At high volume fraction of h-PMMA, a sponge phase was found to coexist with the lamellar structure. The interdomain spacing increased with the overall PMMA content. Macrophase separations became dominate in the blends with h-PMMA of high molecular weight. WAXS studies of the blends indicated the amorphous h-PMMA reduced the correlation of the rod-rod ordered packing. Upon heating, the lamellar structure transformed into a disordered state, and the T$_{ODT}$ was found to be reduced by adding h-PMMA with lower molecular weight. [Preview Abstract] |
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S1.00036: Threaded molecular wires as building blocks for advanced polymer blends: WPLEDs, ultra-broadband optical amplifiers, multi color lasers Sergio Brovelli, Marta Mroz, Giuseppe Sforazzini, Tersilla Virgili, Franco Meinardi, Alberto Paleari, Harry L. Anderson, Guglielmo Lanzani, Franco Cacialli The ability to produce semiconducting polymer blends with white emission spectra, large emission cross sections and broad optical gain is critical to their application in white PLEDs, lasers and broadband amplifiers. Cyclodextrin-encapsulation is an effective means of suppressing detrimental intermolecular interactions, and energy transfer (ET) channels in polymer blends, thus enabling fabrication of white-PLEDs. We show that all such properties combine into a high impact photonic application: ultra-broad optical gain and two-color lasing in a binary polyrotaxane blend. We study the ultrafast photophysics of a blend of a conventional and an encapsulated polyfluorene. The morphology is investigated by microRaman imaging, AFM, and fluorescence lifetime microscopy. We ascribe the ultra-broad optical gain ($>$850 meV), and the simultaneous ASE for both constituents, to the dual effect of reduced polaron formation and suppressed ET. Our results demonstrate that polyrotaxanes could realistically represent the building blocks for advanced polymer blends with highly controlled optical properties, for applications in solid state lightning, lasers and photovoltaic technologies. [Preview Abstract] |
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S1.00037: Measurements of Thermally Stimulated Luminescence in Gamma-Irradiated Ultra-High Molecular Weight Polyethylene in the Presence of Vitamin E Dereje Abdi, Muhammed Jahan, Benjamin Walters Thermally stimulated luminescence (TSL) was detected in medical grade ultra-high molecular weight polyethylene (UHMWPE) GUR 1020 (Ticona) after gamma irradiation at room temperature (22$^{\circ}$C) in air or nitrogen and subsequent heating from 22$^{\circ}$C to 399$^{\circ}$C using a commercial TSL apparatus (Thermec). A typical TSL glow curve exhibits two major glow peaks near 116$^{\circ}$C and 200$^{\circ}$C with a weak shoulder near 250$^{\circ}$C. Additional glow peak is observed near 140$^{\circ}$C in GUR 1020E (UHMWPE containing 0.1{\%} vitamin E (alpha-tocopherol ($\alpha $-T)). Full-width-at-half-max (FWHM) and activation energy for each peak were found as follows. 116$^{\circ}$C: 40$^{\circ}$C, 1.2 eV; 140$^{\circ}$C: 40$^{\circ}$C, 1.3 eV; 200$^{\circ}$C: 64$^{\circ}$C, 1.0 eV; 250$^{\circ}$C: 56$^{\circ}$C, 1.5 eV. The glow peaks seem to follow a kinetic order of 1.5. While the 116-$^{\circ}$C glow is produced in all irradiated samples, the 200$^{\circ}$- and 250-$^{\circ}$C peaks are produced when irradiation is performed in air, suggesting that these latter glow peaks are associated with the oxygen-centered species and the former (at 116$^{\circ}$C) with polyethylene (PE) radicals. The 140-$^{\circ}$C peak could result from thermal breakdown of vitamin E radical ($\alpha $-T-O*). Irradiation dose, 30, 65 or 100 kGy, simply changes the TSL intensity without affecting the TSL characteristic. Vitamin E, which is used as an antioxidant, does not seem to affect the TSL in UHMWPE. [Preview Abstract] |
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S1.00038: Confocal Raman Microscopy on in-situ Structural Evolution of Polyolefin Blends Wansoo Chang, Byungho Jeon, Jong-Won Lee, Chang Y. Ryu Polyolefins account for more than half of world-wide consumption of plastic materials, and are typically blended with fillers and other types of polymers in applications. In particular, understanding the miscibility and phase behaviors of polyolefin blends is important for the advancement of a wide array of new applications in medicine, packaging, and other fields. We have used Confocal Raman Microscopy to take the advantages of it capability to locally probe the transformation of physical states in polymeric materials and to characterize morphology of polyolefin blends in-situ for lateral and in-depth imaging with a micron-scale spatial resolution. Upon distinct changes of Raman spectra associated with the melting of semicrystaline polyolefins, we report the in-situ morphological changes upon heating and cooling of polyethylene-polyethylene and polypropylene-polyethylene using confocal Raman microscopy with heating stage. [Preview Abstract] |
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S1.00039: Polymer Blends for Proton Exchange Membranes Tina Lovato, Kelly McNabb, Jason Meyers, Gaber Rupnik, Qian Ma, Meng Zhao, Jingjing Pan, Joel Walker, Thomas Smith, Peggy Cebe In the present research, the crystal structure of PVDF in semicrystalline composite films composed of poly(vinylidene fluoride) (PVDF) and poly[4(5)-vinylimidazole/vinylimidazolium trifluoro-methyl-sulfonyl-imide] (PVIm/VIm$^+$ TFSI$^-$ ) were studied.~ In these composites, conditions such as choice of solvent, drying conditions, and thermal treatment can affect the crystal phase, crystallite size and degree of crystallinity of PVDF as well as the distribution of the minor component, poly[4(5)-VIm/VIm$^+$ TFSI$^-$ ]. Such composites may have potential in fuel cells as high-temperature proton-exchange membranes. PVDF imparts mechanical strength to the blend, and because of its high crystal melting point (T$_m$ $>$ 160\r{ }C), should improve the high temperature stability of resulting fuel cell membranes. The long range goal is to make a thin, high strength membrane that will exhibit substantial proton conductivity at high temperature and low relative humidity. Thin PVDF/PVIm-PVIm$^+$ composite films have been fabricated and the nature of the PVDF crystalline polymorph and {\%} crystallinity have been evaluated as a function of the HTFSI content. [Preview Abstract] |
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S1.00040: Diffusion Studies of Compatibilizers in Immiscible Polymer Blends Candice Halbert, John Ankner, James Browning, Haskell Beckham, David Bucknall Much is known about how linear polymers and oligomers modify polymer interfaces, and this knowledge forms the basis for some very important commercial processes and products, including impact modifiers and immiscible blend compatibilizers. However, little is known about cyclic polymers at interfaces, despite evidence that indicates that loops are far better at improving interfacial fracture toughness than linear chain entanglements. Generally, polymer films strongly adhere to one another when there is efficient chain interpenetration and entanglement at the interface. When such reinforcement does not exist, as with immiscible polymers, the interfacial fracture toughness is rather weak ($<$ 20 J/m$^{2})$, but even in these cases the adhesion strength can be correlated with interfacial entanglements. Neutron reflectivity measurements have been used to correlate the interfacial width of homopolymer interfaces with fracture toughness measurements. We have performed NR experiments to elucidate the interfacial activity of linear versus cyclic poly(oxyethylene). During our experiments at SNS we studied the effect of surface segregation in poly(methyl methacrylate) films as well as the effects of interfacial segregation in PMMA/polystyrene films. The results from these diffusion studies will be presented. [Preview Abstract] |
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S1.00041: Synthesis of Functional Nanoparticles by Amphiphilic Star-like Block Copolymer as Template Xinchang Pang, Zhiqun Lin New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Organometallic and other organic solution phase synthetic routes have enabled the synthesis of functional inorganic nanoparticles (NPs). However, much research needs to be done to find a simple and unified approach to synthesize nanoparticles with different chemistry and properties. Here we report a novel approach to produce a variety of nanoparticles with different chemistry, properties and controllable diameters, including metallic NPs, ferroelectric NPs, superparamagnetic ion oxide nanoparticle (SPION), semiconducting NPs. These NPs capped with polymer as surface ligand are synthesized using a series of amphiphilic star-like diblock copolymer (forming single component NPs) and triblock copolymer (forming core/shell NPs) as templates. [Preview Abstract] |
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S1.00042: Low temperature electrical conductivity of low-density polyethylene/carbon black composites Tarek Tawalbeh, Subhi Saq'an, Shadi Yasin, Awwad Zihlif, Giuseppe Ragosta The study deals with the electrical characteristics of carbon black/low-density polyethylene (CB/LDPE) composites of various CB filler concentrations (10, 15, and 20{\%} wt.). DC-electrical conductivity was studied as a function of filler concentration in the low temperature range 25--285K. It was found that the composites exhibit a negative temperature coefficient of resistivity (TCR) at low temperatures and a high enhancement in electrical conductivity with both temperature and carbon black concentration. The observed increase of conductivity with the filler concentration was interpreted through percolation theory. The dependence of the electrical conductivity of the given composites on temperature (25--285 K) was analyzed in terms of a formula consistent with the Mott hopping mechanism. [Preview Abstract] |
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S1.00043: Effect of Grain Size on the AC Electrical Properties of Kaolinite/Polystyrene Composites Lina Abdallah, Awwad Zihlif Impedance spectroscopy has been used to study the effect of kaolinite grain sizes on the AC electrical properties of kaolinite/polystyrene composites under different temperatures and applied frequencies. Impedance measurements were performed on prepared composites containing 20{\%} kaolinite mineral of grain sizes 63, 106, 212, and 300 $\mu $m in addition to neat polystyrene. The measured electrical quantities such as impedance, phase angle, dielectric constant and loss, AC conductivity, and thermal activation all showed a temperature and frequency dependence. The dielectric constant and loss increases with both grain size and temperature. The AC conductivity increases with decreasing kaolinite grain sizes. The 63 $\mu $m grain size composite has higher electrical conduction under applied frequencies and temperatures. A statistical model is presented to explain the dependence of the AC electrical properties on the filler grain size. The study concludes that the overall electrical behavior is influenced by some processes such as electron hopping, ion diffusion, and space charge polarization that take place in the composite microstructure. [Preview Abstract] |
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S1.00044: Domain Structure Formation in Swollen Side-Chain Liquid Crystal Elastomers Christopher Grabowshi, Paul Luchette, Peter Palffy-Muhoray Liquid crystal elastomers (LCEs) are soft materials consisting of a crosslinked polymer network that incorporates mesogenic groups, allowing for orientational order in a solid rubber. Maintaining uniaxial strain on a swollen nematic polymer gel will fix the direction of average orientation of mesogens along the strain axis, yielding a monodomain LCE. Failure to strain the swollen gel within $\sim $30 minutes of formation will produce an opaque polydomain LCE that possesses no long-range nematic order unless stretched. Polarized laser light scattering has been previously employed to monitor the size of liquid crystal domains in fully-formed LCEs; however, no studies have focused on the initial stages of domain formation. We have recorded the time evolution of the far-field scattering patterns produced by swollen polymer gels under varying levels of applied strain. These scattering patterns provide dynamical information of domain behavior during synthesis and processing of monodomain and polydomain LCEs. [Preview Abstract] |
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S1.00045: Molecular Alignment and Temperature Effects on Photodriven, Mulitidimensional Oscillation of Azobenzene Liquid Crystalline Polymer Networks Kyung Min Lee, Matthew Smith, Hilmar Koerner, Richard Vaia, Timothy Bunning, Timothy White The photodriven oscillation of uniaxially aligned monodomain azo-LCNs was investigated as a function of molecular alignment and temperature spanning a range of +/- 40 of the glass transition temperature (T$_{g})$. Monodomain azo-LCNs were synthesized between glass slide cells coated with Elvamide with an anti-parallel rubbing direction. In this work, multidimensional oscillations that include in plane bending and out of plane twisting are observed when the orientation of the axis is at intermediate angles to the long axis of the cantilever. The added dimensionality to the previously reported in plane oscillation is a result of a photoinduced shear gradient that causes twisting. The degree of twisting is shown to be dependent on both the polarization of the illuminating 442 nm light, and the orientation of the director to the cantilever geometry. Comparatively, rubbery azo-LCNs (e.g. systems heated $>$ T$_{g})$ show higher amplitude than glassy azo-LCN cantilevers. The relationship between the critical laser intensity and the concentration of azobenzene monomer for the photodriven oscillation behavior of azo-LCNs will also be discussed. [Preview Abstract] |
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S1.00046: The role of uniaxial deformation on microstructure and dynamics of a bulk-polymerized polyurea James Runt, Taeyi Choi, Daniel Fragiadakis, C. Michael Roland Polyureas, formed by the rapid reaction between isocyanates and diamines are attractive for various applications due to their outstanding mechanical properties, which can be tuned by varying component chemistry, molecular weight and stoichiometry. Polyureas synthesized from a modified methylene diphenyl diisocyanate (Isonate 143L) and polytetramethylene oxide-di-p-aminobenzoate (Versalink P1000) are widely utilized and investigated for energy absorbing applications such as impact mitigation and ballistic protection. In order to develop a more complete understanding of their mechanical response, we explore the effect of uniaxial strain on the phase separated microstructure and molecular dynamics. We utilize wide- and small-angle X-ray scattering to investigate amorphous segment and hard domain orientation and broadband dielectric spectroscopy for interrogation of the dynamics Uniaxial deformation was found to significantly perturb the phase separated microstructure and chain orientation, and result in a considerable slowing down and broadening of the polyurea soft phase segmental relaxation. [Preview Abstract] |
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S1.00047: Characterization of a Poly(styrene-block-methylacrylate-random-octadecylacrylate-block-styrene) Shape Memory ABA Triblock Copolymer Pengzhan Fei, Kevin Cavicchi A new ABA triblock copolymer of poly(styrene-block- methylacrylate-random-octadecylacrylate-block-styrene) (PS-b- PMA-r-PODA-b-PS) was synthesized by reversible addition fragmentation chain transfer polymerization. The triblock copolymer can generate a three-dimensional, physically crosslinked network by self-assembly, where the glassy PS domains physically crosslink the midblock chains. The side chain crystallization of the polyoctadecylacrylare (PODA) side chain generates a second reversible network enabling shape memory properties. Shape memory tests by uniaxial deformation and recovery of molded dog-bone shape samples demonstrate that shape fixities above 96\% and shape recoveries above 98\% were obtained for extensional strains up to 300\%. An outstanding advantage of this shape memory material is that it can be very easily shaped and remolded by elevating the temperature to 140$^ {\circ}$C, and after remolding the initial shape memory properties are totally recovered by eliminating the defects introduced by the previous deformation cycling. [Preview Abstract] |
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S1.00048: Structure and dynamics of of solution polymerized polyureas Taeyi Choi, Youmi Jeong, James Runt Polyureas consisting of alternating soft and hard (urea containing) segments exhibit physical properties that are closely related to their microphase separated structure, which consist of rigid (high Tg and sometimes crystalline) hard domains embedded in a matrix dominated by flexible polyether segments. Polyurea properties can be controlled over a rather broad range by varying the chemical structures, molecular weight of the components, and reaction stoichiometry. In the present study, we focus primarily on linear polyureas synthesized using methylene diphenyl diisocyanate and polytetramethylene oxide-di-p-aminobenzoate using a solution polymerization method. Soft segment (diamine) molecular weights were varied from 460 to 860 to 1200 g/mol and characterize their morphology, hydrogen bonding, mechanical behavior and dielectric properties upon varying molecular weight of diamines. This presentation will focus on our latest findings, particularly details of the microphase separated morphology and molecular dynamics as measured using dielectric relaxation spectroscopy [Preview Abstract] |
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S1.00049: The elastic Maier-Saupe-Zwanzig model and some properties of nematic elastomers Danilo Liarte, Silvio Salinas, Carlos Yokoi We introduce a simple mean-field lattice model to describe the behavior of nematic elastomers. This model combines the Maier-Saupe-Zwanzig approach to liquid crystals and an extension to lattice systems of the Warner-Terentjev theory of elasticity, with the addition of quenched random fields. We use standard techniques of statistical mechanics to obtain analytic solutions for the full range of parameters. Among other results, we show the existence of a stress-strain coexistence curve below a freezing temperature, analogous to the $P$-$V$ diagram of a simple fluid, with the disorder strength playing the role of temperature. Below a critical value of disorder, the tie lines in this diagram resemble the experimental stress-strain plateau, and may be interpreted as signatures of the characteristic polydomain-monodomain transition. Also, in the monodomain case, we show that random-fields may soften the first-order transition between nematic and isotropic phases, provided the samples are formed in the nematic state. [Preview Abstract] |
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S1.00050: The Effect of Multiple Parallel Bonds on the Self-healing of Labile Crosslinked Nanogel Networks Isaac G. Salib, German V. Kolmakov, Chet N. Gnegy, Krzysztof Matyjaszewski, Anna C. Balazs We develop a hybrid computational approach to examine the mechanical properties and self-healing behavior of nanogel particles that are crosslinked primarily by highly reactive bonds that can break and readily remake (labile bonds). The individual nanogels are modeled via the lattice spring model (LSM). The crosslinks between the nanogels are simulated via a modified Hierarchical Bell Model (HBM), which allows us to capture both the rupturing and reforming of multiple, parallel bonds due to an applied force. Using our hybrid HBM/LSM, we simulate the behavior of the crosslinked nanogels under a tensile deformation. In these simulations, each labile linkage between the nanogels contains at most $N$ parallel bonds. We reveal that while numerous parallel bonds within a linkage enhance the strength of the material, these bonds diminish the ductility and the ability of the material to undergo the structural rearrangements that are necessary for self-repair. [Preview Abstract] |
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S1.00051: Characterization of hybrid hydrogel with different shape of particles after gamma-ray radiation Donghyun Kim, Hoik Lee, Hyemi Park, Daewon Sohn Due to high specific surface area and the ability to absorb organic molecules, inorganic particles such as silica particle (spherical), imogolite (rodlike), and clay (fan shape) could be used as precursors for hydrogels. The hydrogel which had 3-D network structure was directly prepared by polymerization with acrylic acid (AA) on hydroxide surface of inorganic particles that was irradiated by gamma-ray at ambient condition. Surface of inorganic particles was used as sites of initiator and cross-linker to make hydrogel, so we don't need any additional additives to make hydrogel. The properties of hydrogel were characterized by small angle x-ray scattering (SAXS), universal testing machine (UTM), and Raman spectroscopy. By changing the inorganic particles/monomer ratio, the mechanical strength was significantly changed. The synthesized hydrogel can be elongated maximum 1800{\%}. 2D SAXS pattern was different depending on the shape of inorganic particles. And the hydrogel swelled only in basic solutions at pH $>$ 7. [Preview Abstract] |
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S1.00052: A State-of-Ease Analysis of Shape Memory Elastomers Christopher Lewis, Jiahui Li, Mitchell Anthamatten A state-of-ease model is developed to predict the time-dependent mechanical behavior of a shape memory elastomer. The model assumes continuous mechanical equilibrium between applied stress and stresses of entropic origin arising from a permanent network and a second, independent network composed of reversible bonds. Bonds forming the reversible network are assumed to rearrange at a constant rate, and newly formed bonds are created in a stress-free state. This gives rise to a time-dependent distribution of bond ages and corresponding stresses, and both are accounted for in the model using a delay integral approach. The model is capable of describing creep, stress relaxation, and shape memory responses. The model will be fit to experimental data for a poly(butyl acrylate) shape memory elastomer, and results will be compared to a simpler dashpot-spring model. [Preview Abstract] |
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S1.00053: Real time small angle X-ray scattering from cyclically stretched nanoparticle-filled siloxane elastomers Arthur K. Scholz, Huan Zhang, Elaine R. Chan, Alexander Hexemer, Edward J. Kramer The origin of the cyclic softening and hysteresis (the well known ``Mullins effect'') observed in nanoparticle-filled elastomers is still debated. To probe this question we used synchrotron-based, time resolved, small angle x-ray scattering (SAXS) to observe changes in the structure of silica-filled siloxane elastomers with different filler loading and surface treatments under step cycle tensile deformation. We perform reverse Monte Carlo (RMC) simulations using graphical processing units (GPUs) to infer the real space configuration of the filler network that gives rise to the SAXS pattern and we compute the scattering invariant to quantify any void formation. We observe that the deformation is non-affine on length scales corresponding to the filler particles. The particles collect in ``rafts'' perpendicular to the tensile axis such that most of the deformation occurs in the elastomer-rich regions between rafts. At the largest deformations a scattering streak appears in a direction normal to the tensile axis at very small diffraction vectors (0.01 nm-1) which we attribute to the formation of elliptical voids whose long axis lies in the tensile direction. [Preview Abstract] |
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S1.00054: Investigating Heterogeneous Microenvironments in Hydrogels by Single Quantum Dot Tracking Cheol Hee Lee, Todd Emrick, Alfred Crosby, Ryan Hayward Single particle tracking provides a powerful means to locally characterize physical properties within heterogeneous media. We have employed CdSe/ZnS core/shell quantum dots (QDs) as probes to characterize the heterogeneous microstructures within covalently- crosslinked polyacrylamide (PAAm) hydrogels. For appropriate gel compositions, the QDs show periods of caged motion within trapping sites, interspersed by nearly free diffusion. We analyze the trajectories of single QDs using a variety of statistical approaches to elucidate the distribution of trapping site strengths within gels of different average pore size. [Preview Abstract] |
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S1.00055: Effects of AC Electrical Field on the Dielectrophoresis Force of Dielectric Elastomers and Blends Anuvat Sirivat, Ruksapong Kunanuruksapong The effects of frequency and amplitude of AC electric field on the deflection and the dielectrophoresis force of an acrylic elastomer (AR71), styrene copolymers (SAR and SBR), and the blends of doped PPP and AR71 are investigated. The dielectrophoresis forces of the dielectric elastomers and blends were measured by using a vertical cantilever fixture at various frequencies (0.3 to 60 Hz) and at AC electric field strengths of 200-800 V$_{pp}$/mm. The effects of the thicknesses of the specimens and the particle concentration are studied. The doped PPP particles are embedded in the AR71 with concentrations of 1, 10, and 20 {\%}vol. The dielectrophoresis forces and deflection distance of the dielectric elastomers and blends generally increase with increasing amplitude but slightly decrease with increasing frequency; and they dramatically drop at the cut-off frequency. The cut-off frequencies are 7.84, 1.45, and 0.74 Hz for AR71, SAR, and SBR, respectively, at E of 800 V$_{pp}$/mm and a thickness of 0.7 to 0.8 mm. After blending the AR71 with doped PPP, the cut-off frequencies of the 1 {\%}vol, 10 {\%}vol and 20 {\%}vol of doped PPP are 18.51, 15.28, and 10.67 Hz, respectively, at an E of 800 V$_{pp}$/mm and a thickness of 0.2 to 0.3 mm. The conductive polymer particles are shown here to improve the electromechanical responses at high frequency. [Preview Abstract] |
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S1.00056: Effects of Annealing on the Photovoltaic Performance of All-Conjugated Poly(3-alkylthiophene) Diblock Copolymer Ming He, Wei Han, Yuliang Yang, Feng Qiu, Zhiqun Lin The effects of thermal annealing and solvent annealing on the photovoltaic performance of all-conjugated poly(3-butylthiophene)-b-poly(3-hexylthiophene) diblock copolymer, [6,6]-phenyl-C$_{71}$-butyric acid methyl ester (P3BHT:PC$_{71}$BM) based devices were investigated using the single diode model. Thermal annealing placed a better balance between the crystallization of P3BHT chains and the nanoscale phase separation with PC$_{71}$BM domains, while solvent annealing under chloroform vapor induced a significant improvement in the crystallinity of P3BHT as well as enlarged P3BHT crystalline domains, thereby leading to unbalanced charge transport and increased charge recombination in the blend films. The physical meanings of the parameters in the equivalent single diode model were also discussed in terms of crystallinity and phase separation to gain the fundamental understanding of the mechanism that account for the annealing effects. [Preview Abstract] |
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S1.00057: Role of Succinonitrile in a Poly(ethylene oxide)/LiTFSI membrane for lithium batteries Mauricio Echeverri, Thein Kyu In designing novel flexible lithium battery membranes, high conductivity, peel strength and processability are the main targets for a successful product. Crystallinity of poly(ethylene oxide) (PEO) and lithium salts represent an obstacle to accomplish each of these specifications. We present a systematic study of ternary phase diagrams of PEO, bis(trifluoromethane) sulfonimide (LiTFSI) and succinonitrile (SCN) (i.e., solid plasticizer/co-solvent) mixtures by using DSC and polarized optical microscopy and map out various coexistence regions bound by the liquidus and solidus lines. The eutectic phase diagram of PEO/SCN system was calculated self-consistently using Flory-Huggins theory in conjunction with Landau-type phase field free energy for crystal solidification. Specific interactions such as hydrogen bonding were examined by FTIR. In lieu of PEO, poly(ethylene glycol) diacrylate (PEGDA) were used to completely eliminate all crystals. Further, photopolymerization of PEGDA affords a solid network containing LiTFSI and SCN that shows promising improvements with a conductivity value of 10$^{-4}$S/cm at 25\r{ }C. [Preview Abstract] |
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S1.00058: Synthesis and Photovoltaic Properties of a New Class of Donor-Acceptor Alternating Copolymers Containing Pechmann-Dye Derivatives Jae Woong Jung, Won Ho Jo Over the last decade, various low bandgap copolymers that exhibit over 5{\%} power conversion efficiency have been developed. However, the synthesis of most low-bandgap polymers is complicated with relatively long synthetic routes and low yield. In this work, a new series of novel alternating copolymers composed of thiophene and Pechmann-dye derivatives were synthesized and used as an electron donor material of bulk heterojunction polymer solar cells. Two Pechmann-dye derivatives, 5,5'-bis-(3-octyl-thiophen-2-yl)-[3,3']bifuranylidene-2,2'-dione and 3,7-bis-(3-octyl-thiophen-2-yl)-pyrano[4,3-c]pyran-1,5-dione which have high molar absorption coefficient, strong electron-deficient core, and planar structure, were easily synthesized via simple three steps with high yield. The use of the Pechmann-dye derivatives as a building block for copolymers results in promising optical, electrochemical, and photophysical properties. Morphology, charge transport, and photovoltaic characteristics of the new copolymers will be discussed. [Preview Abstract] |
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S1.00059: Nanostructured photovoltaic materials using conjugated block copolymer assemblies Sarah E. Mastroianni, Thomas H. Epps, III Block copolymers containing a conjugated block offer attractive possibilities for creating nanostructured organic photovoltaic (OPV) devices. Current OPV materials suffer from efficiency losses primarily due to a size-scale discrepancy between exciton diffusion length and domain sizes; excitons that do not reach the interface between electron and hole-conducting materials recombine, preventing charge carrier separation. The inherent nature of block-copolymers to self-assemble into well-defined nanoscale structures with domain spacings on the order of exciton diffusion length offers a potential solution for reducing exciton recombination. In this work, allyl-terminated poly(3-hexyl thiophene) or poly(3-decyl thiophene) acting as electron donors are incorporated into the block copolymer chain via a coupling reaction with poly(styrene) or poly(isoprene-$b$-styrene) derivatives synthesized by anionic polymerization. The resulting block copolymer morphologies are characterized by small angle X-ray scattering and transmission electron microscopy. [Preview Abstract] |
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S1.00060: Structure-performance analysis of donor/acceptor low band gap polymers: Effect of different acceptors Louis Perez, James Rogers, Kristin Schmidt, Guillermo Bazan, Edward Kramer A well established method of designing low band gap polymers for bulk heterojunction solar cells employs what is known as a `donor-acceptor' (D/A) motif. A D/A polymer is an alternating copolymer consisting of a covalently bound electron deficient unit as an electron acceptor and an electron rich component as an electron donor group. A notable D/A polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], (PCPDTBT) was the first to achieve device efficiencies over 5{\%}. Device performance is predicted to improve by changing the acceptor to tune the energy level offsets between the polymers and the fullerene derivative to increase the driving force for exciton dissociation and the internal potential, (Voc). If the BT acceptor is changed to benzooxadiazole (BO) the Voc increases, however the current drops significantly, producing devices with efficiencies less than 2{\%}. In order to understand the current drop, GIWAXS, NEXAFS, DSIMS, and TEM have been employed to elucidate structural and composition differences. [Preview Abstract] |
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S1.00061: PCBM Functionalized Block Copolymer films for Photovoltaic Applications Abul M.A. Huq, Manish M. Kulkarni, Alamgir Karim For efficient charge separation we examine block copolymer thin films as model nanoscale templates that can be utilized for OPV applications. If one can incorporate acceptor and donor in two different blocks, efficient charge separation can be possible. Microphase separation in block-copolymer (BCP) systems, a result of chemical incompatibility of the constituent polymer blocks can be used to control the nanoscale domain sizes. Here, Polystyrene-b-Polyethyleneoxide (PS-PEO) block copolymer, with the PEO being the cylinder forming phase was used because of its robust structural nature to form vertical nanomorphology of cylinders. The acceptor material, PCBM was incorporated into the block-copolymer at different concentration levels up to high levels ($\sim$30\%). Both TEM and AFM study showed that PCBM was well dispersed at up to 3:10 (PCBM:PS-PEO) in the block copolymer matrix. This amount is close to percolation threshold of PCBM at which independent donor and acceptor path is expected to be achieved. Further investigations by neutron scattering methods for possible numerous electronic applications including OPV are underway. [Preview Abstract] |
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S1.00062: Mixing Behavior of a Molecular Acceptor and Polymeric Donors in Organic Solar Cell Blends M.A. Brady, N.D. Treat, L.A. Perez, J.E. Cochran, M.F. Toney, C.J. Hawker, M.L. Chabinyc, E.J. Kramer Organic photovoltaics represent potentially low-cost, solution-processable materials for sustainable energy generation. The concept of a bulk heterojunction relies on the belief that separated domains of donor and acceptor exist to maximize interfacial area for exciton dissociation, while pathways are retained for charge transport to each electrode. Although phase-pure domains are believed to exist due to phase separation of acceptor (PCBM) and donor (P3HT) components, our results suggest otherwise. In this work, the rapid interdiffusion of PCBM and P3HT is investigated using dynamic secondary ion mass spectrometry and grazing-incidence wide angle X-ray scattering, illustrating the significant miscibility of PCBM within P3HT amorphous regions, especially at temperatures (150 $^{\circ}$C) at which devices are often annealed to improve performance. The solubility of PCBM in the P3HT-rich phase decreases at lower temperatures. This mixing behavior is contrasted with that of PCBM with PBTTT, a poly(thiophene) of reduced side chain density. [Preview Abstract] |
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S1.00063: Photophysical Study of Novel Perylene Analogues for Biophysical Applications Jorge Palos-Ch\'avez, Mark Penick, George Negrete, Lorenzo Brancaleon Perylene and perylene derivatives have been shown to be useful in a variety of photoinitiated applications, such as molecular dyes, organic solar cells, etc. Recently we started the characterization of novel 3,9-perylene analogues which could potentially lead to the synthesis of novel molecules with improved ability to separate charges. We have characterized the basic photophysical properties of these molecules, and we are currently investigating the photochemistry that leads to photoproducts in chlorinated compounds. Spectroscopic measurements show the substantial changes in photophysical parameters consistent with the conversion of the original compounds into photoproducts. SEM and AFM imaging show that these photoproducts form ordered particles. Mass spectrometry studies have confirmed the presence of these photoproducts as well. Additional studies are underway concerning the use of these novel perylene analogues in binding to biological structures such as proteins. It is hoped that these compounds will prove useful for biophysical applications, specifically in studying the manipulation of protein conformation via physical methods. [Preview Abstract] |
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S1.00064: Synthesis and Characterization of Quinoxaline-Based Low-Bandgap Copolymers for Bulk Heterojunction Solar Cells Yoonkyoo Lee, Won Ho Jo A series of low-bandgap alternating copolymers consisting of quinoxaline derivatives and electron-donating carbazole or fluorene were synthesized via the Suzuki coupling reaction. For the purpose to improve the molecular packing of polymer chains and to enhance the charge carrier mobility in the packing direction, a new quinoxaline derivative, 5,8-dithien-2-yl-dibenzophenazine which has perfectly planar polycyclic structure, was synthesized and introduced as a new building block for alternating copolymers instead of frequently-used 5,8-dithien-2-yl-2,3-diphenylquinoxaline. The use of planar quinoxaline derivative exhibited better optical, electrochemical, and structural properties of the resulting copolymers as compared to those of polymers with less planar quinoxaline derivatives. Charge transport and photovoltaic properties of these two classes of copolymers are compared and discussed. [Preview Abstract] |
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S1.00065: PL enhancement in MEH-PPV stretched films by suppression non-radiative relaxations Jui-Hung Hsu, Jonathon David White, Arnold C.-M. Yang Due to the strong electro-phonon coupling, excitation in conjugated polymer is easily relaxed through non-radiative decay channels, and the luminescence yield is lowering. It would be crucial to reduce the non-radiative relaxations for the high performance light-emitting applications. We report the study of stretched MEH-PPV blending films by fluorescence lifetime imaging microscopy. Polymer in the stretched region is fully aligned, and the emission yield is improved by 40{\%}. The improvement is well-agreed with the lifetime studies. Our results indicate that the PL enhancement is due to the suppression of non-radiative relaxations while stretching. Comparing the lifetime imaging and the morphology by AFM, molecular strain distribution is provided. The investigation would be useful in the device application and the basic understanding of electronic excitation relaxation in conjugated polymers. [Preview Abstract] |
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S1.00066: Classification of Semiconducting Polymeric Mesophases to Optimize Device Post-Processing Chad Snyder, Ryan Nieuwendaal, Lee Richter, R. Joseph Kline, Dean DeLongchamp, Martin Heeney, Iain McCulloch Semiconducting polymers form a variety of phases and mesophases that respond differently to post-deposition solvent or thermal treatments. Here it is shown that classification of these materials into their appropriate mesophases can be a useful tool to optimize their post-deposition treatments. Calorimetry is used to quantify differences between very similar materials, using a well-established framework based on the kinetics and thermodynamics of phase changes. By way of example, this classification scheme is used to identify differences in three polymers, poly(3-hexylthiophene) and two isomeric bithiophene-thiophene copolymers (pBTTT and pATBT). It is demonstrated that poly(3-hexylthiophene) is a conformationally disordered (condis) crystal, and that the two bithiophene copolymers are liquid crystals. The condis state is used to help explain the wide range of reported values for poly(3-hexythiophene), as two separate glass transitions are clearly resolved. The diverse phase structure is notable in light of the molecular similarity of the three polymers, and it has impact on optimum post-processing conditions for maximum electrical performance in thin film transistor devices. [Preview Abstract] |
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S1.00067: Solution processed organic microarray with inverted structure Patrick Toglia, Jason Lewis, Evan Lafalce, Xiaomei Jiang We have fabricated inverted organic microarray using a novel solution-based technique. The array consists of 60 small (1 square mm) solar cells on a one inch by one inch glass substrate. The device utilizes photoactive materials such as a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Manipulation of active layer nanomorphology has been done by choice of solvents and annealing conditions. Detailed analysis of device physics including current voltage characteristics, external quantum efficiency and carrier recombinations will be presented and complimented by AFM images and glazing angle XRD of the active layer under different processing conditions. The procedure described here has the full potential for use in future fabrication of microarrays with single cell as small as 0.01 square mm for application in DC power supplies for electrostatic Microelectromechanical systems (MEMS) devices. [Preview Abstract] |
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S1.00068: Subpicosecond photonic switching based on bacteriorhodopsin Pal Ormos, Laszlo Fabian, Zsuzsanna Heiner, Mark Mero, Miklos Kiss, Elmar Wolff, Karoly Osvay, Andras Der All-optical data processing is the most promising approach for further improvement in data trafficking. We present a subpicosecond photonic switch where the active role is performed by the chromoprotein bacteriorhodopsin. The changes in the refractive index that accompany the steps of the photocycle of bacteriorhodopsin are used for all optical switching in appropriate integrated optical devices. We use grating coupled planar waveguides and the coupling is modulated by the light induced refractive index changes of bacteriorhodopsin. The switching is demonstrated in ultrafast pump-probe experiments. Different transitions of the photocycle are explored for switching applications. We show that by using the bR to I transition subpicosecond switching can be readily achieved. The approach is a basis for protein-based integrated optical devices, eventually leading to a conceptual revolution in telecommunications technologies. [Preview Abstract] |
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S1.00069: Efficient blue PhOLEDs using host materials of lower triplet energy than the emitter James Swensen, Evgueni Polikarpov, Amber VonRuden, Liang Wang, Asanga Padmaperuma It is a commonly held view that the host material for a phosphorescent emitter in an organic light emitting device (OLED) must have a triplet energy higher than that of the phosphorescent emitter in order to obtain high quantum efficiencies. We show that a combination of HTL, ETL and host with appropriate energy levels can provide high external quantum efficiency (EQE), even with a host triplet energy smaller than that of the emitter. Specifically, we report results for a new host material, 4-(di-p-tolylamino)phenyl)diphenylphosphine oxide, with a triplet energy lower than FIrpic that demonstrate improved OLED performance. Our results suggest modified design rules for the development of new, high performance host materials. Molecular design strategies, device design and OLED data will be discussed. [Preview Abstract] |
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S1.00070: Simulation of DNA Electrophoresis by Coarse-Grained Hybrid Molecular Dynamics Approach Rong Wang Simulation of DNA electrophoresis facilitates the design of DNA separation devices. Various methods have been explored for simulating DNA electrophoresis and other processes using implicit and explicit solvent models. Explicit solvent models are highly desired but their applications may be limited by high computing cost in simulating large number of solvent particles. In this work, a coarse-grained hybrid molecular dynamics (CGH-MD) approach was introduced for simulating DNA electrophoresis in explicit solvent of large number of solvent particles. CGH-MD was further applied to the simulation of DNA electrophoresis in polymer solution and in a well-studied nanofluidic device. Simulation results are consistent with observations and reported simulation results, suggesting that CGH-MD is potentially useful for studying electrophoresis of macromolecules and assemblies in nano-fluidic, micro-fluidic, and microstructure array systems that involve extremely large number of solvent particles, non-uniformly distributed electrostatic interactions, bound and sequestered water molecules. [Preview Abstract] |
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S1.00071: Examining Adsorbed Polymer Conformations with Fluorescence Imaging Maria Parkes, Mourad Chennaoui, Janet Wong The conformation of adsorbed polymers can have significant impact on their properties such as dynamics and elasticity as well as their ability to take part in reactions with other molecules. Experimental research to determine adsorbed polymer conformation has relied mainly on atomic force microscopy (AFM) studies. During an AFM scan, the contact between the scanning probe and the polymer could affect the polymer conformation, particularly where parts of the polymer might have formed projected loops and tails. In this work, conformations of model polymers are examined with total internal reflection fluorescence microscopy (TIRFM). The advantage of TIRFM over AFM is that TIRFM is a non contact technique. Lambda DNA labelled along its length with fluorescent probes was adsorbed in a projected 2D -- 3D state. With TIRFM, the relationship between intensity and depth was used as a basis to determine how the conformation of the adsorbed polymers evolved with time using our custom algorithm. [Preview Abstract] |
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S1.00072: Study of pluronic F68 molecules on silicon with Atomic Force Microscopy (AFM) M.J. Retamal, U.G. Volkmann, V.D. Samith The triblock copolymer pluronic F68 belongs to a class of amphiphilic nonionic surfactants, relevant for applications in medicine, which includes transport of drugs to selective targets in the human body. In the present work, pluronic F68 films have been deposited on Si/SiO2 substrates. Previous to deposition, Si/SiO2 substrates were cleaned in acid and afterwards rinsed with ultra pure water. This cleaning method leaves intact the silicon oxide layer and provides a hydrophilic surface. The aliquots were prepared from aqueous solutions, obtaining different concentrations, which were deposited on the substrates and dried at room temperature. Each of these dispersions is in the range from 0.5 x 10-4 M to 10.0 x 10-4 M. Atomic force microscopy (AFM) shows changes in the morphology of the films, caused by the gradual increase of concentration. These changes occur in a narrow range of concentrations, attributed to the critical micelle concentration (CMC). Supramolecular structures (clusters) coexist at the CMC and above, forming 3D structures such as ``dendritics.'' The percentage of F68 coverage on the substrate depends on the increase in molar concentration. In a ``coverage vs. molar concentration'' plot we obtain a curve with an inflection point that coincides with the CMC reported for a variety of techniques and conditions. [Preview Abstract] |
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S1.00073: Hierarchical self-assembly of spider silk-like block copolymers Sreevidhya Krishnaji, Wenwen Huang, Peggy Cebe, David Kaplan Block copolymers provide an attractive venue to study well-defined nano-structures that self-assemble to generate functionalized nano- and mesoporous materials. In the present study, a novel family of spider silk-like block copolymers was designed, bioengineered and characterized to study the impact of sequence chemistry, secondary structure and block length on assembled morphology. Genetic variants of native spider dragline silk (major ampullate spidroin I, Nephila clavipes) were used as polymer building blocks. Characterization by FTIR revealed increased ?-sheet content with increasing hydrophobic A blocks; SEM revealed spheres, rod-like structures, bowl-shaped and giant compound micelles. Langmuir Blodgett monolayers were prepared at the air-water interface at different surface pressures and monolayer films analyzed by AFM revealed oblate to prolate structures. Circular micelles, rod-like, densely packed circular structures were observed for HBA6 at increasing surface pressure. Exploiting hierarchical assembly provide a promising approach to rationale designs of protein block copolymer systems, allowing comparison to traditional synthetic systems. [Preview Abstract] |
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S1.00074: Tunable surface properties from bioinspired polymers Wendy van Zoelen, Adrianne Rosales, Hannah Murnen, Ronald Zuckermann, Rachel Segalman Anti-fouling properties can be derived from patterned or ``ambiguous'' surfaces displaying multiple surface properties. Biological polymers with precisely controlled chain shapes and self-assembled structures are attractive materials for these applications, in which tunability is of great importance. We have investigated the surface properties of polypeptoids, a class of non-natural biomimetic polymers based on an N-substituted glycine backbone, that combine many of the advantageous properties of bulk polymers with those of synthetically produced proteins. Polypeptoids are of particular interest as they can be made in a sequence controlled fashion with functionalities already known to impart fouling-resistance (ethers, zwitterions, hydrophobicity, and nanoscale patterning). We demonstrate their surface stability and processibility from the standpoint of coating performance and also discuss controlled self-assembly of these materials. Used strategies include mediation of crystallization by incorporating chain defects and specific interactions. [Preview Abstract] |
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S1.00075: Synthesis and Characterization of Thermally Responsive Polysaccharide Nanoparticles Krista Freeman, Sean Sheridan, Imaan Benmerzouga, John McKenna, Kiril Streletzky Environmentally-manipulable nanoparticles (microgels) have been synthesized from the amphiphilic polymer hydroxypropyl-cellulose and characterized using dynamic and static light scattering spectroscopies. Careful synthesis studies have revealed dependences of microgel size and structure on polymer molecular weight, polymer concentration, salt concentration, and crosslinker density. An understanding of these dependences has allowed the synthesis of stable, largely spherical, and relatively small (about 100nm) and monodisperse microgels. The synthesized microgels exhibit a volume phase transition between temperatures of 40 and 41C, under which particles undergo a reversible 15-50-fold change in volume. The microgel structure, dynamics, and longevity have been systematically studied by light scattering both below and above the transition temperature. [Preview Abstract] |
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S1.00076: Uniform Yeast Cell Assembly Based on Microfluidic Microgels Ya-Wen Chang, Peng He, Manuel Marquez, Zhengdong Cheng, Samantha M. Marquez We present a novel microgel templated Yeastosome$^{\textregistered}$ (Yeast-Celloidosome$^{\textregistered}$) based on self-assembly of yeast cells onto liquid-gel interfaces. To organize living cells onto the surface of the gel particles, strong positive charges were first introduced via LbL (layer by layer) polyelectrolyte decoration on monodisperse agarose microgel templates fabricated with a microfluidic flow focusing device. Native yeasts, bearing negative surface charges can then be driven electrostatically to form a monolayer shell around the gel core. Surface coverage/packing density of the yeast biofilm on varying microgel-to-yeast size ratio assemblies is evaluated with optical microscopy. Mechanical properties of the corresponding shells are characterized with buckling or collapse behavior during drying-hydrating cycle. We demonstrate the capability to fabricate narrow size distribution Yeastosome$^{\textregistered}$ with a soft hydrogel core. The combination of microfluidic fabrication with cell assembly offers excellent control over inner core properties and could enable further hierarchy bio-structures. [Preview Abstract] |
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S1.00077: Clay platelets in a matrix of amino acids (of a clay binding peptide M1) homopolymer: binding, unbinding, dispersion, and self-assembly by a coarse-grained Monte Carlo simulation Barry Farmer, Lawrence Drummy, Sharon Jones, Richard Vaia, Rajesh Naik, Hendrik Heinz, Ras Pandey Monte Carlo simulations are performed to study binding and distribution of a stack of clay platelets in a matrix of homo-polymers of residues. The set of residue monomers is selected from a clay binding peptide ($M1)^{1}$. The length of homopolymer is same as that the peptide $M1$. Clay platelet and amino acid polymer (AAP) are described by a bond-fluctuation model$^{2}$ where specificity of each residue interaction is incorporated. Each node (of clay platelets and AAP) performs their stochastic motion via Metropolis algorithm subject to steric and excluded volume constraints. We examine the mobility of AAP and platelets and their density profiles. We find that dispersion and binding of each AAP is unique and differ from that of the clay platelets in peptide $M1$ matrix. [Preview Abstract] |
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S1.00078: Diffusion-driven looping provides a consistent framework for chromatin organization Dieter Heermann, Manfred Bohn Chromatin looping seems to play a dominant role both in transcriptional regulation as well as in chromatin organization and has been assumed to be mediated by long-range interactions in many polymer models. However, it remains a crucial question which mechanisms are necessary to make two chromatin regions become co-located, i.e. have them in spatial proximity. We demonstrate that the formation of loops can be accomplished solely on the basis of diffusional motion. The probabilistic nature of temporary contacts mimics the effects of proteins, e.g. transcription factors, in the solvent. We establish testable quantitative predictions by deriving scale-independent measures for comparison to experimental data. In this Dynamic Loop (DL) model, the co-localization probability of distant elements is strongly increased compared to linear non-looping chains. The model correctly describes folding into a confined space as well as the experimentally observed cell-to-cell variation. Most importantly, at biological densities, model chromosomes occupy distinct territories showing less inter-chromosomal contacts than linear chains. Thus, dynamic diffusion-based looping, i.e. gene co-localization, provides a consistent framework for chromatin organization in eukaryotic interphase nuclei. [Preview Abstract] |
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S1.00079: Synthesis of a novel photopolymerized nanocomposite hydrogel for the treatment of acute mechanical damage to cartilage Kathryn Schlichting, Trishelle Copeland-Johnson, Matthew Goodman, Robert Lipert, Todd McKinley, James Martin, Surya Mallapragada, Zhiqun Lin Posttraumatic osteoarthritis is caused by a cascade of pathobiologic and pathomechanical events starting with intraarticular fractures in the cartilage. Currently, treatment of fractures is completely focused on restoration of the macroanatomy of the joint. The premise is that restoring the macroanatomy will prevent ongoing stresses and in turn prevent cartilage degeneration. However, current treatment ignores acute mechanical damage sustained by cartilage at the time of injury. This study describes the initial development of a novel nanocomposite photopolymerizing copolymer that has potential to restore local structural integrity to acutely injured cartilage, and subsequently act as a carrier for chondrocyte-enhancing bioactive agents. [Preview Abstract] |
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S1.00080: Car--Parrinello Molecular Dynamics Study of Base-Catalyzed Hydrolysis Reactions Sufian Alnemrat, Igor Vasiliev, Haobin Wang We apply the first principles metadynamics simulation technique implemented in the Car-Parrinello molecular dynamics package to study the base-catalyzed hydrolysis of N-methylacetamide in aqueous solution. Our calculations are carried out in the framework of density functional theory combined with the hybrid BLYP exchange-correlation functional The free energy surfaces and hydrolysis reaction pathways for N-methylacetamide are examined in the presence of a hydroxide ion, and 4, 32, and 64 water molecules. We find that at least 32 water molecules must be explicitly included in metadynamics simulations to accurately describe the mechanism of the hydrolysis reaction of N-Methylacetamide. Our theoretical estimate for the dissociation energy of N-Methylacetamide is in good agreement with the results of previous experimental and theoretical studies. [Preview Abstract] |
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S1.00081: Silica-Based Janus Nanoparticles at the Water-Decane Interface Heng Fan, Alberto Striolo It is well known that solid particles adsorb at water-oil interfaces to reduce the contact area between the two immiscible phases. Stable emulsions are obtained when the particles strongly adsorb at the interfaces. We report herein all atom molecular dynamics simulation results for silica-based nanoparticles functionalized with hydrophobic moieties at the decane-water interface. The simulation results are quantified in terms of contact angle at the water-nanoparticle-decane interface, mobility of the nanoparticles, association of multiple nanoparticles at the interface, and free-energy landscapes that dictate the nanoparticle adsorption at the interface. The results are discussed based on the chemical features of the nanoparticle surface. Comparison with experimental data, including but not limited to TEM and cryo-TEM images of water-oil emulsions, are provided. [Preview Abstract] |
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S1.00082: Synthesis of stable Au-PEG nanocomposite chains in a single step precursor free method and its formation mechanism and Di-electric behavior Rajesh Kumar Neogy, Rajib Nath, Gautam Basu, Arup Kumar Raychaudhuri We report a simple and effective one step and one-pot synthesis of stable assembly of Au nanoparticles (diameter 8-10nm) into chains in an Ethylene Glycol medium(MEG), using only a solid metallic Au target and a pulsed excimer laser. No use any external precursor, reducing agent or surfactant so it is a chemistry free synthesis route. The Au-PEG nanocomposite chains (with unbroken lengths often more than few microns) formed in liquid medium are mechanically and thermally stable and can be transferred unchanged into a solid substrate which can span a large surface area. The nanochains show a broad optical absorption near to visible spectrum. Hybrid of Au nanochains and separated nanoparticles can also be formed using a proper choice of the laser fluence and MEG/DI water concentration. The Au-PEG nanocomposite chains in the medium shows enhanced low frequency dielectric constant {\&} electrical conductivity. NMR shows that due to the formation of dimer/trimers of MEG molecules that formed by the ablation process, attach to the Au nanoparticles and facilitate the nanocomposite chain formation. [Preview Abstract] |
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S1.00083: Assembly of carbon nanotube/polymer hybrids at liquid/liquid interface Wenda Wang, Eric Laird, Christopher Li Carbon nanotube (CNT)-templated polymer crystallization has led to controllable patterns on individual CNTs. Previous work has demonstrated that crystalline block copolymers (BCP) can be uniformly patterned on CNTs and the mechanism was attributed to CNT-induced BCP phase separation. Herein, we report that at liquid/liquid interface, CNTs can be bent into nanoscale rings. The structure and morphology of these intriguing CNT rings were investigated using electron microscope and Raman spectroscopy. Furthermore, these CNT rings were used as a template for polymer crystallization. Homopolymer, BCP and gold nanoparticles have been successfully patterned on sub-200 nm CNT rings. These unique hybrids are of great interest in various areas of nanoelectronics and single-electron devices. [Preview Abstract] |
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S1.00084: Nucleation and Growth of Hydroxyapatite on Hierarchically Ordered Polymer Nanofibers Xi Chen, Bin Dong, Bingbing Wang, Christopher Li The hierarchically ordered polymer nanofibers, named as nanofiber shish kebabs (NFSKs), were constructed via combination of electrospinning polycaprolactone (PCL) (shish polymer) and controlled crystallization of polycaprolactone-b-poly acrylic acid (PCL-b-PAA) (kebab polymer). These NFSKs were then employed as a template to control the nucleation and growth of hydroxypatite nanocrystals. Electron microscopy and diffraction technique were used to characterize this novel hybrid structure. The growth of minerals starts on the surface of single crystal kebabs and eventually covers the surface of NFSKs. The formation mechanism of hydroxyapatite on NFSKs is of great interest because of the NFSKs' potential application as bone scaffold materials. [Preview Abstract] |
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S1.00085: Direct nanoparticle assembly in block copolymer based supramolecules containing liquid crystal Myung Im Kim, Clayton E. Mauldin, Jean M.J. Frechet, Ting Xu Block copolymer (BCP)-based supramolecules which combine the nanoscopic assembly of BCPs and molecular ordering can generate hierarchical structure with built-in functionality. Here, we investigated the phase behavior of BCP-based supramolecules containing cholesteric liquid crystal (LC) moieties and achieved directed assembly of nanoparticles. In bulk, we found that BCP-based supramolecules formed a cylinder-in-lamellar structure after solution casting. Upon heating, the order-order transition from cylinder-in-lamella to lamella-in-cylinder was observed. In thin films, supramolecules forming a parallel cylinder-in-lamella structure on silicon substrates were induced by solvent-annealing in chloroform vapor. In addition, we could achieve directed nanoparticle assembly in BCP-based LC supramolecules in bulk and in thin films with control of nanoparticle spatial distribution. [Preview Abstract] |
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S1.00086: Assemble Nanoparticles in Diblock Copolymer-Based Supramolecular Thin Films in Fifteen Minutes Joseph Kao, Vivian Chuang, Seong-Jun Jeong, Ting Xu Controlling nanoparticle assemblies in thin films enables one to exploit their collective properties to generate functional devices such as hybrid photovoltaic cells, capacitors and optical waveguides. This requires precise control over nanoparticle assemblies over multiple length scales with a single particle precision. Moreover, to be compatible with large-scale processing, there is a need to reduce the processing time down to minutes. Here we present a simple yet robust approach where hierarchical assemblies of nanoparticles in thin films can be achieved in 15 minutes with control over the macroscopic alignment of nanoparticle assemblies as well as the inter-particle ordering. We use diblock copolymer-based supramolecules, in which the small molecules are attached to the polymer side chains non-covalently, to direct the assemblies of nanoparticles in thin films. Furthermore, vertical alignment of nanoparticle assemblies can be readily obtained in the films with thicknesses from 50 to 300 nm without balancing the interfacial interactions. The simplicity, robustness and the rate of nanoparticles assemblies in thin films makes it possible to apply this approach to the fabrications of nanoparticle-based nanodevices over macroscopic distances. [Preview Abstract] |
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S1.00087: PS-\textit{b}-PDMS Block Copolymer Thin Film: Pattern Formation and Phase Behavior I-Fan Hsieh, Stephen Z.D. Cheng Recently, block copolymer thin films attract great attention due to their potential applications in surface nano-lithography. In our work, PS-$b$-PDMS with cylinder morphology is chosen due to extremely large $\chi $ value between two blocks. Besides, PS-$b$-PDMS can be transformed into silicon oxide under UV/O$_{3}$ exposure and a layer of silicon oxide with the self-assembled block copolymer patterns can be made. By utilizing the PGMEA as solvent, we can easily obtain sphere morphology in cylindrical composition block copolymer by preserved block copolymer solution morphology during film formation. Furthermore, in thermal annealing process, the phase behavior of the PS-$b$-PDMS thin film is strongly affects by molecular weight, film thickness and annealing temperature. In larger-molecular-weight PS-$b$-PDMS, we only observed spherical domains rearrangement and without morphology transition between sphere and cylinder due to high energy barrier, whereas, in the case of smaller-molecular-weight polymer, depending on the film thickness and annealing temperature, its thin film morphology transits between sphere and cylinder alternatively, which is similar to what we found in solvent annealing. [Preview Abstract] |
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S1.00088: Directing morphology development in Triblock copolymers: A Self-Consistent Field Theory Study Mougeh Mohagheghi, Bamin Khomami Using combinatorial screening method based on self-consistent-field theory for multicomponent polymers, we study ABC block copolymers melt confined between two parallel neutral walls separated by distance L in which the backbone consists of A and B and C is the graft. We analyze the behavior of the system as a function of film thickness. It is shown that confining walls can direct the assembly of thin films of block copolymers. Moreover, by judicious select of film thickness and the position of the graft point, a number of novel morphologies that have not been experimentally realized to date can be created. Overall, These results demonstrate a promising strategy for fabrication of complex nanostructure materials for a variety of important applications such as organic photovoltaic materials. [Preview Abstract] |
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S1.00089: How Fast Liposomes Diffuse in the Extracellular Matrix James Kuo, Bo Wang, Sung Chul Bae, Steve Granick Single-particle tracking is used to compare the diffusivity of soft spheres (liposomes) with that of hard spheres of the same size, when they are embedded within gels whose mesh size is smaller than the particle size. The comparison is made in model systems and also in cell extracts of closer biological relevance. In both environments, the diffusivity of liposomes is systematically faster than that of hard spheres. [Preview Abstract] |
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S1.00090: COMPLEX STRUCTURED MATERIALS III |
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S1.00091: Preparation and Magnetic Properties of Co2Z Hexaferrite From Annealed Mixtures of BaM and Co2Y Hexaferrite Precursor Powders Marc Doyle, Brian Kelly, Thomas Ekiert, Karl Unruh The transformation of fine mixtures of BaM and Co2Y hexaferrite powders to Co2Z hexaferrite has been studied by scanning electron microscopy (SEM), x-ray diffraction (XRD), and vibrating sample magnetometry (VSM) measurements. The precursor hexaferrites were prepared by a solution-phase auto-combustion method and subsequently mixed in a low energy rolling mill. The BaM/Co2Y mixtures were annealed at temperatures between 800 and 1300 \r{ }C in air for 2 hours. Over this temperature range a rapid decrease in the measured coercivity from a value of about 4 kOe, characteristic of the hard BaM component of the mixture, to a value of about 50 Oe, characteristic of the magnetically soft Co2Z phase, was observed. The coercivity reduction was accompanied by a modest increase in the saturation magnetization to a value of about 60 emu/g. [Preview Abstract] |
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S1.00092: A High Energy X-Ray Diffraction Study of the Atomic-Scale Structure of Novel Vitreous Rare Earth Phosphates Erandi S. Gunapala, G.K. Marasinghe, Chris J. Benmore The magneto-optical properties of rare earth phosphate glasses make them good candidates for numerous potential applications including high-energy/high power ($\sim $10$^{15}$ watt) lasers. Because, properties of these materials depend heavily on their atomic structure, a detailed study can facilitate development of additional applications. A series of (Pr$_{2}$O$_{3})_{x}$(P$_{2}$O$_{5})_{1-x}$ glasses where 0.05 $\le x\le $ 0.25 had been characterized by high energy X-ray diffraction. Coordination parameters for nearest coordination neighbors were obtained by Gaussian fitting. The P-O coordination number, $N_{PO}$, and the P-O, O-O, P-P distances were found to be insensitive to the Pr$_{2}$O$_{3}$ content. Coordination numbers $N_{PrO}$ decreased from $\sim $ 8.0 to $\sim $ 7.5 with increasing Pr$_{2}$O$_{3}$ content from 0.12 to 0.23. Pr-O distance did not seem to vary with Pr$_{2}$O$_{3}$ content in the $x$ range that we studied. [Preview Abstract] |
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S1.00093: ABSTRACT WITHDRAWN |
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S1.00094: Characterizing the Structure and Porosity of Organic Molecules of Intrinsic Microporosity by Molecular Simulations and Experiment Lauren J. Abbott, Amanda G. McDermott, Annalaura Del Regno, Kadhum J. Msayib, Mariolino Carta, Rupert Taylor, Neil B. McKeown, Flor R. Siperstein, James Runt, Coray M. Colina Organic molecules of intrinsic microporosity (OMIMs) are amorphous, glassy solids that contain interconnected pores of sizes smaller than 2 nm. The philosophy behind OMIMs is similar to that of polymers of intrinsic microporosity (PIMs); rigid, awkwardly shaped molecules frustrate packing and form low density materials with intrinsically porous structures. Atomistic simulations were performed on OMIMs using our recently developed packing and compression procedure to study the effect of structure on packing behavior. The structure and porosity of the simulated samples were characterized, such as by surface areas and structure factors, and compared to experimental results. The presented computational procedure will further understanding of structure-property relationships and aid in the design of novel materials with high surface areas. [Preview Abstract] |
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S1.00095: Long-Range Potential Fluctuations in GST Chalcogenide Glasses Rajeev Gupta, Ch. Bapanayya, S.C. Agarwal Ge-Sb-Te (GST) alloys are widely used for data recording based on the rapid and reversible amorphous to crystalline phase transformation that is accompanied by an increase in the optical reflectivity and electrical conductivity. However, their application in advanced memory technology is limited by their endurance; Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST225) switch has the longest life. Search for more efficient materials has been on, but has not been fully successful so far. This is primarily because one does not know the algorithm to prepare such a material. In this paper, electrical transport properties - electrical conductivity and thermopower of GST alloys are studied and the widths of long-range spatial potential fluctuations present in thin films are estimated. The study shows that amorphous GST225 has the smallest potential fluctuations among all the alloys studied. This finding is correlated to the performance of the phase change materials. The presence of potential fluctuations increases the minimum free energy of the amorphous phase. This deteriorates the switching ability after a few cycles. This suggests that the material with smaller potential fluctuations is likely to be better suited as a switch with a longer life. [Preview Abstract] |
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S1.00096: Extended X-ray Absorption Fine Structure (EXAFS) Analysis of Novel High Laser Media Aranwela Hemantha, G.K. Marasinghe, Carlo Segre, Richard Brow Rare earth-doped phosphate glasses are useful for a variety of optical and optoelectronic applications including high energy/high power ($\sim $10$^{15}$ watt) Lasers. Binary (R$_{2}$O$_{3})_{x}$(P$_{2}$O$_{5})_{1-x}$ glasses can be prepared in the compositional range 0 $\le $ x $\le \quad \sim $0.30. Atomic-scale structure, especially the coordination environment of R$^{3+}$ ions, play a major role in determining optical/physical characteristics. We have investigated the R$^{3+}$ local environment of Praseodymium and Neodymium ultraphosphate and meta phosphate(REMP) glasses using extended X-ray absorption fine structure technique. For both Nd and Pr phosphate glasses, nearest neighbor (oxygen) coordination decreases with increasing RE concentration. For the first oxygen shell the RE-O distance ranges between 2.38-2.40 {\AA} and 2.39-2.46 {\AA} for Nd and Pr respectively. The second co-ordination shell around the RE ions consists of phosphorus ions, with RE-P distance about 3.4-3.5 {\AA} and co-ordination numbers ranging from 1.5 to 3. There exists an Oxygen shell (third shell) about 4.1 {\AA} from RE ion for both Nd and Pr phosphate glasses. [Preview Abstract] |
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S1.00097: Dynamics of endohedral hydrogen in C$_{60}$: Infrared study Min Ge, U. Nagel, D. Huvonen, T. Room, S. Mamone, M.H. Levitt, M. Carravetta, Y. Murata, K. Komatsu, J.Y.-C. Chen, N.J. Turro Infrared spectra of endohedral hydrogen isotopomers H$_2$, D$_2$, and HD were measured in the temperature range from 6 to 300\,K. A model of a vibrating rotor in a spherical potential together with the translational motion induced dipole moment theory was used to explain the positions and intensities of IR absorption lines. By measuring spectra of a {\it para\/} enriched sample of H$_2$@C$_{60}$, we confirmed the assignment of lines to {\it ortho\/}- and {\it para\/}-H$_2$. Inside C$_{60}$ cage the rotation of hydrogen is unhindered and the translation is quantized and coupled to the rotation. The isotropic and translation-rotation coupling part of the potential are anharmonic and depend on the vibrational states of hydrogen. The analysis of the isotopic effect on the IR transition intensities and interaction potential in the C$_{60}$ cage is presented. [Preview Abstract] |
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S1.00098: Interplay between structural and electronic properties of various fullerene derivatives, and their absorption spectra Sora Park, Jeung Sun Ahn, Young-Kyun Kwon Using density functional theory (DFT), we investigate the geometrical structures and electronic properties of various fullerene derivatives formed by attaching several kinds of addends on C$_{60}$ through [2+2] cycloaddition. Various forms of such derivatives are modeled by considering different kinds, different positions and different numbers of addends to study how structural configurations will affect their electronic structures. Our results reveal that some derivatives with certain symmetries determined by the configuration of addends may have wider energy gap than that of pristine C$_{60}$. This suggests that absorption properties could be adjusted by controlling the addends configurations. To describe the excited state properties, such as absorption spectra, of various C$_{60} $ derivatives more accurately, we performed time-dependent (TD) DFT calculations. We find the position and the intensity of the peak of absorption spectra of derivatives are affected by the specific symmetry of the derivatives defined by the configurations of the addends. To explore such peculiar effects, we analyze the charge distribution and orbital mixing characters. [Preview Abstract] |
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S1.00099: Effective Shear Strain in Helical Rippled Carbon Nanotubes: A Unifying Concept for Understanding Electromechanical Response Traian Dumitrica, Dong-Bo Zhang Despite its importance, little is known about how complex deformation modes alter the intrinsic electronic states of carbon nanotubes. Here we consider the rippling deformation mode characterized by helicoidal furrows and ridges and elucidate that a new intralayer strain effect rather than the known bilayer coupling and $\sigma$-$\pi$ orbital mixing effects dominates its gapping. When an effective shear strain is used, it is possible to link both the electrical and the mechanical response of the complex rippled morphology to the known behavior of cylindrical tubes. In combination with objective molecular dynamics, this concept may be useful for understanding the electromechanical characteristics of large scale carbon nanotube assemblies and other individual nanoscale forms of carbon.\\ Reference: D.-B. Zhang and T. Dumitric\u{a}, ACS Nano (2010) DOI: 10.1021/nn1019658. [Preview Abstract] |
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S1.00100: Spin-dependent Tunneling through a Potential Barrier on a Nanotube Yonatan Abranyos, Godfrey Gumbs, Paula Fekete The electron spin effects on the surface of a nanotube have been considered through the spin-orbit interaction (SOI), arising from the electron confinement on the surface of the nanotube. This is of the same nature as the Rashba-Bychkov SOI at a semiconductor heterojunction. We estimate the effect of disorder within a potential barrier on the transmission probability. Using a continuum model, we obtained analytic expressions for the spin-split energy bands for electrons on the surface of nanotubes in the presence of SOI. First we calculate analytically the scattering amplitudes from a potential barrier located around the axis of the nanotube into spin-dependent states. The effect of disorder on the scattering process is included phenomenologically and induces a reduction in the transition probability. We analyzed the relative role of SOI and disorder on the transmission probability which depends on the angular and linear momentum of the incoming particle, and its spin orientation. We demonstrated that in the presence of disorder perfect transmission may not be achieved for finite barrier heights. [Preview Abstract] |
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S1.00101: A First-Principles Study of SiGe Nanotubes Prabath Wanaguru, Asok K. Ray A systematic study of the electronic structures of three types of SiGe armchair nanotubes from (3, 3) to (11, 11) using periodic boundary conditions has been performed. Geometries of the tubes have been optimized using the hybrid functional B3LYP, the double-zeta LANL2DZ basis set and the GAUSSIAN 03/09 software. Variations of the cohesive energies, band gaps, bond lengths, and Mulliken charges, among others, with the tube diameters will be presented in detail. The cohesive energies of all tubes, in general, increase as the diameters increase and appear to saturate at about 2.98eV for (11, 11) tubes. However, band gaps indicate an oscillatory pattern, with type 2 tubes, in general, with smaller band gaps. Results will be compared with previous results for SiGe tubes using the cluster approximation.\footnote{S. Rathi and A. K. Ray, Chem. Phys. Lett. 466, 79 (2008).} [Preview Abstract] |
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S1.00102: Gas molecule adsorption on silicene nanoribbons: Conductance modulation and contact effects Tim Osborn, Amir Farajian We investigate the effects of adsorption of gas molecules on the quantum conduction of silicene nanoribbons with and without silver contacts, using ab initio methods and Green's function formalism. The adsorption positions and orientations are determined through energy calculations and structure optimizations for NO$_2$,CO$_2$, and CO gas molecules. The conduction change upon gas molecules adsorption is studied for isolated silicene nanoribbons and for silicene nanoribbons on silver side contacts for potential applications as ultrasensitive nanoelectrochemical sensors. [Preview Abstract] |
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S1.00103: A first principles study of the localized electronic states of noble metal atoms doped in Si nanocrystals Cedric L. Mayfield, M. Saif Islam, Mowafak M. Al-Jassim, Muhammad N. Huda The quest for a efficient energy conversion material has necessitated a detail study of semiconductors. Silicon is already playing important roles in many useful nano-applications. To optimize these nano-applications, electronically tailored nano-materials are needed. A number of semiconductor nanomaterials are synthesized using metal as catalysts contributing to various impurities into the nanomaterials. The solubility of a metal in nanomaterials is significantly higher than that in bulk materials. In this presentation, electronic and structural properties of noble metal atoms doping in silicon nano-crystals will be explored using density functional theory. The pristine nanocrystals are based on three different isomers of bulk silicon. We have identified the lower energy isomer and doped it with noble metals. Characterization of the structural changes is accomplished by studying the bonding near the impurity as a function of dopant site. Furthermore, energetic of these nano-structures, both doped and un-doped, such as binding energies, formation energies, and HOMO LUMO gaps will be compared along with their charge densities to identify localizations with respect to impurity site. Magnetism and surface terminations will also be addressed. [Preview Abstract] |
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S1.00104: Electronic Properties and Work Functions of Metallic Hexaboride Rods and Slabs Lu Wang, Guangfu Luo, Renat F. Sabirianov, Wai-Ning Mei, Jing Lu, Chin Li Cheung In this work, we performed electronic structure calculations of quasi one-dimensional metallic hexaboride XB$_{6}$ nanorods, where X are mostly rare-earth metals with 4f levels such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. In addition we included Ca, Sr, Ba, Sc, Y, and Si for comparison and then complimented those with calculations of LaB6 slabs with different boundaries and low index surfaces. Our purpose is to facilitate the research and manufacture of metal boride probes, thus we study extensively the size-dependence and element-specificity of the electronic properties, particularly the work functions, in nanorods and slabs composed of the rare-earth metal borides, which usually regarded as good thermoelectric materials. We uncovered few general features that elucidate their excellent thermionic and field emission property. To accomplish our calculations, we applied density functional theory together with minimization scheme based on the ensemble density functional theory to facilitate convergence when optimizing structures of these rare-earth metallic haxaboride rods, which have plenty of 4f levels at the Fermi levels. [Preview Abstract] |
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S1.00105: Anisotropic Electrical Properties of Nanostructured Metallic Thin Films Mo Ahoujja, Piyush Shah, Andrew Saragan, Said Elhamri, Elena Guliants High surface area, porous, metallic (Ti, Cr) nanorod thin films with columnar microstructure can be deposited using conventional physical vapor deposition technique of E-beam evaporation. The technique relies on the physical vapor deposition onto a static substrate oriented in a position where flux from the source material (Ti, Cr) arrives at oblique angle. The adatoms provides geometrical shadowing which results in growth of nanorod columns in the direction of vapor source. Deposition conditions such as angle of the incoming vapor flux, substrate temperature, surface diffusion etc. have strong influence on the shape and arrangement of the columnar thin films. In this work, we demonstrate the growth and electrical characterization of these nanostructured thin films. Preliminary results on these films exhibit electrical resistivity anisotropy, when characterized by measuring their electrical resistivity using conventional van der pauw method. Origin and possible causes of this resistivity anisotropy is discussed. [Preview Abstract] |
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S1.00106: An \textit{Ab Initio }Study of SiC Double-Walled Nanotubes of Types 2 and 3 Kapil Adhikari, Asok Ray A hybrid density functional study of armchair SiC double walled nanotubes (DWNTs) of types 2 and 3 is presented. The geometries of individual DWNTs of types 2 and 3 have been spin optimized using the hybrid functional B3LYP (Becke's three-parameter exchange functional and the Lee-Yang-Parr exchange-correlation functional) and the basis set 3-21G* and the GAUSSIAN 09 software. A study of binding energies, Mulliken charge, density of states and HOMO-LUMO gaps has been performed for all nanotubes from (n,n)@(n+3,n+3) to (n,n)@(n+6, n+6) (n=3-6). Type 2 DWNTs do not conserve the coaxial geometry when the difference in chirality of outer and inner tube is 5 or less. For type 3, this occurs when the chirality difference of 4 or less. The gaps of types 2 and 3 DWNTs are less then the corresponding single-walled nanotubes and are significantly less than those of type 1 DWNTs. [Preview Abstract] |
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S1.00107: Effects of NO$_2$ physisorption and chemisorption on the conduction of graphene nanoribbons Ahmed Hassan, Cory Knick , Amir Farajian Graphene nanoribbons have the potential of being used as the functional part of nanoelectronic gas sensors. This study focuses on the changes induced in the conduction of graphene nanoribbons upon adsorption of NO$_2$. Both chemisorption and physisorption situations, i.e., NO$_2$ adsorption with and without chemical bond formation, are studied. We use ab initio electronic structure calculations with MP2 correlation energy in order to optimize the structures of graphene nanoribbons, with hydrogen-terminated edges, in presence of NO$_2$. Subsequently, quantum conductance calculations are performed using Green's function implementation of the Landauer's approach. We explain different conductance modulation patterns in terms of charge transfer and dipole interactions. The results clarify some of the basic functionality issues of nanoelectronic-based gas sensors. [Preview Abstract] |
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S1.00108: An \textit{Ab Initio }Study of Atomic Hydrogen and Oxygen Adsorptions on Armchair Si Nanotubes Haoliang Chen, Asok Ray First principles calculations based on hybrid density functional theory have been used to study the electronic and geometric properties of armchair silicon nanotubes from (3, 3) to (12, 12). Full geometry and spin optimizations have been performed without any symmetry constraints with an all electron 3-21G* basis set and the B3LYP functional. The largest silicon nanotube studied has a cohesive energy of 3.47eV/atom. Atomic hydrogen and oxygen adsorptions on a (6, 6) tube have been studied by optimizing the distances of the adatoms from both inside and outside the tube. The on-top external site is the most preferred site for hydrogen with an adsorption energy of 5.97eV and an optimized distance of 1.50 A. For oxygen, the external bridge site is the most preferred site with an adsorption energy of 11.36eV, the optimized distance being 1.66A. [Preview Abstract] |
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S1.00109: Structural, Electronic and Transport Properties of Gd/Eu Atomic Chains Encapsulated in Single-walled Carbon Nanotubes Jing Zhou, Xin Yan, Guangfu Luo, Rui Qin, Hong Li, Jing Lu, Zhengxiang Gao, Wai Ning Mei Structural, electronic, and transport properties of Gd/Eu atomic chains encapsulated in single-walled carbon nanotubes (SWCNTs) are studied by using first-principles density functional theory and nonequilibrium Green's function method. We find that the linear single-atom Gd and Eu chains occupy an off-centered position when encapsulated in the (8,0), (10,0), and (6,6) SWCNTs and considerable electrons are transferred from the Gd and Eu chains to the SWCNTs. The resulting composites are all ferromagnetic metals, with conductivity significantly larger than those of the pristine SWCNTs and the free-standing Gd/Eu linear single-atom atomic chains. The spin polarization of the finite Gd linear single-atom chain at the Fermi level is 67{\%} when encapsulated in the (8,0) SWCNT from the quantum transport calculation. [Preview Abstract] |
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S1.00110: Anisotropic Conductivities of Magnetic Carbon Nanotubes Embedded in Epoxy Matrices Il Tae Kim, Allen Tannenbaum, Rina Tannenbaum Maghemite ($\gamma $-Fe$_{2}$O$_{3})$/carbon nanotubes (CNTs) hybrid-materials were synthesized and their anisotropic electrical conductivities resulting from their alignment in a polymer matrix under a magnetic field were investigated. The tethering of $\gamma $-Fe$_{2}$O$_{3}$ nanoparticles on the surface of CNT was achieved by a modified sol-gel reaction. These hybrid-materials, specifically, magnetized carbon nanotubes (m-CNTs) were readily aligned parallel to the direction of a magnetic field even when using a relatively weak magnetic field. The conductivity of the epoxy composites formed in this manner increased with increasing m-CNT mass fraction in the polymer matrix. Furthermore, the conductivities parallel to the direction of magnetic field were higher than those in the perpendicular direction, indicating that the alignment of the m-CNT contributed to the enhancement of the anisotropic electrical properties of the composites in the direction of alignment. [Preview Abstract] |
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S1.00111: Double Layer Charging for Conductivity Enhancement of Pure Metallic and Semiconducting Single Wall Carbon Nanotubes Nathanael Mayo, Alexander Kuznetsov, Anvar Zakhidov Injecting high electronic charge densities can profoundly change the optical, electrical, and magnetic properties of materials. Evidence suggests a possibility of significantly improving conductivity of carbon nanotubes through double layer charge injection. Double layer charge injection can prove to be a powerful method when applied to carbon nanotubes because of theirs high surface area and chemical stability. Investigation has commenced on the effect of charging on various types of carbon nanotubes, specifically 99{\%} purified single wall semiconducting and single wall metallic tubes. An electrical double layer is electrochemically introduced upon a sheet of carbon nanotubes via application of potential (up to $\pm $5 volts) to a sample immersed in ionic-liquid-based electrolyte. Resistance of carbon nanotube as a function of applied charging voltage is recorded to determine the effects of charge injection. Results show that the electrical double layer considerably reduces the resistance across both samples. ESR/LFMA studies combined with low temperature magnetic and transport measurements are conducted to search for charge injection induced superconductivity in carbon nanotubes. [Preview Abstract] |
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S1.00112: Synthesis, micro and electronic structure investigation of diamond nanorod spherules by High resolution NEXAFS coupled PEEM and field emission performance Swathi Iyer, Paul Maguire We report the synthesis of Diamond nanorods/flake Spherules (DNRS) predominantly consisting of UNCD enveloped by graphite in the form of flake or a rod with nanodimension, projecting randomly outward in all directions. The diamond nanoflake with a diameter of $\sim $2 nm has a central diamond (111) core encapsulated by graphitic (0002) lacing. The structure composition by High Resolution Transmission Electron Microscopy (HRTEM) and X ray Photoemission Electron Microscopy (XPEEM) revealed that the nanoflakes predominant with core sp$^{3}$ laced with sp$^{2}$, is embedded in carbon matrix consisting of other nanocarbon, such as the nanotubes, nanoonion and nanowires/sheets. High resolution localized XPEEM combined with XAS complimented the Raman and the XPS with a weak $\pi $* peak, a prominent exitonic and a second band dip, which are the signature of diamond. The congregated nanorod spherules exhibits a low-threshold, high current-density of 10 mA/cm$^{2}$ at 2.9 V/m which appears to be exceptional when compared to many other electron emitting nanostructures. Bias enhanced DNRS were also characterized by XPEEM and their FE's compared. [Preview Abstract] |
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S1.00113: Heat transfer through a dual-walled carbon nanotube Khoa Bui, Cedric Cousin, Huong Nguyen, Alberto Striolo, Dimitrios Papavassiliou Molecular Dynamics simulations are used to investigate the resistance to heat tranfer between the walls of dual-walled carbon nanotubes (DWCNTs). Recent computional results have indicated that the carbon nanotube to carbon nanotube thermal boundary resistance (TBR) can be as high or higher than the TBR between a nanotube and the surrounding matrix (e.g., epoxy or octane) in thee case of composites. This generates the question of whether heat transfer in multi-walled carbon nanotubes occures through the outer nanotube only or not. We discuss here results for a DWCNT composed of a (5,5) nanotube inside a (10,10) nanotube, as well as the differences between this case and the case of a (6,6) inside a (19,0). [Preview Abstract] |
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S1.00114: Aspect Ratio Dependant Buckling Mode Transition in Single-Walled Carbon Nanotubes under Compression Chun Tang, Jeremy Feliciano, Changfeng Chen We have conducted molecular dynamics simulations on compressing behaviors of single-walled carbon nanotubes (SWCNTs) with a large variaty of aspect ratios. It is found that SWCNTs with large aspect ratios experience column buckling behavior at low strain levels, in contrast to commonly observed shell buckling of short SWCNTs. Further compression leads to a transition to a shell buckling mode, which is distinct from those of short SWCNTs under compression. It originates from the column buckling induced bending loadings. We extract the scaling law with respect to the aspect ratio of SWCNTs based on an analytical model of bending buckling. [Preview Abstract] |
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S1.00115: Intershell Interaction in a Double Wall Carbon Nanotube with Determined Chiral Indices under a Torsional Strain Letian Lin, Taoran Cui, Sean Washburn, Lu-Chang Qin We have used a double wall carbon nanotube to build a torsional pendulum. The nanotube worked as a torsional bearing for a metal block. An external electric field was used to rotate the metal block to cause a fully elastic torsional deformation on the nanotube. Nano-beam electron diffraction patterns were taken before and while the nanotube was twisted. By analysis of the shift of the diffraction patterns, we were able to determine the nanotube chiral indices and measure the inner-shell torisonal responses to the torsional stress applied on the outer-shell. The inter-shell interactions and nanotube shear modulus were also calculated and discussed in connection to the theoretical estimations. [Preview Abstract] |
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S1.00116: Large Band Gap in Graphene Induced by Inhomogeneous Mechanical Deformation Ivan Naumov, Alexander Bratkovsky Graphene is a prospective material for future electronics. However, in order to become useful and work in electronic chips, graphene should have a semiconducting energy gap. The seemingly simplest way to induce a gap is to subject the graphene to a strain. Recently, it was predicted within tight-binding approximation that by combining shear deformations and uniaxial strains one can open the gap up at moderate strains ($\sim $12{\%}), well before the elastic limit of the material is reached. Here, we show with the help of ab-initio calculations that, in fact, the gap \textit{cannot} be opened up by any kind of homogeneous deformations smaller that the graphene failure strain. The gap, however, can be opened up by \textit{inhomogeneous} deformation, e.g. by the periodic out-of-plane atomic displacements with an ``amplitude-to-wavelength'' ratio on the order of 0.1, similar to Ref. [2], which translates roughly to only 10{\%} elongation. The gap can be quickly pushed to values up to 1 eV by further increase of strain still far enough from the point of mechanical failure. \\[4pt] [1] G. Cocco, E. Cadelano, and L. Colombo, Phys. Rev. B \textbf{81}, 241412 (2010). \\[0pt] [2] I. Naumov, A. M. Bratkovsky, and V. Ranjan, Phys. Rev. Lett. \textbf{102}, 217601 (2009). [Preview Abstract] |
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S1.00117: BIOLOGICAL PHYSICS |
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S1.00118: Substrate Recognition of Histone H2B by DUBm Elizabeth Henderson, Christopher Berndsen, Cynthia Wolberger The SAGA complex is a transcriptional coactivator that regulates gene expression in eukaryotes via histone acetylation and deubiquitination, which are crucial for transcription. Our lab is investigating the SAGA-dependent deubiquitination of histone H2B. The deubiquitinating module (DUBm) of SAGA is comprised of a ubiquitin-specific protease, Ubp8, and three other proteins. It is known that Ubp8 cleaves ubiquitin from histone H2B, however, the specific way in which the enzyme binds to the substrate remains elusive. In order to unravel this mechanism, we attempted to determine the crystal structure of the substrate binding complex. We obtained this substrate by exploiting the techniques of intein chemistry to artificially ubiquitinate a histone H2B peptide, which we then co-crystallized with DUBm. Additionally, we synthesized Ub-K63R-linked chains and Ub-K48-linked chains and co-crystallized them with DUBm. [Preview Abstract] |
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S1.00119: pH Dependent Photoinduced Effects of Protoporphyrin IX to Human Serum Albumin Sarah Rozinek, Jorge Palos-Chavez, Lorenzo Brancaleon Irradiation of the non-covalent complex between protoporphyrin IX (PPIX) and $\beta $-lactoglobulin (Blg), causes a modest unfolding of the protein localized to Trp19. That binding site is affected by pH of the solution. At physiological pH, PPIX is known to bind HSA in hydrophobic binding sites. However, no evidence is presented for the binding behavior of PPIX to HSA in non-physological pH confirmations, nor on the effects of irradiation on the bound system at any pH. The combination of spectroscopic data and molecular simulations suggests that distinct PPIX-compatible binding sites become available at each confirmation of HSA at pH 7.4, and 9 while the pH 3 conformation is unfavorable for binding. Photoinduced mechanisms produce changes in the ligand as well as the protein but they do not appear to be dependent on the presence of O$_{2}$ in solution. Therefore, the mechanism is not mediated by the formation of singlet oxygen and is likely the result of electron transfer between the porphyrin and amino acid residues. [Preview Abstract] |
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S1.00120: Docking ellipticine to the V-VI transmembrane domain of the Kv11.1 potassium channel Dawn Lipscomb, Lorenzo Brancaleon, S. Gentile Ellipticines such as 9-methoxy-N-2-methylellipticinium acetate (MMEA) and 9-hydroxy-N-2-methylellipticinium acetate (NMEA, Celiptium$^{\textregistered}$) are antineoplastic drugs exerting their selective cytotoxicity against leukemia and endometrial carcinoma. Ellipticine's action is also related to severe physical side effects, but the link between undesired effects and pharmacological application is not well understood. We investigated the binding of Ellipticine derivatives with the Kv11.1 potassium ion channel using Autodock and revealed that hydroxyellipticinium derivatives provide binding configurations with Kv11.1, but the energy, location and estimated dissociation constant varied. The binding energy is as follows: Chloroceliptium (-6.60 kcal/mol) $>$ Celiptium (- 6.37 kcal/mol) $>$ Methoxyceliptium (- 6.20 kcal/mol) $>$ Datelliptium (-6.08 kcal/mol). The data shows that some configurations enable these molecules to bridge among channel subunits, thus potentially inhibiting the flow of ions. [Preview Abstract] |
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S1.00121: Effects of the range and strength of interparticle attraction on gelation Toni Perez, James Gunton, Amit Chakrabarti Range and strength of interparticle attraction determine whether a complex assembly of particles will be ordered or disordered. For very short range interactions, the system seems to get trapped into a gel state as a result of arrested spinodal decomposition. On the other limit, for long range interactions, spinodal decomposition leads to phase separation. The nature of the gel transition at low volume fraction is still not well understood in between these two limits. Here, we study the dynamics of the gel transition at low volume fraction as a function of the range and strength of the attractive interparticle interaction. We perform Brownian dynamics simulations and study how gelation is affected as the range and strength of interparticle interaction are varied. [Preview Abstract] |
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S1.00122: Explore the physical mechanism of Hofmeister series on protein structural dynamics Sandip Kaledhonkar, Lorand Kelemen, Aihua Xie Hofmeister series, a classification of ions, are known to change the solubility and stability of proteins. We have found that Hofmeister series suppress functionally important structural dynamics of photoactive yellow protein (PYP). Here we investigate two possible mechanisms: (1) Hofmeister series increases the pK$_{a}$ of Glu46, an active site proton donor to chromophore protonation of PYP, (2) Hofmeister series alter the energy landscape of surface exposed groups due to effective dehydration, making it difficult to change protein conformations. We will test these two hypotheses using strategic combination of protein engineering and time-resolved step-scan and rapid-scan FTIR difference spectroscopy. A variety of N-terminus tags are designed and employed to study the effect of effective dehydration of protein due to Hofmeister series. Time-resolved infrared structural biology will be used to capture light-triggered structural dynamic motions of PYP. [Preview Abstract] |
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S1.00123: Time-resolved infrared structural biology: from active-site structural dynamics to proton transfer mechanism of photoactive yellow protein Shuo Dai, Lorand Kelemen, Zhouyang Kang, Wouter Hoff, Aihua Xie Proton transfer is a fundamental process in biology. We employ photoactive yellow protein (PYP), a bacterial blue light receptor protein, as an ideal model system to study the physical mechanism of intra-molecular proton transfer in proteins. We employ time-resolved step-scan FTIR spectroscopy to detect functionally important structural changes in the active site of PYP before and after proton transfer from Glu46 to the negatively charged phenolic group of the $p$-coumaric acid chromophore in PYP, which occurs on a 250 microsecond time scale. In addition, we employ a combination of isotope editing and site-specific mutations to identify the vibrational modes and structural origins of infrared signals, and we develop and utilize vibrational structural markers to translate infrared signals to structural information. We will demonstrate the power of time-resolved infrared structural biology in structure-function studies of proteins and in proton transfer mechanism in photoactive yellow protein. [Preview Abstract] |
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S1.00124: Exploring the effects of Hofmeister series ions on structural dynamics of water Ningning Xu, Thomas Wright, Sandip Kaledhonkar, Aihua Xie Water is known as the lubricant of life. Most proteins lose their biological function upon dehydration. We found that in a variety of high concentration salt solutions, photoactive yellow protein, a blue light bacterial photoreceptor protein, loses its functionally important structural motions for receptor activation. We hypothesize that this effect is caused by reduced structural dynamics of water due to strong water-ion interactions. Here we report our experimental studies on the effects of salts on changes in structural dynamics of water at different time scales. The results are expected to provide deep insight regarding how Hofmeister series ions alter the structural dynamics of proteins. [Preview Abstract] |
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S1.00125: Molecular Dynamics Simulations of Alpha-synuclein Maria Sammalkorpi, Carl Schreck, Abhinav Nath, David DeWitt, Elizabeth Rhoades, Corey O'Hern We investigate the conformational dynamics of single alpha-synuclein proteins, which have been implicated in amyloid diseases such as Parkinson's and Alzheimer's disease, in solution using unconstrained and constrained all-atom, explicit solvent molecular dynamics simulations. The constraints on inter-residue separations are obtained from our single-molecule FRET measurements of eleven FRET pairs that span the protein. By comparing the simulation data satisfying different combinations of FRET constraints, we are able to identify those constraints that are most important in determining the radius of gyration and key features of the contact map of the protein. [Preview Abstract] |
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S1.00126: InaD PDZs 4-5 Act as an Allosterically-Regulated Dynamic Scaffold Stephen Helms, Prashant Mishra, Michael Socolich, Rama Ranganathan The Drosophila scaffolding protein InaD is required for proper visual signaling. We previously identified that the fifth PDZ domain of InaD undergoes light-dependent PKC-mediated formation of a disulfide bond which disrupts the binding site. We investigated the interaction of this switch with the adjacent PDZ4 of InaD. We showed that PDZ4 destabilizes the disulfide bond and promotes binding of PDZ5 to its ligand, indicating a previously unidentified allosteric interaction between the two domains. We solved the structure of PDZ45 to 2.4{\AA}, which revealed that PDZ4 forms an extensive interface with PDZ5 but does not alter its conformation. NMR HSQC spectra, however, indicated that nearly all of PDZ5 is in a different chemical environment in PDZ45. Finally, we identified that PDZ45 is phosphorylated by PKC in vitro at a site located near the domain interface. Intriguingly, the disulfide bond in PDZ5 is an evolutionary adaptation of just fast-flying flies, revealing the remarkable ability of evolution to rapidly build novel regulatory features into scaffolding proteins. [Preview Abstract] |
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S1.00127: Tracking the Growth Transitions of A Solvent-Charged Model Globular Protein Jeremiah Babcock, Jacob Friday, Lorenzo Brancaleon Biophysical studies have shown that solutes like proteins undergo aggregation through specific pathways that often lead to long polymeric structures called fibrils. The knowledge of the size of early-stage protein aggregates (oligomers) has an important bearing on the elucidation of the dynamics of the process of protein unit combinations. In this study, bovine serum albumin, a well-characterized model protein known to polymerize in alkaline and acidic conditions in the normal (N) to basic (B) or (N) to (E) transition, was incubated at pH 9.0 and pH 3.1 for longer than eight days. Particle growth in solution was monitored by absorption, fluorescence and circular dichroism spectroscopy and concurrently measured by atomic force microscopy (AFM) methods to yield BSA oligomer size distributions. Results show that the BSA aggregation pathway is concentration-dependent and rapidly forms spherical aggregates, which preferentially come together to form flexible polymers. [Preview Abstract] |
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S1.00128: Low frequency Raman study of the nucleosides Craig Koontz, Scott Lee In both transcription and replication, the two helices of the DNA molecule move apart. Consequently, vibrations involving the relative motions of large portions of the molecule with respect to one another are of intrinsic interest. Such vibrations have relatively low frequencies because they involve weak bonds and large masses. Low frequency modes are difficult to observe in Raman spectroscopy because they are very close to the signal from the Rayleigh scattered light (which is very intense). In this poster, we will describe our results for the eight nucleosides: adenosine, deoxyadenosine, guanosine, deoxyguanosine, cytidine, deoxycytidine, uracil and deoxythymidine. [Preview Abstract] |
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S1.00129: A temperature-dependent study of the low-frequency vibrational excitations in polynucleotides in solution Kristina Woods, Scott Lee Far-infrared spectroscopy is a useful probe of low-frequency collective excitations of biomolecules, including DNA. These vibrational modes are believed to be related to conformational changes that occur in these molecules during their biological function and, therefore, are very important to study. In order to further our understanding of these modes, THz spectroscopy experiments were performed on solutions of polynucleotides between 20 to 100 cm$^{-1}$ from room temperature to 90 $^{\circ}$C, covering the premelting and melting regimes. The samples studied include Poly(dA-dT), Poly(dA)-Poly(dT), Poly(dI-dC) and Poly(dI)-Poly(dC). Of particular interest, the intensity of a band at about 67 cm$^{-1}$ is observed to increase as the melting proceeds. [Preview Abstract] |
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S1.00130: Modification of DNA towards high conductance and transport measurements with mechanically controllable break junction electrodes Shoupeng Liu, Benjamin Bornemann, Samuel Weisbrod, Zhuo Tang, Andreas Marx, Artur Erbe, Elke Scheer The DNA molecule is proposed to be used as building block for molecular electronic devices by virtue of its unique recognition and self-assembling properties. However, electron transport properties of DNA are still not well established mainly because poor binding between DNA and gold electrodes. Here, we synthesized new DNA samples with terminal bases modified with a thiol group on its C5 atom and protected with Me3Si for better binding with gold electrodes and better conductivity because of better electron overlap. Its transport properties were measured with mechanically controlled break junction. Conductance with a current of 700 nA in 0.25V were obtained, which is higher than most of the former reports. We also measured conductance through DNA G-quadruple instead of double-stranded structure., which shows a more stable conductance when the distance between electrodes reversibly varied over a several nm. [Preview Abstract] |
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S1.00131: QM/MM/3D-RISM study of solvation and electronic structure of DNA Norio Yoshida, Fumio Hirata It is well known that a DNA has high electronic conductivity in wet condition, while it doesn't in dry condition. Therefore, the solvent effects on the electronic properties of DNA got much attention in the field of biology, chemistry and physics. In the present study, we employ three-dimensional reference interaction site model method combined with quantum mechanics and molecular mechanics (QM/MM) method to treat the large DNA chain in solvent. By this theory, the electronic structure of DNA and solvent distribution around DNA can be determined simultaneously. The result shows the dramatic change of electronic structure of solute DNA molecule by solvation. The change strongly depends on the sequence of DNA. [Preview Abstract] |
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S1.00132: The driving forces of membrane remodeling by non-intrinsically curved proteins Christopher J. Ryan, Jeanne C. Stachowiak, Eva M. Schmid, Daniel A. Fletcher, Phillip L. Geissler Membranes are dynamically remodeled during numerous processes essential to cells. Among the most well-studied effectors of this remodeling are BAR family proteins, which are small and have a banana-like intrinsic curvature that senses, forms, and stabilizes curved membranes without expending energy as ATP or GTP. Recent experiments in reduced systems have shown, however, that small proteins that feature no such intrinsic curvature can similarly cluster at and dramatically remodel membranes. These proteins have no distinguishing features other than their size and their membrane-binding sites, and the dominant effect that is driving curvature is not well understood. Here, we present a coarse-grained simulation study that captures protein steric and binding effects as well as membrane fluctuations at large scales. We use this model to systematically test for the role that such attributes play in the resulting dynamics and equilibrium structures of remodeling processes that feature this motif. [Preview Abstract] |
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S1.00133: Analysis of Striped Nanoparticle Complexation with Lipid Bilayers Reid Van Lehn, Alfredo Alexander-Katz A recent study has shown that a new class of synthetic ligand-protected gold nanoparticles is able to penetrate the cell membrane without inducing poration or endocytosis. Furthermore, these nanoparticles fuse with pure lipid bilayers while retaining high solubility in biological conditions. This complexation behavior is related to the morphology of the ligand shell, which is composed of alternating ribbon-like domains of linear alkanes with either hydrophobic or charged end-groups. Spontaneous complexation is surprising given the large free energy barrier for moving charges through the hydrophobic bilayer core. In this work, we provide a thermodynamic analysis of bilayer complexation supported by multiscale simulations. We show that the key to bilayer complexation is the rearrangement of ligands by bending to maximize hydrophobic matching and minimize charge exposure. We believe this result will improve our understanding of transmembrane proteins and enable the design of nanoparticles for drug delivery and biosensing applications. [Preview Abstract] |
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S1.00134: The Comparison of Lipid Compositional Uniformity of Giant Unilamellar Vesicles Synthesized From the Rapid Solvent Exchange liposomes with That From Dry Lipid Film Eda Baykal-Caglar, Juyang Huang Lipid bilayer, which is an important constituent of cell membranes, has been extensively studied. Cell membranes perform many vital cell functions such as signal transduction and transportation of materials needed for the functioning of the cell organelles. Understanding the dynamics of lipid bilayers is important for understanding the processes taking place in cell membranes. Giant Unilamellar Vesicles (GUVs) are cell-sized model systems that allow direct visualization of membrane-related phenomena using fluorescence microscopy. In this study, we synthesized DOPC/DSPC/cholesterol GUVs and diPhyPC/DPPC/cholesterol GUVs by the standard electroformation method using dry lipid film as well as by a modified method using liposomes made from Rapid Solvent Exchange (RSE) method. Second method has a potential of incorporating more varieties of membrane proteins to GUVs. We compare the uniformity of lipid composition of GUVs synthesized by the two methods by measuring the variation of phase transition temperature of individual GUVs through fluorescence microscopy; since a narrower distribution of transition temperature should correspond to a more uniform distribution in GUV lipid composition. We will present the results at several bulk lipid compositions and buffer ionic strengths. [Preview Abstract] |
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S1.00135: Machanistic basis of rigidity sensing at biological interfaces Alireza Sarvestani We have outlined a framework to investigate the thermodynamic equilibrium adhesion of a bio-membrane to a compliant substrate functionalized with immobilized bio-adhesive ligands. The membrane is modeled as a soft elastic shell, subjected to surface tension and reconstituted with mobile receptors and a repelling layer on the ventral side. The free energy function of the system is assumed to be comprised from the following contributions: the membrane--substrate non-specific interactions, stored elastic energy (in deformed membrane and substrate), binding enthalpy, and mixing entropy of mobile receptors. Assuming a van der Waals form for the interfacial non-specific potential, the equilibrium configuration of the system is studied in detail. We have shown that the equilibrium spread area of the adherent membrane is very sensitive to the rigidity of the underlying substrate and decreases as the surface compliance increases. This prediction is reminiscent of the experimental observations of spread area of cells attached to soft substrates. This is an interesting result considering the lack of contribution of intracellular signaling or actively regulated cytoskeleton in the proposed physical model for the adhesion. This suggests that the mechanistic pathways inherent to membrane--substrate thermodynamic interactions can be equally important as intracellular signaling pathways to mediate the process of rigidity sensing by cells. [Preview Abstract] |
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S1.00136: Curved inclusions surf membrane waves Roie Shlomovitz, Nir Gov There is mounting recent evidence for the existence and biological importance of a large family of curved membrane proteins (CMPs). In addition there is increasing interest in membrane waves, and the role they play in cell function. In this theoretical work, we examine the interaction between CMPs and membrane waves. We find that CMPs are advected on the cell surface by membrane waves. We calculate the relative drift velocity of the CMPs with respect to the wave velocity, for the case of sinusoidal waves. For relatively slow waves the CMPs move at the wave velocity, i.e. ``surfing the wave.'' For fast waves the CMPs move back and forth with a Stokes drift that is inversely proportional to the quadrant of the wave velocity. For the more realistic case of decaying sinusoidal waves, we determine the equilibrium distribution of the CMPs, and find that such waves create a ``hole'' in the distribution of the CMPs on the cell membrane and calculate the size of that hole. Based on these calculations, we show how such proteins can be used in experiments to measure the properties of propagating membrane waves. [Preview Abstract] |
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S1.00137: Chemotaxis and Autotaxis in Biofilm-Forming Systems Shinji Strain, Samuel Bienvenu, Travis Thatcher, Benjamin Cooley, Vernita Gordon Biofilms are multicellular, surface-bound communities of interacting unicellular organisms. In the initial stages of biofilm formation, discrete cells populate the surface and eventually form microcolonies (dense surface-bound clusters of cells). How much these microcolonies arise from clonal growth and how much they arise from attraction and active motility of non-clonal cells is not well-understood. One potentially important form of attraction is autotaxis, movement of cells toward like cells. Another is chemotaxis, movement of cells toward an attractive chemical, which could act to concentrate cells with no direct intercellular interaction. While both autotaxis and chemotaxis have been studied for three-dimensional, swimming, dense bacterial systems, they remain largely unstudied in sparse, surface-bound populations that initiate biofilms. Using microscopy and automated tracking and analysis algorithms, we will study how bacteria respond to each other and to chemoattractants, in a spatially-dependent manner. We will determine how variations in neighbor density and arrangement stimulate changes in the motility of E. coli and P. aeruginosa cells on a surface. [Preview Abstract] |
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S1.00138: 3D single molecule super-resolution imaging of cellular samples using MUM Andrea Grosso, Anish Abraham, Jeffrey Kang, Jerry Chao, Ramraj Velmurugan, Sripad Ram, Stephen Anthony, Zhuo Gan, E. Sally Ward, Raimund J. Ober Localization based super-resolution imaging techniques (e.g., PALM, fPALM, STORM, etc.) represent a powerful tool to image single molecules at nanoscale resolution in two dimensions. However, the extension of these techniques to three dimensions poses several technical challenges, foremost being the poor depth discrimination inherent to conventional microscopes which is typically used by these techniques. Previously, we developed an imaging modality, multifocal plane microscopy (MUM), which overcomes the poor depth discrimination capability of conventional microscopes. We also introduced a 3D localization algorithm MUMLA and demonstrated experimentally that it provides the best possible accuracy with which the 3D position of single molecules can be determined. Here, we extend the application of MUM and MUMLA for super-resolution imaging and demonstrate 3D imaging of single molecules at nanometer scale resolution in a cellular sample. [Preview Abstract] |
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S1.00139: Accuracy of single molecule localization using electron-multiplying charge-coupled device cameras Jerry Chao, E. Sally Ward, Raimund J. Ober The electron-multiplying charge-coupled device (EMCCD) is an important technology for imaging under extremely low light conditions. Whereas a weak signal acquired under low light conditions can be overwhelmed by the readout noise of a conventional charge-coupled device (CCD), it is amplified in the case of an EMCCD such that the readout noise becomes insignificant. The EMCCD is therefore a commonly used image detector in applications such as single molecule microscopy. However, despite its wide use, there has been a lack of rigorous analyses to determine how accurately parameters of interest (e.g., location of a single molecule) can be estimated from an image it produces. Here, we model the EMCCD's stochastic multiplication of electrons as a geometrically multiplied branching process, and develop the theory for calculating the Fisher information for estimating parameters from an EMCCD image. A ``noise coefficient'' is also introduced which enables the comparison of a CCD and an EMCCD in terms of the best accuracy with which parameters can be estimated from the images they produce. [Preview Abstract] |
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S1.00140: Simultaneous AFM force spectroscopy and FRET measurements on single biological molecules Hui Li, Chi-Fu Yan, Sanjeevi Sivasankar Single Molecule Fluorescence Resonance Energy Transfer (FRET) and single molecule force measurements with the Atomic Force Microscope (AFM) are two powerful techniques that have facilitated much progress in the biological sciences. However each of these techniques suffers from limitations that can be overcome by the use of a combined single molecule AFM-FRET approach. Here, we describe an instrument that successfully combines single molecule AFM with FRET to apply forces on individual biological molecules and simultaneously monitor their conformational dynamics. To validate this technique, we measured the force induced shearing of dye-labeled, double stranded DNA. Single DNA molecules were sheared and mechanical transitions corresponding to DNA rupture were correlated with changes in FRET. [Preview Abstract] |
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S1.00141: The Heterogeneity of Mutational Tolerance in a Protein is Dependent on the Strength of Selective Pressure Correlating with Sectors of Co-evolving Residues Michael Stiffler, Rama Ranganathan Proteins are capable of tolerating mutations at many positions while still maintaining fold and function. Previous studies have failed to consider how tolerance to random mutagenesis might depend on the strength of selective pressure. To examine this, we measured the fitness of every single point mutation of TEM-1 beta-lactamase across a range of ampicillin concentrations utilizing a novel application of deep-sequencing. We found that the relative mutational robustness between positions varied considerably with respect to ampicillin concentration: at a low ampicillin concentration only a few positions are intolerant of mutations, while at a higher ampicillin concentration many additional positions are as equally intolerant of mutations. Using an analytic method termed statistical coupling analysis (SCA) to measure the co-variation between all positions in a sequence alignment of beta-lactamases revealed sectors of co-evolving positions associated with groups of residues having increased sensitivity to mutagenesis at either low or high ampicillin concentrations. Our findings suggest that nature has ``designed'' proteins to be robust to random mutagenesis by loading the constraints for fitness on discrete networks of co-evolving positions depending on the strength of selective pressure. [Preview Abstract] |
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S1.00142: The Evolutionary Design of Proteins Frank J. Poelwijk, Arjun S. Raman, Stanislas Leibler, Rama Ranganathan Proteins fold spontaneously into precise, well-packed 3D structures, and execute complex functions such as specificity in molecular recognition, and efficient catalysis. Despite this, many studies show that proteins are robust to random mutagenesis. Additionally, proteins are evolvable. What principles underlying the design of natural proteins explain these properties? Recent work examining correlated evolution of amino acid positions shows that many positions in proteins are nearly statistically independent while 10-20\% are organized into groups of co-evolving positions \ \textendash \ termed ``protein sectors'' \textendash \ that underlie conserved, independently varying biological activities. These findings suggest that the basic design of natural proteins is fundamentally tied to the nature of fluctuations in the selection pressures during evolution. We propose to test this hypothesis using a system for high-speed laboratory evolution and determine how variation in selection pressures influences the architecture of amino acid interactions within a protein. [Preview Abstract] |
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S1.00143: Laser-Neuron Interaction with Femtosecond Beat-Modulated 800-1200 nm Photon Beams, as the Treatment of Brain Cancer Tissue. Laser Neurophysics V. Alexander Stefan I propose a novel mechanism for the brain cancer tissue treatment: nonlinear interaction of ultrashort pulses of beat-photon, ($\omega _{1}$-- $\omega _{2})$, or double-photon, ($\omega _{1}+\omega _{2})$, \footnote{ Maria Goeppert-Mayer, \textbf{\"{U}ber Elementarakte mit zwei Quantenspr\"{u}ngen}\underline {,} \textit{Ann Phys} \textbf{9}, 273, 95. (1931). } beams with the cancer tissue. The multiphoton scattering is described via photon diffusion equation. The open-scull cerebral tissue can be irradiated with the beat-modulated photon pulses with the laser irradiances in the range of a few mW/cm$^{2}$, and repetition rate of a few 100s Hz generated in the beat-wave driven free electron laser.\footnote{V. Alexander Stefan, \textbf{Laser Neurophysics.} 2010 \textbf{APS March Meeting}, V. Alexander Stefan, 2009 \textbf{APS March Meeting}; V. Stefan, B. I. Cohen, and C. Joshi, \textbf{Nonlinear Mixing of Electromagnetic Waves in Plasmas}\textit{Science} 27 January 1989: V. Alexander Stefan, \textbf{Genomic Medical Physics: A New Physics in the Making}, (S-U-Press, 2008).} This highly accurate cancer tissue ablation removal may prove to be an efficient method for the treatment of brain cancer. [Preview Abstract] |
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S1.00144: The effect of Ag nanoparticles on PC3 cells ultraweak bioluminescence Marius Hossu, Xiaoju Zou, Lun Ma, Wei Chen Ultraweak intrinsic bioluminescence of cancer cell is a noninvasive method of assessing bioenergetic status of the investigated cells. This weak emission generated by PC3 cell line was measured during various stages of growth with or without the presence of Ag nanoparticles. The comparison between nanoparticles concentration, bioluminescence and cell survival showed that even though Ag nanoparticles doesn't significantly affect cell survival at used concentration it affects cell metabolism, possibly making them more susceptible to other form of therapies. [Preview Abstract] |
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S1.00145: Steinberg "AUDIOMAPS" Music Appreciation-Via-Understanding: Special-Relativity + Expectations "Quantum-Theory": a Quantum-ACOUSTO/MUSICO-Dynamics (QA/MD) Lee Fender, Russell Steinberg, Edward Carl-Ludwig Siegel Steinberg wildly popular "AUDIOMAPS" music enjoyment/appreciation-via-understanding methodology, versus art, music-dynamics evolves, telling a story in (3+1)-dimensions: trails, frames, timbres, + dynamics amplitude vs. music-score time-series (formal-inverse power-spectrum) surprisingly closely parallels (3+1)-dimensional Einstein(1905) special-relativity "+" (with its enjoyment-expectations) a manifestation of quantum-theory expectation-values, together a music quantum-ACOUSTO/MUSICO-dynamics(QA/MD). Analysis via Derrida deconstruction enabled Siegel-Baez "Category-Semantics" "FUZZYICS"="CATEGORYICS ('TRIZ") Aristotle SoO DEduction , irrespective of Boon-Klimontovich vs. Voss-Clark[PRL(77)] music power-spectrum analysis sampling-time/duration controversy: part versus whole, shows QA/MD reigns supreme as THE music appreciation-via-analysis tool for the listener in musicology!!! Connection to Deutsch-Hartmann-Levitin[\underline {This is Your Brain on Music}, (06)] brain/mind-barrier brain/mind-music connection is subtle/compelling/immediate!!! [Preview Abstract] |
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S1.00146: CuS Nanoparticles for Photothermal Ablation of Tumor Cells Wei Chen, Yuebin Li, Chun Li, Wei Lu, Qian Huang, Miao Huang Here, we report the photothermal ablation effects of 3-nm CuS nanoparticles. CuS nanoparticles exhibited strong absorption in the near infrared (NIR) region. Irradiation by a laser beam at 808 nm elevated the temperature of aqueous solutions of CuS nanoparticles as a function of exposure time and nanoparticle concentration. CuS nanoparticles mediated photothermal destruction of HeLa cells in a laser dose- and nanoparticle concentration-dependent manner, and displayed minimal cytotoxic effects with a profile similar to that of gold nanoparticles. Owing to their unique optical property, small size, low cost of production, and low cytotoxicity, CuS nanoparticles are promising new nanomaterials for cancer photothermal ablation therapy. [Preview Abstract] |
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S1.00147: Characterization of Blood Flow in Capillaries by Numerical Simulation Tong Wang, Zhongwen Xing We presents a numerical investigation of the axisymmetric, pressure driven motion of single file erythrocyte (i.e., red blood cell) suspensions flowing in capillaries of diameter 8-11$\mu$m. The governing Navier-Stokes equations are discretized using the operator splitting technique and solved by the finite element method. The study takes consideration the particulate nature of the blood. The red blood cell (RBC) is modeled as a closed membrane filled with a Newtonian fluid which has the same viscosity as the surrounding plasma. The cell membrane is described by a spring model so that the deformability of the cells can be considered. An immersed boundary method is also developed for dealing with the cell/fluid interaction in the flow. Our study successfully recreates several important in vivo hemodynamic and hemorheological properties of microscopic blood flow, such as parachute shape of the cells, blunt velocity profile, and the Fahraeus effect, and they have been shown to have strong dependence on cell deformability, hematocrit and vessel size. [Preview Abstract] |
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S1.00148: Sensing Labeled and Immunocomplexed DNA with solid-state nanopores Brian Thomas, Daniel Fologea, David S. McNabb, Jiali Li We report the detection of labeled and immunocomplexed DNA molecules using silicon nitride nanopores. We compared the characteristics of the current blockade signal measured from double-stranded DNA, biotinylated DNA, and immunocomplexed DNA samples. Single biotin-binding site Fab fragments as well as multiple-binding sites Monoclonal Biotin Antibodies were used to bind biotinylated DNA molecules. The electrical current blockage signature measured from the nanopores show that the current drop amplitude, time duration, and the integrated area of events can be used to discriminate DNA with and without labels, and the species of the labels. Our studies show that the single molecule nanopore measurement is more sensitive than bulk electrophoresis in detecting labeled DNA molecules. [Preview Abstract] |
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S1.00149: The translocation time of DNA and protein molecules in solid-state nanopores Bradley Ledden, Ryan Rollings, David Talaga, Jiali Li The time that a biopolymer takes to translocate through a nanopore contains the properties of the polymer including its size, conformation, electrical charge and charge distribution. We measured the dependence of the translocation times on the size, charge and charge distribution, voltage, and conformation states of DNA and protein molecules. To quantitatively fit the time distributions measured, 1-D Langevin and 1-D Fokker-Planck equations were used for DNA and native state proteins. Kramers reaction rate theory was used to fit the time distribution of unfolded proteins. It was observed that native-state protein and DNA translocation approximately follows simple one-dimensional biased diffusion of charged particles. Due to the heterogeneous charge sequence of polypeptides, unfolded proteins obey a coupled electrophoretic and thermally activated process that is sequence specific. Deviations between models and experimental results as well as future challenges for single molecule DNA and protein characterization using solid-state nanopores will be discussed. [Preview Abstract] |
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S1.00150: Emission line shape of B850 band of light-harvesting complex II Praveen Kumar, Seogjoo Jang A theoretical framework is developed for the emission line shape of the single complex spectroscopy (SCS). The quantum mechanical characteristics of the single complex emission line shapes for the model B850 band of the light harvesting complex 2 of purple bacteria are studied including both static and quasi-static disorders within the exciton Hamiltonian. The bath is modeled as an infinite sum of harmonic oscillators. For the Gaussian type of disorder, we examined the dependencies of the spectral line shapes on the temperature, polarization of the radiation, and on the type of exciton-bath coupling. Theoretically obtained emission profile is also compared with the absorption profile in the frequency domain. It is observed that emission profile contains an extra inhomogeneous term coming from the entanglement of the system and bath degrees of freedom in the initial equilibrium density operator. Contribution of this term to the overall emission line shape is studied in detail. [Preview Abstract] |
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S1.00151: Quantum Mechanisms of Electronic Signal Propagation Along a Microtubule Travis Craddock, Douglas Friesen, Jack Tuszynski Evidence has been accumulating for the involvement of quantum coherence and entanglement in light harvesting photosynthetic complexes. This tests the adage that biological systems are too ``warm and wet'' to support quantum phenomena. Recent advancements in experiment and theory have allowed investigators to probe other warm systems for coherent phenomena including polymer chains, bacteriorhodopsin and ion channels. A debate has raged for over a decade regarding hypothetical quantum coherence/ entanglement in microtubules. Here we theoretically investigate coherent energy transfer in microtubules via dipole excitations coupled to the environment in networks of chromophoric amino acids. We present the spatial structure and Hamiltonian, containing localized site energies and couplings between aromatic amino acids, for the microtubule constituent protein tubulin. Energy transfer is discussed in terms of quantum walk formalism and energy transfer efficiency. Plausibility arguments are presented for the conditions favoring a quantum mechanism of electronic signal propagation along a microtubule. [Preview Abstract] |
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S1.00152: An exactly solvable model for decoherence-assisted transport Adriana Marais, Ilya Sinayskiy, Francesco Petruccione, Artur Ekert The processes of energy and information transfer in quantum networks play an important role for quantum communication and quantum computation. Unavoidable interaction of the quantum system with the environment leads to decoherence and dissipation, processes typically associated with a destruction of quantum coherence in the system. However, recently the signature of long-lasting quantum coherence has been identified in conjugate polymers and in photosynthetic light harvesting complexes. Here we present an exactly solvable model where interaction with a decoherent environment plays a crucial role in assisting the transport in a quantum subsystem. Based on exact solution, we study different regimes of the parameters of the system, and identify the role of the correlations between the environments for assisting of the transitions in the quantum subsystem. [Preview Abstract] |
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S1.00153: Circularly Polarized Light and Growth of Plants Pavel Shibayev, Robert Pergolizzi The influence of linearly polarized light on the direction of plants growth has been recently demonstrated. The state of circularly polarized (CP) light can also change when it is reflected from the surface of leaves and stems. However, the role of light handedness in the development of plants and CP light interaction with the complexes of chlorophyll molecules have still not been studied enough. In this work, the role of left CP light in the accelerated growth of lentil and pea plants is revealed and studied. The mechanism of such an enhancement is discussed in terms of the model considering transmission, absorption, and scattering of CP light on micro and macro levels of leaf organization. Theoretical modeling of light interaction with the interior of the leaf was conducted for a number of recently proposed models of organization of chlorophyll molecules and chloroplasts. All the calculations were performed by employing a 4x4 matrix method in solving Maxwell equations. It is shown that left-handed chiral organization of chlorophyll molecules can greatly enhance the absorption of light and therefore lead to the enhanced growth of the whole plant under CP light. [Preview Abstract] |
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S1.00154: Design of Targeted Inhibitors of Polo-like Kinase 1 (Plk1) D.S. Dalafave Computational design of small molecule inhibitors of Polo-like Kinase 1 (Plk1) is presented. Plk1, which regulates cell cycle, is often overexpressed in cancers. Its downregulation was shown to inhibit cancer progression. Most inhibitors of kinases' interact with the highly conserved ATP binding site. This makes the development of Plk1-specific inhibitors challenging, since different kinases have similar ATP sites. However, Plk1 also contains the polo-box domain (PBD), which is absent from other kinases. In this study, the PBD site was used as a target for designed Plk1 inhibitors. Common structural features of experimentally known Plk1 ligands were first identified. The information was used to design putative small molecules that specifically bonded Plk1. Druglikeness and possible toxicities of the designed molecules were determined. Molecules with no implied toxicities and optimal druglikeness were used for docking studies. The docking studies identified several molecules that made stable complexes with the Plk1 PBD site. Possible utilization of the designed molecules in drugs against cancers with overexpressed Plk1 is discussed. [Preview Abstract] |
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S1.00155: DelPhi webserver: Comprehensive suite for electrostatic calculations of biological macromolecules and their complexes Shawn Witham, Brett Boylen, Barr Owesen, Walter Rocchia, Emil Alexov Electrostatic forces and energies are two of the major components that contribute to the stability, function and interaction of biological macromolecules. The calculations of the electrostatic potential distribution in such systems, which are comprised of irregularly shaped objects immersed in a water phase, is not a trivial task. In addition, an accurate model requires any missing hydrogen atoms of the corresponding structural files (Protein Data Bank, or, PDB files) to be generated in silico and, if necessary, missing atoms or residues to be predicted as well. Here we report a comprehensive suite, an academic DelPhi webserver, which allows the users to upload their structural file, calculate the components of the electrostatic energy, generate the corresponding potential (and/or concentration/dielectric constant) distribution map, and choose the appropriate force field. The webserver utilizes modern technology to take user input and construct an algorithm that suits the users specific needs. The webserver uses Clemson University's Palmetto Supercomputer Cluster to handle the DelPhi calculations, which can range anywhere from small and short computation times, to extensive and computationally demanding runtimes. The work was supported by a grant from NIGMS, NIH, grant number 1R01GM093937-01. [Preview Abstract] |
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S1.00156: Using DelPhi capabilities to mimic conformational reorganization with amino acid specific dielectric constants Lin Wang, Subhra Sarhar, Walter Rocchia, Emil Alexov Many molecular events are associated with small or large conformational changes occurring in the corresponding proteins. Modeling such changes is a challenge and requires significant amount of computing time. From point of view of electrostatics, these changes can be viewed as a reorganization of local charges and dipoles in response to the changes of the electrostatic field, if the cause is insertion or deletion of a charged amino acid. Here we report a large scale investigation of modeling the changes of the folding energy due to single mutations involving charge group. This allows the changes of the folding energy to be considered mostly electrostatic in origin and to be calculated with DelPhi assigning residue-specific value of the internal dielectric constant of protein in the range from 2 to 20. The predicted energy changes are benchmarked against experimentally measured changes of the folding energy on a set of 300 single mutations. The best fit between experimental values and predicted changes is used to find out the effective value of the internal dielectric constant for each type of amino acid. [Preview Abstract] |
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S1.00157: Normal mode analysis with reduced Hessians for multi-scale modeling techniques An Ghysels, Benjamin T. Miller, Michel Waroquier, Bernard R. Brooks Normal mode analysis is a straight-forward technique to gain insight into the principal motions of molecular systems. Diagonalizing the mass-weighted second derivative matrix (Hessian) results in eigenfrequencies and eigenmodes which indicate the time scale and spatial shape of the vibrations. For large systems, it is often necessary to use Hessians of reduced size in order to limit the required computational resources as well as the amount of information. Methods such as coarse-grained multi-scale models, the Mobile Block Hessian approach, the Vibrational Subsystem Analysis, or the Partial Hessian Vibrational Analysis, focus on specific parts of the spectrum: localized and/or global modes with varying degrees of coupling with the environment. In this presentation, the link between the different approaches will be studied with size-independent metrics and overlap techniques. [Preview Abstract] |
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S1.00158: Raman Spectroscopy Studies of Normal and Burned Biological Tissue Faranak Zarnani, David Maass, Ahamed Idris, Robert Glosser Burn injuries are a significant medical problem, and need to be treated quickly and precisely. Burned skin needs to be removed early, within hours (less than 24 hrs) of injury, when the margins of the burn are still hard to define. Studies show that treating and excising burn wounds soon after the injury prevents the wound from becoming deeper, reduces the release of proinflammatory mediators, and reduces or prevents the systemic inflammatory reaction syndrome. Also, removing burned skin prepares the affected region for skin grafting. Raman spectroscopy could be used as an objective diagnostic method that will assist burn surgeons in removing burned skin precisely. As a first step in developing a diagnostic tool, we present Raman spectroscopy information from normal and burned ex vivo rat skin, and a comparison of our findings. Raman spectroscopy is explored for its specificity and sensitivity. [Preview Abstract] |
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S1.00159: Time-resolved infrared structural biology: Identification of Signature Vibrational Signals from the Active Site Tyrosine of Photoactive Yellow Protein Zhouyang Kang, Beining Nie, Lorand Kelemen, Rachana Rathod, Wouter D. Hoff, Aihua Xie Hydrogen bond interactions are indispensable for protein structure and function. We are developing techniques for time-resolved infrared structural biology that offers high sensitivity to hydrogen bonding interactions, excellent time resolution, and a broad time window. Here we report the identification of signature vibrational signals from the active site Tyr42 of photoactive yellow protein for quantifying hydrogen bond interactions using a strategic combination of site-directed mutagenesis (Y76F, Y94F, Y98F, Y118F), specific Tyr isotope labeling, and time-resolved FTIR spectroscopy. These PYP mutants preserve functional activity, thus optimal for probing functionally important structural changes at the active site. This experimental approach is broadly applicable to other proteins, paving the way to transform time-resolved infrared spectroscopy to time-resolved infrared structural biology. [Preview Abstract] |
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S1.00160: Fluorescence Measurement of Burned Skin Tissues Hector Michael de Pedro, Chuan-I. Chang, Hue Nguyen, Anton Malko, Faranak Zarnani, Robert Glosser, D. Maas, A. Idris Early removal of affected tissues from burn patients can significantly increase the success of their recovery, since burns continue to spread and damage surrounding tissues after hours of injury. The rationale behind this procedure is that burns trigger the body's immune system to overreact, causing additional damage. Therefore it is important to locate and identify the burn (area and thickness) so that it can be removed as quickly as possible. Our project explores the use of autofluorescence as a tool to identify the burned tissues from healthy ones. Here we present that our fluorescence results show differences between burned and normal skin in both its spectra and lifetime. [Preview Abstract] |
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S1.00161: Point Spread Diffraction Patterns and Super-Resolution Particle Localization Stephen Anthony, Sripad Ram, Anish Abraham, Jerry Chao, E. Sally Ward, Raimund Ober Sub-diffraction limit localization of fluorophores depends upon fitting the observed photon distribution to the point spread function (PSF). As such, accurate knowledge of the PSF is important to super-resolution microscopy and critical to determining the trajectories and dynamics of molecules within cells. While simple geometrical optics serves well to represent light propagation on the macroscopic level, more elaborate wave representations are necessary to describe light propagation within a few wavelengths of focal points, such as single fluorophores imaged by microscope objectives. As a result, numerous theoretical approximations to experimental PSFs exist as the exact theoretical PSF is unknown. Further consideration must be given that for realistic experiments, frequently events of interest will not entirely match the design conditions of the microscope; most events of interest will not be perfectly in focus, nor can the index of refraction of a living cell be controlled. Additionally, a number of imaging modes explicitly rely upon out-of-focus images. Through serial sectioning microscopy, we explore the experimental PSF in comparison with various models, determining which models are robust and provide accurate sub-diffraction limit localization for realistic data. [Preview Abstract] |
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S1.00162: Sensing calcium ions at high hydrostatic pressure using the dual-wavelength calcium-sensitive dye indo-1 Jordan Ryan, Paul Urayama Because calcium often serves as a signaling ion in biological systems, accurate sensing of calcium-ion concentration under pressure is important in understanding cellular piezophysiologic effects. Indo-1 is a dual-wavelength fluorophore routinely used for calcium-ion sensing at ambient pressure, with an emission spectrum that changes upon calcium-ion binding. When subject to physiological pressures of up to 50 MPa, we observe piezochromic behavior in the excited-state emission which depends more on solvent polarity than on solvent viscosity. A two-state model is used to determine the thermodynamic volume change upon calcium dissociation from indo-1, which we find to be consistent with the value for other metal-ion chelators. Since, despite its piezochromicity, indo-1 continues to follow two-state binding-unbinding behavior, indo-1 remains useful under pressure as a probe for quantitative calcium-ion sensing. [Preview Abstract] |
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S1.00163: DLS microrheology at the onset of weak elasticity during thermal denaturation of BSA Ulf Nobbmann, Carlos A. Rega, Hanna Jankevics, Samiul Amin The ability to precisely detect the onset of protein aggregation to draw insights into microstructural characteristics plays a critical role in a variety of biotechnological applications such as therapeutic protein stability.\footnote{A Saluja et al., ``Ultrasonic rheology of a monoclonal antibody (IgG$_{2}$) solution: implication for physical stability of proteins in high concentration formulations'' J. of Pharm. Sci. (2007) 96, 3181-3195.} Rheological techniques are very sensitive to evolution of an aggregating network but have been limited in biotechnology, due to large sample volume and moderately high viscosity requirements in traditional mechanical rheometry. Dynamic Light Scattering (DLS) overcomes these limitations as experiments can be carried out on very dilute samples and small volumes. We present a method based on optical microrheology\footnote{D Weihs et al., ``Bio-microrheology: a frontier in microrheology'' Biophys. J. (2006) 91, 4296-4305.} to study the onset of bovine serum albumin (BSA) aggregation to develop an understanding of the evolving network structure. The exponent of the tracer mean squared displacement power law fit and the elastic modulus G' emerge as two key parameters. The impact of probe chemistry and probe size on the extracted microrheological response is discussed. [Preview Abstract] |
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S1.00164: Bacteria turn on surfaces by oversteering with Type IV pili Fan Jin, Jacinta C. Conrad, Maxsim L. Gibiansky, Gerard C.L. Wong Type-IV pili (TFP) are linear nano-actuators that enable bacteria to crawl on surfaces. Analysis of TFP-mediated crawling in \textit{P. aeruginosa} reveals that it always alternates between two types of distinct movements: a linear translation of constant velocity is followed by a combined translation-rotation that is $\sim $10x faster in instantaneous velocity. The latter process can turn the cell body by over-steering so that the rear of the cell loses traction with the surface. Orientational distributions of these movements suggest that the former is due to pulling by multiple TFP, whereas the latter is mostly due to release by single TFP. [Preview Abstract] |
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S1.00165: Automated detection and analysis of key transitions in biofilm formation Travis Thatcher, Benjamin Cooley, Vernita Gordon Biofilms are cooperative, dynamic, multicellular systems made of interacting, surface-bound bacteria and/or yeast. The growth of biofilms is an inherently developmental process, characterized by changes in gene expression in response to cues from the environment and other cells. These changes in gene expression are associated with transitions in the behavior of bacteria in the developing biofilm. There are other transitions in behavior that may result from nongenetic influences, such as the conditioning of the surface with bacteria-produced extracellular materials. The early development of biofilms show several key transitions as bacteria move from discrete, swimming cells into surface-bound, dense microcolonies. Each of these transitions is associated with a loss of entropy and, therefore, must result from biological activity that compensates for this loss of entropy. We present a set of approaches for automatically identifying each of these transitions and localizing them in space and time. [Preview Abstract] |
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S1.00166: Noise Induced Biological Adaptation Differs between Analogous Differentiation Circuits Mark Kittisopikul, Andrew Mugler, Aleksandra M. Walczak, Tolga \c{C}agatay, Chris H. Wiggins, G\"{u}rol S\"{u}el Analogous genetic regulatory networks with alternate orders of activation and repression can have comparable functions and generate similar average dynamics but differ in terms of stochastic variability (noise). Here we examine if noise affects biological adaptation to stress by comparing the induction dynamics of the native {\em B. subtilis} competence differentiation network to a synthetic network implemented {\em in vivo} by \c{C}agatay et al. that recapitulates mean dynamics but differs in noise. We use fluorescence microscopy to study the networks in live cells and stochastic models solved via the spectral method. The adaptability of the organism is affected by the circuit's ability to access different dynamic regimes as a function of stress. [Preview Abstract] |
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S1.00167: CHEMICAL PHYSICS |
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S1.00168: ABSTRACT WITHDRAWN |
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S1.00169: Where the Periodic Table of Elements Ends? Additional Explanations Albert Khazan Already 40 years ago, physicists claimed that the elements with number higher than 110 cannot exist. However at this day, Period 7 has been complete. Experiementalists syntesed 10 new syperheavy elements during only the last because. The method of synthesis is so finely developed that the experimentalists of Dubna tell about element No.150 as the higher limit of theTable of Elements (they do not provide a ground to the calculation). In contrast, our calculation are based neither on calculation of the stability of the electronic shells of the atoms, nor synthesis of the superheavy elements. Our caculation is based on study of the chemical processes, which give a new law of the Periodic Table (Albert Khazan. Upper Limit in Mendeleev's Periodic Table---Element No. 155. Svenska fysikarkivet, Stockholm, 2009). The core of the delusion of numerous scientists was that they, in their calculationsbased on Quantum Mechanics, initially set up the number of the elements (number of the protons) then calculated the atomic mass proceeding from the data. According to our theory, the atomic mass of the last element (411.66) should be calculated first, only then its number (155)! [Preview Abstract] |
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S1.00170: Scaling of Nonclassical Nucleation Rates of Methanol Gerald Wilemski, Fawaz Hrahsheh, Abdalla Obeidat Nonclassical gradient theory (GT) calculations of nucleation rates are presented for methanol, an associating vapor system. The calculations use the SAFT-0 equation of state (EOS) that accounts for the effects of molecular association based on the statistical association fluid theory (SAFT). Calculated rates were compared to the experimental rates of Strey, et al. [\textit{J. Chem. Phys.} \textbf{1986}, $84$, 2325]. The GT nucleation rates showed improved $T$ and $S $dependence compared to classical nucleation theory (CNT). The GT rates were also improved by factors of 100-1000 compared to CNT. Despite these improvements, GT does not describe the reported $T$ and $S$ dependence of the nucleation rates. To explore this further, the GT and experimental rates were analyzed using Hale's scaled model [\textit{J. Chem. Phys.} \textbf{2005}, $122$, 204509]. This analysis reveals an inconsistency between the predictions of GT, which scale relatively well, and the experimental data, which do not scale. It also shows that the measured rate data have an anomalous $T$ and $S$ dependence. A likely source of this anomaly is the inadequate thermodynamic data base for small cluster properties that was used originally to correct the raw rate data for the effects of association. [Preview Abstract] |
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S1.00171: Hybrid Monte Carlo Method In Path Space Patrick Malsom, Frank Pinski We are interested in understanding the ways a collection of atoms are able to undergo conformational change, or change of state. In particular, we are studying atoms as they move under Brownian (over-damped Langevin) dynamics. In many cases, such transitions are blocked by an energy barrier and conformational changes become rare events when the thermal energy is small compared to the barrier height. Our technique attempts to sample these transition paths efficiently while preserving the sample's thermodynamic significance. Our approach is based on a Hybrid Monte Carlo scheme (Beskos \textit{et al.}) that incorporates auxiliary variables. The relative probability of paths is computed using the Onsager-Machlup functional. This method correctly handles the fractal nature of the Brownian paths. We illustrate this method by investigating one of the low energy transitions in the 14-atom Lennard-Jones cluster. In addition, we will show preliminary results for the gas-to-liquid transition in a 2-dimensional Lennard-Jones system. [Preview Abstract] |
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S1.00172: Small methanol cluster growth/decay rate constant ratios and application to nucleation data analysis Barbara Hale, Gerald Wilemski The Bennett Monte Carlo technique is used to calculate growth/decay rate constant ratios for small methanol clusters using the model potential of van Leeuwen and Smit [J. Chem. Phys. \textbf{99}, 1831 (1995)] at temperatures of 220K, 240K and 260K. The resulting data are used to examine temperature scaling properties of the rate constant ratios and to illustrate how heat release from subcritical cluster formation affects the results of adiabatic nucleation rate measurements. [Preview Abstract] |
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S1.00173: A Look at a Seires of Alkyl and Perfluoroalkyl Bromides Brittany Long, Garry Grubbs, Stephen Cooke The pure rotational spectrum of bromoperfluoroethane between 9.0-13.0 GHz has been measured on a chirped pulse Fourier transform microwave spectrometer. A total of 839 transitions were observed for the six isotopolouges. Only the $trans$ conformer was observed for which the rotational constants are reported. Nuclear electric quadrapole coupling constants have been determined and reported. Also, two dipole forbidden/quadrapole allowed $\Delta J$ = 2 transitions were observed in the spectra. [Preview Abstract] |
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S1.00174: Water-like Anomalous Properties and Polyamorphism in a Liquid with Smooth (Differentiable) Pair Interactions Joel Abraham, Nicolas Giovambattista We perform molecular dynamics simulations of a system of particles interacting via a spherically symmetric, core- softened pair potential, which is a smooth version of the (non- differentiable) Jagla pair potential. Although liquid properties are extremely sensitive to the details of the pair interactions, we show that the smooth version of the Jagla potential preserves the main properties of the original model. Specifically, both pair potentials result in liquids that show (i) water-like thermodynamic and dynamical anomalous properties, as well as (ii) liquid and (iii) glass polymorphism (i.e., the presence of more than one liquid and glass form, respectively). The pressure-temperature phase diagram of our smooth potential shows, as observed in computer simulations using the Jagla model, a liquid-liquid first order transition line separating two liquid phases and ending in a critical point; such a critical point being accessible in equilibrium simulations. [Preview Abstract] |
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S1.00175: Modeling Adsorption on fcc(\textit{nnm}) Surfaces Alain Phares, David Grumbine, Jr., Francis Wunderlich In general, fcc(\textit{nnm}) surfaces consist of very long armchair (111) terraces separated by steps. The number $M$ of atomic sites in the width of the terraces depends on the Miller indices (\textit{nnm}). The model considers values of $M \le $ 6, with adsorbate-substrate interaction energy on step-sites different from those on bulk sites, takes into account first- and second-neighbor adsorbate-adsorbate interactions, and specializes to the case of attractive first-neighbors. We obtain the complete low temperature, 3-dimensional, energy phase diagrams. The occupational configurations of the phases exhibit features similar to those of the phases obtained in the infinite-width limit, or flat fcc(111) surfaces. This yields a classification of the phases into types, and, within each type, the phases are grouped into families. This suggests a number of generalizations for any value of $M$ beyond 6, leading to a better understanding of the competing interaction energies and of the evolution of the phase diagrams with increasing width $M$ of the terraces. The relevance of these results to experiments is discussed within the context of preferential adsorption on step sites, and applied to the adsorption of water on Pt(335). [Preview Abstract] |
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S1.00176: Tethering Peptides to Functionalized Self-Assembled Monolayers on Gold Through Two Chemical Linkers Using the Huisgen Cycloaddition Ignacio Gallardo, Lauren Webb A biocompatible platform has been made by tethering a helical peptide to a surface at two points. The presence of the peptide should be an ideal interface between inorganic substrates and proteins. The artificially synthetized alpha-helical peptide composed of alternating leucine and lysine residues, with two residues replaced with cyanophenylalanine to react with two neighboring surface-bound azide groups is linked to the azide-terminated self-assembled monolayer through a tetrazole made by a Husigen Cycloaddition. Surface analysis is done with ellipsometry, infrared spectroscopy and x-ray photoelectron spectroscopy. The cycloaddition and reaction conditions are supported by similar reactions of other smaller molecules like Methoxybenzonitrile and controls show no physisorption under our reaction conditions. Reaction yields from 80 to 98 percent are reported from the optimized reactions. The helical structure of the peptide in solution has been confirmed under our reaction conditions with circular dichroism and the peptide amide I and II modes studied by infrared spectroscopy and their comparison with a computational model of the peptide showed that the peptide is probably randomly oriented on the surface. [Preview Abstract] |
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S1.00177: Size effect of silicon nanowires on their pH response Seongjae Lee, In-Bok Baek, Xianhong Li The silicon nanowire is a promising material for the bio-chemical electronic sensors because the local change in the surface charge density can be easily transduced to the conductivity change of the nanowire due to its high surface-to-volume ratio. We investigated the pH-dependent electronic transport characteristics of FETs comprised of silicon nanowire channels of different sizes. Starting from the p-type SOI wafer with the top silicon layer of 40 nm thickness, we employed the conventional `top-down' process to fabricate the FET devices with various silicon nanowires: 100, 135, 180, 220, 300 nm in width and 2, 5, 10, 20 $\mu $m in length. The devices were electrochemically characterized by I$_{D}$-V$_{G}$ measurements with a reference electrode as a gate in the phosphate buffer solutions of a pH value ranging from 2 to11. The threshold voltages of all devices were extracted from the I$_{D}$-V$_{G}$ curves and their relations to pH were compared with simulation results based on the Gouy-Chapman-Stern-Graham model. A good linear relation between the threshold voltage and pH was observed for all devices in the range of 4 $<$ pH $<$11 with a high sensitivity of 56 mV/pH which is much higher than the bulk devices and very close to the Nernst limit. However, the systematic increase of a threshold voltage shift as decreasing nanowire's dimension (width and length) was also observed and possible origins are discussed within the scope of the Gouy-Chapman-Stern-Graham model. [Preview Abstract] |
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S1.00178: Role of Surfactant Molecular Structure on Self Assembly: Aqueous SDBS on Carbon Nanotubes Manaswee Suttipong, John R. Thompson, Naga Rajesh Tummala, Boonyarach Kitiyanan, Alberto Striolo Stabilizing aqueous dispersions of carbon nanotubes mono-dispersed in diameter and chirality remains elusive. Surfactants have proven useful in deploying ultra-centrifugation techniques, but the molecular mechanism responsible for their effectiveness remains not fully understood. Based on a number of recent molecular simulation results, including those from our group, it appears that the morphology of the self-assembled surfactant aggregates on the carbon nanotubes strongly affects the effective potential of mean force between pairs of interacting carbon nanotubes. In this work we explore the effect of surfactant molecular structure on the properties of aqueous surfactant self-assembled aggregates. We employ equilibrium all-atom molecular dynamics simulations. We consider the surfactant SDBS (sodium dodecyl benzene sulfonate) with benzene ring located on the fifth or on the twelfth carbon atom in the tail, and the surfactant AOT [sodium bis(2-ethylhexyl) sulfosuccinate]. The simulations are conducted at room conditions for different surface coverages on (6,6), (12,12), and (20,20) single walled carbon nanotubes. These new results will help us identify the surfactant properties that allow us to manipulate nanotube-nanotube effective interactions. [Preview Abstract] |
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S1.00179: Properties of Aqueous Electrolytes within Narrow Slit-Shaped Pores Tuan A. Ho, Dimitrios Argyris, Alberto Striolo We report equilibrium molecular dynamics simulation results for structural and dynamic properties of aqueous electrolyte solutions confined within narrow pores. The slit-shaped pores are carved from cristobalite silica, corundum alumina, magnesium oxide, and other materials. The pore width is in the range 0.8 -- 2.0 nm. The aqueous solutions contain NaCl, CsCl, CaCl$_{2}$, and SrCl$_{2}$ electrolytes at 1M concentration or larger. Equilibrium simulations are performed at ambient conditions within the NVT ensemble. The data suggest the formation of layered structures, which are consistent with results obtained for thin films of solution supported on free-standing surfaces. However, confinement enhances the differences in transport properties observed between those ions that are near the solid and those at the pore center. Because the self-diffusion coefficient is faster as the distance from the solid increases, the ions that are at the pore center diffuse more quickly through the pore than those adsorbed closer to the wall. Thus our results could be used to design membranes to separate, e.g., aqueous NaCl from CsCl solutions. [Preview Abstract] |
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S1.00180: Chemisorption of Guanine on Cu(110) Jeronimo Matos, Abdelkader Kara We use density functional theory (PBE) to calculate the adsorption of a guanine molecule on Cu(110). At saturation coverage, guanine adsorbs tilted with the oxygen atom strongly bound to one of the surface atoms at a height of 2.12 {\AA} above this surface atom with a binding energy of 430 meV/molecule. The substrate top layer atoms show a buckling of 0.22 {\AA} , while the molecule experiences a twist from the flat configuration in the gas phase. The dz$^{2}$ state of the copper atom -that is bound to the oxygen atom- presents an enhancement in its density near the Fermi level. We calculated a drop in the work function of 0.34 eV upon adsorption of guanine on Cu(110). These effects classify this system as chemisorption. [Preview Abstract] |
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S1.00181: Proton transfer induced by receding water in Glycine---(Water)$_{2}$ Complex Rajeev Pathak We investigate molecular co-operativity in the zwitterionic configuration of Glycine (Gly) with two proximal water molecules, Gly---(Water)$_{2}$, by deliberately making one of the water molecules recede from the remaining complex. The consequent intra-molecular proton transfer that renders the zwitterionic configuration into a neutral one is viewed under two scalar field descriptors: Molecular Electrostatic Potential (MESP), reflecting the modifications in the environment and the HOMO (highest occupied molecular orbital) electron density. We quantify the process further by energetics, through a many-body analysis of the interaction energy as well as salient IR spectral signatures associated with the proton-transfer. While we employ the decent MP2/aug-cc-pvDZ level of theory to seek optimal structures, it is gratifying that a prescription within density functional theory (DFT) also provides a reliable description of this process. [Preview Abstract] |
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S1.00182: Compositional-Dependent Structural Analysis of Cu$_{x}$Pt$_{38-x}$ Nanoparticles Josafat Guerrero-Jordan, Roy L. Johnston, Alvaro Posada-Amarillas We present an exhaustive study of the lowest energy Cu$_{x}$Pt$_{38-x}$ clusters structures obtained through a genetic algorithm, which incorporates the Gupta potential to mimic interatomic bonding. A symmetric parameterization of the Gupta potential was used including a weighting factor (w) in order to search for different potential energy surfaces describing 38-atom Cu-Pt nanoparticles. This weighting factor was varied from 0 to 1 in steps of 0.1 to obtain a structure map which provides information on the structural distribution in terms of the composition. According to this structure map, the most abundant structural motif corresponds to the truncated octahedron. Atomic segregation was maximum for w = 1.0. We also present the plot of excess energy as a function of the weighting factor values for the complete compositional range. The most stable structures were found for w = 0.0. The most relevant structures were chosen to be reoptimized by using the DFT method. We found that the interatomic distances changed compared to those obtained with the genetic algorithm. [Preview Abstract] |
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S1.00183: Evidences of Homogenous Nucleation in Nano Confined Secondary Alcohol Samuel Amanuel, Amer Khraisat, Jargalsaikhan Dulmaa We have made comparative measurements to study the phase transition of physically confined 2-decanol in nano porous silica in the presences of excess bulk 2-decanol. We have systematically controlled the amount of excess bulk and studied how its existence influences freezing and melting temperatures. It appears that there is a lower limit in size, where freezing of the confined is not influenced by the presences or absence of the bulk. In our case this lower limit occurred with the average pore diameter of 100 nm. For 2-decanol confined in pore sizes larger than 100 nm, however, its freezing occurred at T = -23\r{ }C, which was triggered by the freezing of the excess bulk. In absence of the bulk, freezing occurred at a lower temperature depending on size. Melting of the confined 2-decanol, on the other hand, was not influenced by the presences or absence of the bulk. Generally, the melting of the confined 2-decanol preceded the melting of the bulk. These suggest that the nucleation of 2-decanol confined to pore sizes less than 100 nm is homogenous and controlled by its extent of supercooling. [Preview Abstract] |
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S1.00184: Universal Patterns of Cluster Growth in Aqueous Sugars Observed by Dynamic Light Scattering Tri Tran, David Sidebottom Dynamic light scattering was performed on aqueous sugar solutions to monitor the growth of sugar clusters as a function of sugar concentration and temperature. Three sugars (glucose, maltose and sucrose) were investigated. Analysis of the hydrodynamic radius of the diffusing clusters suggests a two-stage process of cluster growth. At low volume fractions of sugar, a cluster phase consisting of nearly monodisperse clusters forms with a mean cluster mass that increases in proportion to the volume fraction. A second stage of growth develops when clusters reach a size where they begin to overlap. In this later stage, cluster-cluster aggregation occurs and the cluster size grows in a common, but temperature dependent, power law fashion in advance of a percolation threshold near 83 wt{\%} sugar. [Preview Abstract] |
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S1.00185: Quantification of molecular topology using small angle scattering. Ramnath Ramachandran, Durgesh Rai, Gregory Beaucage A recent method to quantify molecular topology of various materials using small angle scattering will be presented. Small angle x-ray and neutron scattering has been used to characterize ceramic aggregates and polymer structures systems respectively. The structural differences in various systems arise from the competition between thermal and spacial constraints. The details in ceramic aggregates like branch fraction, number of segments in an aggregate and the short circuit path, coordination number, the number end groups \textit{etc }are extracted. Amongst the polymer systems, details of topological quantification of polymer systems such as stars, cyclics and branched polymers like polyolefins will be presented. In polyolefins, the method provides a unique measure of the average long-chain branch length and the hyperbranched (branch-on-branch) characteristics. The quantification using scaling models are important in order to understand the structure-property relationship amongst materials. [Preview Abstract] |
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S1.00186: Effects of Iridium interfacial nanolayers on stability and barrier hights of TCO/Si nano-holes Solar cell structures Bed Sharma, Mohemad Bouanani There is still a significant gap between currently achieved efficiencies and theoretical one. A fundamental understanding of physico-chemical and electronic properties as well as tuning and control of transparent conducting oxides (TCOs) and nano-structured semiconductor absorber material interfaces is critical. One of the many issues is the suspected formation of silicon oxides due to transport of oxygen from TCO to silicon that degrades the effectiveness of light generated charge transfer which eventually degrades final efficiency of solar cell. The fabrication of 3-D nano-holes in Si was obtained by electrochemical etching through anodic nano-porous alumina. The nano-porous alumina was prepared by depositing thick 1micrometer aluminum layer on RCA cleaned Si samples, annealing in Ar and using hard anodization process. One to few mono-layers of Ir were inserted at the TCO/Si interfaces to block the depletion of oxygen to stabilize the interface and tune its barrier height. Both ITO and ZnO were used as TCOs. The effect of Ir on the band alignment at these interfaces is evaluated by Ultraviolet Photoelectron Spectroscopy (UPS). The interface stability and chemical nature is evaluated by X-ray Photoelecton Spectroscopy (XPS). [Preview Abstract] |
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S1.00187: Charge transfer energies of tetraphenyl-porphyrin-fullerene dyads Rajendra Zope, Marco Olguin, Tunna Baruah Porphyrin-fullerene dyads are extensively studied for their photoinduced charge transfer properties. They form a donor-acceptor pair where the fullerene is the acceptor. Accurate theoretical estimate of the charge transfer energies in such systems has proven to be a challenge. In this study we examine the charge transfer energetics for such dyads using our recently developed density functional based excited state method which can yield reliable estimates of charge transfer energetics. In this study the effect of varying both the donor and acceptor components are studied by changing the tetra-phenyl-porphyrin (TPP) to Zn-TPP. Similarly the acceptor component is changed from C60 to C70. The structures were optimized using DFT-D3 theory at the all-electron level. Among the donor-acceptor pairs studied, we find that the ZnTPP-C60 has the lowest charge transfer energy (1.69 eV) and the TPP-C70 (2.13 eV) has the highest charge transfer energy. [Preview Abstract] |
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S1.00188: Strong field DC slice imaging Lu Yan, Michael Doyle, Yunfei Lin, Wen Li, Arthur Suits A new, ``universal'' variation of the DC slice ion imaging method is reported. This approach allows the central slice of the photofragment ion cloud to be recorded and the relevant speed and angular distributions for a molecular photodissociation to be obtained without any inversion methods, but does so using femtosecond non-resonant strong-field ionization. The probe laser is also implemented in a ``raster imaging'' approach that records only the central section of an expanded photofragment distribution and avoids interaction with the molecular beam itself. This is achieved by using the probe laser displaced off-axis from the molecular beam with application a narrow time gate to a multichannel plate detector. To avoid high background level and space charge effect, the detection region is in ultrahigh vacuum and we utilize a second differential stage to the molecular beam. Several examples will be presented illustrating the method. [Preview Abstract] |
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S1.00189: FLUIDS AND SOFT MATTER |
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S1.00190: Molecular Dynamics of Colloidal binary mixtures in an electric field Manuel Valera, Athula Herat, Ethan Corle We have studied a system of colloidal binary mixtures in an external electric field. The simulations were performed in the string fluid regime, low packing fraction, and high density regime under the influence of a strong electric field. In the dilute regime we studied the system structure for different concentrations and size ratios. For the high density regime we studied a 50:50 concentration with a size ratio or 1.2/1.0. We show the pair correlation function and diffusion coefficient. A partial phase diagram for the 50:50 concentration and 1.2/1.0 size ration is also presented. [Preview Abstract] |
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S1.00191: Capillary Condensation: Novel Method for Patchy Particle Fabrication Nina Ivanova, Nicole Zacharia Patchy particles are patterned particles with at least one patch for anisotropic interaction. A novel route for their synthesis involves capillary condensation of a chemical species into the voids of an ordered colloidal sphere array. Polystyrene and silica particles ranging in diameter from 20 nanometers to 1 micron are assembled into crystalline arrays via evaporation induced self-assembly. The chemical condensed into the voids is then reacted with metal nanoparticles to produce novel patchy particles. The particles are characterized using FTIR, EDX and SEM. The size of these patches is quantitatively shown to reduce in size in proportion with increased particle radius. Surface Enhanced Raman Spectroscopy is explored as one of the possible applications for these novel particles. [Preview Abstract] |
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S1.00192: Phase Equilibrium Model for Nanoparticle-Filled Nematic Liquid Crystals Ezequiel Soule, Jonathan Milette, Linda Reven, Alejandro Rey This work presents an integrated characterization of phase transitions and structure formation in mixtures of nanoparticles (NP) and liquid crystals (LC), by means of a model for phase equilibrium and an experimental study on the system composed by 5CB and gold NPs. The model takes into account mixing, nematic ordering of the LC, crystalline ordering (self-assembly) of NPs, and LC-NP interactions. Generic features of phase diagrams for NP-LC mixtures are discussed. The model can explain some experimental observations, like the formation of NP aggregates and distinctive nematic textures, as a function of experimental parameters like NP concentration and the nature of the NP surface are changed. The parameters that produce these changes in phase behaviours can be directly correlated with experimental variables. [Preview Abstract] |
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S1.00193: Observation of nematic/smectic liquid crystal configurations in a prolate spheroidal confinement Joonwoo Jeong, Mahn Won Kim Polymer-dispersed liquid crystal (PDLC) is a composite of dispersed LC droplets in a polymer matrix. The electro-optic properties of PDLCs, such as reorientation field strength and response time, are strongly related to the director configuration. Various factors including the intrinsic properties of LC/polymer and the size/shape of droplets affect the liquid crystal configuration. A balance between the bulk elastic energy and the surface anchoring energy determines the configuration. To study systematically the effect of size/shape of droplets on the configuration, we have prepared thin PDLC films with 4-Cyano-4'-pentylbiphenyl (5CB)/ 4-Cyano-4'-octylbiphenyl (8CB) and Polydimethylsiloxane (PDMS) elastomer. Using polarized optical microscopy, we have observed the change in the director configuration of LC droplets as a function of the aspect ratio up to 6 by stretching the film unidirectionally. We have also observed the effect of surface anchoring on the configuration. [Preview Abstract] |
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S1.00194: Automation of Dielectric Characterization of Liquid Crystals Shane Drye, Josaphat Uvah, Chandra Prayaga This report describes the complete automation of a setup for the dielectric characterization of liquid crystals (LC). A capacitor cell filled with the LC 8CB is housed in a temperature controlled environment. The temperature of the sample is varied between 25$^{\circ}$C and 45$^{\circ}$C with a stability and precision of 0.001K, with a PTC10 PID controller. The range covers the phase transitions of the LC. The purpose is to measure the dielectric properties of the liquid crystal near the phase transitions. The capacitance is measured with a SR830 lock-in amplifier and a Fluke4360 LCR meter upto 100kHz. An Agilent 4395A Network Analyzer is used to extend the frequency into the MHz range. In this work, the entire process is automated. All the instruments are connected to a computer through a GPIB (IEEE-488) interface. The program is designed using LabVIEW to control the instruments, send commands and inputs including temperature range and frequencies, receive data, calculate the capacitance, and plot the data automatically. Results of measurements will be presented. [Preview Abstract] |
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S1.00195: Carbon nanotubes effects on the order parameter and crystal structure of 5CB liquid crystal Georgi Georgiev, Erin Gombos, Michael McIntyre, Peggy Cebe Carbon nanotubes (CNTs) are elongated anisotropic molecular size cylinders that can form a liquid crystal (LC) phase in lyotropic solutions. When dispersed in LCs their nematic directors couple. We have observed a large downshift in transition voltage during Freedericksz transition in LC/CNT nanocomposites. We are interested in the effect that CNTs have on the order parameter of LCs and their phase diagram and crystal structure. We measured using polarized UV/Vis absorption spectra a systematic increase of the order parameter of LC/CNT cells with increase of the CNTs content. The order parameter vs temperature slope decreases with increased CNTs content, which shows that CNTs support an increased order of the LCs to higher temperatures. This makes the Nematic-to-Isotropic transition sharper increasing its first order phase transition characteristics. The main mechanism for the strong nematic coupling is pi-pi stacking between the aromatic rings of the CNTs and LCs which we measure using FTIR and Raman difference spectroscopy. Through Polarized Microscopy, Ellipsometry and DSC we observed a change in crystalline order and an increase in nematic to crystal phase transition temperature with increasing CNTs concentration due to their crystal nucleation activity. [Preview Abstract] |
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S1.00196: Brownian motion of particles in nematic fluids Xuxia Yao, Karthik Nayani, Jung Park, Mohan Srinivasarao We studied the brownian motion of both charged and neutral polystyrene particles in two nematic fluids, a thermotropic liquid crystal, E7, and a lyotropic chromonic liquid crystal, Sunset Yellow FCF (SSY). Homogeneous planar alignment of E7 was easliy achieved by using rubbed polyimide film coated on the glass. For SSY planar mondomain, we used the capillary method recently developed in our lab. By tracking a single particle, the direction dependent diffussion coefficients and Stokes drag were measured in the nematic phase and isotropic phase for both systems. [Preview Abstract] |
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S1.00197: Fluorescence of CdSe nanoparticles in the Liquid Crystal 8CB near the Phase Transitions Jodie Gray, Shane Drye, Darren North, Samuel Beck, Tim Royappa, Laszlo Ujj, Chandra Prayaga The liquid crystal 4'octyl---4-cyanobiphenyl (8CB) doped with cadmium selenide nanoparticles was injected into a commercially available liquid crystal cell (INSTEC, Inc). The cell was housed in a temperature controlled environment constructed in the lab and exposed to light from a frequency doubled Nd: YAG laser. Fluorescence from the sample was filtered from the incident light and detected using a photodiode and measured with a lock-in amplifier. Measurements have been made over the temperature range 25$^{\circ}$ to 45$^{\circ}$C. The sample was stabilized at each temperature, and the fluorescence intensity was measured at several temperatures. The results show a significant change in fluorescence near the nematic-isotropic phase transition. The temperature control and precision allowed more than 1000 data points to be taken between 25-50$^{\circ}$C, with most of these clustered in the transition region between 38.5-- 39.5$^{\circ}$C, where the change in intensity was observed. [Preview Abstract] |
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S1.00198: Spectral Measurements of Fluorescence of CdSe nanoparticles in Liquid Crystals near Phase Transitions Samuel Beck, Jodie Gray, Shane Drye, Darren North, Tim Royappa, Chandra Prayaga, Laszlo Ujj The liquid crystal 4'octyl-4-cyanobiphenyl (8CB) doped with cadmium selenide nanoparticles was injected into a commercially available liquid crystal cell (INSTEC, Inc). The cell was housed in a temperature controlled environment constructed in the lab and exposed to light from a frequency doubled Nd: YAG laser. The spectrum of fluorescence from the sample was measured at several temperatures over the range 250 to 450C, covering the smectic-nematic and nematic-isotropic phase transitions. The sample was held at each temperature with a precision and resolution of 1mK before taking the spectrum. It was therefore possible to approach very close to the phase transitions. The results show a significant change in the fluorescence spectrum near the nematic-isotropic phase transition. [Preview Abstract] |
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S1.00199: Electro-optical properties of polymer-dispersed liquid crystals containing gold nanoparticles Alfonso Hinojosa, Suresh Sharma It is known that additions of relatively small concentrations of gold nanoparticles (Au NPs) can significantly change electro-optical properties of a polymer-dispersed liquid crystal (PDLC). For example, it has been shown that the addition of Au NPs to a PDLC microstructure lowers the operating voltage and increases transmission in a manner that depends on the concentration of the NPs and applied electric field.\footnote{A. Hinojosa and S. C. Sharma, Applied Physics Letters, \textbf{97}, 081114 (2010)} We have extended these measurements to PDLCs synthesized with a different liquid crystalline material and doped with varying concentrations of the Au NPs. We discuss the electro-optical data on two different PDLCs as functions of the concentration of the Au NPs, as well as the polarization and intensity of the incident laser beam. We also present ideas to assess the role of the surface plasmon excitations in modifying the electro-optical properties of Au NPs containing PDLCs. [Preview Abstract] |
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S1.00200: Fluorescence decay of CdSe nanoparticles in Liquid Crystals near Phase Transitions Darren North, Samuel Beck, Jodie Gray, Shane Drye, Chandra Prayaga, Laszlo Ujj, Tim Royappa The liquid crystal 4'octyl-4-cyanobiphenyl (8CB) doped with cadmium selenide nanoparticles (Sigma-Aldrich) was injected into a commercially available liquid crystal cell (INSTEC, Inc). The cell was housed in a temperature controlled environment constructed in the lab and exposed to light from a frequency doubled pulsed Nd: YAG laser. The decay of fluorescence from the sample was measured at several temperatures over the range 25$^{\circ}$ to 45$^{\circ}$C, covering the smectic-nematic and nematic-isotropic phase transitions. The sample was held at each temperature with a stability and resolution of 1mK before taking the measurement. The fluorescence was detected using a high-speed detector and the decay was measured using a boxcar averager. With the temperature control available, it was possible to approach very close to the phase transitions, with milliKelvin resolution. The results show a significant change in the decay of fluorescence near the nematic-isotropic phase transition. [Preview Abstract] |
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S1.00201: Deformable viscoelastic cholesteric films with nanoparticles Petr Shibaev, Cristina Schlesier Large spectral shifts of the selective reflection band and color changes are achieved in highly viscous mixture of cholesteric polymers and low molar mass liquid crystals filled with nanoparticles and subject to mechanical deformations. The color of the material changes instantaneously during deformation; the time for the color to be completely restored increased with the viscosity of the polymer mixture. The viscosity increases with increasing concentration of polymer or nanoparticles. This composite material was used to build highly sensitive mechanical sensor that was used to visualize both stress and deformation. The model describing the relation between the color and deformation is suggested. This model takes into account non-linear response to deformation and structural rearrangements inside the liquid crystalline matrix. \\[4pt] P.V. Shibaev, R. Uhrlass, S.Woodward, C. Schlesier, and Eckhard Hanelt, Liquid Crystals, v.37, pp. 587-592, 2010 [Preview Abstract] |
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S1.00202: Specific heat at the micellization and phase transitions in a triblock copolymer-water system Lorenzo Dumancas, David Simpson, D.T. Jacobs The triblock copolymer (``unimer'') of PPO-PEO-PPO (commercially known as 17R4) has hydrophobic ends and a hydrophilic center. When placed in water, a network of unimers can self-assemble at higher concentrations or temperatures to form micelles of different geometries. We have measured the micellization line marking the transition from only unimers in solution to some micelles. There is also a one- to two-phase transition at higher temperatures that is an Ising-like, LCST critical point. Specific heat measurements from our adiabatic calorimeter provide the enthalpy, entropy and free energy of micellization along the micellization line at different prepared compositions. [Preview Abstract] |
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S1.00203: Vesicle membrane fluctuations at nm resolution Kejia Chen, Sung Chul Bae, Chang-Ki Min, Steve Granick We measure membrane thermal fluctuations with nanometer spatial resolution and microsecond time resolution, extending a scattering technique used at the Curie Institute to study red blood cell dynamics (Timo Betz et al., Proc. Nat. Acad. Sci. USA 106, 15320, 2009). A laser beam is focused at the leading edge of a phospholipid vesicle membrane and the forward scattered light is detected by a quadrant photodiode. The measurements over 4 orders of magnitude of frequency allow quantification of more complete fluctuation spectra than competing methods, and therefore fuller understanding of the vesicle membrane mechanics. As a proof of concept, we quantify how adsorbed nanoparticles stiffen giant unilamellar vesicles (GUVs). [Preview Abstract] |
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S1.00204: Interactions of End-Functionalized Nanotubes with Lipid Vesicles: Spontaneous Insertion and Nanotube Self-organization Meenakshi Dutt, Olga Kuksenok, Michael Nayhouse, Steven R. Little, Anna C. Balazs Via Dissipative Particle Dynamics (DPD) approach, we study the self-assembly of amphiphilic nanotubes into a lipid vesicle, which is immersed in a hydrophilic solvent. Individual lipids are composed of a hydrophilic head group and two hydrophobic tails. Each nanotube encompasses an ABA architecture, with a hydrophobic shaft (B) and two hydrophilic ends (A). To allow controlled transport through the nanotube, we also introduce hydrophilic tethers at one end of the tube. We show that nanotubes initially located in the outer solvent spontaneously penetrate the vesicle's membrane and assume a trans-membrane position, with the hydrophilic tethers extending from the surface of the vesicle. We add nanotubes one at a time after the previous nanotube has been inserted. We characterize the interactions among the nanotubes that have self-assembled into the vesicles' membrane and focus on their clustering within the membrane. We also show that the nanotube insertion and clustering within the vesicle strongly affects the vesicle shape in cases of a sufficiently large number of tubes. Ultimately, these nanotube-lipid systems can be used for making hybrid controlled release vesicles. [Preview Abstract] |
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S1.00205: Electrospray fabrication and osmotic response of fluid core-viscoelastic shell microcapsules Zhiyong Meng, Chinedum Osuji Microcapsules with fluid-core in viscoelastic shell is interesting partially because of their unusual elasticity/rigidity. Electrospray technique, more flexible and scalable than traditional bulk and microfluidic emulsification, was used to generate spherical microcapsules. In particular, sodium alginate fine droplets generated by electrospray was surface cross-linked by either Ca(II) or chitosan to form polyelectrolyte microcapsules. By adjusting the needle inner diameter, concentration of sodium alginate, and applied voltage, we can control the droplet size to the designated range. Furthermore, we can tune the thickness and thereby rigidity/elasticity of the viscoelastic shell by adjusting the residence time of microcapsules in gelation solution to control the rigidity/elasticity of microcapsules. These polyelectrolyte microcapsules were subject to the osmotic pressure of synthetic water-soluble polymers, such as poly(ethylene glycol), with progressively lower concentration to observe their osmotic swelling behavior. [Preview Abstract] |
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S1.00206: Crossover Between 2D and 3D Fluid Dynamics in the Diffusion of Islands in Ultra-Thin Freely Suspended Smectic Films Zoom Nguyen, Markus Atkinson, Cheol Park, Joseph Maclennan, Matthew Glaser, Noel Clark fluid requires no force, leads, via the Einstein relation, to an infinite diffusion coefficient $D$ for the disc. Saffman and Delbr\"uck proposed that if the 2D fluid is a thin film immersed in a 3D viscous medium, then the film should behave as if it were of finite size, and $D \sim -\ln(a\eta')$, where $a$ is the inclusion radius and $\eta'$ is the viscosity of the 3D medium. By studying the Brownian motion of islands in freely suspended smectic films a few molecular layer thick, we verify this dependence using no free parameters, and confirm the subsequent prediction by Hughes, Pailthorpe and White of a crossover to 3D Stokes-like behavior when the diffusing island is sufficiently large. [Preview Abstract] |
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S1.00207: Decoupling of ionic conductivity from the structural relaxation in ionic liquids Philip Griffin, Alexander Agapov, Alexander Kisliuk, Alexei Sokolov In numerous technological applications, notably battery technology, the need for a highly conductive ionic material is critical. Ionic liquids are well suited for these applications, but the fundamentals of their physical properties are still not well understood. To investigate the temperature dependence of the conductivity and structural relaxation in these systems, a combination of light scattering techniques as well as dielectric spectroscopy measurements were performed on the ionic liquid [C4mim][NTf2]. Combining these measurement techniques enables us to characterize the dynamics in a time window that spans more than twelve decades. Detailed analysis of our results shows that the temperature dependence of the conductivity decouples from that of the structural relaxation. Furthermore, the structural relaxation exhibits a dynamical crossover similar to that observed in many glass forming liquids, while the conductivity exhibits no sign of the crossover. Contrary to the traditional theory, these observations suggest that the mechanism controlling ionic conductivity in this system is different from the mechanism controlling structural relaxation. [Preview Abstract] |
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S1.00208: Bistable Shear-Induced Alignment and Isotropy in Nematic Cylindrical Micelles Louis Madsen, Kyle G. Wilmsmeyer, Xiaolin Zhang Wormlike micelles (WLMs), such as cetyltrimethylammonium bromide in water, are long flexible cylinders of surfactant molecules that self-assemble as a function of concentration and temperature. By placing a driven rheological cell into an NMR instrument, we use ``rheo-NMR'' to correlate molecular-scale to micron-scale details available by NMR with macroscopic behaviors, with precise control over the sample shear rate. We directly observe alignment of WLMs induced by shear and magnetic field, as well as anisotropic diffusion, providing us with a nematic phase diagram that is modulated by shear. Here we focus on conditions where WLMs do not spontaneously field align (at 9.4 T), but rapidly and stably field align after application of shear. This ``bistable'' fluid persists in either the isotropic state or the field aligned state (after shearing) for $>$ 12 hrs. We will further describe measurements of the nonlinear dynamics of director reorientation, with which we quantify anisotropic elastic constants and viscosities. [Preview Abstract] |
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S1.00209: A phase-separation perspective on dynamic heterogeneities in glass-forming liquids Chiara Cammarota, Andrea Cavagna, Irene Giardina, Giacomo Gradenigo, Tomas Grigera, Giorgio Parisi, Paolo Verrocchio We study dynamic heterogeneities in a model glass-former whose overlap with a reference configuration is constrained to a fixed value. The system phase-separates into regions of small and large overlap, so that dynamical correlations remain strong even for asymptotic times. We calculate an appropriate thermodynamic potential and find evidence of a Maxwell's construction consistent with a spinodal decomposition of two phases. Our results suggest that dynamic heterogeneities are the expression of an ephemeral phase-separating regime ruled by a finite surface tension. [Preview Abstract] |
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S1.00210: Measuring the Nonergodicity in Glasses by Ensemble-Averaged Photon Correlation Spectroscopy Eric Svingen, David Sidebottom Although dynamic light scattering is used to monitor the dynamics of glass-forming liquids above the glass transition temperature, in the glass phase the absence of ergodicity results in a partial arrest of these dynamics and traditional time-averaged measures fail to monitor the remaining dynamics. Instead, scattering data must be processed in an ensemble-averaged manner by integrating the scattering from multiple regions by slowly translating the sample. We report studies of glass-forming 2Ca(NO3)2:3KNO3 (CKN) obtained below the glass transition temperature using a motorized translation system. Our findings will be used to assess the temperature dependence of the so-called nonergodic level that is predicted by certain mode-coupling theories to exhibit ``cusp'' near the mode coupling critical temperature. [Preview Abstract] |
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S1.00211: Direct imaging of spatially and temporally heterogeneous two-state dynamics on metallic glass and amorphous silicon surfaces well below T$_{g}$ Sumit Ashtekar, Gregory Scott, Joseph Lyding, Martin Gruebele Probing glassy dynamics of atomic glass formers with atomic resolution far below the glass transition has remained elusive due to the long waiting times and the small length scales involved. Here we report atomic resolution movies acquired using time-lapse scanning tunneling microscopy on metallic glass and amorphous silicon (a-Si) surfaces at room temperature well below their respective glass transition temperatures (Tg of glasses studied lie between 600-1000K). We find the clusters on metallic glass surfaces with size 2-8 atomic spacings exhibit dynamics which are almost exclusively two-state (P$_{3-state}\sim $0.06) [1]. The two-state dynamics was found to be both spatially and temporally heterogeneous. We attribute the two-state dynamics to the secondary $\beta $ relaxations which remains active well below the glass transition. Similar dynamics were found on amorphous silicon surfaces providing the first evidence for the existence of glass-like dynamics on pure a-Si surfaces at non-cryogenic temperature. \\[4pt] [1] S. Ashtekar et.al. J. Phys. Chem. Lett., 2010, 1 (13), pp 1941--1945 [Preview Abstract] |
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S1.00212: Frequency Dependence of Aging Dynamics in a Colloidal Glass Ajay Negi, Chinedum Osuji The aging response of glassy particulate systems originates due to slow structural rearrangements of its constituent matter. It is reasonable to speculate that structural rearrangements on different length scales should manifest themselves in dynamical response on different timescales. Here we consider the frequency dependence of aging in a colloidal glassy system using parallel superposition bulk rheology. The aging behavior of the system is characterized by time evolution of the complex modulus in response to a sinusoidally varying probe stress of different frequencies superimposed on a steady background stress. Strikingly, the system displays more rapid aging when observed at smaller frequencies. This suggests that, by comparison, it is more arrested on shorter length scales (higher frequencies) than on the longer length scales where many-particle correlated motions are in effect. Such correlated motions are believed to be responsible for relaxation in glassy materials. The variation in the aging dynamics at different frequencies is more prominent at higher background stresses where the system is more fluidized. [Preview Abstract] |
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S1.00213: Scaling, clustering and avalanches for steel beads in an external magnetic field Alyse Marquinez, Ingrid Thvedt, S.Y. Lehman, D.T. Jacobs We investigated avalanches using uniform 3mm steel spheres (``beads'') dropped onto a conical bead pile within a uniform magnetic field. The bead pile is built by pouring beads onto a circular base where the bottom layer of beads had been glued randomly. Beads are then individually dropped from a fixed height after which the pile is massed. This process is repeated for thousands of bead drops. By measuring the number of avalanches of a given size that occurred during the experiment, the resulting avalanche size distribution was compared to a power law description as predicted by self-organized criticality. As the magnetic field intensity increased, the beads clustered to give a larger angle of repose and we measured the change in the avalanche size distribution. The moments of the distribution give a sensitive test of mean-field theory as the universality class for these bead piles. [Preview Abstract] |
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S1.00214: Particle trajectories in 2D granular avalanches with imposed vibrations Nora Swisher, Brian Utter We study particle trajectories of photoelastic grains in a 2D circular rotating drum subjected to imposed vertical vibrations in order to characterize the jamming behavior of granular materials. Jamming appears in many systems (grain silos \& chutes, landslides, mixing industrial materials, etc.) and vibration (granular temperature) is a primary factor in the jamming/unjamming transition. Images are taken and each particle's position is found for every frame then compared between frames to find the velocities. Particle tracking allows us to quantitatively measure the flow and mixing properties in our experiment. We present data on avalanching statistics, mean flow, the width of the shear band, and properties related to mixing (fluctuations and trajectories of neighboring grains). We find that vibrations induce more rearrangements of the grains and cause the pile of grains to become more compact over time. At constant peak acceleration we find that low frequency/high amplitude caused more grain movement than high frequency/low amplitude in both the stationary and rotating case. [Preview Abstract] |
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S1.00215: Submerged granular flow of hydrophobic and hydrophilic sand Ben Foltz, Brian Utter We experimentally investigate submerged granular flows of hydrophobic and hydrophilic grains in a rotating drum. While slurry and suspension flows are common in nature and industry, effects of surface chemistry on flow behavior have received little attention. The experiment consists of a cylindrical drum containing various concentrations of hydrophobic and hydrophilic grains of sand submerged in water and rotated at a constant angular velocity. Images of the resulting avalanches are taken and analyzed. While it is known that at slow speeds, submerged avalanches appear qualitatively similar to dry flows, our results suggest that the surface properties of the grains affect underwater flow significantly. High concentrations of hydrophobic grains result in the formation of aggregates. At concentrations larger than 75\% hydrophobic sand, the avalanches do not behave in a manner which is typical for sand, but as the concentration decreases, the aggregates are smaller, the angle of repose decreases, and the grains start showing properties similar to those in regular sand. We present data on the size of the aggregates, slope, and avalanche statistics with changes in concentration. [Preview Abstract] |
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S1.00216: Phase transition of colloidal particles on curved surfaces Guangnan Meng, Jayson Paulose, David Nelson, Vinothan Manoharan Defects and disclinations have to appear in crystalline domains on a curved surface with non-zero Gaussian curvature. These geometrical frustrations can qualitatively change the physics of phase transition. We encapsulate micron sized polystyrene (PS) colloidal particles within emulsion droplets and use nanometer sized polyNIPAM hydrogel particles to introduce depletion attraction between PS particle and interface, as well as between PS particles. We use this experimental model system and confocal microscopy to study phase transitions on curved surfaces. We will present both experimental phenomena and theoretical analysis. [Preview Abstract] |
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S1.00217: Self and Directed Assembly of Thin Metallic Films exposed to Pulsed Laser Irradiation Yueying Wu, Jason Fowlkes, Philip Rack, Lou Kondic, Javier Diez The synthesis and assembly of functional metallic nanomaterials is critical for realizing many important applications of nanoscience and nanotechnology. In this study, we investigate dewetting of metal films via pulsed nanosecond laser melting. We study film instabilities that result from the interplay of capillary forces and liquid-solid interaction, which can lead to thin film break-up and subsequent nanoparticle formation. We have also explored the dewetting and nanopattern formation of other liquid metal geometries, such as rings and lines. We will discuss how nano-lithographically defined features can be used to direct the assembly of nanoparticles with desired properties, concentrating in particular on the role of stochastic fluctuations. [Preview Abstract] |
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S1.00218: Molecular design of self-propelled building blocks for dynamic self-assembly Yunfeng Shi, Yanping Chen Our research focuses on molecular design of self-propelled nanoscale objects serving as basic building blocks for dynamic self-assembly. Unlike static self-assembly which is driven thermally towards equilibrium, dynamic self-assembly evolves to a non-equilibrium steady state under a dissipative driving force. In this work, we use reactive molecular dynamics simulations to investigate how catalytic chemical reactions drive the motion of nanoscale building blocks. A fuel-catalyst reactive potential based on the reactive-state summation (RSS) scheme is designed for a model exothermic reaction. By strategically placing catalysts on the nanoscale building-blocks, asymmetric chemical reactions can be achieved which stimulate linear or rotational motion of the building-blocks. The observed propulsion can be understood in terms of momentum transfer. Importantly, the conversion efficiency from chemical to mechanical work is analyzed and used as an optimization target for molecular design of the chemically propelled building blocks. [Preview Abstract] |
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S1.00219: Fabrication and Characterization of High Aspect Ratio Membranes and Microporous Filters made from PMMA Alex Burant, Brian Augustine, Chris Hughes This experiment shows a new way to create high aspect ratio membranes and microporous filters by curing a liquid monomer, methyl methacrylate (MMA), into poly(methyl methacrylate) (PMMA) structures. Holes were cut in 200 $\mu $m PMMA sheets by laser cutting. Membranes were made by filling these holes with wax and cooling until the wax solidified. The liquid monomer solution was flowed over the wax-filled holes and photopolymerized to make a thin membrane. The membrane thickness could be controlled by adding 3-10 $\mu $m, 30-50 $\mu $m, or 50-100 $\mu $m silica beads to the monomer solution. Filters were made by filling the holes with curing solution containing 3-10 $\mu $m beads, photopolymerizing, and etching the silica with hydrofluoric acid. The filter porosity could be controlled by varying the weight percentage of silica beads added to the monomer solution. Scanning electron microscopy was used as a method for characterizing both membrane thickness and filter porosity. [Preview Abstract] |
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S1.00220: Enhanced shear separation for chiral magnetic colloidal aggregates Carlos Mendoza, Carlos Marques, Fabrice Thalmann We study the designing principles of the simplest colloidal propeller, an architecture built from four identical spheres that can couple translation with rotation to produce controlled drift motion. By considering superparamagnetic beads, we show that the simultaneous action of a magnetic field and a shear flow leads to the migration of the cluster in the vorticity direction. We investigate the dependence of the migration velocity on the geometrical parameters of the cluster, and find that significant cluster separation can be achieved under the typical operation conditions of microfluidic devices. Reference: C.I. Mendoza, C.M. Marques, and F. Thalmann, ``Enhanced shear separation for chiral magnetic colloidal aggregates'' arXiv:1011.1488 [Preview Abstract] |
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S1.00221: Numerical Analysis of Micromixers for Optimization of Mixing Action Yogendra Panta, Param Adhikari Micro-bio/chemical applications often require rapid and uniform mixing of a number of fluid streams that carries bio/chemical species in the solution. At microscale, fluid flow is highly laminar with low Reynolds number, fluids mixing mechanism is primarily by diffusion and free from any turbulence. Demand for highly efficient micromixers for microfluidic networks is due to slower mixing process for larger bio-molecules such as peptides, proteins, and nucleic acids compared to micro-scale molecules. Passive and active mixers are two basic mixers that are currently in use for these applications. Passive mixers often require very long mixing channels where are most active mixers require bulky moving parts to stir the fluids. In this study, electroosmotic effects orthogonally aligned with the fluid flowstream are utilized for optimum mixing effect in various micromixers. Cross-dependencies among several geometrical, electrical, and fluid parameters and their significance are studied in order to achieve an optimum mixing effect. It has been planned to optimize the mixer by non-moving stirring actions provided by an external magnetic field. [Preview Abstract] |
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S1.00222: A multiscale model for nanoparticle binding dynamics under shear flow Yaling Liu, Jifu Tan, Kytai Nguyen Nanomedicine poses a new frontier in medical technology with the advantages of targeted delivery and patient specific design. In applications of nanoparticle targeted drug delivery, the delivery efficiency is controlled by the physical properties of the nanoparticle such as its size, shape, ligand density, as well as external environmental conditions such as blood flow rate, blood vessel diameter. Proper drug dosage choice relies on determination of the attachment and detachment rates of the nanoparticles at the active region and the understanding of the complex process of targeted drug delivery. A few particulate models have been proposed to study the adhesion probability of individual spherical or non-spherical nanoparticles. Meanwhile, continuum convection-diffusion-reaction models have been widely used to calculate the drug concentration, which usually assumes specific binding and de-binding constants. However, there has not been any study that links the particulate level nanoparticle size and shape information to the system level bounded particle concentration. A hybrid particle binding dynamics and continuum convection-diffusion-reaction model is presented to study the effect of shear flow rate and particle size on binding efficiency. The simulated concentration of bounded nanoparticles agrees well with experimental results in flow chamber studies. [Preview Abstract] |
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S1.00223: Modeling spreading of nematic droplets Te-Sheng Lin, Linda Cummings, Lou Kondic Experiments by Poulard \& Cazabat\footnote{C. Poulard, A. M. Cazabat, Langmuir, 6270, vol. 21 (2005)} on spreading droplets of nematic liquid crystal reveal a surprisingly rich variety of behavior, including at least two different emerging lengthscales resulting from a contact line instability. In earlier work\footnote{L. J. Cummings, T.-S. Lin, L. Kondic, sumitted (2010)} we modified a lubrication model for nematic liquid crystals due to Ben Amar and Cummings\footnote{M. Ben Amar, L. J. Cummings, Phys. Fluids, 1160, vol. 13 (2001)}, and showed that, in a qualitative sense, it can account for much of the observed behavior. In the present work we propose a new approach, that allows us to explore the effect of anchoring variations on the substrate. This in turn gives a simple way to model the presence of defects, which are always present during such liquid crystal flows. The new model leads to additional terms in the governing equation. We first explore the influence of these additional terms for some simple flow scenarios, to gain a basic understanding of their influence, before extending our simulations to the experimental geometry and comparing our results to the experiments. [Preview Abstract] |
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S1.00224: Drop evaporation and triple line dynamics Benjamin Sobac, David Brutin, Jerome Gavillet Sessile drop evaporation is a phenomenon commonly came across in nature or in industry with cooling, paintings or DNA mapping. However, the evaporation of a drop deposited on a substrate is not completely understood due to the complexity of the problem. Here we investigate, with several nano-coating of the substrate (PTFE, SiOx, SiOc and CF), the influence of the dynamic of the triple line on the evaporation process. The experiment consists in analyzing simultaneously the motion of the triple line, the kinetics of evaporation, the internal thermal motion and the heat and mass transfer. Measurements of temperature, heat-flux and visualizations with visible and infrared cameras are performed. The dynamics of the evaporative heat flux appears clearly different depending of the motion of the triple line [Preview Abstract] |
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S1.00225: Nanoscale heterogeneity in alkyl-methylimidazolium bromide ionic liquids David Price, Bachir Aoun, Marie-Louise Saboungi, Andreas Goldbach, Miguel A. Gonz\'alez, Shinji Kohara High-energy x-ray diffraction measurements on 1-alkyl-3-methylimidazolium bromide ionic liquids with ethyl, butyl and hexyl alkyl chains reveal a peak at low scattering vector $Q$ that rises and moves to lower $Q$ with increasing chain length. Atomic molecular dynamics simulations, which give results in excellent agreement with the x-ray data, show that this behavior is most pronounced in the partial structure factor for the tails of the alkyl chains but is also seen in those for the imidazolium ring centers and anions. The heterogeneity with a length scale of 1.9 nm established for the liquid with the hexyl chain is quantified by a density heterogeneity order parameter that shows a clustering of the tails. Our results are consistent with explanations in the literature of the increase in viscosity with alkyl chain length in terms of nanoscale segregation. [Preview Abstract] |
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S1.00226: On segregation of noble gases in water-based Single Bubble Sonoluminescence Mogens Levinsen A long-standing issue in the field of long time stable water based single bubble sonoluminescence has been the close similarity of the spectra to that of blackbody radiation. Looking for the effects of possible segregation of noble gases has been suggested as a means to investigate whether the similarity is just a weird coincidence with the bubbles being on the whole transparent to their own radiation. We have investigated spectra from bubbles seeded with various mixtures of helium and neon with xenon and argon using a novel transformation that allows for a single parameter characterization of the spectra, with the surprising result that although no trace of segregation is found, the radiation seems to be highly thermalized in all cases. [Preview Abstract] |
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S1.00227: Generating a Pulsatile Pulmonary Flow after Fontan Operation by Means of Computational Fluid Dynamics (CFD) Mostafa Ghoreyshi This study considers blood flow in total cavopulmonary connection (TCPC) morphology, which is created in Fontan surgical procedure in patients with single ventricle heart disease. Ordinary process of TCPC operation reduces pulmonary blood flow pulsatility; because of right ventricle being bypassed. This phenomenon causes a lot of side effects for patients. A cardiac surgeon has suggested that keeping main pulmonary artery (MPA) partially open, would increase pulmonary flow pulsations. MPA gets closed in ordinary TCPC operation. The purpose of current study is to verify the effects of keeping MPA partially open on pulmonary flow pulsations, by means of computational fluid dynamics (CFD). 3D geometry is reconstructed from CT Angiography (CTA) scan of a patient who has undergone an ordinary TCPC procedure. The stenosed MPA or pulmonary stenosis (PS) is virtually added to the original geometry. Flow field is studied in six different models in which average antegrade flow (AF) -coming through PS- increases gradually. Results show that adding AF increases flow pulsations in both pulmonary arteries. Moreover, power loss increases with respect to average AF. We conclude that adding AF is an impressive way to increase pulsations of pulmonary flow, but energy losses should be considered too. [Preview Abstract] |
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S1.00228: Designing self-oscillating cilia using active polymer gels Pratyush Dayal, Amitabh Bhattacharya, Olga Kuksenok, Anna C. Balazs Using theory and simulations, we model the dynamic behavior of synthetic cilia made from soft, active materials. In designing this system, we harness the properties of polymer gels that undergo photosensitive Belousov-Zhabotinsky (BZ) reaction. Driven by the periodic reduction and oxidation of a ruthenium catalyst that is grafted onto the polymer backbone, these BZ gels undergo rhythmic swelling and de-swelling by chemo-mechanical transduction. When these BZ gels are tethered to a substrate, they form cilia that can pulsate autonomously in response to the BZ reaction. To simulate the behavior of the BZ cilia, we developed a nonlinear 3D model that captures the effect of the diffusive exchange of BZ reagents between the gel and the fluid. Using this approach, we determine the factors that govern the bending and beating of individual cilium. We then turn our attention to multiple cilia and show that their collective dynamics strongly depends on the spacing between them. We also establish criteria to regulate the collective behavior of multiple cilia using light as the external stimuli. Our findings provide guidelines for designing ciliated surfaces that can exhibit biomimetic functionality. [Preview Abstract] |
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S1.00229: APPLICATIONS |
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S1.00230: Terahertz microbolometers based on disordered GaAs and GaN heterostructures Kai Wang, R. Ramaswamy, A. Muraviev, A. Sergeev, V. Mitin, R. Gaska We present our results on design, fabrication, and characterization of hot-electron bolometers based on low-mobility two-dimensional electron gas (2DEG) heterostructures for THz heterodyne detection. Microbolometers based on GaAs/AlGaAs and GaN/AlGaN heterostructures have been fabricated and tested. Low contact resistances (0.2 ohm-mm for GaN and 0.7 ohm-mm for GaAs) were achieved. We determined the carrier concentration from the Hall measurements and the electron relaxation time from the mobility measurements. We also investigated kinetic parameters: temperature derivate of the resistivity and the electron cooling time. Optical characterization includes the transitivity measurements. The results show that the coupling to the THz radiation is mainly due to the Drude absorption, which increases in disordered structures. Temperature-dependent resistivity and electron cooling are determined by inelastic electron scattering on optical phonons. Finally, we compare GaAs and GaN microbolometers and analyze their parameters for various applications in THz sensing. [Preview Abstract] |
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S1.00231: Quantum cascade lasers as LO for THz mixers Rahul Ramaswamy, Andrey Muraviev, Kai Wang, Christoph Deutsch, Jaekyu Choi, David Eason, Gottfried Strasser, Michael Shur, Andrei Sergeev, Vladimir Mitin In this research we fabricate and characterized a number of Fabry-Perot type, multi mode terahertz quantum cascade lasers operating in the range 2 -- 3 THz. AlGaAs/GaAs heterostructures for terahertz QCLs have been grown using molecular beam epitaxy (MBE) on a SI-GaAs substrate. The active region design is based on a vertical transition in which a combination of resonant tunneling and LO-phonon scattering is used to selectively depopulate the lower radiative state. Double-sided metal waveguide is employed for QCL mode confinement. Spectral properties of the QCLs have been investigated by means of Fourier transform spectroscopy. All QCLs show the gain spectral band tunability by varying the applied bias voltage. Single mode laser operation is observed in a certain range of applied bias voltages. Our QCLs have an inherently narrow line-width, which is limited in our measurements by the spectrometer resolution of 0.1cm$^{-1}$. [Preview Abstract] |
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S1.00232: Voltage Tunable Multicolor GaAs/AlGaAs Coupled Quantum Well Infrared Photodetector Jae Kyu Choi, David Eason, Gottfried Strasser, Nizami Vagidov, Vladimir Mitin Tunable quantum well infrared photodetectors (QWIP) has attracted attention because of the mature growth technique of GaAs/AlGaAs quantum wells and their diverse applications such as remote temperature sensing, chemical analysis, military applications, and so on. We have designed, grown, and characterized a voltage tunable multicolor QWIP for the long wavelength infrared detection (7.5 -- 12.4 $\mu $m). The QWIP structure was grown by MBE, and the device is designed to have bound to bound and bound to quasi-continuum transitions in an asymmetrically doped double quantum well. At zero bias we observed several distinctive spectral lines in photoresponse. The device demonstrates strong dependence on a magnitude and a polarity of the bias that is confirmed by the shift of energy levels in the electric field calculated by nextnano$^{3 }$software. In particular, switching bias from +3V to -5V we change the photoresponse of our detector from 8.39 $\mu $m to 10.21 $\mu $m. [Preview Abstract] |
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S1.00233: Localized and Synchronous Measurement of Second and Third Order Nonlinearity in Superconductive Transmission Line Resonators Annelle Eben, Stephen Remillard A method to locally observe the generation of nonlinearity of multiple orders inside the passband of Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$ and YBa$_{2}$Cu$_{3}$O$_{7}$ superconducting resonators has been developed. Nonlinear emission is stimulated locally in the vicinity of the probe by off-resonance, low frequency signals. By mixing of two very low frequency local currents and of one current in the passband, 2$^{nd}$ and 3$^{rd}$ order intermodulation distortion (IMD) occurs around resonance, permitting the determination of the currents associated with each order of nonlinearity. Synchronous measurement of different orders eliminates the ambiguity of emissions occurring on different time scales and at different skin depths. Comparison of synchronous 2$^{nd}$ and 3$^{rd}$ order IMD characterizes the extent of time reversal symmetry breaking (TRSB) in the superconductor. This technique is being used to perform spatially resolved TRSB studies, to examine the effect of doping on nonlinearity in Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8}$, and to search for a correlation between lithographic edge quality and 2$^{nd}$ and 3$^{rd}$ order nonlinearity. [Preview Abstract] |
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S1.00234: ABSTRACT WITHDRAWN |
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S1.00235: Analysis and Simulation of Generating Terahertz Surface Waves in Laser-Assisted Field Emission Mark Hagmann, Gagan Kumar, Shashank Pandey, Ajay Nahata When the radiation from two lasers is focused on a field emission diode the electric field from the radiation is superimposed on the applied DC field, and the nonlinear dependence of the emitted current on the electric field causes the current to oscillate at the difference frequency for the two lasers. Finite Difference-Time Domain simulations and analytical solutions for a paraboloidal model of the field emission tip show that the current oscillations create a transverse-magnetic (TM) surface wave on the tip. The analytical solution for the TM fields in paraboloidal coordinates consists of products of regular and irregular Coulomb wave functions. The width of the tip is much smaller than the skin depth so interior and exterior solutions are required and a summation of the products is required to satisfy the boundary conditions at the surface of the tip. The simulations are consistent with the analytical solution and show that there is a quasi-stationary region near the apex, a transition region where the surface waves are formed, and the far-field where the waves propagate outward on the tip. [Preview Abstract] |
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S1.00236: Antireflective Coatings using Layer by Layer Self Assembly of Silica and Titania Nanoparticles Anitesh Lal, Raisa Velasco Castedo, Dan Mazilu Antireflective coatings have a wide range of applications and its usefulness can be found in devices such as cameras, binoculars, microscope lenses, solar panels etc. The major expectation for this research is to add an antireflective coating to a glass substrate which will reduce the reflectance and increase the transmittance of light of the substrate. From theory it is known that uncoated glass substrates transmit approximately 92{\%} of light and reflect approximately 8{\%} of it. However, if an antireflective coating is introduced on the surface of the substrate, there will be some light reflected from the first interface and some from the second interface. If these two reflected rays are made to interfere destructively, reflection can be minimized thus maximizing transmittance. We conducted various experiments with silica particles only in which we tried to change the properties of this antireflective coating such that maximum destructive interference could be achieved. Currently, we are working with a combination of silica and titania nanoparticles with varying thicknesses whereby layers have thickness of a quarter of the desired wave length. So far a number of different factor-level combinations have exhibited transmittance in excess of 96{\%}, well above that of an untreated slide and comparable to commercial coatings. [Preview Abstract] |
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S1.00237: Light Instability in Pulsed Quantum Cascade Lasers Yuting Huang, Yu Yao, Kais Al-Naimee, Claire Gmachl The instability observed in the light output of high power, pulsed Quantum Cascade (QC) lasers is investigated for potential periodic behavior. We built a set-up to monitor the real-time pulse shape of up to 5,000 sequential light pulses at a fixed pulsed current. In analyzing the data, we use the Fast Fourier Transform to find their frequency components. We found likely quasi-periodic behavior, as well as a broader range of frequencies around the fundamental pulse frequency. To also research a potential spatial component in the laser instability, i.e. beam steering, we modified the set-up to split the beam spatially into two parts, each monitored in real-time over 5,000 pulses. A correlation between the two pulse trains on the two detectors separates the spatial and pure power components of the instability. Subsequently eliminating this instability will help to achieve QC lasers with optimal performance. [Preview Abstract] |
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S1.00238: Modeling Laser-Tissue Interactions: Implementing the Heat Diffusion Equation and Wave Equation to Simulate Thermal Interactions of Absorber Distributions in Biological Tissues Frederick Barrera, Elharith Ahmed, Patrick Nash, Dhiraj Sardar The tracking of photons through turbid media (e.g. tissues) has been studied extensively from an experimental vantage point. These turbid media are difficult to characterize- since their components are exceedingly variegated- and thus present many challenges to clinicians who require models which precisely predict the location and time evolution of energy deposition. Furthermore, the interaction of the turbid media sample with the source of radiation typically involves many dynamic mechanisms (e.g. photothermal etc.) Using diffuse light transport, and an electromagnetic wave approach (e.g. Maxwell's equations), an analysis of thermal energy distribution in tissues is performed. Assuming a highly absorbing chromophore model of melanocytes in tissues, a comparison of the variation of thermal energy is determined for different collections of melanocyte spatial distributions. [Preview Abstract] |
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S1.00239: Tunable TiO2 Nanotubes as Nanotemplate for Solar Cells Jia Lu, Dongdong Li Titanium oxide (TiO2) is an n-type semiconductor with a bandgap energy of 3.0-3.2 eV. It has broad applications, because of the versatile functionalities. Synthesis of anodic titanium oxide (ATO) nanotube templates has gained significant progress in fluoride-ion-contained electrolytes. The one-dimensional (1D) structure provides a large specific surface area as well as a direct pathway for charge transport, thus rendering superior capabilities in lightharvesting, electrochromic switching, environmental sensing, energy storage, etc. In this work, highly ordered ATO nanotubes film has been synthesized by two-step anodization method. After using a reductive doping approach, the metal materials (Cu and Ni) can be electrodeposited into the nanotubes. The versatile process yields reproducible tubular structures in ATO nanotubes due to the conductive nature of crystallized TiO2, indicating great potential for nanotemplate application. A dye-sensitized solar cell is also demonstrated by employing the ATO films. It is observed that bottom treatment greatly enhances short current density and filling factor resulting in improved energy conversion efficiency. [Preview Abstract] |
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S1.00240: Theoretical Investigation on Cysteine Interactions with Gold Nanoparticles Jessica Carr, Hong Wang, James Lewis Gold nanoparticles have been intensely investigated due to wide applications in colloidal chemistry, catalysis, medical science, etc. Lately, experiments have shown that ligand-stabilized gold nanoparticles provide a platform for precisely probing the structural and electronic properties of isolated gold nanoparticles, allowing us to further understand the interaction between gold nanoparticles and attaching ligand molecules. Using density functional theory approach, we investigate a series of gold nanoparticles with a size scale of 0.5 to 2 nm that are passivated by a monolayer of cysteine molecules [R-SH, with R=CH$_{2}$CH(COOH)(NH$_{2}$)]. There is a controversy about the attaching pattern of the cysteine monolayer around the gold nanoparticles. We speculate that there is hydrogen bonding between the cysteine molecules, leading to stabilized gold nanoparticles. This research shows potential hydrogen bonding forming with the gold nanoparticle surface, as well as hydrogen bonding between cysteine molecules. [Preview Abstract] |
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S1.00241: Photocurrent enhancement of an individual gallium nitride nanowire decorated with gold nanoparticles Jency Pricilla Sundararajan, Meredith Sargent, David N. McIlroy Variation in electron transport properties of individual n-type gallium nitride (GaN) nanowire and gold decorated gallium nitride (Au-GaN) nanowire were studied with respect to laser exposure of different wavelength and intensity. Single nanowire devices were manufactured by photolithography process in nanotechnology cleanroom, were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). A drop in electrical conductivity of Au-GaN nanowire was observed relative to bare GaN nanowire. Under laser illumination, we noticed an enhancement in photocurrent in Au-GaN nanowire, which increased with increase in excitation power at ambient conditions. We present a comparative study of the opto-electrical behavior of bare GaN nanowire vs Au-GaN nanowire and explain the IV characteristics and FET characteristics with respect to the length and diameter of nanowire. [Preview Abstract] |
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S1.00242: Pulsed Laser Synthesized Magnetic Cobalt Oxide Nanoparticles for Biomedical Applications Hari Bhatta, Ram Gupta, Kartik Ghosh, Pawan Kahol, Robert Delong, Adam Wanekawa Nanomaterials research has become a major attraction in the field of advanced materials research in the area of Physics, Chemistry, and Materials Science. Biocompatible and chemically stable magnetic metal oxide nanoparticles have biomedical applications that includes drug delivery, cell and DNA separation, gene cloning, magnetic resonance imaging (MRI). This research is aimed at the fabrication of magnetic cobalt oxide nanoparticles using a safe, cost effective, and easy to handle technique that is capable of producing nanoparticles free of any contamination. Cobalt oxide nanoparticles have been synthesized at room temperature using cobalt foil by pulsed laser ablation technique. These cobalt oxide nanoparticles were characterized using UV-Visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), and dynamic laser light scattering (DLLS). The magnetic cobalt oxides nanoparticles were stabilized in glucose solutions of various concentrations in deionized water. The presence of UV-Vis absorption peak at 270 nm validates the nature of cobalt oxide nanoparticles. The DLLS size distributions of nanoparticles are in the range of 110 to 300 nm, which further confirms the presence nanoparticles. This work is partially supported by National Science Foundation (DMR- 0907037). [Preview Abstract] |
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S1.00243: Diffusion Through Tubular Nanotubes Divya Narayan Elumalai, Hervin MonLouis, Pedro Derosa Nanotubes exhibit exceptional properties that make them promising candidates for many applications that require the transport, storage and/or delivery of fluids, through nanotubes. In order to efficiently plan potential applications, transport properties and interactions such as adsorption, diffusion, and solvent interactions must be understood. Our study focuses on the mechanisms that inhibit or encourage diffusion through these nanostructures and the nature of the interactions responsible for movement of any sort in these regimes. As a specific case we study diffusion through tubular nanotubes. This work treats each interaction individually and aims at successfully modeling the diffusion of particles through the nanotubes as a function of the interaction between the diffusing particles and the nanotube walls. To conduct this research we have employed Monte Carlo calculations, implementing a specific forced random walk algorithm. Preliminary results suggest that any delay in diffusion occurs due to a strong molecule-wall interaction. We believe this is due to the columbic attraction between the diffusing particles and the wall. [Preview Abstract] |
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S1.00244: Role of CNTs in inorganic electroluminescence Jin-Young Kim, SeGi Yu Inorganic electroluminescence (EL) has been considered to be utilized in flat panel displays in the future. However, the progress of the display device utilizing EL phosphor is rather mild due primary to its low brightness, high voltage operation, and poor expectation lifetime. Carbon nanotubes (CNTs) has been focused in many areas since this material has a number of useful characteristics such as good chemical inertness, high aspect ratio, good thermal conductivity, and etc after the first observation by Dr. Iijima. By adopting (CNTs) in inorganic EL devices of ZnS-based powder phosphor, the performance of devices has improved substantially, i.e., high brightness but with reduced current density. The main reason for this improvement is considered to be caused by the strong local field near the end tips of CNTs. Further efforts have been poured to use the enhanced local field around CNTs but with an intention to maintain the low current density. The details will be posted in this poster and underlying mechanism for this phenomenon will be explained. Email: segiyu@hufs.ac.kr [Preview Abstract] |
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S1.00245: Graphene Transistor fabricated by Helium Ion Milling Kaiwen Zhang, Xiangming Zhao, Xiangfan Xu, Viswanathan Vignesh, Baowen Li, Daniel Pickard, Barbaros \"Ozyilmaz We report the direct patterning of graphene for various nano-device applications. The Helium Ion Microscope (HIM), able to resolve nano-scale features on solid samples with an edge resolution of a mere 0.25 nm, has a number of attributes which make it attractive for the imaging of graphene structures. Even more compelling is the ability to directly modify graphene, through surface sputtering, enabling direct pattern transfer for the fabrication of graphene devices. The integration of the HIM with a vector pattern generator (Nano Pattern Generation System, NPGS), provides the capability to directly pattern graphene into nano-ribbons. We have successfully fabricated sub-100nm graphene nano-ribbon devices on Si/SiO2 substrate. Resistance measurement has been made as a function of temperature. [Preview Abstract] |
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S1.00246: Novel nanostructured high efficiency light-harvesting device structure for a solar cell application Kyung-Min Lee, Pooja Singh, Arup Neogi, Sang-Kwon Lee, Tae-Youl Choi In this study, we present a novel photoconductive device structure for a solar cell application. $\beta $-Silicon Carbide ($\beta $-SiC) nanowire(NW) was placed in between silver (Ag) nanodot(ND) array. With much shorter size than an incoming photon wavelength, Ag ND created plasmonic oscillation, mainly attributed to dipole oscillating term, according to Mie scattering theory. Because of more optical modes in the higher refractive index, the radiation pattern from the dipole oscillation was mostly expanded onto the $\beta $-SiC NW rather than free space. We found that Ag ND array played role as collecting and concentrating light to create denser optical paths into the semiconducting $\beta $-SiC NW, which in turn provided higher quantum yield for photoconductivity. Since the structure was nanoscaled (i.e. NW and ND), this novel device structure can be a miniaturized building block for high demanding solar cell applications as one of the energy solutions. [Preview Abstract] |
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S1.00247: Ultrafast Optical Measurements of Thermal Conductivity and Sound Velocity of Amorphous SiC Donald Hondongwa, Lauren Olasov, Brian Daly, Sean King, Jeff Bielefeld We present ultrafast optical measurements of longitudinal sound velocity and thermal transport in hydrogenated amorphous carbon (a-SiC:H) films. The films were grown on Si wafers by PECVD using combinations of methylsilanes and H$_{2}$ and He diluent gases. The films were well characterized and found to have densities (1.0 -- 2.5 g cm$^{-3})$ and dielectric constants (2.8 -- 7.2) that spanned a wide range of values. Prior to their measurement, the a-SiC:H films were coated with 40-70 nm of polycrystalline Al. The pump-probe measurements were performed at room temperature using a modelocked Ti:sapphire laser. Transient reflectivity changes that are associated with very high frequency sound waves (picosecond ultrasonics) and the cooling rate of the SiC sample (Time Domain Thermorerflectance (TDTR)) were measured. We extract values for the thermal conductivity and sound velocity of the SiC films, and analyze the results in terms of rigidity percolation effects within the SiC layers. [Preview Abstract] |
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S1.00248: Ultrafast optical measurements of ultrasound attenuation in amorphous silicon at 50 and 100 GHz Brian Daly, Donald Hondongwa, Theodore Norris, Baojie Yan, Jeff Yang, Subhendu Guha We present ultrafast optical measurements of the attenuation of 50 -- 100 GHz ultrasound in hydrogenated amorphous silicon (a-Si:H) thin films. The films were grown using a modified very high frequency glow discharge method on steel substrates. The deposition conditions were similar to those used for high efficiency solar cells. The measurements were performed at 300 K using the picosecond ultrasonics technique. Films of varying thickness were measured so that the effect of intrinsic acoustic loss within the a-Si:H could be determined. We find that the ultrasonic attenuation in a-Si:H at 100 GHz is more than an order of magnitude lower than is found in other amorphous materials. Our results may impact theoretical models of thermal transport in amorphous materials, and could provide a new avenue for studying voids in a-Si:H and nanocrystalline Si films. [Preview Abstract] |
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S1.00249: Charge Carrier Mobility in Conjugated Organic Polymers--A Multi-Step Computational Approach Yaping Li, Jolanta B. Lagowski In this work, we investigate charge transport characteristics of conjugated organic polymers (mostly fluorene and carbazole based) used in the construction of the organic solar cells using computational means. In particular we employ a multi-step approach that involves the use of the density functional theory (DFT), semiempirical (ZINDO), and Monte Carlo (MC) theoretical methods to determine their transfer integrals, reorganization energies, transfer rates and mobilities. We find that, in organic conjugated polymers, one dimensional (1D) approach to estimating trends in mobilities gives reasonable results, i.e. is in good agreement with experiment trends, provided their relative intermolecular distances can be obtained with some accuracy. However, greater understanding of the mobilities must take into account the three dimensional (3D) structure and/or the inherent disorder that is present in the organic thin films. We illustrate this requirement with some case studies. Another case study involving orientational disorder will also be presented. The proposed approach illustrates that theoretical computations/simulations based on chemical structure and known morphology of organic semiconductors is an important and reliable approach to studying charge mobility in organic materials used in devices such as solar cells. [Preview Abstract] |
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S1.00250: High Thermoelectric Performance from Solution-Processed Conducting Polymer/Inorganic Composite Films Nelson Coates, Shannon Yee, Kevin See, Jeffrey Urban, Rachel Segalman Conducting polymer/inorganic composite films have great potential for use as thermoelectrics due to the possibility of combining the high electrical conductivity of inorganic materials with the low thermal conductivities of polymer materials. Additionally, the possibility of engineering nanoscale interfaces in these hybrid systems provides a unique means of optimizing thermoelectric figures of merit. We have fabricated films from this new class of materials, and examined their thermoelectric properties. Our solution-processed films, which consist of an inorganic nanostructure matrix linked with conducting polymer ligands, exhibit an electrical conductivity that is greater than either of its components and a thermopower that varies as a function of inorganic nanocrystal-conducting polymer ratio. [Preview Abstract] |
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S1.00251: Probing the Fluid-Graphene Interface for Electrochemical Storage by \textit{in-situ} Synchrotron X-ray Scattering Hua Zhou, Paul Fenter, Jake McDonough, Volker Presser, Yuri Gogotsi, Pasquale Fulvio, Sheng Dai The interactions of electrolyte fluids with solids control many complex interfacial processes encountered in electrochemical energy storage systems. In this talk, we will demonstrate how to develop a fundamental atomic-scale understanding of interfacial structures and processes at the electrolyte-graphene interface. We have performed systematic measurements of high resolution X-ray reflectivity from epitaxial graphene films in contact with electrolytes including aqueous solutions and room temperature ionic liquids. The electron density profiles and structural models from the fully analyzed data reveal the intrinsic interfacial structures of these systems. Moreover, we have developed successfully a customized electrochemical sample cell that allows the solvent reorientation and ion adsorption measurements to be done in-situ with control of the surface potential. Specular Bragg rod and resonant anomalous X-ray reflectivity measurements were performed in combination with electrochemical characterizations. The combination of in-situ structural measurements with electrochemical controls will lead to fundamentally new insights and provide unique tests of atomistic fluid-solid interface models for energy storage systems. [Preview Abstract] |
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S1.00252: \textit{ab initio} Thermodynamic Approach to Identify Good Solid Sorbents for CO$_{2}$ Capture Applications Yuhua Duan By combining thermodynamic database searching with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify most promising candidates for CO$_{2}$ sorbents has been proposed (Duan {\&} Sorescu, PRB(2009), JCP(2010)). For given solids, first we can search their thermodynamic properties from thermodynamic databases and literatures. If their thermodynamic properties are unknown, we perform \textit{ab initio} thermodynamic approach to calculate them out. These properties are used for computing the thermodynamic reaction equilibrium properties of CO$_{2}$ absorption/desorption cycle based on the chemical potential and heat of reaction analysis. According to the pre- and post- combustion technologies and conditions in power-plants, based on our calculated thermodynamic properties of reactions for each solid capturing CO$_{2}$ varying with temperatures and pressures, only those solid materials, which result lower energy cost in the capture and regeneration process and could work at desired conditions of CO$_{2}$ pressure and temperature, will be selected as promised candidates of CO$_{2}$ sorbents and further be considered for experimental validations. [Preview Abstract] |
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S1.00253: ABSTRACT WITHDRAWN |
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S1.00254: Development of semi-rigid coaxial cables for application to low temperature experiments Akihiro Kushino, Soichi Kasai Fast signal readout with low noise is essential for spectrometric research. Superconducting spectrometers operating below $\sim $1K are promising with their high spectral resolution, detection efficiency and counting rate. Cables connecting these spectrometers and electronics at high temperature must be coaxial and have low thermal conductance in order to reduce heat into low temperature. We have developed thin semi-rigid coaxial cables using low thermal conductivity alloys, CuNi, SUS and NbTi, for both center and outer conductors. The outer conductor is seamless and separated from the center conductor by a PTFE electrical insulator. We have assembled an adiabatic demagnetization refrigerator (ADR) at the 2nd stage of a GM cryocooler, which enables to cool the coaxial cables below 1K, and have measured low thermal conductance and performance of the cables at high frequencies up to $\sim $5 GHz. [Preview Abstract] |
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S1.00255: HIGH PRESSURE PHYSICS |
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S1.00256: High-Pressure Structural Studies of AuX$_{2}$ (X = Al, Ga, In) Jason Baker, Ravhi Kumar, Andrew Cornelius High-pressure x-ray diffraction experiments were performed on the group of intermetallic compounds, AuX2 (X = Al, Ga, and In), which at ambient conditions crystallize in the CaF2 [Space group Fm3m] structure. The previously reported retention of the CaF2 phase until 24 GPa in AuIn2 was not observed in these experiments, and instead was observed to undergo a pressure-induced phase transition at 13 GPa. Both AuAl2 and AuGa2 undergo pressure-induced phase transitions at 15 GPa and 9 GPa, respectively. The structural details and the phase transition sequence in these compounds will be presented. [Preview Abstract] |
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S1.00257: High Pressure XRD Structural Study of Intermetallic Hydrogen Storage Material ZrFe2 Daniel Antonio, Ravhi Kumar, Andrew Cornelius Intermetallic compounds show high hydrogen sorption capacities when pressurized with hydrogen. Further, they are also used in hydride compressors [1]. The structure of intermetallic ZrFe$_{2}$, which can contain about 1.7 wt/% hydrogen around 0.18 GPa, was studied using XRD at high pressures up to 47 GPa using a diamond anvil cell and synchrotron x-rays. The cubic Fd3m Laves phase is found to be stable and the bulk modulus was found to be 163.5 GPa which compares well with other intermetallics. The variation of unit structural parameters and the equation of state are discussed. [Preview Abstract] |
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S1.00258: Towards a phase diagram for accreting neutron star crusts: total energy calculations of close packed lattices Tyler Engstrom, Vincent Crespi, Benjamin Owen Neutron star crusts are somewhat less exotic than their cores, but may still play an important role in observable astrophysical phenomena, such as pulsar glitches and cooling rates. Recent nucleosynthesis calculations of accreting material being burned and buried on a neutron star crust indicate the possible presence of many species, ranging from around Z=8 to Z=34. In the outer crust regime where these species are completely pressure ionized and have screened-Coulomb interactions due to the relativistic Fermi electron gas, we expect some close-packed lattices may have a lower free energy than the bcc structure that is usually assumed to exist. Our poster shows the results of ground state energy calculations for several candidate binary and ternary close-packed lattices. We compare these ground state energies to those for pure phase separated bcc and fcc structures. [Preview Abstract] |
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S1.00259: Structure stability of multiferroic compound Bi2NiTiO6 under high pressure and temperature Jinlong Zhu, Changqing Jin, Yanchun Li, Xiaodong Li, Jing Liu Structural of multiferroics Bi2NiTiO6 under high pressure was studied in diamond-anvil cell (DAC) combined with synchrotron radiation X-ray diffraction. Crystal structure refinement shows that there are two isostructural phase transitions at $\sim $2 GPa and in the range of 15.5$\sim $18.5 GPa, respectively. The bulk modulus was derived from Birch-Murnaghan equation of state (EOS). Bi iron discontinuous movement is thought to be the source of all the isostructural phase transitions. Temperature dependence of X-ray diffractions were collected from room temperature up to 550 $^{\circ}$C. Structure refinement shows that an isostructural phase transition at temperature higher than 550 $^{\circ}$C can be compare with the isostructural phase transition in the range of 15.5$\sim $18.5 GPa. [Preview Abstract] |
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S1.00260: GENERAL PHYSICS II |
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S1.00261: Proposal to reduce the carcinogenic character of electromagnetic radiation (EMR) Marjorie Lundquist Non-ionizing electromagnetic radiation (NIEMR) interacts with matter in 3 ways:\footnote{M. Lundquist, {\bf BAPS 51}(1):518 (2006).} it can transfer energy, linear momentum, and angular momentum to matter. At high frequencies ({\it e.g.}, microwaves), evidence exists of a carcinogenic effect on living creatures irradiated with NIEMR.\footnote{M. Lundquist, {\bf BAPS 49}(1):1296 (2004).} Which effect is carcinogenic? NIEMR heats matter by transfer of energy; this effect is used to {\bf kill} established cancers. Transfer of linear momentum to matter merely alters the local pressure; cancer has never been associated with pressure changes. So the transfer of non-zero angular momentum to matter is the interaction most likely to be carcinogenic. EMR polarization can be circular, elliptical, or plane. Only plane-polarized EMR possesses {\bf zero} angular momentum and therefore {\bf cannot} transfer any angular momentum to matter. Everything that is true of NIEMR is also true of ionizing EMR, so it seems likely that the carcinogenic potential of {\bf all} EMR (whether ionizing or non-ionizing) will be minimized by filtering it or taking other steps to make it plane-polarized before using it to irradiate a person or animal. Obvious applications are medical/dental X-rays and the full body scanners used on travelers at airports. [Preview Abstract] |
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S1.00262: Good science, deceptive science, and fraud, plus a brief discussion of peer review Marjorie Lundquist What makes scientific publication different from other types of publication? Traditionally, it was that scientists published not only their conclusions, but also their data (which enabled others wanting to re-evaluate the data to do so). Publishing their data helped keep scientists honest. In the mid-20$^{th}$ century the policies of scientific journals changed, partly because very large data sets were being evaluated via computer. Many (but not all) scientific journals paid homage to scientific tradition by establishing archives for data serving as the basis for published scientific papers, while only a description of the study and the conclusions were published in the peer-reviewed scientific journals. This set the stage for scientific deception and scientific fraud, which became widespread in certain fields of study during the latter part of the 20$^{th}$ century. Indeed, some organizations were established that appeared to be legitimate scientific societies, but in fact existed for the purpose of promoting the {\bf incorrect} evaluation of scientific data and publishing deceptive studies masquerading as sound scientific studies. The field of medicine has also become more science than art, with its current emphasis on ``evidence-based medicine.'' The different types of scientific deceit/fraud are identified, and a lifetime of experience with the correction of scientific error, plus encounters with scientific deception and scientific fraud, is summarized. [Preview Abstract] |
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S1.00263: Both Perelmans Thrown Down Gauntlets Versus Would-Be "Science" But Alas Sadly Mere "SEANCES" Put Jargonial-Obfuscation Sociological-Dysfunctionality(S-D) Ridden/Dominated Would-Be "Sciences" But Alas Sadly Mere SEANCES in "Peril, Man"!!! J. Carlson, F. Young, London Clay, Edward Carl-Ludwig (Physical-Mathematicist/Mathsicist) Siegel Both Perelman (Grigory[Poincare-conjecture: partial(with Richard Hamilton!!!)-"sole"-prover: by turning down first the Fields Medal at International Congress of [S-D right there: not mathematICS, but mathematicIANS!!!] Mathematicians (2007: Madrid); then the million-dollar Clay-Institute of Mathemat"ICS" (but really mathematicIANS POLITICIANS: Carlson, Yau,...et. al.) millennium-problem prize, revealing that it and its INSIDER POLITICS/POLITICIANS has/have "Feet of Clay"!!!], as sumarized by Naser-Gruber[Manfold-Destiny, The New Yorker, (August, 2007)] and separately Carlos Castro[with Corredoira: Against the Tid (2008)] put, by revealing the Jargonial-Obfuscation(J.-O.) (Bradshaw[Healing the SHAME that BINDS You, Hazelden(1980s)]-Martin[Brian, Wollongong University]-...ad INFINITUM (i.e. most if not all scientists), ad NAUSEUM!!! (disgusted with "games people play!!!)) S-D ridden/ dominated "games people play" would-be "sciences" (maths, physics,...: ad infinitum; ad NAUSEUM!!!) but alas sadly only mere Bradshaw-Martin S-D DOMINATED "SEANCES"!!!, in "peril, man"!!! [Preview Abstract] |
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S1.00264: Jargonial-Obfuscation(J-O) DISambiguation Elimination via Siegel-Baez Cognition Category-Semantics(C-S) in Siegel FUZZYICS=CATEGORYICS (Son of TRIZ)/(F=C) Tabular List-Format Dichotomy Truth-Table Matrix Analytics Carl Ludwig Siegel, Edward Carl-Ludwig Siegel NOT "philosophy" per se but raising serious salient Arnol'd [Huygens and Barrow, Newton and Hooke(96)] questions begged is Rota empiricism Husserl VS. Frege maths-objects Dichotomy controversy: Hill-Haddock[Husserl or Frege?(00)]as manifestly-demonstrated by Hintikka[B.U.]-Critchey[Derrida Deconstruction Ethics(78)] deconstruction; Altshuler TRIZ; Siegel F=C/C-S; Siegel-Baez(UCR) Cognition C-S = "Category-theory ``+'' Cognitive-Semantics[Wierzbica-Langacker-Lakoff-Nunez[Where Maths Comes From(00)]-Fauconnier-Turner[Blending(98)]-Coulson[Semantic-Leaps (00)]]-Hofstadter[Fluid-Analogies For Creative-Thinking(94)]]-Holyoak[Analogy/ Metaphor] -Hademard[Maths-Mind(45)]-Graeser[Text-\underline {\textit{comprehension}} VIA (7-dimensional orthogonal-QUERY-space: WHAT?, WHERE?, (+) WHEN?, WHY?; (DYS-functional)WHO?) VS. TRADITIONAL/BY-ROTE: How?; How Much?]-Belew [Finding Out About(00)]-Hubbard[World According to Wavelets(96)]. Detailed are Siegel PHYSICS discoveries/approaches to ostensibly "pure"-maths Benford-law and Millennium-Problems proofs: FLT (CCNY;1964) $<<<$ Wiles(1994); P=/NP; BSD-Conjecture; Riemann-hypothesis. [Preview Abstract] |
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S1.00265: POST-DEADLINE |
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S1.00266: Structural and Dielectric Study of (Dy,Er,Ho)CrO$_{3}$ Biferroic Compounds Cesar Meza, Jesus Siqueiros, Alejandro Duran Technological progress, especially in electronic applications, demands increasingly advanced substances, capable of performing a variety of tasks while simultaneously occupying less space than their predecessors. An answer to this demand lies within the realm of multiferroics. Multiferroic materials are defined as those single phase compounds where more than one ferroic order coexists; they generally belong to the perovskite group. One manifestation of multiferroicity, magnetoelectricity, requires the coexistence of spontaneous electric polarization and magnetic ordering. It is for this reason that rare-earth chromites have been selected as suitable candidates. This work is concerned with synthesis, characterization and dielectric response of the DyCrO$_{3}$, ErCrO$_{3}$ and HoCrO$_{3}$ ceramic compounds. The samples were synthesized by both the traditional solid state ceramic method, and the self-propagating combustion method. The resultant chromites were characterized by TG, DTA and XRD, which confirms the Pbnm space group. Additionally, conductivity analysis was performed and the associated activation energy determined for each system using experimental values and Arrhenius law. [Preview Abstract] |
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S1.00267: Simulation of infrared photodetectors from single-electron models Nelson Studart, Marcos H. Degani, Marcelo Z. Maialle, Paulo F. Farinas We present results from simulations of potential structures with the method of the split operator. The method is applied to solve for electrons in potential profiles that are typical in the description of quantum dot infrared photodetectors. Various quantities of interest are calculated without the necessity of having the energy spectrum, simulating quantities like the photocurrent directly from a model hamiltonian. By using realistic band offset and mass parameters taken from devices, we are able to explain recent exeperimental results by referring to multiple-photon absorptions. In particular, strong resonance peaks observed in the $\sim 10\mu $m wavelength range in recently fabricated InAs quantum dot infrared photodetectors are obtained from the direct use of intrinsic band and mass parameters. Multiphoton scattering of electrons localized in the quantum dots are not only in accordance with the observed patterns, but are also necessary to explain the photocurrent spectrum obtained in the single-electron calculations. [Preview Abstract] |
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S1.00268: Extremely nondegenerate two-photon absorption in semiconductors David Hagan, Claudiu Cirloganu, Scott Webster, Dmitry Fishman, Eric Van Stryland Degenerate two-photon absorption, 2PA, in direct-gap semiconductors has long been known to scale with the inverse third power of the band gap, resulting in very large 2PA coefficients for narrow-gap semiconductors. We show that for any given pair of photon energies, (sum =\textit{h$\omega $}$_{1}$\textit{ + h$\omega $}$_{2})$, the 2PA is smallest for the degenerate case, \textit{$\omega $}$_{1}$\textit{ = $\omega $}$_{2}$, and is enhanced by orders of magnitude in the extremely nondegenerate case \textit{($\omega $}$_{1}$\textit{/$\omega $}$_{2}$\textit{ $>>$ 1 or $\omega $}$_{1}$\textit{/$\omega $}$_{2}$\textit{ $<<$ 1}). We experimentally demonstrate that 2PA in direct-gap semiconductors (e.g. GaAs, CdTe, ZnSe, ZnO, GaN) is enhanced over the degenerate value by up to 3 orders of magnitude using extremely nondegenerate pairs of photons (energy ratios $\sim $10/1). These extremely nondegenerate 2PA coefficients are similar in magnitude to coefficients obtained in narrow-gap semiconductors such as InSb and make 2PA feasible for applications such as subfemtosecond gated detection, all-optical switching etc. We demonstrate gated detection in a GaN LED used in a reverse-biased detection mode with fs 5.6$\mu $m and 400nm pulses. We see nearly 4 orders of magnitude enhancement over the degenerate case and can also easily detect sub-nW of IR light using modulation methods. [Preview Abstract] |
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S1.00269: Transport properties of superconducting La and Ce-based ferropnictides S.J. Singh, J. Prakash, A.K. Ganguli, S. Patnaik To understand the role of chemical pressure, we have synthesized a variety of La and Ce-based ferropnicides (La/Ce)OFeAs with substitution of Y, F, Co and Sb in place of La/Ce, O, Fe and As respectively. A broad spectrum of characterizations involving XRD, SEM, magnetoresistance, magnetization, penetration depth, Hall effect and thermoelectric power have been undertaken on these phase pure superconducting compounds. The transition temperature and upper critical field reached maximum of 48.6 K {\&} 146 T in Ce-based sample whereas 35 K and 122 T in La-based superconductor. The magnetization measurements of all samples showed negligible hysteresis reflecting weak link behaviour or an imperfectly connected superconducting state. The thermoelectric power and Hall measurement confirmed the dominant role played by electrons in these multiband superconductors. The rf penetration depth analysis indicated s-wave pairing symmetry with multiple gap values. [Preview Abstract] |
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S1.00270: Pulsed versus d.c. I-V characteristics of charge-ordered LuFe$_{2}$O$_{4}$ Bertina Fisher, Jan Genossar, Larisa Patlagan, George Michael Reisner We report on electronic transport measurements in a polycrystalline sample of LuFe$_{2}$O$_{4}$, over a wide range of electric fields and at temperatures above 230 K , - the range of temperatures was limited by the high resistivity of the sample . This work was motivated by reports about striking non-linear conductivity in polycrystals and single crystals of this multiferroic, in relatively moderate electric fields. Using short ($\sim $msec) single current pulses four probe measurements detected no deviations from linearity in the I-V characteristics, in fields up to E $\approx $ 500 V/cm. However, strong non-linearity and hysteresis were found in d.c. measurements at fields that decreased with increasing temperatures, suggesting self-heating. We include a set of oscillograms showing the time dependence of the voltages between the various probes at fixed current and temperature, which emphasize the importance of time domain studies of non-linear conductivity effects. We gratefully acknowledge Prof. Young Sun from the Institute of Physics, Chinese Academy of Sciences, Beijing, P.R. China, for providing us with the LuFe$_{2}$O$_{4}$ sample. [Preview Abstract] |
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S1.00271: A Ferroelectric Photovoltaic Capacitor Capable of Direct Solar Energy Conversion and Storage Chi-Wei Lo, Chensha Li, Hongrui Jiang Current solid state photovoltaics and conventional photoelectrochemical cells are not capable of directly storing the converted energy which has to be facilitated by connecting to external storing devices, thus increasing the system complexity. It would thus be highly desirable to create photovoltaic devices that can store solar energy directly. We here report a photo-rechargeable photoelectrochemical capacitor with direct conversion and storage capability by utilizing ferroelectric polyvinylidene fluoride (PVDF\textbf{)} gel with energy storing capability between anode and cathode. With the aid of ferroelectric effect, the device is able to maintain equilibrium between electric field and diffusion force. Results have shown that the device can be charged photovoltaically under 1 sun equivalent of irradiance to an open-circuit voltage of 0.47V, and with capacity of 40.63mC/cm$^{2}$. The storage lasts more than 24 hours. Electrochemical impedance analysis and ferroelectric hysteresis are also carried out to show its energy storing capability. [Preview Abstract] |
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S1.00272: Chiral noncoplanar magnetic ordering driven by itinerant electrons on the pyrochlore lattice Gia-Wei Chern In magnets with strong geometric frustration, the inability of spins to simultaneously satisfy the preferred local correlations leads to an extensive ground-state degeneracy at the classical level. The macroscopic degeneracy is lifted when other perturbations are taken into account. In general, collinear or coplanar magnetic orders are selected by perturbations which preserve the spin-rotational symmetry. Here we show that a complex {\em noncoplanar} magnetic order with a quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore lattice [1]. Specifically we consider a Kondo-lattice model in which itinerant electrons interact with localized spins via on-site exchange coupling. The electron Fermi `surface' at quarter filling is topologically equivalent to three intersecting Fermi circles. The noncoplanar magnetic order stems from a weak-coupling instability caused by perfect nesting of the Fermi circles. The magnetic structure characterized by a definite handedness also breaks the chiral symmetry. The chiral order might persist without magnetic order in a chiral spin liquid at finite temperatures. \\[4pt] [1] Gia-Wei~Chern, Phys. Rev. Lett. {\bf 105}, 226403 (2010). [Preview Abstract] |
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S1.00273: Including many-body screening into self-consistent calculations--tight-binding model studies with Gutzwiller approximation Yongxin Yao We introduce a scheme to include many-body screening process explicitly into self-consistent equations for electronic structure calculations by employing Gutzwiller approximation. The method is illustrated by applying to a tight-binding model of the strongly correlated $\gamma$-Ce. The critical Coulomb repulsion $U_{ff}^{c}$ between the $4f$ electrons for electronic phase transition can be greatly raised over the usual screened value by including the main onsite many-body screening $5d$ channels. The method provides a promising way towards parameter-free \textit{ab initio} Gutzwiller density functional theory. [Preview Abstract] |
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S1.00274: Predicting Sommerfeld coefficients for heavy-fermion materials Munehisa Matsumoto, Sergey Savrasov, Junya Otsuki From electronic-structure calculation standpoint we predict the appearance of heavy-fermion behavior for Cerium and Plutonium-based materials. Local-density approximation (LDA) combined with dynamical-mean field theory (DMFT) formulated for localized f-electrons gives an efficient realistic Kondo-lattice description [1] for the target materials, yielding a quasiparticle renormalization factor $z_c$ for conduction electrons. We invert the data to get the quasiparticle renormalization factor $z_f$ for f-electrons, and restore the effective total density of states to predict the Sommerfeld coefficient $\gamma$. Summarizing our data on an analogous ``Doniach phase diagram'' plotted for $z_c$, $z_f$, and $\gamma$, $\gamma$ is found to have a peak around the magnetic quantum critical point and Ce-115's are found to have the largest $\gamma$'s among target materials.\\[4pt] [1] PRL {\bf 103}, 096403 (2009). [Preview Abstract] |
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S1.00275: Atomic Green's function calculations using GPU Rei Sakuma GPU computing or GPGPU has been successfully applied to many scientific computations, such as Monte-Carlo and molecular dynamics. In this presentation we present the application of GPU computing to the calculations of non-relativistic and relativistic atomic Green's functions including the Coulomb interaction. [Preview Abstract] |
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S1.00276: Production of Short-Lived $^{37}$K Heather Stephens, Dan Melconian, Praveen Shidling The purpose of our work during the summer months of 2010 was to produce a beam of $^{37}$K with $\ge $ 99{\%} purity and characterize in detail the remaining contaminants. A projectile beam of $^{38}$Ar at 25 and 29 MeV/nucleon from the K500 cyclotron generated the $^{37}$K by reacting with an H$_{2}$ gas target. The \textit{MARS} spectrometer was then used to separate the reaction products of interest from the primary beam and other unwanted reaction products. From analysis of our production experiment, we were able to successfully produce 807 counts/nC of $^{37}$K with 99.19{\%} purity at 25MeV/u and 1756 counts/nC with 98.93{\%} purity at 29MeV/u. The purity of this beam and rate of production is more than adequate for use in determining the half-life of $^{37}$K, the next step to be done by the team in August 2010. This measurement will be accomplished by implanting the activity into a Mylar tape, placing it between two high-efficiency gas counters and counting the amount of beta decays as a function of time. It is expected the half-life will be measured using the $^{37}$K produced from $^{38}$Ar at 29MeV/u. [Preview Abstract] |
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S1.00277: Self-Assembled Double-Quarter Antireflective Coatings using Silica and Titania Nanoparticles Anitesh Lal, Raisa Castedo Velasco, Dan Mazilu Antireflective coatings have a wide range of applications, from eyeglass and camera lenses, to solar panels and optoelectronic devices, to name just a few. Our study examines several factors that affect the quality of antireflective coatings created by the self-assembly of alternating layers of SiO2 and/or TiO2 nanoparticles and poly(diallyldimethylammonium chloride) polycation on glass substrates. We use a factorial design to investigate the effects of the molarity of the nanoparticle solution, the size of the nanoparticles, the pH of the nanoparticle and polycation solutions, and the number of nanoparticle-polycation bilayers on the optical properties of the films. The first order effects of these factors, as well as their interactions, on the reflectance, transmittance, and uniformity of the coatings are reported. [Preview Abstract] |
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S1.00278: Magnetic domain configuration of La$_{0.7}$Sr$_{0.3}$MnO$_3$ patterned elements Carlos A.F. Vaz, Jan Rhensius, Andre Bisig, Mathias Kl\"aui, Laura Heyderman, Miguel Ni\~no, Andrea Locatelli, F. Gaucher, Alice Galdi, Laurence M\'echin The magnetization configuration in small La$_{0.7}$Sr$_{0.3}$MnO$_3$ elements is investigated as a function of geometry, film thickness, magnetic field, and temperature using x-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM). The patterned elements were defined by focused ion beam (FIB) lithography, and consist of elements varying in shape (from circular, triangular and quadrangular) and size, from 200 nm up to 10 $\mu$m. A strong magnetic contrast is observed for all thicknesses (10-50 nm). The magnetic state in the larger elements tends to be multidomain, with complex configurations that are determined by the presence of local pinning sites. These pinning sites are overcome with increasing temperature, and the magnetic configuration evolves into lower energy states. In contrast, the magnetic configuration of the smaller elements are largely determined by the magnetostatic energy contribution, which gives rise to highly symmetric states as found in 3d ferromagnetic structures. Our results show that the magnetism of small LSMO elements is robust nearly up to the critical temperature, with magnetic configurations that can be controlled by suitable geometrical design. [Preview Abstract] |
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S1.00279: Visible light photoreactivity from Carbon nitride bandgap states in Nb and Ti oxides Hosik Lee, Takahisa Ohno Lamellar niobic and titanic solid acids ($\mathrm{HNb_3O_8}$, $\mathrm{H_2Ti_4O_9}$) are photocatalysts which can be used for environmental cleanup application and hydrogen production through water splitting. To increase their efficiency, bandgap adjustment which can induce visible light reactivity in addition to ultraviolet light has been one of hot issue in this kinds of photo-catalytic materials. Nitrogen-doping was one of the direction and its microscopic structures are disputed in this decade. In this work, we calculate the layered niobic and titanic solid acids structure and bandgap. Bandgap reduction by carbon nitride absorption are observed computationally. It is originated from localized nitrogen state which is consistent with previous experiments. [Preview Abstract] |
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S1.00280: Statistical Analysis of Biotissues Mueller Matrix Images in Cancer Diagnostics Roman Tsylyak This work is directed to the investigation of the scope of the technique of laser polarimetry and polarization spectrometry of oncological changes of the human prostate tissue under the conditions of multiple scattering, which presents real experimental clinical situation. Statistic moments of the first (M), second ($\sigma )$, third (A) and fourth (E) orders were used as the analytical tool for estimating the ensemble of random values of $z$, that characterize the image of biological object (intensity I, polarization azimuths $\alpha $ and ellipticities $\beta )$ and its optical-geometrical structure (orientation directions of the protein fibrils and birefringence index of their substance $\Delta n)$. It was shown that the difference between the values of average and dispersion of distributions I (0 - 0), I (0 - 90), the intensities of images of various types of prostate tissues are insufficient and are within 10{\%}-25{\%}. The values of the excess of intensity distribution of the images of oncologically changed prostate tissues differ from the similar parameter of a sound tissue by 1-2 times. The third statistic moment proved to be the most sensitive because it's value in the intensity distribution of polarization image I (0 - 90) of oncologically changed tissue is 21 times higher if compared with healthy tissue. [Preview Abstract] |
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S1.00281: The Itinerant Electron and Local Moment Hybrid Model of Iron-based Superconductors Yizhuang You, Fang Yang, Shupeng Kou, Zhengyu Weng An itinerant electron and local moment hybrid model for iron-based superconductors is studied, with the band structure modeled simply by two pockets. Reasonable phase diagram is obtained on the mean field level. The spin and charge dynamics are further studied by the random phase approximation (RPA). The dynamic spin susceptibility displays a Goldstone mode of the collective itinerant electron and local moment excitations in the SDW phase, and a resonance mode in the superconducting phase which persists all the way to the normal state phase. It is found that the scattering with local moment always tends to reduce the pocket depth of the itinerant electron. The study also suggests that, to correctly account for the features in transport experiments, the multi-band effect that give rise to the nodal SDW should be included. [Preview Abstract] |
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S1.00282: Synthesizability of Superhard Carbon by Cold Compression of Graphite Salah Eddine Boulfelfel, Artem Oganov, Stefano Leoni We present an efficient scheme combining Monte Carlo walk in the space of transition pathways with molecular dynamics simulations for predicting matter modification under high pressure. If crystal structure prediction is a top-interest field for science and technology, the quest is even more exciting for elements such as boron and carbon. While under pressure above 15 GPa and at high temperatures (1600-2500 K) graphite is converted into diamond, room temperature compression gives a new superhard modification of carbon. Its nature remained unresolved until recent theoretical investigations predicted two candidate structures, M-Carbon and BCT4. Both structures have comparable physical properties and refine well the XRD data. To elucidate the nature of the final product of graphite cold compression we performed molecular dynamics transition path sampling simulations and we determined the energy profile of each transition (graphite to M-carbon and graphite to BCT4). The intrinsic mechanism of the reconstruction and the reasons of the favoring of one structure over the other have been determined. A detailed picture of events of nucleation and growth during the transition is finely reproduced. Our procedure do not only determine the nature of a transition final product but predicts its synthesizability under given conditions of pressure and temperature. [Preview Abstract] |
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S1.00283: Infrared optical absorption spectra of CuO single crystals: Fermion-spinon band and dimensional crossover of the antiferromagnetic order E.J. Choi, Jooyeon Kim, Y. Seiko, T. Kimura, J. Lorenzana We have obtained mid-infrared optical absorption spectra of the $S=1/2$ quasi one-dimensional CuO using polarized transmission measurement and interpreted the spectra in terms of phonon assisted magnetic excitations. When the electric field is parallel to the main antiferromagnetic direction a $\Delta$ shaped peak is observed with the maximum at $\omega = 0.23$~eV which is attributed to spinons along Cu-O chains. At low temperatures in the antiferromagnetic phase another peak appears at $\omega = 0.16$~eV which is attributed to two-magnon absorption but the spinon peak remains. This behavior is interpreted as due to a dimensional crossover where the low temperature three- dimensional magnetic phase keeps short range characteristics of a one- dimensional magnet. [Preview Abstract] |
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S1.00284: ABSTRACT WITHDRAWN |
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S1.00285: Development of Graphene for High Frequency Electronics Joshua Robinson, David Snyder, Mark Fanton, Matthew Hollander, Michael LaBella, Kathleen Trumbull, Randall Cavalero, Brian Weiland The practicality and success of a graphene technology depends on the ability to regularly and controllably synthesize graphene; integrate it with metals and dielectrics; and to develop device designs that take advantage of graphene's unique properties. We demonstrate graphene synthesis on SiC(0001) and Sapphire with 1.5{\%} variation in sheet resistance across 100mm wafers. Hall mobility measurements indicate that direct growth of graphene on sapphire leads to a 2x increase in mobility (2200 cm$^{2}$/Vs) compared to silicon sublimation from SiC(0001). Additionally, we have developed high quality ohmic contacts to graphene, which improves the contact resistance by nearly 6000x (5x10$^{-8}$ Ohm-cm$^{2})$ compared to untreated metal/graphene interfaces. Finally, we discuss integration of ultra-thin high-k dielectrics and their impact on graphene transport. Atomic layer deposited oxide heterostructures (seed not equal to overlayer) have deleterious effects on Hall mobility while homostructures lead to an increase in Hall mobility. Importantly, 5nm thick EBPVD HfO$_{2}$ gate dielectrics are successfully demonstrated and show improved Hall mobility, on-off ratio, and transconductance relative to Al$_{2}$O$_{3}$ gates and heterostructure gates. [Preview Abstract] |
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S1.00286: Synthesis and properties of artificially layered (Ba,K)BiO$_3$ and Ba(Bi,Pb)O$_3$ structures G.W.J. Hassink, K. Munataka, R.H. Hammond, T.H. Geballe, M.R. Beasley The possibility of superconductivity in a negative U material due to the proximity effect with a normal metal (Berg, Phys.Rev.B 78, 094509), and of doping via charge transfer at interfaces (Ohtomo, Nature 427, 423-426) has led us to investigate the properties of artificially-layered films of BaBiO$_3$ (a negative-U insulator) and BaPbO$_3$ (a normal metal) and of their doped variants (Ba,K)BiO$_3$ and Ba(Bi,Pb)O$_3$, both of which are isotropic (3D) and are superconducting over a specific range of doping. Samples were either Ruddlessden-Popper phases of (Ba,K)BiO$_3$ synthesized by pulsed laser deposition or bi-layers of BaPbO$_3$ and BaBiO$_3$ and their variants by e-beam evaporation. We studied the transport properties of these samples to investigate the presence of superconductivity and the influence of anisotropy. [Preview Abstract] |
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S1.00287: Unique microstructure of $\alpha \to \varepsilon \to \alpha $ transition in shock-compressed iron Man-Ling Sui, Shu-Juan Wang, Yong-Tao Chen, Qing-Zhong Li, Hai-Bo Hu Unique microstructure in recovered samples of shock-compressed iron is founded by transmission electron microscope (TEM) research. This confirms that the $\alpha \to \varepsilon \to \alpha $ martensitic transformation occurs during shock condition. Based on the specific features we reveal the mechanisms of both the transitions. [Preview Abstract] |
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S1.00288: Alignment Behavior of Liquid Crystals on Nanoscopically Heterogeneous Surface Kyunghee Lee, Hyo Kang, Guiduk Yu, Bong Seock Kim, Jong-Chan Lee, Kyusoon Shin We investigated the alignment behavior of liquid crystal molecules (LCs) on highly ordered polystyrene nanorod arrays. The diameter-controlled and height-controlled substrate was obtained from anodized aluminum oxide template. Upon the introduction of 1D nanostructures to the surface, the LC alignment was strongly influenced by the size of surface pattern. When the diameter of nanorods increased, the LC alignment changed from random planar to vertical orientation. The LC orientation was also altered by the increase of the height of nanorods. This transition happened in a small difference of nanorod diameter/height. The orientation change on the variation of nanorod dimension can be explained by the distortion of elastic-energy. The space between adjacent nanorods is sufficiently narrow to impose entropy penalty on LC molecules, and thus the LCs undergo elastic distortion near nanorod surface. [Preview Abstract] |
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S1.00289: Metal--nanotube interactions -- wetting properties Ruzeng Zhu, Shuwen Cui The wetting properties of metal nanoparticles in large-diameter single Carbon nanotubes (LDSWNT) is studied by considering the size effect on surface tension of the metal cluster. For the case of macro-nonwetting, we get finite critical atom number N such that the metal cluster with any atom number smaller than it has contact angle $\pi$, and so it shrinks into a ball. For an experiential formula of the surface tension of cluster expressed by the number of atoms, we determine the parameters in it for Pd and Pt respectively by density functional theory (DFT). Taking a graphene sheet as a representative of LDSWNT and using the known data of the surface tensions of solid and liquid, we obtain solid-liquid interface tension through Berthelot rule. Based on these results, we obtain N=5 for Pd and N=6 for Pt. For cluster containing 13 Pd atoms and that containing 13 Pt atoms, we use the above mentioned experiential formula to obtain their contact angles in LDSWNT consistent with those shown by the pictures given by DFT (A Maiti and A Ricca, Chem Phys Letters 395 (2004) 7--11), and thus the validity of our method is proved. [Preview Abstract] |
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S1.00290: Magnon spectrum in a spiral magnetic order on the pyrochlore lattice: application to CdCr$_2$O$_4$ Eunsong Choi, Gia-Wei Chern, Natalia Perkins Recent neutron scattering measurement on a geometrically frustrated antiferromagnet CdCr$_2$O$_4$ observed an unusual ground state in which a spiral magnetic order characterized by an incommensurate wavevector ${\bf Q}=(0,\delta,1)$ is accompanied by a tetragonal lattice distortion [1]. These results can be consistently explained by a model of Heisenberg interaction with anisotropic exchange constants perturbed by the Dzyaloshinski-Moriya interaction [2]. Based on this spin Hamiltonian, we numerically integrate the Landau-Lifshitz-Gilbert equation to obtain the linear magnon spectrum [3]. Exact diagonalization based on the conventional Holstein-Primakoff transformation is ineffective in our case due to the lack of translational symmetry in the magnon Hamiltonian. We also compare the numerical spectrum with the experimental results and discuss its implications on the model Hamiltonian. \\[4pt] [1] J.-H. Chung {\em et al.} Phys. Rev. Lett. {\bf 95}, 247204 (2005).\\[0pt] [2] G.-W. Chern, C.~J.~Fennie, and O.~Tchernyshyov. Phys. Rev. B. {\bf 74}, 060405 (2006).\\[0pt] [3] M. Mochizuki, N. Furukawa, and N. Nagaosa. Phys. Rev. Lett. {\bf 104}, 177206 (2010). [Preview Abstract] |
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S1.00291: Vortex Confinement in Superconducting/Ferromagnet Hybrid Structures M. Iavarone, A. Scarfato, F. Bobba, M. Longobardi, F. Giubileo, G. Karapetrov, V. Novosad, V.G. Yefremenko, A. Cucolo Magnetically coupled superconductor-ferromagnet hybrids offer advanced routes for nanoscale control of superconductivity. Scanning tunneling microscopy (STM) and scanning magnetic force microscopy (MFM) coupled to magneto-transport measurements reveal rich vortex phase diagram. The magnetic stripe domain of the ferromagnet induces periodic local magnetic induction in the superconductor, creating a series of pinning and anti-pinning channels for vortices observed with low temperature STM and MFM. Such laterally confined Abrikosov vortices form chains. We also found general equilibrium condition for which vortex-antivortex pairs are spontaneously formed during zero-field cooling. In the non-equilibrium state the strong magnetic pinning of the vortex lattice results in avalanches of antivortices when changing the polarity of the applied magnetic field. [Preview Abstract] |
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S1.00292: Lipid Bilayer Vesicle extrusion through nanopores: a coarse grained molecular dynamics study Martin Bertrand, Bela Joos We conducted Coarse-Grained Molecular Dynamics simulations of the pressure extrusion of vesicles in nanopores that confirm and help explain prior experimental observations (Patty, P. and Frisken, B., Biophys. J., 85, 2003). We demonstrate that, to a first approximation, the final size of extruded vesicles can be obtained by considering an invariable inner vesicle volume enclosed by a finitely extensible lipid bilayer. Using our data, we also describe in details the mechanics of vesicle rupture in a nanopore when pushed by various pressure gradients. This is made possible by tracking local variations of the stress in the lipid membrane via changes in surface area using a triangulation algorithm. The simulations are executed using state of the art GPU accelerated software. Our findings could potentially be useful in the design of liposome based drug delivery systems and in getting a better understanding of how the cell nucleus and the cell as a whole react in similar conditions. [Preview Abstract] |
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S1.00293: Spin-dependent 8x8 k.p Hamiltonian in silicon Pengke Li, Hanan Dery Silicon is a promising material choice in spintronics devices due to its long electron spin lifetime and dominant technology. We present a theory that describes the spin properties of conduction electrons in different valleys in silicon. Using the method of invariants, we have developed an $8\times8$ Hamiltonian with spin-orbit interaction that captures the symmetry of the zone edge states and their spin dependent parameters. We derive analytical results of the energy bands, and more important, of the spin mixing of states. Both are in perfect agreement with the numerical results of an empirical pseudopotential method with spin orbit interaction. The new theory is capable of filling a dominant role in studying spin properties of electrons silicon similar to the way that the Kane model in being used in direct band-gap semiconductors. [Preview Abstract] |
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S1.00294: Polaron formation and multi-band multi-gap superconductivity in layered materials Annette Bussmann-Holder, Hugo Keller In cuprates and novel layered superconductors electron-lattice interactions are not strong enough to achieve the high transition temperatures. However, polaron formation may occur locally at intermediate sized regions around the dopants thus leaving the surrounding matrix remains almost unaffected. The coexistence of the dynamical polarons and the host matrix represents a multi-component system, where different physics are combined. The consequences of this scenario are manyfold: The strong \textit{local }electron-lattice coupling induces a \textit{local soft mode} which gives rise to divergences in the relative Cu-O, Fe-As squared displacements. The electronic bands are renormalized and experience an exponential reduction which is the origin of unconventional isotope effects. Superconductivity is characterized by multi-components, which can have system dependent different pairing symmetries. Cuprates and other layered superconductors are discussed and comparison to experimental data is made. [Preview Abstract] |
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S1.00295: Node-node correlations and transport properties in scale-free networks Bibiana Obregon, Lev Guzman We study some transport properties of complex networks. We focus our attention on transport properties of scale-free and small-world networks and compare two types of transport: Electric and max-flow cases. In particular, we construct scale-free networks, with a given degree sequence, to estimate the distribution of conductances for different values of assortative/dissortative mixing. For the electric case we find that the distributions of conductances are affect ed by the assortative mixing of the network whereas for the max-flow case, the distributions almost do not show changes when node-node correlations are altered. Finally, we compare local and global transport in terms of the average conductance for the small-world (Watts-Strogatz) model [Preview Abstract] |
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S1.00296: Controlling Rotational Molecular Rotor by Selection of Anchoring Sites Hyo Won Kim, M. Han, H.-J. Shin, S. Lim, Y. Oh, K. Tamada, M. Hara, Y. Kim, M. Kawai, Y. Kuk In future nano-electro-mechanical-systems (NEMS), a molecular motor may become a key component to produce nanoscopic dynamical motions. At the level of a single molecule, rotational motions of various molecules have been observed on clean metal or semiconductor surfaces in scanning tunneling microscope (STM) images. Based on the observations, molecular bearings, nanocars, pinwheels, a rack and pinion device, wheels and gears have been proposed using a hindered molecular rotation. Despite extensive studies, the control of rotational motion in a molecular rotor is quite difficult. In this talk we report a controlled rotational-motion of an azobenzene derivative, EtO-Azo-C10, by inducing a reversible hopping motion between an immobile and a mobile site on a Au(111) surface with tunneling electrons in STM geometry. [Preview Abstract] |
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S1.00297: Entropic transport - a step beyond Fick-Jacobs Steffen Martens, Gerhard Schmid, Lutz Schimanky-Geier, Peter H\"{a}nggi We investigate the transport of point-size Brownian particles under the influence of a constant and uniform force field through a three-dimensional channel with smoothly varying periodic cross-section. We apply the standard long-wave asymptotic analysis and show that the leading order term is equivalent to the Fick-Jacobs approximation. Using the higher order corrections of the probability density we derive an expression for the spatially dependent diffusion coefficient. In addition, we demonstrate that in the diffusion dominated regime the averaged velocity and the effective diffusion coefficient are determined by the product of the Fick-Jacob result and the expectation value of the spatially dependent diffusion coefficient. Analytic findings are confirmed by numerical simulations of the particle dynamics in a reflection symmetric sinusoidal channel. [Preview Abstract] |
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S1.00298: Thermally activated fragmentation of a homopolymer chain Simon Fugmann, Igor M. Sokolov We consider the thermally activated fragmentation of a homopolymer chain, which can exhibit strongly non-Markovian behavior on the timescale of interest. In our model the dynamics of the intact chain is a Rouse one until a bond breaks and bond breakdown is considered as a first passage problem over a barrier to an absorbing boundary. Using the framework of the Wilemski-Fixman approximation we calculate activation times of individual bonds for free and grafted polymer chains. We show that these times crucially depend on the length of the chain and the location of the bond yielding a minimum at the free chain ends. Going beyond the Wilemski-Fixman approximation we show that a generalized form of the renewal equation for barrier crossings serves to improve the quantitative agreement between numerical simulations and analytical predictions. [Preview Abstract] |
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S1.00299: Non-equilibrium ballistic phonon transport in microstructures Obafemi Otelaja, Jared Hertzberg, Richard Robinson A non-thermal spectral distribution of phonon modes may be excited in silicon microstructures by using the decay of quasiparticles injected into an adjacent superconducting film. [1] We demonstrate generation, ballistic transport and detection of phonons of frequency of order 100 GHz in microstructures of dimension 10 to 50 microns. We describe the fabrication process for the superconducting transducers, the measurement procedure, and plans to extend these techniques to build a nanoscale phonon spectrometer. This work is supported by KAUST (KUS-C1-018-02), NSF (DMR 0520404), and DOE (DE-SC0001086). \\[4pt] [1] W. Eisenmenger, A. H. Dayem, Phys. Rev. Lett. 18, 125 (1967). [Preview Abstract] |
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