Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session C1: Poster Session I (2-5:00pm): Polymer Physics; Applications; Complex Structured Materials; Quantum Fluids; Nano/Bionanotechnology; Fluids; General; Statistical & Nonlinear; Superconductors |
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Room: Exhibit Hall A |
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C1.00001: POLYMERIC AND ORGANIC MATERIALS I |
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C1.00002: High Electric Energy Storage in a Three-Phase Polymer Nanocomposite Jing Wang, Fangxiao Guan, Lei Zhu Two-phase polymer/ferroelectric ceramic composites have attracted great interests for electric applications, such as transducers, piezo-sensors, and hydrophone materials, because they combine good processability of polymers and high dielectric constant of ferroelectric ceramics together. The polymer-ceramic composites generally show a high effective dielectric constant only at a high ceramic volume fraction ($>$35 vol.{\%}). Here, a high dielectric constant tetrameric Cu-phthalocyanine (Cu-TMPc) was used as an interfacial phase between the ceramic particles (50-nm BaTiO3) and the polymer matrix [poly(vinylidene fluoride-co-hexafluoropropylene), or P(VDF-HFP)]. To avoid the agglomeration of nanoparticles in P(VDF-HFP), poly(methyl methacrylate) is grafted from Cu-TMPc-coated BaTiO3 nanoparticles using surface-initiated radical polymerization. High electric energy storage and low conductivity were achieved at low filling ratios ($<$15 vol.{\%}). [Preview Abstract] |
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C1.00003: Rheological Singularity near the Phase Transition of Hairy Nanoparticles in Polymer Melts Xiaorong Wang, Victor Foltz, Mindaugas Rackaitis, Georg Bohm The dynamics of hairy nanoparticles in polymer melts of chemically identical chains has been investigated as function of both molecular weight and volume fraction. This work demonstrates that there is a strong connection between the rheological dynamics of the system and the thermodynamics of the phase separation behavior. The shear-induced nonlinearity in the system appears to display features of a surprising singularity near the phase transition point. Our theoretical calculation also agrees qualitatively well with that observed experimentally. [Preview Abstract] |
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C1.00004: The use of the radius of gyration in a WLC polymer model of cancer cell adhesion to glycosaminoglycans substrates Antonio Peramo, Garrett Matthews Glycosaminoglycans (GAG) are a group of polysaccharides involved in several biological functions, including cell adhesion. Most of their biological properties are derived from the interactions of the chains with their environment, hence the interest in developing physical models that could describe their interactions with whole cells. As linear biopolymers with low polydispersity, GAG can be described using polymer models of Gaussian chain distributions, like the WLC (worm-like chain) model. We found that the adhesion of whole cancer cells to glass substrates coated with GAG appear to be dependent on the charge per dimer and degree of sulfation of the GAG chain. We have hypothesized that the adhesion of whole cancer cells to GAG substrates can be described as a function of polysaccharide radius of gyration and used the WLC model describing the global structure of the GAGs to analyze this relationship. We will show that the adhesion of the cancer cells has a linear response with the radius of gyration and is essentially controlled by the charge per dimer. This dominating mechanism is not eliminated when the cells are resuspended in media with heparin. We then propose how these physical properties could be used to predict the preferred molecular structures of compounds for use as anti-metastatic or anti-inflammatory agents. [Preview Abstract] |
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C1.00005: Polymer dynamics and ion conduction in modified soluble starch HyungKi Lee, James Runt The dynamics of neat and plasticized carboxylated starch is investigated using broadband dielectric relaxation spectroscopy (DRS). The sodium single ion conductor is prepared by a 2,2,6,6- tetramethylpiperidin-1-oxyl (TEMPO) mediated oxidation process, in which the primary hydroxyl groups in alpha-D-glucose units are replaced by carboxylic salts. DRS measurements show that the ionic conductivity increases with increasing degree of oxidation. For example, 78 percent carboxylated starch with 25 weight percent glycerol displays around 3 orders of magnitude higher ionic conductivity than the comparable glycerol- plasticized 25 percent carboxylated material, principally due to the higher content of mobile cations. The role of salts and plasticizers including water on the relaxation behavior of amylose-rich starch is explored. Other complimentary techniques are used in the investigation, including FTIR, XRD and DSC. [Preview Abstract] |
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C1.00006: Responsive Block Copolymer and Gold Nanoparticle Hybrid Nanotubes. Sehoon Chang, Srikanth Singamaneni, Seth Young, Vladimir Tsukruk We demonstrate the facile fabrication of responsive polymer and metal nanoparticle composite nanotube structures. The nanotubes are comprised of responsive block copolymer, polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP), and gold nanoparticles. PS-b-P2VP nanotubes were fabricated using porous alumina template and \textit{in situ} reduction of the gold nanoparticles in P2VP domains. Owing to the pH sensitive nature of P2VP (anionic polymer with a pK$_{a}$ of 3.8), the nanotubes exhibit a dramatic change in topology in response to the changes in the external pH. Furthermore, the gold nanoparticles in the responsive block exhibit a reversible aggregation, causing a reversible change in optical properties such as absorption. [Preview Abstract] |
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C1.00007: Magnetic Field Alignment of Rod-Coil Block Copolymers and Identification of Liquid Crystalline Orientation X. Gu, B.D. Olsen, A. Hexemer, E. Gann, R.A. Segalman Conjugated rod-coil block copolymers are potentially useful for a number of optoelectronics applications, but properties rely strongly on the orientation of both the conjugated rods and of the nanodomains. Here, a magnetic field was used to control the self-assembly of a model conjugated rod-coil block copolymer (poly(alkoxyphenylenevinylene-b-isoprene) such that the rods align with the field direction. After alignment, the samples were re-annealed below the microphase order-disorder transition temperature to allow equilibration of the rod orientation within the lamellar nanodomains. Small angle and wide angle X-ray scattering simultaneously determine the rod tilt relative to the lamellar normal. Rods were found to be parallel to the lamellar normal for coil fractions of 42-85 percent at all temperatures below the microphase order-disorder transition temperature. The orientation of the rod blocks in rod-coil block copolymers impacts carrier transport and optical properties in organic electronic devices, making the control of rod orientation necessary for device optimization. [Preview Abstract] |
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C1.00008: A New Level of Hierarchical Structure Control by Use of Supramolecular Self-assembled Dendronized Block Copolymers Raffaele Mezzenga, Chaoxu Li, Dieter Schluter, Afang Zhang Block copolymers in which microphase segregation can be combined with supramolecular attachment of side chains to one block, constitute very appealing systems to design hierarchically self-assembled macromolecular materials. Self-organization of these systems is achieved at two length scales: that of the side chains ($\sim $10$^{0}$nm) and that of the block copolymers ($\sim $10$^{1}$-10$^{2}$nm). Because of the linear nature of the hosting block, only lamellar organization is typically observed at small length scales. Here we demonstrate that by replacing the linear polymer block with a dendronized polymer capable of participating in supramolecular interactions, one additional degree of freedom (the generation of the dendronized polymer) is introduced to engineer the self-assembly into unprecedented hierarchically ordered bulk structures. Not only this allows controlling beyond current possibilities the structures at the smaller length scale, with the introduction for example, of new columnar rectangular, hexagonal and tetragonal phases, but it may also lead to new functional template materials with increased 3D topological complexity for advanced technologies. References: C. Li, D.A. Schl\"{u}ter, A.Zhang, R. Mezzenga, \textit{Advanced Materials}, in press. [Preview Abstract] |
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C1.00009: Fabrication of Highly Ordered Nanostructured Block Copolymer Templates using Supramolecular Assembly Approach E. Bhoje Gowd, Manfred Stamm The ability to create reactive nanoporous templates using polymer thin films is important for such applications as antibody or enzyme immobilization, separation of biomolecules, and nanofabrication. Self-assembly of polymeric supramolecules could be an elegant method to this end. The present approach consists in supramolecular assembly of vinylpyridine fragments of polysterene-block-poly(4-vinylpyridine) (PS-b-P4VP) with various additives. Thin films of PS-b-P4VP + additive revealed cylindrical morphology with the cylinders formed by the minor-block of the assembly. Extraction of these additives with selective solvent results in nanoporous templates where the reactive P4VP chains are constituted on the walls of the channels. The periodicity of the hexagonal lattice remains same irrespective of the additive used and on the other hand, the pore diameter was found to be dependent upon the additive. In addition, switching between different alignments of the cylindrical domains was also dependent on the nature of the additive used. The templates obtained using different additives were compared with the surface reconstructed block copolymer (PS-b-P4VP) templates in order to understand the bottom P4VP layer, which is located at the film-substrate interface. [Preview Abstract] |
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C1.00010: Neutron Reflectivity Study of dPS Brushes Grown from an Inimer Embedded Photopolymer Matrix Onome Swader, Damla Koylu, Kenneth Carter, Mark Dadmun Robust methods for directing the self-assembly of macromolecules over large areas are necessary in order to meet the demands for fabrication of next generation devices. Polymer brushes grown from soft interfaces composed of an inimer embedded photopolymer (PP) network provide a unique method to create tuned surfaces and interfaces for such devices. In this study, neutron reflectivity is used to characterize such functionalized interfaces. Inimer concentration and the amount of monomer available for polymerization was systematically varied in an attempt to nanoscopically tune brush growth. These results suggest that the brushes are not initiated at one particular interface, but rather throughout the PP network. Further analysis revealed that brush density increased as the amount of inimer concentration in the PP network increased. However, it is interesting to note that the brush at the surface of the PP network is significantly less dense than in the melt. [Preview Abstract] |
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C1.00011: Surface Dynamics of Branched Polystyrene films Shih-Fan Wang, Jae Sik Lee, Sewoo Yang, Roderic P. Quirk, Mark D. Foster, Zhang Jiang, Suresh Narayanan, David Wu Thermally stimulated fluctuations of a polymer surface have been studied for films containing branched polymers for the first time. The surface fluctuations were probed using x-ray photon correlation spectroscopy (XPCS), a recently-developed technique already applied to study the surfaces of melts of linear polystyrene chains. A continuum hydrodynamic theory of thermally stimulated capillary waves with a nonslip boundary condition is adequate to fit plots of relaxation time as a function of scattering vector. Changes in Tg with molecular architecture certainly play a role. However, comparison of data from a star made without the usual butadiene (BD) linking units with data from a star with 1-2 BD units per arm shows that the BD end capping of the arms affects the dynamics profoundly. This effect may not be described adequately by simply accounting for the reduction in Tg caused by the presence of the BD units. Acknowledgements: NSF support (CBET 0730692) [Preview Abstract] |
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C1.00012: Magnetic Field Driven Alignment of Lamellar and Hexagonal Surfactant Mesophases for Templated Synthesis of Nanomaterials Pawel Majewski, Chinedum Osuji The use of both ionic and non-ionic surfactants as structure directing agents in the solvothermal synthesis of nanomaterials has become a well established practice. Nevertheless, the production of monolithic well aligned surfactant mesophases for use in the templated synthesis of ordered, anisotropic nanomaterials remains a significant challenge, particularly in the thin film geometry where shear alignment cannot be conveniently applied. Magnetic fields hold promise in this area, but to date have only been used in the alignment of hexagonal phases of ionic surfactants. We show that judicious application of high magnetic fields can in fact be used for diamagnetic alignment of non-ionic surfactants in both the lamellar and hexagonal phases, leading to very highly ordered systems suitable for nanomaterials synthesis. [Preview Abstract] |
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C1.00013: Long Range Order of Block Copolymer/C$_{60}$ Thin Films Katie Campbell, David Bucknall, Yonathan Thio The use of block copolymers as a template to localize C$_{60}$ particles was investigated. The addition of C$_{60}$ fullerenes to poly(styrene-$b$-dimethylsiloxane) thin films leads to disorder in a system that is otherwise ordered in the range of tens of microns. Because C$_{60}$ segregates into the PS phase, the degree of disorder is dependent on the concentration of C$_{60}$ as a weight percent of the PS block, as indicated by AFM studies. Disorder effects are exacerbated by fullerene aggregation in the solution prior to spin coating on a substrate. Several strategies are proposed for achieving and maintaining long-range order in block copolymer/C$_{60}$ thin films. First, the aggregation of C$_{60}$ in solution is controlled by preparing thin films from solutions with C$_{60}$ and block copolymer co-dissolved at a time when aggregation is at a minimum to achieve good dispersion of the C$_{60}$. Secondly, several methods for achieving long-range order have been investigated including the use of solvent annealing in combination with shear and topographic substrates. Results have shown that solvent annealing alone orders poly(styrene-$b$\textbf{-}butadiene-$b-$styrene) copolymers without C$_{60}$; however, addition of C$_{60}$ to the system alters the order seen with solvent annealing. [Preview Abstract] |
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C1.00014: Orientation distribution in a uniaxially and biaxially drawn poly(L-lactic acid) by Raman spectra Min Sang Park, Yee Shan Wong, Subbu Venkataraman, Mohan Srinivasarao In this study, we used the polarization modulation of Raman scattering intensities to study molecular orientation distribution in the crystalline and amorphous regions of uniaxially and biaxially drawn poly(L-lactic acid) (PLLA) film. Changes of orientation distribution were detected as a function of stretching ratios and different characteristics of orientation between crystalline and amorphous region were analyzed using Raman bands which are assigned to the each region. As results, quantification of oriented molecule information named orientation order parameters was determined. From experimentally obtained order parameters, the most probable molecular orientation distribution functions for the crystalline and amorphous regions in the film could be constructed. [Preview Abstract] |
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C1.00015: Highly Ordered Nanoporous Template from ABC Triblock Copolymer Dong Hyun Lee, Soojin Park, Thomas Russell In this study, silicon nanoporous templates from polyisoprene-\textit{block}-polystyrene-\textit{block}-poly(2-vinyl pyridine) (PI-b-PS-b-P2VP) were fabricated. The films, spin-coated from toluene. showed a dimpled texture with short-range lateral order. When exposed to a mixed solvent vapor (toluene/hexane), a highly ordered and oriented core-shell structure of PI-b-PS-b-P2VP copolymers was obtained. The morphology consisted of an external shell of PI, a middle shell of PS, and a core of P2VP. After removal of the PI from by UV-Ozone treatment, subsequently, polydimethylsiloxane (PDMS) was spin coated onto this film and allowed diffused into the pores by capillary action. When the film was exposed to oxygen plasma, the PDMS was converted to silicon oxide, while all other remaining polymer was removed. This led to a highly ordered and oriented nanoporous structure that could be used as an etching mask or templates for secondary metal loading. Highly ordered arrays of gold nanoparticles for the potential applications for surface enhanced plasmon, immobilization of DNA or organic dyes, or epitaxial growth of crystal were obtained by loading gold salt into well-defined core-shell structure. [Preview Abstract] |
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C1.00016: Morphology and Ionic Conductivity of Block Copolymer--Ionic Liquid Systems M.L. Hoarfrost, J.M. Virgili, J.B. Kerr, R.A. Segalman Block copolymer--ionic liquid systems are of interest for ion exchange membranes due to the ionic conductivity and thermal stability of the ionic liquid combined with the thermal stability and morphological control arising from a structural component in a block copolymer. It is anticipated that the morphology and connectivity of the resulting structural and ionic liquid-containing nanodomains will affect conduction properties. This relationship was investigated for poly(styrene-$b$-2-vinylpyridine) (S2VP) in ionic liquids composed of varying molar ratios of imidazole and bis(trifluoromethanesulfonyl)imide (Im:TFSI). ~A stoichiometrically balanced ionic liquid (1:1 Im:TFSI) swells the 2VP lamellar domains for copolymer concentrations as low as 60wt{\%}. With 9:1 Im:TFSI the lamellar structure tolerates more swelling, forming lamellar structures with as little as 30wt{\%} copolymer. Ionic conductivities were derived from AC impedance measurements. The S2VP-Im:TFSI systems, characterized by microphase separated domains, demonstrate ionic conductivities comparable to those of P2VP--ionic liquid systems when normalized by 2VP (monomer) to Im:TFSI ratio. [Preview Abstract] |
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C1.00017: Ionic Salt Effect on the Phase Transition of PS-b-P2VP Copolymers Bokyung Kim, Hyungju An, Du Yeol Ryu, Jehan Kim Solid-state electrolytes have long been considered as suitable candidates owing to the simple and easy processes for rechargeable battery manufactures, compared to conventional liquid electrolyte counterparts. Especially, polymer/salt systems involving PMMA and PVP complex forms have been studied since they provide stable electrochemical characteristics as well as mechanical properties. We studied the phase behavior of PS-b-P2VP upon the salt addition by small angle x-ray scattering (SAXS) and depolarized light scattering. Transition temperatures of block copolymer were significantly influenced by the salt addition in addition to the changes of d-spacings, which is caused by the effective coordinative interaction between P2VP block and salt. This study suggests a simple approach to solid-state block copolymer electrolytes. [Preview Abstract] |
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C1.00018: Comb Polymer Architectures for Versatile Nanoparticle Assembly Alexander Mastroianni, Kari Thorkelsson, Yue Zhao, Joseph Luther, Jill Millstone, Paul Alivisatos, Jean Frechet, Ting Xu Nanoparticles are a material of interest in photovoltaic research due to their optical absorption properties. However, there have been many challenges for device fabrication. It has been difficult to produce continuous, homogenous films, and successes in this area have been highly dependent on the actual nanoparticles used, and have thus been hard to apply generally to different materials of interest. We show how this challenge can be overcome using a comb polymer architecture. Here, pentadecyl phenol small molecules are hydrogen bonded to polyvinyl pyridine. This alkyl moiety produced is compatible with the ligand shells of many nanomaterials. We incorporated these small molecules and nanoparticles into polystrene-polyvinyl pyridine block copolymers. This strategy was successful for assembling nanoparticles made out of a variety of materials, without special considerations for the actual core material or morphology. Following these successes in bulk samples we extended our studies to thin films of these composites. Here, the morphology is controlled by the interfacial interactions. These materials have the potential to be used for photovoltaic devices, as they are easily solution-processible. This strategy is generally applicable with the choice of small molecule mediating interactions with any desired nanomaterial. [Preview Abstract] |
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C1.00019: Electric Energy Storage in P(VDF-HFP) Copolymers with Different Crystallinities Fangxiao Guan, Steven Boggs, Lei Zhu Poly(vinylidene fluoride) (PVDF) is a well known ferroelectric polymer. It attracts much attention as a candidate material for electric energy storage in recent years because of its relatively high dielectric constant and high electric breakdown strength. By modifying PVDF with bulky comonomers such as hexafluoropropylene (HFP), P(VDF-HFP) random copolymers can achieve even higher electric energy density than PVDF. This is because bulky HFP comonomers disrupt the PVDF run length and thus reduce the average crystallite size. Additionally, bulky HFP comonomers at the crystal surface constrain the $\alpha ->\delta ->\beta $ phase transitions at elevated electric fields. Both the reduced crystallite size and constrained phase transition affect electric energy storage. For P(VDF-HFP) copolymers with different crystallinities, different crystal size and phase transition behaviors are studied, and their relationships with the electric energy storage capability is correlated. [Preview Abstract] |
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C1.00020: Multi-scale simulation on solid benzene Hua Liu, Hendrik Heinz Solid Benzene is used in organic semiconductors for photovoltaics, which often include pi-conjugated systems. We use MD simulations method to explore the relationship between the structure and interaction energy of two kinds of solid benzene, with the Pbca and P21c crystallgraphic structures respectively. Simple relevant force fields (PCFF and CVFF) are examined with regard to their performance on the structure and energetics of benzene dimers and benzene crystals which serve as well characterized model systems. However, MD simulations cannot get the transport properties. So the combination of reliable classical atomistic simulations and quantum-mechanical methods is needed to understand the dynamics of charge transport and self-assembly processes involving pi-conjugated oligomers and polymers. As alternative and accurate models, we explore atomistic models with additional sites which represent the location of the pi electrons and are characterized by suitable charges and van-der-Waals parameters. With these parameters, it will be possible to reproduce the dimer geometries and energies, the crystal structure of solid benzene, as well as pi-stacking forces and free energies for similar systems. [Preview Abstract] |
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C1.00021: Viscoelastic Properties of Nanoimprinted Polymers Christopher Soles, Yifu Ding, Hyunwook Ro, Kyle Alvine, Jing Zhou, Jack Douglas Nanoimprint Lithography (NIL) is a versatile nanopatterning technique, combining high patterning resolution with low cost. In the thermal embossing form of NIL, a supported thin polymer film is transferred into surface patterns under controlled thermo-mechanical environments. Intuitively, the polymer chains within the as-imprinted patterns will display strongly non-equilibrium characteristics. Here we present systematic measurements of the viscoelastic properties of the nanoimprinted polymers by controlled thermal annealing experiments. In particular, a combinatorial approach was used for the experiments where a temperature gradient was applied for the annealing. The effective viscoelastic properties of the patterns were extracted by analyze the pattern decay along the temperature gradient. The viscoelastic properties of the imprinted patterns were greatly influenced by the patterning conditions. [Preview Abstract] |
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C1.00022: Examination of Nonliquidlike Behaviors in Molten Polymer Films Z.H. Yang, Y.J. Wang, L. Todorova, O.K.C. Tsui Several experiments have shown that polystyrene (PS) films with thicknesses of $h \approx $ 2$R_{G}$ (where $R_{G}$ is the radius of gyration of the polymer) exhibited nonliquidlike behaviors even in the molten state. By measuring the surface spectrum of PS films subjected to different thermal annealing, we show that similar nonliquidlike behaviors can be produced if the annealing time is below \textit{$\tau $}($q_{lc}^{eq}(h))$, the relaxation time of the capillary wave mode with wave vector equal to the lower-cutoff wave vector $q_{lc}^{eq}(h)$, which characterizes the equilibrium surface spectrum. At the same time, annealing above \textit{$\tau $}($q_{lc}^{eq}(h))$ recovers the liquid behaviors. Because \textit{$\tau $}($q_{lc}^{eq}(h))$ often amounts to days and even years, insufficient annealing constitutes a likely cause for the nonliquidlike behaviors. Nonetheless, the previously suggested strong pinning of the polymer chains to the substrate can also be a cause. To elucidate the origin of the observed nonliquidlike behaviors, we measure the surface dynamics of PS films with $h$ = 2$R_{G}$ to 8$R_{G}$ undergoing the glass-to-rubber transition and find that they are all the same. Our result favors insufficient annealing to be the cause of the observed nonliquidlike behaviors. [Preview Abstract] |
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C1.00023: Preparation of Mesoporous Ceramics from Polymer Nanotubes Dian Chen, Soojin Park, Jiun-Tai Chen, Emily Redston, Thomas Russell Poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) nanotubes were prepared by placing polymer solution into the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. The PS-b-P4VP nanotubes within the AAO membranes were exposed to tetrahydrofuran vapor to produce uniform spherical micelles along the tube. The tubes were removed from the membranes, then suspended in ethylene glycol, a preferential solvent for P4VP. At 95$^{ o}$C, near the glass transition temperature (Tg) of PS, nanotubes with uniform nanopores were obtained by a reconstruction of the nanotubes. As the temperature was increased, mesoporous polymer structures were obtained. Tetraethyl orthosilicate or titanium tetraethoxide, ceramic precursors, were introduced into the 4VP microdomains. After exposure to an oxygen plasma or high temperature, the copolymer was removed and the precursor converted to a mesoporous ceramic. This process offers a simple route for the fabrication of tunable mesoporous ceramic or metallic structures by changing molecular weight of copolymers. [Preview Abstract] |
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C1.00024: Coarse Grained Simulation of Block Copolymer Systems Ludwig Schreier, Marco Pinna, Xiaohu Guo, Andrei Zvelindovsky We present results of coarse-grained computer modelling of block copolymer systems based on Cell Dynamics Simulation. Phase transitions induced by external factors in various block copolymer systems are investigated. This contribution puts focus on dynamics of systems subjected to two examples of external fields such as an applied electric field and confinements. [Preview Abstract] |
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C1.00025: Computer Simulation of Metallo-Supramolecular Networks Shihu Wang, Chun-Chung Chen, Elena Dormidontova Using Monte Carlo simulation we studied formation of reversible metallo-supramolecular networks based on 3:1 ligand–metal complexes between end-functionalized oligomers and metal ions. The fraction of 1:1, 2:1 and 3:1 ligand-metal complexes was obtained and analyzed using an analytical approach as a function of oligomer concentration, c and metal-to-oligomer ratio. We found that at low concentration the maximum in the number-average molecular weight is achieved near the stoichiometric composition and it shifts to higher metal-to- oligomer ratios at larger concentrations. Predictions are made regarding the onset of network formation, which occurs in a limited range of metal-to-oligomer ratios at sufficiently large oligomer concentrations. The average molecular weight between effective crosslinks decreases with oligomer concentration and reaches its minimum at the stoichiometric composition, where the high-frequency elastic plateau modulus approaches its maximal value. At high oligomer concentrations the plateau modulus follows a $c^{1.8}$ concentration dependence, similar to recent experimental results for metallo-supramolecular networks. [Preview Abstract] |
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C1.00026: Heat Capacity of \textit{B. Mori} Silk Fibroin Based on the Vibrational-Motion of Poly(amino acid)s. Marek Pyda, Xiao Hu, Peggy Cebe \textit{Bombyx mori} silk fibroin heat capacities with and without water have been determined based on the vibrational motions of poly(amino acid)s and water, using the Advanced Thermal Analysis System (ATHAS) Data Bank. The heat capacities, C$_{p}$, of dry silk and silk-water were linked to their vibrational spectra based on the group and skeletal vibration contributions. For dry silk, the experimental and calculated C$_{p}$ agree to better than $\pm $3{\%} between 200 K and 435 K. The heat capacity of the solid silk-water system, below the glass transition, was estimated from a sum of linear combinations of the molar fractions of the vibrational heat capacities of dry silk and glassy water. Calculations are compared to experimental data obtained from calorimetric methods, using hermetic and non-hermetic pans. The approach presented allows one to predict the low temperature vibrational heat capacity for dry silk and for the silk-water system down to zero kelvin, and, together with an extension to higher temperatures, above the glass transition.~ This can be used as a reference baseline for quantitative thermal analysis of this biomaterial.. [Preview Abstract] |
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C1.00027: Heat Capacity of the Silk-Water System Based on Vibrational-Motions of Poly(amino acid)s and Water. Marek Pyda, Xiao Hu, Peggy Cebe The experimental heat capacities of \textit{B. Mori} silk-water system are presented based on measurements by standard differential scanning calorimetry. Effect of plasticizing of silk by molecules of water leads to lowering of T$_{g}$ of amorphous silk fibroin in the presence of water. The calculated heat capacities of silk fibroin with water were determined based on the vibrational motions of poly(amino acid)s and water, using the Advanced Thermal Analysis System (ATHAS) Data Bank. The heat capacities, C$_{p}$, of silk-water were linked to their vibrational spectra based on the group and skeletal vibration contributions. The heat capacity of the solid silk-water system, below T$_{g}$, was estimated from a sum of linear combinations of the molar fractions of the vibrational heat capacities of dry silk and glassy water. The vibration heat capacity of dry silk was constructed using a sum of vibrational heat capacity of poly(amino acid)s components. Calculations are compared to experimental data obtained from calorimetric methods, using hermetic and non-hermetic pans. The approach presented allows one to predict the low temperature vibrational heat capacity for the silk-water system down to zero kelvin, and, together with an extension to higher temperatures, above T$_{g}$. This can be used as a reference baseline for quantitative thermal analysis of this biomaterial with water. [Preview Abstract] |
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C1.00028: A Generic Fourier-Space Approach for Discovering Ordered Phases of ABC Star Triblock Copolymers Feng Qiu, Guojie Zhang, Ping Tang, Hongdong Zhang, An-Chang Shi We have developed a generic approach to solve the self-consistent field theory (SCFT) equations for block copolymers. In this method, all spatially varying functions are expanded in terms of Fourier series which are essentially determined by computational box parameters. Then, SCFT equations can be cast in terms of expansion coefficients. With this method, we successfully reproduce phases observed in diblock copolymers and ABC linear triblock copolymers. Emphasis has been focused on phase behaviors of ABC star-shaped triblock copolymers, in which noncentrosymmetric phases can be formed. Two groups of star triblock copolymers, with symmetric and asymmetric interaction parameters, respectively, have been studied in detail. Qualitative agreement is reached in terms of phase transition sequence along composition lines between the SCFT calculations and experimental results. [Preview Abstract] |
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C1.00029: Collapse Transitions in Thermosensitive Alternating Copolymers: A Monte Carlo Study Ioannis Bitsanis, Anastasia Rissanou, Stanislav Burov, Eveangelos Manias Alternating copolymers are expected to exhibit a rich transition behavior in selective solvents with implications in biology and the design of thermo and pH-sensitive materials. We studied transitions of model alternating copolymers of the type (AAA...)n1(BBB...)n2, in selective solvents by MC simulations. Results showed that the eminent factor, controlling response to external stimuli, is co-polymer's chemical composition.. We focused on the extreme case of a single polymer chain of N = 1000 units, distributed equally in alternate blocks of n1= n2 =100 units (A- and B- blocks). The solvent was quite selective, i.e. good for 5 100-A-blocks, whereas the 5 100 B-blocks were quite insoluble. An extended critical region, characterized by the presence of several distinct intermediate states between coil and globules, and by fluctuations strong enough to induce spontaneous transitions among these states was observed. Our findings underline that in the case of strong blockiness the alternating architecture induces collapse transitions that proceed through stages not existing in the analogous homopolymer and di-block copolymer transitions. GSRT-05-MAT-USA- 14; INTASDMR-0602877; NSF-DMR-0602877; INTAS 05-1000008-8020. [Preview Abstract] |
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C1.00030: Dynamics of Polystylen (PS) Melts: Multi-Scale Molecular Dynamic(MD) Approach Won Bo Lee, Vagelis Harmandaris, Dominik Fritz, Kurt Kremer Multi-scale approaches provide a systematic way to simulate much longer time and bigger systems, which allows us to study both large space and time scale problems. Dynamics of entangled polymer melts is one of those problems since it is always related to long time scales and large system sizes. Coarse- grained potentials of PS are obtained by multi-scale (atomistic to coarse-grained) MD approach. Time mapping (connection between atomistic and coarse-grained time units) is performed via matching mean square displacements of chain center of mass from both atomistic and coarse-grained simulations. One of interesting dynamic properties is stress autocorrelation functions (SAF) since they are directly related to physical properties of entangled polymer melts such as moduli, viscosities and entanglement lengths. SAF's of PS melts are evaluated by MD simulations. In order to reduce strong noise in SAF, we use time-averaged stresses, where averaging time is small enough to capture local chain relaxations. [Preview Abstract] |
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C1.00031: Differential AC-chip nanocalorimeter for measurements at low pressure Mathias Ahrenberg, Heiko Huth, Christoph Schick, Kenneth Kearns, Mark D. Ediger We intend to use nanocalorimetry to investigate the formation of extraordinarily stable glasses prepared by vapor deposition. For that purpose we have built a vapor deposition chamber that will allow in-situ characterization of vapor-deposited films made from organic molecules. The use of the nanocalorimeter in the deposition system permits us to produce and investigate stable glasses under well controlled conditions. Moreover, the developed nanocalorimeter enables us to simultaneously measure the heat capacity at a particular frequency and the overall enthalpy change upon heating. A quartz crystal microbalance (QCM) is used to monitor film thickness and rate of deposition. For conventional DSC experiments on extraordinary stable glasses, the sample thickness must be on the order of 50 $\mu $m. The nanocalorimeter is able to measure films below 100 nm thick, and therefore, slower deposition rates can be explored. In this way, we expect to prepare and characterize glasses with even greater stability than is possible with current techniques. [Preview Abstract] |
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C1.00032: Phase Stability in Nanoparticle/Homopolymer Thin Film Mixtures Jenny Kim, Peter Green We examined the phase behavior of thin film mixtures of polystyrene (PS), of degree of polymerization P, with Au nanoparticles, onto which with PS chains of varying degrees of polymerization, N, were attached. Scanning transmission electron microscopy (STEM), secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS) measurements indicate that when the total nanoparticle radius (particle core + grafted chains), R$_{np}$, was comparable to or larger than the radius of gyration of the host chains, R$_{g}$(P), the system were miscible. However, for R$_{np}<$R$_{g}$(P), the system was incompatible. Scanning force microscopy (SFM) measurements showed evidence of surface roughening, prior to phase separation. Under conditions where N$<<$P and R$_{np}<$R$_{g}$, the system was immiscible and the nanoparticles segregated to both interfaces. These results will be discussed in light of current simulations and theory. [Preview Abstract] |
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C1.00033: Healing of Crack on Brittle Substrate by Dual Cross-Linked Nanogel Coating German Kolmakov, Krzysztof Matyjaszewski, Anna Balazs We use computational modeling to design a gel coating that undergoes structural rearrangement in response to mechanical stress, and thereby prevents catastrophic failure of the underlying brittle substrate. The material is composed of nanoscopic polymer gel particles, which are connected by a network of labile and strong, stable bonds. The stable bonds between the nanogels play an essential role by imparting structural integrity, and the reactive, labile bonds provide the healing properties. We demonstrate that the combination of capillary and van der Waals forces, and an external load draws the nanogel particles into the crack on the surface of the substrate. Within this crack, the nanogel particles can bind to the exposed surface, fill the void and thereby, effectively heal the damaged region. The introduction of nanoparticles into the gels units leads to an increase in the strength of the coating. The results provide guidelines for designing polymer coatings that extend the life span of the entire structure by imparting self-healing mechanisms into the system. [Preview Abstract] |
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C1.00034: Design of responsive polymer surfaces with ultrafast response time Jan Genzer, Evren Ozcam, Julie Willoughby Responsive surfaces with tailorable surface-reconstruction kinetics and switching hysteresis were prepared from poly(vinylmethylsiloxane) (PVMS) networks modified with thiol alkanes to provide hydrophobic or hydrophilic surface properties. The cooperative effects of polymer mobility, arising from the high flexibility of the siloxane backbone, and the enthalpic interactions between the contacting medium and the PVMS functionalized surface control the degree of responsiveness. Exposing the modified-elastomer surfaces to water resulted in rearrangement of the hydrophilic alkanes at the surface. The kinetics of reconstruction and reversibility were established by measuring the surface wettability via dynamic contact angle. By controlling the formation of semi-crystalline regions in our substrates we demonstrate either ``sluggish'' kinetics and eventual surface ``freezing'' and stability or stimuli-responsive substrates with a magnitude of change and repeated reversibility unparallel to most polymeric surfaces. [Preview Abstract] |
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C1.00035: Swelling Behavior of Diblock Copolymer Brushes. Bulent Akgun, Sushil Satija, Gokce Ugur, Mark D. Foster Diblock copolymer brushes (DCBs) have garnered enormous interest in recent years due to their stimuli-responsive behavior. The characteristics of a surface of a DCB can be changed reversibly from those of one type to those of another by using a selective solvent for one block. There has not been any experimental study to prove either the dry state structure or the surface rearranged structure or the mechanism of that rearrangement. To understand the switching mechanism we have investigated the swelling behavior of DCBs in selective and good solvents using in-situ using neutron reflectivity. When DCBs are treated with selective solvents, in-situ measurements show that the structure changes to minimize the unfavorable interaction between solvent and the block that does not like the solvent. When swollen with a liquid solvent good for both blocks, DCBs behave similarly to homopolymer brushes, establishing a parabolic profile of chain segment density. [Preview Abstract] |
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C1.00036: Effect of density and structure on dynamics within self-assembled monolayers Derrick Stevens, Mary Scott, Jason Bochinski, Laura Clarke Previously, we have observed interacting dynamics within self-assembled alkylsiloxane monolayers, and characterized this motion via sensitive dielectric spectroscopy (along with more traditional techniques such as ellipsometry, contact angle, and force microscopy). In these monolayers, molecules are covalently bound to the surface and thus cannot spontaneously change density, as in an adsorbate system. We identified this relaxation as akin to the polyethylene-like glass transition observed in polymers with phase-segregated alkyl side chains [1]. As a next step, we deliberately manipulated the physical structure of the monolayers (via different film growth procedures and/or post-deposition heat treating) and the monolayer density (from $\sim $10{\%} to full coverage), and observed the resultant changes in dynamics. This experimental system may prove a useful model for more complex materials, such as glassy polymers or traditional molecular glasses, where density cannot be explicitly tuned. As density increases, the steepness index increases, indicating a more complex or fragile relaxation. At low densities, the motion has an almost-Arrhenius dependence on temperature. [1] M.C. Scott, D.R. Stevens, J.R. Bochinski, L.I. Clarke, ACS Nano. DOI: 10.1021/nn800543j. [Preview Abstract] |
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C1.00037: Partial Crystallinity in Alkyl Side Chain Polymers. Vasav Sahni, Shishir Prasad, Johanna Villate, Zhang Jiang, Sunil Sinha, Ali Dhinojwala Surface freezing is the formation of a crystalline monolayer at the free surface of a melt at a temperature $T_{s}$, a few degrees above the bulk freezing temperature, $T_{b}$. This effect, $i.e. T_{s} \quad > \quad T_{b}$, common to many chain molecules, is in marked contrast with the surface melting effect, $i.e. T_{s} \leq T_{b}$, shown by almost all other materials. Various theoretical and experimental studies have been done to characterize the monolayer formed when the surface freezes before the bulk. We have studied the structure of a novel crystalline surface monolayer on top of a disordered melt of the same material (poly($n$-alkyl acrylate)s) using grazing incidence x-ray diffraction. The grazing incidence x-ray diffraction, surface tension, and bulk latent heat results show that there is partial side-chain crystallinity. Also, the surface tension results explain the trend of the difference between the surface order-to-disorder transition temperature and the bulk melting temperature ($\Delta $T) as a function of side chain length. The behavior of the crystal length, crystal spacing and tilt with varying alkyl chain length and temperature was also studied. [Preview Abstract] |
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C1.00038: Modifying material surfaces by siloxane-based coatings Ali Ozcam, Jan Genzer We report on a simple, robust, and rapid method of modifying materials surfaces by using poly(vinylmethyl siloxane)-trichlorosilane (PVMS-TCS) coatings. PVMS-TCS is synthesized by hydrosililation coupling between trichlorosilane (TCS) and poly(vinylmethyl siloxane) (PVMS). Spin-coating PVMS-TCS onto a substrate results in a uniform coating layer, which can be further stabilized by cross-linking. Exposing the coating to minute amounts of moisture generates a large density of surface-bound hydroxyl groups on the surface of PVMS-TCS. Moreover, by treating the PVMS-TCS substrates with ultraviolet/ozone (UVO) treatment increases one can both further increase the density of the surface-bound hydroxyl groups and the coating's elastic modulus. The applicability of PVMS-TCS and PVMS-TCS/UVO coatings was tested by decorating various surfaces, including, poly(ethylene terephthalate) and glass, with semifluorinated organosilanes and organosilane-based initiators for surface initiated polymerization. The physico-chemical properties of the functional coatings were studied with a battery of experimental probes, including near-edge x-ray absorption fine structure spectroscopy, x-ray photoelectron spectroscopy, contact angle, atomic force microscopy, ellipsometry, and nanoindentation. [Preview Abstract] |
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C1.00039: Carbon Nanotube Intra-connects With Conductive Polymers Seon Woo Lee, Haim Grebel, Andrei Sirenko, Daniel Lopez, Avi Kornblit The electrical and optical properties of carbon nanotube (CNT) channels, electroplated with conductive polymers were measured. Individual, single-walled CNT (SWCNT) channels were grown by chemical vapor deposition (CVD) technique precisely between very sharp metal tips on a wafer. The conductive polymers, either polycarbazole (PCZ) or, polypyrrole (PPy) were then electroplated using the CNT as an electrode. Field effect transistors were fabricated and a gate-controlled, N-shaped negative differential resistance (NDR) was observed. A large photoconductance effect, which was associated with the NDR, was demonstrated, as well. [Preview Abstract] |
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C1.00040: Orientation Dynamics in Multi-Wall Carbon Nanotube Dispersions under Shear Flow Saswati Pujari, Sameer Rahatekar, Jeffrey Gillman, Krzysztof Koziol, Alan Windle, Wesley Burghardt We report studies of the orientation state of multi-walled carbon nanotubes (MWNTs) dispersions in steady and transient shear flows. Uncured epoxy was used as a viscous, Newtonian suspending medium, and samples were prepared from 'aligned' MWNTs. Orientation was studied in both the flow- gradient (1-2) and flow-vorticity (1-3) plane of simple shear flow using in-situ x-ray scattering techniques. Steady state measurements in the 1-2 plane indicate that the MWNT orientation is shear rate dependent, with the MWNTs orienting closer to the flow direction at higher shear rates. In steady shear, anisotropy was measured to be higher in the 1-2 plane than in the 1-3 plane, demonstrating that the nanotube orientation state is not unaxially symmetric in shear. The steady state MWNT orientation is governed by a rate-dependent state of nanotube aggregation/ disaggregation, which was separately characterized by optical microscopy. A partial relaxation of flow-induced anisotropy was observed following flow cessation, despite the very small rotational diffusivity estimated for these nanotubes. Long transients are observed in step-down experiments, as the orientation state changes in response to the slow tube aggregation process. [Preview Abstract] |
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C1.00041: Defect Structures in Block Copolymer/Nanoparticle Blends Hyung Ju Ryu, Michael Bockstaller We present a systematic study of the implications of nanoparticle additives on the defect formation in block copolymer/nanoparticle blends (BCP). The morphology of lamellar styrene/isoprene-based di- and triblock copolymers blended with polystyrene-coated gold nanocrystals at various filling fractions was analyzed using electron microscopy using stereology and image reconstruction. Three structural characteristics, i.e. the grain size distribution, grain orientation distribution and grain boundary structure, were analyzed as a function of polymer chain architecture, particle filling fraction and film processing conditions. With increasing particle filling fraction the average anisotropy as well as average grain size is observed to decrease as is the rate of grain growth during thermal annealing. The results are interpreted in terms of the stabilization of grain boundary structures through segregation of particle fillers to the grain boundary regions. [Preview Abstract] |
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C1.00042: Effect of Nanoparticle Core Size on Polymer-Coated Gold Nanoparticle Location in Block Copolymers J. D. Petrie, G. H. Fredrickson, E. J. Kramer Gold nanoparticles modified by short chain polymer thiols [Au-PS] can be designed to strongly localize either in the PS domains of a polystyrene-b-poly(2-vinylpyridine) [PS-PVP] block copolymer or at the interface.~ The P2VP block has a stronger attractive interaction with bare gold than the PS block.~ Thus, when the areal chain density $\Sigma $ of end-attached PS chains falls below a critical areal chain density $\Sigma _{c}$ the Au-PS nanoparticles adsorb to the PS-b-P2VP interface.~ The effect of the polymer ligand molecular weight on the $\Sigma _{c}$ has been shown to scale as $\Sigma _{c} \quad \sim $ ((R + Rg)/(R*Rg))\^{}2, where R is the curvature of the Au nanoparticle core radius.~ To test this scaling relation for $\Sigma _{c}$ further we are synthesizing gold nanoparticles with different core radii and will present preliminary results on $\Sigma _{c}$ as a function of R. [Preview Abstract] |
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C1.00043: Segmental dynamics in poly(cyclohexyl methacrylate) / poly(alpha-methylstyrene) blends. Gareth Royston, Paul Sotta, Didier Long Study of the dynamics of polymer blends near the glass transition has a long history and remains of great current interest. We present broadband dielectric spectroscopy and mechanical spectroscopy data from miscible blends of poly(cyclohexyl methacrylate) and poly(alpha-methylstyrene) across the entire composition range. Results are compared to known data on a range of other systems. [Preview Abstract] |
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C1.00044: Surface segregation of end-functionalized homopolymers in a homopolymer matrix Michael Dimitriou, Cheng Wang, Kristin Schmidt, Harald Ade, Craig Hawker, Edward Kramer Surface segregation of end-functional poly(2-vinylpyridine) in a blend with P2VP was measured by X-ray photoelectron spectroscopy. A series of chain end functionalized P2VP homopolymers were synthesized \emph{via} either anionic polymerization or Reversible Addition Fragmentation Chain Transfer (RAFT) and end capped with either a single fluorinated oligomer or a perfluorinated dendrimer. The degree of end functionalization was characterized using NMR spectroscopy, IR spectroscopy and gel permeation chromatography. Further surface characteristics were determined using Near Edge X-ray Absorption Fine Structure Spectroscopy and Resonant Soft X-ray Reflectivity. When 5wt\% P2VP end capped with a perfluorinated dendrimer was added a top layer saturated with fluorocarbons formed. It was also found that the surfactant segregation is dependant on its ability to form micelles. [Preview Abstract] |
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C1.00045: Co-crystallization of Alkanes with Longer Methlyene Segments within a Statistically Random Copolymer Jeffrey Kalish, Suriyakala Ramalingham, Yuning Yang, Shaw Ling Hsu Binary blends of alkanes (C$_{n}$H$_{2n+2}$, n=24, 32, 36) and statistically random ethylene-co-vinyl acetate (EVA) copolymers with different vinyl acetate (18, 28 and 40{\%}) contents have been studied to understand the phenomenon of co-crystallization of longer chain fractions. Using thermal fractionation, the distribution of various crystallizable ethylene chain sequences was established in EVA copolymers. Co-crystallization in blends was observed by changes in spectroscopic features of various unit cells (triclinic, even n$<$26; monoclinic, even n$>$26 and orthorhombic, odd n) using vibrational spectroscopy. In order to distinguish these changes, deuterated alkanes were blended with EVA. Orthorhombic unit cells show a doublet in the C-H rocking region due to crystal field splitting; this splitting was removed upon co-crystallization. In Raman spectra, the Longitudinal Acoustic Modes (LAM) are used to validate co-crystallization. LAM did not change significantly when an alkane was co-crystallized with EVA in comparison to the neat alkane. The Raman C-H stretching region changed when a monodispersed alkane was blended. Thermal and X-ray analysis support these spectroscopic results upon co-crystallization. [Preview Abstract] |
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C1.00046: Phase Behavior of a Weakly Interacting Polystyrene and Poly(n-hexyl methacrylate) System Hyungju Ahn, Sudhakar Naidu, Du Yeol Ryu, Junhan Cho Understanding the phase behavior of multi-component polymeric materials has been of great concern in polymer community, since this provides us a key to the compatibility in most applications involving polymer blends and block copolymers. In the weakly interacting binary blends, UCST-type polymer blends generally undergo a transition from the homogeneous to phase- separated state by the nonfavorable segmental interactions, while LCST-type blends show an opposite tendency as a consequence of thermal compressibility (or thermal expansion) difference between two components. We report an experimental evidence for the coexistence of both UCST and LCST behavior in a weakly interacting deuterated PS (dPS) and PnHMA blend system. A new phase diagram involving both UCST and LCST was obtained by the delicate control of molecular weights between dPS and PnHMA. Whereas for the block copolymers such as deuterated polystyrene-b-poly(n-hexyl methacrylate) (dPS-b- PnHMA) and PS-b-PnHMA, an order-to-disorder transition (ODT) on heating was observed within experimental temperature range depending on the molecular weight. [Preview Abstract] |
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C1.00047: Polydisperse Block Copolymer Melts: Beyond the Schulz-Zimm Distribution Nathaniel Lynd, Marc Hillmyer, Mark Matsen Using self-consistent mean field theory, we compared the effects of polydispersity on the phase behavior of block copolymer melts possessing two distinct distributions: the Schulz-Zimm distribution (SZD), and a realistic distribution resulting from a numerical simulation of the kinetics of an equilibrium polymerization (EQD). When the polydispersity indices (PDIs) were matched, the SZD and EQD imparted significant differences in the number of chains pulling free of the interface. This resulted in large differences in domain spacing, but negligible differences in phase boundaries. [Preview Abstract] |
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C1.00048: Network Phase Behavior of ABC Triblock Copolymer-Homopolymer Blends for Nanoporous Membranes Maeva Tureau, Thomas H. Epps, III ABC-type block copolymers exhibit morphological diversity not found in diblock copolymers and are becoming a versatile route to nanoscale devices. ABC triblocks are capable of self-assembling into triply-periodic network structures with a high degree of internal interfacial area and tailored chemical and mechanical properties. These unique characteristics make ABC triblock network structures ideal candidates for nanoporous membranes. Our work focuses on the morphological behavior near the network phase window in the poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) system using neat triblocks and selective homopolymer blending. Morphological characterization is accomplished through a combination of small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and dynamic mechanical analysis (DMA) techniques. Neat triblocks exhibit network structures while blended systems show phase transitions including an alternating gyroid to lamellar phase transition. The neat and blended systems are mapped on a phase diagram to locate the network phase window. [Preview Abstract] |
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C1.00049: Solution self-assembly behavior of block copolymer blends with restricted hydrophilic block Jiahua Zhu, Sheng Zhong, Ke Zhang, Karen Wooley, Darrin Pochan Novel assembled structures due to segregation of hydrophobic domains trapped within the same micelle core have been produced via a block copolymer blend in tetrahydrofuran/water solution. The block copolymer blend is composed of two/or more block copolymers with shared poly(acrylic acid) (PAA) hydrophilic block, but distinctive hydrophobic blocks. The blended micelles are created by taking advantage of the electrostatic association in the hydrophilic PAA shell between the negatively charged acid of the PAA block and added, positively charged organoamine molecules. Unlike hydrophobic blocks undergo local segregation. This segregation gives rise to new nanostructures deviated from traditional polymeric assemblies such as spheres, cylinders and vesicles. Transmission electron, cryogenic transmission electron, and atomic force microscopy along with x-ray and neutron scattering have been applied to characterize the assembled structures. [Preview Abstract] |
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C1.00050: Time-composition superpositioning in the rheological behavior of triblock copolymer/selective co-solvent blends Arjun Krishnan, Rudolf Bukovnik, Richard Spontak Thermoplastic elastomers composed of styrenic triblock copolymers are of great importance in applications such as adhesives and vibration dampening due to their resilience and facile processing. The swelling of these polymers by adding midblock selective solvents or oligomers provides an easy route by which to modify the morphology and mechanical behavior of these systems. In this study we consider a ternary blend of a poly[styrene-$b$-(ethylene-\textit{co}-butylene)-$b$-styrene] triblock copolymer and mixtures of two midblock selective co-solvents: a mineral oil that is liquid at ambient temperature, and a glassy tackifier resin that exhibits limited solubility in the midblock matrix. We use dynamic rheology to study the viscoelastic response of a wide variety of systems under oscillatory shear. The copolymer concentration is varied between 15 to 35 wt{\%}, while the resin/oil ratio in the midblock-solvent matrix is independently varied. Frequency spectra acquired at ambient temperature display viscoelastic behavior that shifts in the frequency domain depending on the resin/oil ratio. At high oil loadings, the materials behave as physical gels. For each copolymer concentration, all the frequency data can be shifted by time-composition superpositioning to yield a single master-curve. [Preview Abstract] |
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C1.00051: Drop shape analysis of poly-styrene acrylic acid gradient copolymer at oil/water interfaces Wa Yuan, Michelle Mok, John Torkelson, Kenneth Shull The behavior of poly-styrene/acrylic acid gradient and block copolymers at liquid/liquid interfaces was investigated using drop shape analysis. Copolymers were dissolved in chloroform and then pendant drops of the solutions were created in water. The drop shape was monitored as a function of time in order to determine interfacial parameters. Molecular movements at the interface were inferred by measuring changes in interfacial pressure as the interface was contracted and expanded through control of the drop volume. A picture of the interfacial structure of gradient copolymer system was obtained from an analysis of these results. This analysis suggests that gradient copolymers are more interfacially active than block copolymers. The interfacial properties depend more strongly on the hydrophilic/hydrophobic ratio and sequence distribution than on the molecular weight. [Preview Abstract] |
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C1.00052: Influence of Binding Strength on the Structure of Supramolecular Polymer-Surfactant Complexes Manesh Gopinadhan, Evan Beach, Paul Anastas, Chinedum Osuji Specific interactions between small molecule species and host binding sites on a polymer chain can be used to engineer supramolecular complexes which display liquid crytalline order. In particular, hydrogen bonding interactions represent a flexible platform for the creation of graft-copolymer like structures by the reversible, specific association of small molecules with complementary sites on the polymer backbone. We use hydrogen bonding between the imidazole termination of mesogenic species and the carboxylic acid groups of poly(acrylic acid) to form side-chain liquid crystalline polymers in solution and in the melt state. We investigate their phase behavior and binding using a combination of calorimetry (DSC), x-ray scattering (SAXS), infrared spectroscopy (FTIR) and optical microscopy. We find that there is a critical interaction strength and critical stoichiometry required for the formation of a liquid crystalline mesophase in these systems. The manipulation of the binding equilibria via temperature makes for an interesting class of stimuli responsive materials in solution and in the melt state. [Preview Abstract] |
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C1.00053: Registration of Lamellar Microdomains of PS-b-PMMA to Topographic Guiding Patterns Sang-Min Park, Charles Rettner, Jed Pitera, Ho-Cheol Kim In addition to the control over orientation and lateral alignment, the control over precise placement of microdomains is critical for block copolymer lithography. We report here an approach for spatial registration of the lamellar microdomains of poly(styrene-b-methly methacryalte) (PS-b-PMMA) using topographic guiding patterns prepared by E-beam lithography. By employing two levels of topographic patterns, we could achieve both alignment and registration of lamellae on surface. Details on the limitations and challenges of this approach will be addressed along with potential applications to device fabrications. A mean field Monte Carlo simulation on an IBM BlueGene/L which provides additional structural insights into the influence of the topographic guiding patterns will be presented as well. [Preview Abstract] |
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C1.00054: The Assembly of Cyclopeptide-Polymer Conjugates and Block Polymer Nana Zhao, Brett Helms, Ting Xu The co-assembly of cyclopeptide-polymer conjugates and block polymer affords a simple route to generate hierarchical structures with molecular level control over the assemblies. By coupling synthetic homopolymer to a preformed cyclic (D-alt-L)-R- octapeptide, a family of coil-ring-coil bioconjugates was synthesized. The controlled self-assembly of the conjugate leads to uniform nanoparticle structures, 2.5-3nm in height and 25- 30nm in diameter. The assembly of blends of cyclopeptide-polymer conjugates and block polymer has been further investigated. The co-assembly of cyclopeptide-polymer conjugates and diblock copolymer provide a base to generate nanoporous materials and improve our understanding in the self-assembly of mutli- component hybrid systems. [Preview Abstract] |
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C1.00055: Block Copolymer Based Supramolecules for Organoelectronics Benjamin Rancatore, Shih-Huang Tung, Clayton Mauldin, Paul Tillberg, Claire Woo, Jean M.J. Frechet, Ting Xu Block copolymer (BCP)-based supramolecules present unique advantages over conjugated BCPs to fabricate functional devices such as OLEDs and photovoltaics. The self assembly of 5'''-(3,7-dimethyloctyl)-5-(3-(3-hydroxyphenyl)propyl)-[2,2';5',2'';5'',2'''] quaterthiophene (4T) hydrogen bonded to the poly(4-vinylpyridine) (P4VP) block of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCP was studied in bulk and thin films. Lamellae-within-lamellae hierarchical structure was observed and can be macroscopically oriented at both length scales in thin films. Films of pure 4T, P4VP(4T) and PS-b-P4VP(4T) composites were investigated as organic field-effect transistors (OFETs). Phase behavior of blends of the BCP-based supramolecule and PCBM were also investigated to guide the fabrication of organic photovoltaics. [Preview Abstract] |
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C1.00056: Chain Bridging in Semicrystalline Multiblock Copolymers Manas Shah, Venkat Ganesan The structure development in semicrystalline/rubbery multiblock copolymers involves complex interplay between two self-ordering mechanisms -- microphase separation and crystallization of one of the components. Experiments have suggested connection between the mechanical properties and the molecular architecture of such linear copolymers, especially the role of bridging conformations in multiblock copolymers. We present a theoretical study to evaluate the bridging/looping fractions in these multiblock copolymers as a function of the morphology and the molecular architecture. We model the non-crystalline (rubbery) component as a flexible Gaussian chain and the crystalline component as a semiflexible chain with a temperature dependent rigidity and a favorable tendency to form parallel bonds. We calculate the domain spacing in lamellar phases of diblock copolymer where one flexible chain is attached to the semiflexible chain and compare the scaling exponents with existing scaling theories for semicrystalline diblock copolymers. Using self-consistent field theory, the bridging fractions of the various domains in these complex multiblock copolymers (triblock and pentablock) are evaluated as a function of the sequence of the chains and other parameters in the system. [Preview Abstract] |
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C1.00057: Tuning the Structure-Directing Block in Crystalline-Crystalline Diblock Copolymers Sheng Li, Sasha Myers, Richard Register Crystalline-crystalline block copolymers containing two or more chemically distinct crystallizable blocks are fascinating because their solid-state structures can be set either by block incompatibility or by crystallization of one or more blocks, depending on macromolecular design and processing history. Double-crystalline diblock copolymers of linear polyethylene (LPE) and hydrogenated polynorbornene (hPN) were synthesized, and their crystallization behavior and morphology were examined using two-dimensional simultaneous time-resolved synchrotron small-angle and wide-angle x-ray scattering. In previous work (Macromolecules 2008, 41, 6773), we showed that for diblock molecular weights of 50 kg/mol and above, the hPN block always crystallized first and set the solid-state microstructure. In the present work, we exploit the difference in molecular weight dependence of the melting/freezing points of LPE vs. hPN to create materials where LPE is the structure-directing (templating) block. In 20 kg/mol diblocks, LPE block crystallizes first, even when LPE is the minority component, and restricts hPN to crystallize between the LPE lamellae. In hPN-rich diblocks, LPE crystallization triggers hPN crystallization and the two blocks crystallize at almost the same rate. During cooling to room temperature, hPN transitions from a rotationally disordered pseudohexagonal phase to a monoclinic structure. [Preview Abstract] |
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C1.00058: Tethered Polyhedral Oligomeric Silsesquioxane on Lamellar Single Crystal of Poly(D-lactide) Xin-Fei Yu, Wen-Bin Zhang, Ryan Van Horn, Roderic Quirk, Stephen Cheng Lamellar single crystals can be used as the templates for nanoparticles. Poly(D-lactide) (PDLA) was successfully ?grafted from? the polyhedral oligomeric silsequioxane (POSS) by coordination-insertion ring opening polymerization (ROP) of D-lactide. The reaction was conducted in toluene at 60 $^{o}$C and initiated by hydroxypropyl(isobutyl) POSS nanoparticles with tin(II) 2-ethylhexanoate (SnOct2) as the catalyst. Under these conditions, the molecular weight was controlled well by adjusting the monomer-initiator molar ratio monitored by size exclusion chromatography (SEC) and proton nuclear magnetic resonance ($^{1}$H NMR). $^{13}$C NMR spectroscopy showed that the synthesized poly(D-lactide) was more than 99{\%} isotactic. Single crystals of POSS-PDLA grown in dilute solution and were examed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Tethering density of POSS was controlled by the molecular weight of PDLA crystalline chain and by varying the crystallization temperature. Tethering density was increased as molecular weight of PDLA was lower and crystallization temperature was increased higher. [Preview Abstract] |
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C1.00059: A simple method to control the porosity in thin block-copolymer films Wonjoo Lee, Xin Zhang, Robert M. Briber We report a simple way developed to control the porosity in block-copolymer films. PS-P4VP block copolymer/P4VP homopolymer was dissolved in THF at 80 $^{o}$C for 12 hours and cooled to room temperature. Depending on the amount of P4VP homopolymer added to PS-P4VP solutions in THF, the ratio of P4VP and PS was changed from 3 to 45 wt{\%}. The solutions were spincoated onto various substrates such as silicon wafer and mica. The morphology of the resulting films was examined using AFM or TEM. Interestingly, large scale of macrophase-separation was not found regardless of the ratio of P4VP and PS. Instead, it was found that microphase-separation occurred during the spincoating process for all concentrations of P4VP homopolymer studied. The size of the microphase-separated domains increased as the ratio of P4VP to PS increased, indicating that the added P4VP homopolymer was contained within the P4VP microdomains. The PS-P4VP/P4VP blend films were then immersed for 3 hours in ethanol which induced a reconstruction of the film structure and removed the P4VP homopolymer. The resulting morphology exhibited nanoscale porosity with the pore size increasing with increasing concentration of P4VP homopolymer. A possible mechanism for the microphase-separation for the formation of the nanoporous structure will be discussed. [Preview Abstract] |
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C1.00060: Nanoscale functionalized surface pattern by combining block copolymer template and click chemistry Xinyu Wei, Wei Chen, Thomas Russell Poly(ethylene oxide)-b-poly(n-butyl methacrylate-r-3-trimethylsilylprop-2-ynyl methacrylate) block copolymer was successfully prepared by atom transfer radical polymerization (ATRP) starting from a PEO macroinitiator, with good control of molecular weight, polydispersity and comonomer composition. The trimethylsilyl protecting group can then be quantitatively converted to terminal alkyne groups under mild conditions. Microphase separation of these block copolymers has been confirmed by small angle X-ray scattering (SAXS). Orientation of microdomains in thin films can be controlled by thermal or solvent annealing. Nanoparticles or biological macromolecules can be selectively immobilized onto the methacrylate microdomains through the cycloaddition between terminal alkynes and azides, which leads to a functionalized surface pattern for many applications. [Preview Abstract] |
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C1.00061: Controlled morphology of Nafion$^{\mbox{{\textregistered}}}$ perflourinated ionomer membrane and poly(vinylidene-co-trifluoroethylene) blends for swelling suppression. Nadzrinahamin Ahmad Nazir, Thein Kyu The major objective of the present study is concerned with the swelling suppression of Nafion$^{\mbox{{\textregistered}}}$ membrane upon hydration through blending with poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) copolymer. The phase diagram of the Nafion/PVDF-TrFE blend was established by differential scanning calorimetry, cloud point measurement, and optical microscopy. A theoretical phase diagram was calculated by self-consistently solving the combined Flory-Huggins free energy for liquid-liquid demixing and the phase field free energy for crystal solidification. The resulting phase diagram is the combined LCST-UCST and/or an hour glass type. Guided by the phase diagram, the phase separated domain morphology can be controlled to exhibit bicontinuous or dispersed domains via phase separation by solvent casting or thermal quenching. The blends thus prepared not only afford suppression of water uptake, but also render dimensional stability. Fourier transform infrared spectroscopy studies and water uptake measurement showed infallible evidence that modification of Nafion$^{\mbox{{\textregistered}}}$ with PVDF-TrFE reduces swelling upon hydration. [Preview Abstract] |
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C1.00062: Synthesis and Morphology Study of Copolymers Containing Imidazolium Group David Salas-de la Cruz, Sharlene R. Williams, John Layman, Matt Green, Timothy E. Long, Karen I. Winey We report the synthesis and characterization of two copolymers having imidazolium based-ionic groups located either in the backbone or side chain. Imidazolium ionene segmented block copolymers, containing imidazolium group in the backbone, were synthesized from 1,1'-(1,4-butanediyl)bis(imidazole), 1,12-dibromododecane hard segments, and PTMO dibromide. Vinyl imidazolium random copolymers, containing the imidazolium group in the side chain, were synthesized from 1-butyl-bromide and 3-vinylimidazolium in ethyl acetate and copolymerized with methylmethacrylate. The scattering result for the imidazolium group located in the backbone reveals evidence of hierarchial structure. The driving force for the hierarchial structure is due to the incompatibility of the PTMO segments and the ionic domains. The scattering results for the imidazolium group located at the side chain suggest the formation of ionic aggregation. The ionic aggregation peak intensity broadens as the methylmethacrylate content increases in the copolymer. [Preview Abstract] |
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C1.00063: Nanoscale Ionic Aggregate Morphology in Zwitterionic Copolymers Jae-Hong Choi, Rebecca Huyck, David Salas-de la Cruz, Timothy E. Long, Karen I. Winey The morphology of two different zwitterionic copolymers, poly(sulfobetaine methacrylate-\textit{ran}-butyl acrylate), and poly(sulfobetaine methacrylamide-\textit{ran}-butyl acrylate) are investigated as a function of the mol {\%} content of SBMA (7 and 9 mol {\%}) and SBMAm (6, 10 and 13 mol {\%}), respectively. In both copolymers, X-ray scattering results show a new structure in the material arising from ionic aggregates. The sizes of the ionic aggregates are obtained through the scattering model. The sizes of the ionic aggregates increase as the ion content increases. The application of scanning transmission electron microscopy to the study of ionomer morphology has enabled direct, model-independent visualization of the ionic aggregates. The correlation between X-ray scattering results and the real space imaging for morphology of these zwitterionic copolymers will be presented. [Preview Abstract] |
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C1.00064: Dynamics and Morphology of Sulfonated Polystyrene Ionomers by Dielectric Spectroscopy Alicia Castagna, Wenqin Wang , Karen I. Winey , James Runt The dynamics of sulfonated polystyrene (SPS) ionomers, in both the acid and neutralized forms, were investigated using broadband dielectric spectroscopy. The influences of acid content, counterion type (Zn, Na and Cs), degree of neutralization, and microphase separated morphology on segmental and local dynamics, as well as on Maxwell -- Wagner -- Sillars interfacial polarization, were examined. Ionomers prepared from SPS containing 1.9 mol{\%} sulfonic acid species exhibit a broader segmental process indicative of a considerably broader distribution of local environments, as compared to those in unneutralized SPS. Moreover, multiple segmental relaxations were identified in the dielectric spectra of Zn and Na neutralized SPS (1.9 mol{\%}) ionomers, likely indicating two distinct environments arising from ion clustering. A combination of STEM imaging and X-ray scattering confirmed the presence of monodisperse spherical ionic aggregates that were homogeneously distributed in the polymer matrix. [Preview Abstract] |
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C1.00065: Dynamics of Strongly Associating Polymer Blends Using Broadband Dielectric Spectroscopy Kevin Masser, James Runt In this study we investigate the dynamics of miscible polymer blends that preferentially form strong intermolecular hydrogen bonds. Random copolymers of p-(hexafluoro-2-hydroxyl-2-propyl)styrene [HFS] and 2,3-dimethylbutadiene [DMB] were synthesized for this study, as was the HFS homopolymer. HFS units are capable of forming strong intermolecular hydrogen bonds with complimentary species on a second miscible polymer, while minimizing the extent of intramolecular associations. The copolymers/homopolymers were blended with select homopolymers that form intermolecular hydrogen bonds of varying strength. Broadband dielectric relaxation spectroscopy is used to study segmental and local blend dynamics, which are observed to vary significantly in the presence of hydrogen bonding. Fourier transform infrared spectroscopy was used to determine the degrees and strengths of hydrogen bonding present in the blends. [Preview Abstract] |
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C1.00066: Investigating void development in filled elastomers under uniaxial strain Ailish O'Halloran, Arthur Scholz, Kristin Schmidt, Lixia Rong, Shigeyuki Toki, Benjamin Hsiao, Ed Kramer Development of voids during cyclic, uniaxial extension and retraction, of both silica and resin filled elastomers, was studied by combining synchrotron-based time resolved small angle X-ray scattering (SAXS) and primary X-ray beam attenuation with stress-strain curves measured simultaneously. These data were used to calculate the volumetric strain due to the development of voids during extension and their subsequent disappearance during retraction as well as the size and shape of the smaller voids. Four samples were investigated, one silica-filled polydimethylsiloxane (PDMS), one resin filled PDMS, and two silica filled polyphenylmethylsiloxane (PPMS), all candidate materials for dielectric elastomer actuators, in which void development would lead to decreased dielectric breakdown electric fields and premature failure. [Preview Abstract] |
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C1.00067: Probing the Mullins Effect in Filled Elastomers by Small Angle X-ray and Neutron Scattering Arthur Scholz, Rex Hjelm, Mark Taylor, Ed Kramer While there has been considerable effort made to understand and model the effect that filler particles have on the mechanical properties of filled elastomers, the origins of a striking characteristic strain softening known as the Mullins Effect are still debated. Several micro-mechanical models have been proposed using a variety of mechanisms to describe the polymer-filler and filler-filler interactions to fit mechanical test data without any direct observation of microstructural changes. Small angle x-ray and neutron scattering provide complimentary methods for observing these changes on the relevant length and time scales necessary for identifying and characterizing the proposed mechanisms. We designed and built a modular uniaxial load frame for use in a variety of lab and user facilities. Its capabilities include a 350mm of symmetrical travel and a non-contact strain measurement system using speckle pattern digital image correlation. The system was developed and tested on silica-filled polydimethylsiloxane (PDMS) and polyphenylmethylsiloxane (PPMS) elastomers using the Low Q Diffractometer at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. [Preview Abstract] |
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C1.00068: Segmented polyurethanes containing carbon nanotube nanohybrid shishkebabs Matthew Hood, James Sands, John LaScala, Rick Beyer, Christopher Li Segmented polyurethanes (SPUs) are linear, multiblock copolymers that possess a wide range of tailorable properties via control during synthesis and processing. Phase separation between SPU's segments produce superior elastomeric properties with hard domains maintaining the polymer matrix under stress, while soft domains provide flexibility allowing for a high degree of strain. We have synthesized a variety of SPU systems using different molecular weight macrodiol soft segments and various concentrations of hard segments, which are composed of hexamethylene diisocyanate and butanediol. SPU morphology control via tuning the hard/soft segment ratio was achieved. Furthermore, adding carbon nanotubes (CNTs) that have been periodically patterned with functionalized crystalline polymers, to form nanohybrid shishkebabs, drastically changes the mechanical properties of our SPU system even at low CNT concentrations. Differential scanning calorimetry, dynamic mechanical analysis, wide angle X-ray diffraction and transmission electron microscopy have been used to characterize these systems and compare them to neat SPU. By tailoring SPU composition and shishkebab concentration we have produced a system with significant mechanical improvement with potential for use as a shape memory polymer. [Preview Abstract] |
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C1.00069: Efficient Synthesis of Poly(hydroxyethyl Methacrylate)-b-Poly(dimethylaminoethyl Methacrylate) Block Copolymer by Atom Transfer Radical Polymerization. Wei Tang, Yueh-Lin Loo Polymers containing hydroxyethyl methacrylate (HEMA) and dimethylaminoethyl methacrylate (DMAEMA) have found wide applications in areas such as bioseparation, tissue engineering and controlled drug delivery. The controlled synthesis of block copolymers of PDMAEMA-b-PHEMA from PDMAEMA macroinitiator by atom transfer radical polymerization (ATRP), however, has not been successful due to the loss of chain end functionality during polymerization. We report an ATRP system that affords efficient chain extension from PDMAEMA to HEMA using Cu(0)/1,1,4,7,10,10-hexamethyltriethylenetetramine as the catalyst, 2-chloropropionitrile as the initiator in methanol at room temperature. A clear peak shift in the gel permeation chromatography trace towards shorter elution times indicates chain growth on HEMA addition. The chain end functionalities of PDMAEMA are thus retained and can be used to efficiently initiate chain extension reaction of HEMA. This new synthetic route opens new possibilities for the synthesis of pH- and temperature-responsive systems containing DMAEMA. [Preview Abstract] |
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C1.00070: Atom Transfer Radical Copolymerization of Gradient Copolymers of HEMA/DMAEMA with Arbitrary Composition Profiles Keith Gallow, Yueh-Lin Loo Gradient copolymers represent a new class of statistical copolymers where a non-uniform composition profile is controllably introduced along the length of the polymer chain. Gradient copolymers have thermal and mechanical properties that are different from random or block copolymers having the same average composition. Due to synthetic limitations, however, the introduction of arbitrary composition profiles remains challenging. Here, we demonstrate the ability to controllably introduce arbitrary composition profiles along copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) by atom transfer radical copolymerization in a semi-batch reactor. Using gas chromatography to monitor monomer consumption, we have constructed a kinetic model which we use as a basis to synthesize copolymers with linear and parabolic composition profiles. The overall DMAEMA content and molecular weight of these gradient copolymers were determined using nuclear magnetic resonance spectroscopy and size exclusion chromatography, respectively, and both show good agreement with our model's predictions. [Preview Abstract] |
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C1.00071: Improving the Electrical Conductivity of Polyaniline Through Molecular Control Joung Eun Yoo, William Krekelberg, Tracy Bucholz, Thomas Truskett, Yueh-Lin Loo We have investigated the electrical conductivity of polyaniline (PANI) that is template synthesized with a polymer acid of poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA. The conductivity of PANI-PAAMPSA is determined by the particle density when PANI-PAAMPSA is cast as films. The PANI-PAAMPSA particle density can in turn be tuned by manipulating the molecular characteristics of PAAMPSA. Specifically, templating aniline polymerization with a higher molecular weight PAAMPSA results in bigger PANI-PAAMPSA particles; templating aniline polymerization with a broader molecular weight distribution PAAMPSA results in particles with a larger size distribution. The conductivity of drop-cast films of PANI-PAAMPSA therefore depends on how the particles pack in the solid state. In particular, we find the conductivity of PANI-PAAMPSA to increase with particle density. Additionally, PANI is preferentially segregated to the surface of these particles. The conductivity of PANI-PAAMPSA thus scales superlinearly with the surface area per unit volume of the cast film. [Preview Abstract] |
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C1.00072: An Investigation of Polyelectrochromism in Water-Dispersible Polyaniline Jacob Tarver, Joung Eun Yoo, Yueh-Lin Loo The promise of polyaniline (PANI)-based devices, such as electrochromic windows or billboards, is motivated by the coupled nature of PANI's redox and chromic properties. In its fully reduced and oxidized form, PANI is electrically insulating and characteristically transmits yellow and violet, respectively. Protonation of PANI's intermediate oxidation state induces electrical conductivity and shifts its transmission to green. This proton dependence has historically limited the use of small molecule acid doped PANI to acidic media. Template synthesis of PANI on poly(2-acrylamido-2-methyl-1-propanesulfonic acid), or PAAMPSA, yields electrostatically stabilized PANI-PAAMPSA particles; films comprising these particles maintain electroactivity in solutions as high as pH 10. Exposure to dichloroacetic acid moderates the electrostatic interactions, thereby relaxing the material's globular structure. This structural rearrangement significantly improves the stability and reversibility of repeated cycling between PANI's redox states. Relaxation of PANI-PAAMPSA's structure thus affords enhanced robustness to this readily-processible system. [Preview Abstract] |
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C1.00073: Development of Polymer Electrolyte Mambrane (PEM) from Bisphonol S for Direct Methanol Fuel Cell (DMFC) Sairung Changkhamchom The currently used Proton Exchange Membrane (PEM) in a Direct Methanol Fuel Cell (DMFC) is Nafion$^{\mbox{{\textregistered}}}$, an excellent proton conductor in a fully hydrated membrane. However, it has major drawbacks, such as very high cost, and loss of conductivity at elevated temperature and low humidity. In this work, a novel PEM based on sulfonated poly(ether ether ketone) (S-PEEK). Poly(ether ether ketone) (PEEK) was synthesized by the nucleophilic aromatic substitution polycondensation of Bisphonol-S and 4,4'-difluorobenzophenone for system A, and Bisphenol S and 4,4'-dichlorobenzophenone for system B. Bisphenol-S helps to increase the thermal stability due to its high melting point (245$^{\circ}$C). The post-sulfonation reaction was performed by using concentrated sulfuric acid. Sulfonated poly(ether ether ketone) (S-PEEK) samples were characterized by FTIR and $^{1}$H-NMR to confirm the chemical structure of the S-PEEK, and by TGA to investigate the thermal property. [Preview Abstract] |
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C1.00074: Iontophoresis of Salicylic Acid From Salicylic Acid Doped Poly(p-phynylene vinylene)/ Polyacrylamide Hydrogels Sumonman Niamlang The apparent diffusion coefficients, D$_{app}$, and the release mechanisms of salicylic acid from salicylic acid-loaded polyacrylamide hydrogels, SA-loaded PAAM, and salicylic acid-doped poly(phenylene vinylene)/polyacrylamide hydrogels, SA-doped PPV/PAAM, were investigated. In the absence of an electric field, the diffusion of SA from the SA-doped PPV/PAAM hydrogel is delayed in the first 3 hr due to the ionic interaction between the anionic drug and PPV. Beyond this period, SA can diffuse continuously into the buffer solution through the PAAM matrix. D$_{app}$ of SA-doped PPV/PAAM is higher than that of the SA-loaded PAAM, and the former increases with increasing electric field strength due to the combined mechanisms: the expansion of PPV chains inside the hydrogel; iontophoresis; and the electroporation of the matrix pore. Thus, the presence of the conductive polymer and the applied electric field can be combined to control the drug release rate at an optimal desired level. [Preview Abstract] |
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C1.00075: Morphology of Hole Injection Layers for Polymer Light Emitting Diodes Kristin Schmidt, Karen E. Sohn, Fabrice Amy, Ling Yang, Edward J. Kramer Hole injection layers (HIL) play important roles in improving the device efficiency and stability of polymer light emitting diodes (PLED) as they can enhance the hole injection from the ITO electrode. It was shown that thermal annealing of the PLEDs results in a remarkable improvement in the long-term stability of the device. These reports lead to the hypothesis that changes in the morphology of the phase separated mixture of the polymers in the HIL is responsible for this improvement. However, no experimental evidence of such morphological changes exists. To investigate the morphological changes during annealing we performed NEXAFS, SAXS and GISAXS experiments on thin films of different blends consisting of poly(3,4-ethylene dioxythiophene) (PEDOT) with either poly(fluoroethylene-r-fluoroether-sulfonic acid) (PFFSA) or polystyrene sulfonic acid (PSSA) before and after the annealing procedure. The results indicate that a surface reconstruction takes place during annealing so that Nafion or PSSA cover the polymer film to lower the surface energy. In addition, we found a poorly ordered structure with a mean spacing of 5 nm as spun cast which coarsens during the annealing procedure. [Preview Abstract] |
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C1.00076: Nanoparticle Tethered Perylene Tetracarboxylic Diimides as Novel Photo Harvesting Antennae Wenbin Zhang, Bin Sun, Hui Li, Matthew Panzner, Wiley Youngs, Roderic Quirk, Stephen Cheng Shape-persistent, well-defined, incompressible nano objects, such as polyhedral oligomeric silsequioxane (POSS) and C60, have been connected covalently to perylene tetracarboxylic diimide (PDI) to give a series of nanoparticle tethered PDI molecules, which could self-assemble into various ordered structures. For example, POSS end-capped PDI, namely POSS-PDI- POSS, grows single crystal lamellae of dimensions up to the centimeter scale in length. The crystal structure has been determined to be triclinic with a = 1.14 nm, b = 2.09 nm, c = 2.31 nm and $\alpha$ = 89.9$^{\circ}$, $\beta$= 81.9$^{\circ}$, $\gamma$= 82.3$^{\circ}$. It shows that POSS forms bilayers in the crystal separated by PDI dimer molecular planes along the c axis. The self-assembly of the asymmetric POSS-PDI-C60 is even more intriguing. It gives single crystals with alternating POSS and C60 layers separated by PDI planes, which holds promising applications as photo harvesting antennae in photovoltaics. Our results show that nanoparticles could interplay with the strong p-p interaction and assist the self- assembly to ordered structures. [Preview Abstract] |
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C1.00077: Highly Ordered Phases in Electrochemically Deposited Poly(3,4-ethylenedioxythiophene) (PEDOT)---LiBr Jinghang Wu, Sarah Spanninga, David Martin Poly(3,4-ethylenedioxythiophene) (PEDOT) is a widely used $\pi $-conjugated polymer of considerable current interest for a variety of different applications such as biosensors, antistatic layers, electroluminescent devices, and hole injection layers in organic light emitting diodes and photovoltaics. These films have high conductivity, as well as thermal and chemical stability. PEDOT films prepared by chemical or electrochemical polymerization with different counter ions have shown different levels of modest order and crystallinity, typically with limited molecular orientation and relatively small crystallites. We have developed methods for preparing highly ordered phases by the electrochemical polymerization of PEDOT onto polycrystalline conducting substrates with LiBr as the counterion. The polymerizations are conducted at room temperature from aqueous solution. These phases have ordered crystalline domains that are hundreds of microns in size, and are uniformly birefringent. The structure of the ordered phase was characterized by optical and electron microscopy, X-ray diffraction, as well as infrared and X-ray photoelectron spectroscopy. [Preview Abstract] |
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C1.00078: Sensitivity Enhancement of PEDOT-PSS towards CO by Zeolite ZSM-5 Additive Pojjawan Chanthaanont Polymer-based gas sensors have received considerable interest in recent years, due to their gas sensing ability through the electrical conductivity changes when exposed to gases. In our research, poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid), PEDOT-PSS, was synthesized via the oxidative polymerization and zeolites were used as selective microporous adsorbent to improve selectivity and sensitivity of the sensors. PEDOT-PSS were fabricated with zeolites by dry mixing and compressed to form PEDOT-PSS/zeolite composites. Zeolites ZSM-5 were chosen to investigate the effect of Si/Al mole ratios of zeolite on the electrical conductivity sensitivity response of PEDOT-PSS{\_}1:1/zeolite ZSM-5 composites when exposed to CO. The electrical conductivity sensitivity of PEDOT-PSS{\_}1:1/zeolite composites towards CO negatively increases with decreasing Si/Al mole ratios of zeolite ZSM-5. The highest electrical conductivity sensitivity response is obtained from PEDOT-PSS{\_}1:1/ZSM-5(Si/Al = 23). [Preview Abstract] |
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C1.00079: Flexible Field Emission Devices Sunny Sethi, Ali Dhinojwala We report synthesis of flexible field emission devices using patterned and non-patterned vertically aligned carbon nanotube arrays and use of such devices to induce phosphorescence. Carbon nanotube is known to have excellent electron emitting properties. On macroscopic scale, emission current density is much less than that for a single nanotube for reasons like screening effect and non uniform emission. Here, we report a very unique way to fabricate flexible field emission devices using partially entrapped aligned nanotubes in an elastomer as cathode. Using this process not only helps in fabricating a flexible geometry but also helps in the reduction of screening effect, thus increasing the emission efficiency. Emission current for these devices was studied with respect to the area and total perimeter for patterned nanotubes. These studies help to understanding the mechanism to translate nanoscopic emission to a macroscopic scale. [Preview Abstract] |
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C1.00080: Effect of light attenuation on motion of photo-responsive polymer gels Pratyush Dayal, Olga Kuksenok, Anna C. Balazs Nature has found an efficient way to utilize chemical reactions to produce mechanical work. Whenever the need for energy arises, the chemical reactions in our body produce energy, which is used to generate mechanical response. Scientists have been trying to replicate the same functionality in man-made systems. One of the recent approaches couples the Belousov-Zhabotinsky (BZ) reaction and the mechanical properties of the gel to produce self-sustained oscillations. To study the effect of light on the mechanical behavior of the gel, we use our recently developed 3D gel lattice spring model (gLSM) which couples the BZ reaction kinetics to the gel dynamics. In order to include the effect of the polymer on the reaction kinetics, the Oregonator model for the photo-sensitive BZ reaction was modified. Using modeling and simulations, we have been able to control gel's shape and its locomotion using light as an external stimulus. Here we show that the intrinsic non-homogeneity in light intensity, created by gel can induce autonomous motion of the gel away from light. [Preview Abstract] |
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C1.00081: Watching Nanoparticles Move through Polymers Juan Guan, Bo Wang, Stephen Anthony, Sung Chul Bae, Steve Granick Several recent experiments show that the Stokes-Einstein equation used to describe particle diffusion is violated when nanoparticles are surrounded by polymer chains. In some systems, particles move faster; in others, more slowly, depending on the size of the probe. It is generally agreed that the relative timescale for a polymer chain to relax and a nanoparticle to diffuse the size of a polymer chain are what matter. In this work, we embed fluorescently-labeled nanoparticles within polymer solutions and use single-particle tracking to understand the relative motions of the two. A unique aspect is that we track motions not just of the nanoparticles but also those of the polymer chains in which they are embedded. The worst-case resolution of 30 nm in nanoparticle relative position is improved when slow motions improve the signal-to-noise. [Preview Abstract] |
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C1.00082: An emerging theoretical picture of yielding for entangled polymeric liquids undergoing sudden deformation and flow Shi-Qing Wang, P.E. Boukany, S. Ravindranath, Y.Y. Wang, X. Li Recent particle-tracking velocimetric observations coupled with conventional rheological measurements have offered us a window to peek into processes responsible for a whole family of phenomena in entangled polymeric liquids. At a high rate of deformation imposed suddenly, entangled liquids can only respond like a solid and must undergo yielding before eventual flow is to take place. Until recently, how such a yielding process produces the observed scaling characteristics of the stress overshoot has remained elusive. More surprising and perplexing to many is that an elastic yielding process can also occur after cessation of any further external deformation. These experimental observations have provided the essential ingredients in the emerging theoretical picture of polymer deformation and flow. [Preview Abstract] |
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C1.00083: Gas Diffusion and Free Volume Behavior of Ethylene Vinyl Alcohol Copolymers: Effect of Hydrogen Bonding Interaction Justin Brandt, Sergei Nazarenko, Brian Olson, Alexander Jamieson The main objective of this work was to develop fundamental understanding of oxygen transport in a broad range of EVOH copolymers as it is related to free volume characteristics and hydrogen bonding interaction. FTIR was used to directly characterize H-bonding network as a function of copolymer composition and temperature. Positron annihilation lifetime spectroscopy (PALS) was used to study free volume behavior. The measure of intermolecular interaction, cohesive energy density, was calculated through group contribution methods and also obtained using molecular dynamics computer simulations. Oxygen transport characteristics of the copolymers, i.e. permeability, diffusivity, and solubility were measured at various temperatures, and the apparent activation energy parameters calculated. [Preview Abstract] |
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C1.00084: The Viscoelastic Bulk Modulus: Effect of Crosslink Density Jiaxi Guo, Sindee Simon The pressure relaxation response is measured at various temperatures in the glass transition region for two polycyanurate networks of differing crosslink density using a pressurizable dilatometer. Master curves are formed by the time-temperature superposition theory using vertical shifts to account for the temperature dependence of the bulk moduli. The results show that the pressure relaxation response has a small dependence on the crosslink density of the polycyanurate. However, the horizontal and vertical shift factors show a similar dependence on temperature when plotted as the departure from Tg, i.e. as T-Tg. The horizontal shift factors also agree well with those from the shear viscoelastic response. The relaxation spectra obtained from the pressure relaxation measurements will also be compared to those from shear stress relaxation experiments, and the validity of Leaderman's hypothesis that the bulk and shear responses arise from different molecular mechanisms will be discussed. [Preview Abstract] |
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C1.00085: Adhesion Behavior of Non-planar Wrinkled Surfaces Santanu Kundu, Ravi Sharma, Alfred Crosby Topological patterns on polymer surfaces can be used to significantly alter the surface properties, such as adhesion and contact angles. Conventional patterning methods, including photo- and imprint lithography, are difficult to apply to non planar surfaces. Surface wrinkling induced by swelling of a soft substrate constrained by a stiff, thin surface layer offers an attractive approach. Using this method, surface patterns of various length scales over a large area on curved geometries were obtained. Controlling the thickness of the stiff layer (silicate) on a soft foundation (polydimethylsiloxane elastomers) and the strain conditions, amplitude and wavelength of the wrinkles were varied. We quantified the effect of wrinkle morphology on the adhesion of non-planar substrates. [Preview Abstract] |
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C1.00086: Microvoid formation and strain hardening in highly cross-linked polymer networks Debashish Mukherji, Cameron Abrams Highly cross-linked polymer (HCP) networks are becoming increasingly important as high-performance adhesives and multifunctional composite materials. Because of their cross-linked molecular architectures, HCP's can be strong but brittle. One key goal in improving the performance of HCP is to increase their toughness without sacrificing their strength. We use molecular dynamics simulations to study the mechanical properties of HCPs. We observe strain hardening in HCP glasses under tensile deformation. We show that formation of micro-voids, without bond-breaking, constitutes the microscopic origins of strain hardening. Micro-void-based strain hardening is not observed in a separate model by imposing a tetrahedral bond angle constraints. Strain hardening makes HCP networks ductile, thus indicating that flexible cross-linkers may be a possible means to control toughness of an HCP without sacrificing its strength. [Preview Abstract] |
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C1.00087: Quantification of Molecular and Nanostructural Topology Ramnath Ramachandran, Gregory Beaucage We have recently derived a method for the description of complex molecular and nanostructural topologies based on a statistical analysis. The method has been applied to a wide range of materials from long chain branched polyolefins, hyperbranched polymers, star polymers, H-branched polymers to cyclics, biopolymers, and branched nanostructured aggregates. This method, when applied to neutron scattering data from dilute polymer solutions, yields the mole fraction of a structure involved in long chain branching, the branching density, and the average branch length. Moreover, quantitative measures of the convolution or tortuosity of the structure and the connectivity of the molecules can be made, opening a new window for our understanding of complex molecular topologies. When applied to neutron scattering the approach is applied to the chain-scaling regime at low to moderate values of the scattering vector. At high scattering vector the Kuhn length is observed that has been shown to be directly related to short chain branching in polyolefins. By combining information of short and long chain branching a topological map of complex molecular structure becomes possible. The method is quite generally applicable. This understanding has recently been applied to model long-chain branched polyethylene. [Preview Abstract] |
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C1.00088: Computer simulation study of solvent quality and reaction geometry on controlled radical polymerization Salomon Turgman, Jan Genzer Bulk- and surface-initiated controlled radical polymerizations are simulated using a stochastic Monte Carlo algorithm by following the bond-fluctuation model scheme and an attractive potential acting among bonded monomer beads. Specifically, we investigated the changes in polymer molecular weight and molecular weight polydispersity index (PDI) due to conformational variations of the chains that occur upon altering solvent quality. Variations in reaction geometry, temperature, initial monomer and initiator concentration, probability of initiation, initial probability of monomer addition, probability of termination, fraction of living polymers and their lifetime were studied. Synergistic effects among these parameters and the geometry of the reaction were also explored. Preliminary results suggest that polymerization in poor solvent quality solvents result in shorter polymers and increased molecular weight PDI. [Preview Abstract] |
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C1.00089: Borylation of Polystyrene: Random Blocky vs. Truly Random Copolymers Wayne Powers, Zachariah Norman, Chang Ryu, Chulsung Bae, Jan Genzer Borylated PS with tuned blockiness of borylated styrene segments has been synthesized in methylcyclohexane, using bis(pinacolato)diboron as the borylating agent, and 4,4'-di-tert-butyl-2,2'-bipyridine and bis(1,5-cyclooctadiene)diiridium(I) dichloride as catalysts. By performing the borylation reaction below and above the theta temperature of PS in methylcyclohexane, 70 degrees Celsius, the co-monomer sequence distribution in the borylated PS changed from random-blocky to random, respectively. The ``chemical coloring'' is carried out at low PS concentration in order to ensure that individual chains do not coagulate during the borylation at temperatures below the theta temperature. NMR, SEC, cloud point measurements, and adsorption-based interaction chromatography are used to characterize the properties of borylated PS and elucidate the effects of blockiness on solubility and surface adsorption. [Preview Abstract] |
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C1.00090: Phase behavior study of polystyrene and deuterated polystyrene in alkyl-cyclohexanes Zachariah Norman, Wayne Powers, Chang Ryu To advance the controlled chemical modification of polystyrene (PS) and deuterated polystyrene (dPS) in solution, the phase behavior of PS and dPS in alkyl-cyclohexane solvents has been studied. Cloud point measurements have been performed by a house-made turbidity instrument using a picolog thermistor and a laser with a photoelectric cell converted to interface with a picolog TH-03 three channel thermistor converter. Solution phase diagrams for molecular weights of PS varying from 67 thousand to 1.8 million have been presented for methyl cyclohexane, propyl cyclohexane, isopropyl cyclohexane, butyl cyclohexane and isobutyl cyclohexane for the measurements of critical solution temperatures as a function of molecular weight. The theta temperature of polystyrene in each of these solvents has been estimated through extrapolation from the molecular weight dependence of the critical temperatures from the cloud point measurements. [Preview Abstract] |
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C1.00091: Zero-dimensional organic nanoparticles via copolymer directed self-assembly Dequan Xiao, Kunhua Lin, Qiang Fu, Qinjian Yin Inspired by inorganic nanomaterials, low-dimensional organic nanostructures have emerged as a new field of nanomaterials with the presence of size-dependent physical properties. Here, we report a zero-dimensional organic nanoparticles formed by copolymer-directed self-assembly. The nanoparticles are thermally stable up to $\sim $200$^{o}$C. The nanoparticle morphologies are probed by TEM and SEM images. The quantum confinement effect is suggested by the appearance of strongly broadened Raman shift spectra. By proof-of-principle quantum chemical calculations, we suggested that both vibration-vibration and electron-vibration coupling at nanoscale can cause the Raman broadening. The present organic nanoparticles provides a new class of nanostructures to exploring size-dependent physical properties. [Preview Abstract] |
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C1.00092: Capillary thinning and break-up of hydrogel-elastomer composites Yinan Lin, Darrell Reneker The development of a filament stretching rheometer with a high magnification and high speed digital imaging system enabled real-time video observation of the extensional behavior of the hydrogel-elastomer complex fluids. Under a motor-controlled process of tip-plate separation, ethanol solutions of polyurethane with superabsorbent particles, which can be electrospun into nanocomposite nanofibers, evolved in profile. The rapidly shrinking jet diameter was measured from video images. As in extensional rheology of homogeneous polymer solutions, the elongational viscosity and the relaxation time calculated from the time dependence of midpoint diameters define a two-dimensional operating diagram for capillary self-thinning and capillary break-up.\footnote{Rodd, L.E.; Scott, T.P.; Cooper-White, J.J.; McKinley, G.H. Capillary break-up rheometry of low-viscosity elastic fluids. Applied Rheology, 2005, 15(1), 12-27.} [Preview Abstract] |
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C1.00093: Ultrafast Nanocalorimetry and Superheating in Linear Polymers Christoph Schick, Alexander Minakov, Andreas Wurm To study phase transition kinetics on submillisecond time scale a set of new membrane gauges for ultrafast scanning nanocalorimetry were constructed. Controlled ultrafast cooling, as well as heating, up to 10E6~K/s was attained. The characteristic rate R0 corresponding to the quasi-static limit of the temperature change in the membrane-gas system was determined. The rate R0 equals 10E5~K/s for the different gauges in helium gas. The method was applied for the measurements of the superheating phenomenon in a set of linear polymers iPS, PBT, PET, iPP. A power law relation between the superheating and the heating rate was observed in the broad range 10E-2~--~10E4~K/s of the heating rates. A limiting superheating of about 10{\%} of the melting temperature was observed at rates above 10E4~--~10E5~K/s. This limit depends on the annealing conditions before the sample melting. The observed superheating limit, as well as the power law, can be accounted for the internal stresses induced by the superheating near the crystalline-amorphous interface in semicrystalline polymers, which are related to the thermal expansion gradients inherent for a semicrystalline material. [Preview Abstract] |
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C1.00094: Intermolecular Interactions in Polymer/C60 Blends Peter Mirau, Marjan Lyons Solid-state NMR and x-ray scattering are used to study intermolecular interactions in blends of C60 with polystyrene, poly(9-vinyl carbazole) and poly(ethylene oxide). Miscible C60 blends prepared by solution precipitation with polystyrene and poly(9-vinyl carbazole) are purple in color, show intermolecular C60-polymer cross polarization and do not show the scattering peaks from C60 crystallites. In contrast, phase separation is observed in poly(ethylene oxide) blends. The C60 dynamics in the miscible blends are measured using the chemical shift anisotropy filter NMR pulse sequence, and the results show that the C60 in the rotating rapidly enough at ambient temperature to average the 18 kHz-wide chemical shift anisotropy line shape. Blending with C60 has no effect on the polystyrene dynamics as measured by the carbon spin-lattice relaxation times but leads to a narrowing of the proton line shapes as measured by 2D wide line correlation NMR. These results show that C60 interacts weakly with polymers, and the implications for weak interactions between polymers and carbon nanotubes are considered. [Preview Abstract] |
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C1.00095: Effect of Hydrophobicity on the Adsorption of Human IgG to Thiolated Gold Surfaces as Characterized by SPR Kristen Duthie, Adele Poynor In order to enhance our understanding of the role of hydrophobicity in nonspecific human immunoglobulin G [hIgG] surface interactions, we studied the adsorption of hIgG to thiol self assembled monolayers [SAMs] on gold using surface plasmon resonance [SPR]. The hydrophilic and hydrophobic SAMs had hydroxyl and methyl terminal groups respectively. Protein adsorption to thiolated surfaces was measured looking at relative SPR resonance angles. [Preview Abstract] |
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C1.00096: Understanding Rubber Friction in the Presence of Water Using Sum Frequency Generation Spectroscopy Ping-Yuan Hsu, Kumar Nanjundiah, Ali Dhinojwala Infrared-visible sum-frequency-generation spectroscopy (SFG) was used to study the molecular structure of water between a poly (dimethylsiloxane)(PDMS) and a sapphire substrate. The observation of SFG peaks associated with the dangling surface hydroxyl groups (3690 cm$^{-1})$ and water bands (3000-3400 cm$^{-1})$ indicates that the contact spot between the PDMS lens and the sapphire substrate is heterogeneous. Within the contact spot there are regions where the methyl groups of the PDMS chains are in direct contact with the surface hydroxyl groups on the sapphire substrate. In the other regions, a thin water layer is trapped between the two surfaces with spectral features that are different from that of the unconfined water next to the sapphire or the PDMS surface. The higher adhesion and friction values observed in these experiments are consistent with the hypothesis that the contact spot is heterogeneous. These results have important implications in understanding the sliding behavior of wet, deformable hydrophobic materials on hydrophilic substrates. We have extended this experimental technique to study oil/water/solid interfaces. [Preview Abstract] |
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C1.00097: Protected Plasmonic Nanostructures for High Resolution Chemical Imaging using Tip Enhanced Raman Spectroscopy Rebecca Butt, Carlos Barrios, Andrey Malkovskiy, Alexander Kisliuk, Alexei Sokolov, Mark Foster Tip enhanced Raman spectroscopy (TERS), an emerging technique that combines optical microscopy and scanning probe microscopy, provides the sensitivity and selectivity necessary for high-resolution chemical imaging of polymer surfaces. An unprecedented 20 nm lateral resolution for the chemical imaging has been achieved. Unfortunately, the fragile plasmonic structures used to enhance the electric field are prone to mechanical, chemical, and thermal degradation. Developing robust noble metal nanostructures with stable plasmonic resonance is essential to reliable high resolution chemical imaging. Covering the metal layer with organic and inorganic ultrathin coatings is being investigated to extend the plasmonic activity of the engineered nanostructures. Addition of an ultrathin aluminum oxide (Al$_{2}$O$_{3})$ coating to a silver-coated scanning probe microscopy tip for TERS significantly improves plasmonic structure stability without sacrificing the initial TERS efficiency. This ultrathin coating provides wear resistance and stops chemical degradation responsible for the loss of signal enhancement. [Preview Abstract] |
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C1.00098: Infrared and optical spectroscopy study of UHMWPE polymers M.S. Wolf, J.N. Morvan, S.V. Dordevic, N. Stojilovic Ultra-High Molecular Weight Polyethylene (UHMWPE) is very often the material of choice for the bearing surfaces of most hip and knee implants primarily due to its low friction combined with good toughness and abrasion resistance. We investigate optical properties of biomedical-grade UHMWPE GUR 1020 powders and sheets using infrared and UV-vis spectroscopy and compare results with those from industrial grade samples. In addition, we use X-ray diffraction spectroscopy to monitor the changes in crystal structure of these polymers as a function of temperature. Finally, we deliberately oxidize and subsequently characterize these materials since the oxidation of UHMWPE bio- implants is believed to be responsible for their failure in vivo. [Preview Abstract] |
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C1.00099: ABSTRACT WITHDRAWN |
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C1.00100: A spectroscopic ruler to measure chain conformations at the solid-liquid interface Subhalakshmi Kumar, Janet Wong, Sung Chul Bae, Steve Granick There do not appear to exist prior measurements of the conformations of polymers adsorbed to dilute coverage at the solid-liquid interface, in spite of abundant theoretical predictions. Here direct information is obtained by monitoring the fluorescence energy transfer between dyes located at the two ends of adsorbed polymer chains. The basic idea is that the farther the chain ends are spaced, the less efficient, and slower, is energy migration between these dyes. It occurs on the nanosecond time scale and is measured here by time-correlated single photon counting. From corresponding experiments performed with the same polymer chains labeled at one sole end, the contribution of rate of energy transfer to rotational anisotropy is decoupled from intrinsic rotational motion of the dyes themselves. [Preview Abstract] |
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C1.00101: Vibrational Relaxation and Dynamical Transitions in Atactic Polystyrene Hanqing Zhao, Yung Park, Paul Painter Infrared bands and Raman lines recorded in the frequency domain have a counterpart in the time domain in the form of time-correlation functions, which are sensitive to molecular dynamics on the picosecond time scale. This is explored by calculating time correlation functions and their variation with temperature for the conformationally insensitive modes observed near 1601 cm-1 and 1583 cm-1 in the infrared spectrum of atactic polystyrene. The correlation functions were modeled by assuming that there is a fast relaxation process characterized by a single relaxation time that is inhomogeneously broadened by a slower process, also characterized by a single relaxation time. The fundamental mode, near 1583 cm-1, is inhomogeneously broadened, but the relaxation time calculated for this mode is sensitive to temperature as a result of anharmonic coupling to a combination mode. A change in the modulation of the 1583 cm-1 band becomes apparent about 10--20 degrees below the thermally measured Tg. Relaxation times at first increase then decrease and becomes negligible at temperatures near 180 degrees. These results are consistent with theories of the glass transition. [Preview Abstract] |
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C1.00102: Specific Heat Spectroscopy of Simple Chain Models Jonathan R. Brown, John D. McCoy, Douglas Adolf, Brian Borchers Molecular dynamics simulations were run on bead-spring polymer models. Small amplitude temperature variations were imposed, and energy response was monitored. The real and imaginary components of the frequency dependent specific heat were extracted. A low frequency peak is seen to develop at high packing fractions. The non-Debye parameter -- $\beta$ -- is seen to decrease as the glass transition is approached. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000. [Preview Abstract] |
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C1.00103: APPLICATIONS |
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C1.00104: Reversible hydrogen storage in LiBH4/CaH2 with NbF5. Jae-Hag Lim, Jae-Hyeok Shim, Young-Su Lee, Young Whan Cho, Joonho Lee Reversible hydrogen storage properties of 6LiBH4 + CaH4 composite have been investigated. 6LiBH4 + CaH4 composite with catalytic additives have been prepared using high-energy ball milling. Among various catalytic additives, the addition of NbF5 exhibits the lowest dehydrogenation temperature. During dehydrogenation, this composite is decomposed into LiH and CaB6 releasing about 9 wt pct hydrogen. The van't Hoff plot from the equilibrium pressures measured at different temperatures predicts that the equilibrium temperature under 1 bar of hydrogen is 582 K and the reaction enthalpy change is 56.5 kJ/mol H2. This is consistent with the results of thermodynamic calculation. Rehydrogenation of this composite is accomplished at 723 K under 100 bar of hydrogen after dehydrogenation, presenting a reversible hydrogen capacity of about 9 wt pct. [Preview Abstract] |
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C1.00105: LiBH$_{4}$+Ca(BH$_{4})_{2}$ composite system for hydrogen storage Ji Youn Lee, Yoonyoung Kim, Young-Su Lee, Jae-Hyeok Shim, Young Whan Cho, Dorthe Ravnsbæk, Torben Jensen, Yngve Cerenius LiBH$_{4}$ is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, dehydrogenation of LiBH$_{4}$ occurs above 400$^{\circ}$C, which limits its use in its pristine form. By mixing with Ca(BH$_{4})_{2}$, we have tried to lower the dehydrogenation temperature. The underlying design principle of this composite system is the recently proven reversibility of 6LiBH$_{4}$+CaH$_{2}$ composite and Ca(BH$_{4})_{2}$ itself. Using differential scanning calorimetry and in-situ synchrotron XRD measurement, we observed eutectic melting of (1-$x)$LiBH$_{4}+x$Ca(BH$_{4})_{2}$ at around 200$^{\circ}$C in a wide range of $x$. The decomposition characteristics and the hydrogen capacity of this composite vary with $x$, and at a certain value of $x$ we found that decomposition was finished below 400$^{\circ}$C showing more than 10 wt{\%} hydrogen capacity. Reversibility of this system was also confirmed. [Preview Abstract] |
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C1.00106: Nonlinear thermoelectric behavior in double-barrier quantum-dots Eric Hoffmann, Natthapon Nakpathomkun, Henrik Nilsson, Ann Persson, Lars Samuelson, Heiner Linke Thermovoltage in bulk material systems is to good approximation linear in applied temperature difference, $\Delta T$, with the constant of proportionality being the thermopower, $S$. However, this linear relationship does not necessarily hold true for nanoscale thermoelectrics[1]. Here we report on basic research which uses a single quantum dot as an example nanoscale system for studying nonlinear thermoelectric phenomena. Specifically, we show experimentally as well as theoretically that strong modulations in the transmission function of the quantum dot manifests into thermovoltages and thermocurrents which are not linear in $\Delta T$ at $\Delta T$ as small as $\Delta T/T = 0.1$. Quantum-dot thermometry[2] has been used to measure $\Delta T$. Understanding these nonlinearities is important for the development of thermoelectric materials that aim to exploit quantum phenomena. 1. J.M. Wang \textit{et al}, \textit{Nonlinear thermoelectric transport through a double barrier structure}, Mod. Phys. Lett. B, \textbf{20}, 215-223 (2006). 2. Hoffmann, E.A. \textit{et al}, \textit{Quantum-dot thermometry}, Appl. Phys. Lett. \textbf{91}(25), 252114 (2007) [Preview Abstract] |
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C1.00107: Thermopower measurements of arrays of trigonal bismuth nanowires: the density, mobility, and charge-sign of Bi surface carriers. Tito Huber, Ajibola Adeyeye, Tosin Odunfa, Alla Nikolaeva, Leonid Konopko, Ryan Johnson, Michael Graf We investigated the thermopower S of Bi nanowires with 20 nm $<$ diameter $<$ 200 nm) between 4 K and room temperature in well-characterized samples. Shubnikov-de Haas oscillations give evidence of light-effective-mass bulklike carriers, Dirac electrons and holes, and also high-effective-mass surface carriers. The latter are likely related to the surface states that are observed using ARPES of Bi surfaces (Hofmann, Prog. Surf. Sci. \underline {81}, 191 (2006)). Whereas the bulklike carriers's concentration decreases for decreasing diameter in accordance with theoretical predictions (Lin, Sun, and Dresselhaus, Phys. Rev. \underline {62}, 4610 (2000)) for the quantum-confinement-driven semimetal-to-semiconductor transition, the surface carrier concentration is relatively independent of diameter. S exhibits a trend from positive towards negative values as the diameter decreases from 200 nm to 35 nm. The measurements are interpreted in terms of the diffusion thermopower model. We find that the S of the semiconductor nanowires is dominated by surface electrons. [Preview Abstract] |
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C1.00108: Thermoelectric Figure-of-Merit of Nanostructured Silicon with a Low Concentration of Germanium Gaohua Zhu, Hohyun Lee, Yucheng Lan, Xiaowei Wang, Giri Joshi, Dezhi Wang, Jian Yang, Mildred Dresselhaus, Gang Chen, Zhifeng Ren The thermoelectric properties of nanostructured silicon (Si) with a low concentration of germanium (Ge) are investigated. A low concentration of Ge leads to a significant cost reduction of the final product since Ge is at least 100 times more expensive than Si. By using only 5 atomic {\%} Ge (Si$_{95}$Ge$_{5})$, we have achieved a thermoelectric figure-of-merit (\textit{ZT}) of 0.95, similar to the \textit{ZT} in the large grained Si$_{80}$Ge$_{20}$ alloy that is three times more expensive, and is almost four times that of the large grained bulk Si. The enhancement in the thermoelectric \textit{ZT} for the nanostructured Si$_{95}$Ge$_{5}$ is mostly due to the reduced thermal conductivity caused by phonon scattering at the increased grain boundaries and the Ge alloying effect. [Preview Abstract] |
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C1.00109: Thermoelectric and electronic properties of AgSbSe$_{2}$ Makram Qauder, Ravhi Kumar, Rama Venkat, Andrew Cornelius Cubic I-II-VI$_{2}$ semiconductors have been studied widely for potential thermoelectric applications by several groups [1]. Recent investigations show minimal thermal conductivity for AgBiSe$_{2}$ and AgSbTe$_{2}$ resulting from intrinsic phonon scattering process due to strong anharmonicity in bonding [2]. AgSbSe$_{2 }$is structurally similar to chalcogenides and crystallizes in the cubic structure at ambient conditions [3]. The thermoelectric figure of merit, Seebeck co-efficient and thermal conductivity were measured as a function of temperature from 10 K to 350 K. We have also measured the conductivity type, Hall co-efficient and carrier concentration at ambient conditions. We compare our results with its ternary analogues. [1]. C. Wood et al., Prog. Phys. 51 (1988) 459 [2]. D.T. Morielli et al., Phys.Rev.Lett., 101 (2008) 035901 [3]. Ravhi S. Kumar et al., J.Alloys and Compds., 285 (1999) 48 [Preview Abstract] |
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C1.00110: Thermoelectric properties of mechanically milled AgSbTe$_{2}$ SathishKumar Veeramalai, Ravhi Kumar, Seigi Yoneda, Andrew Cornelius AgSbTe$_{2}$ and AgBiTe$_{2}$ have gained much importance recently due to their low thermal conductivity and possible potential thermoelectric applications [1, 2]. AgSbTe$_{2}$ is the parent composition for the AgPbSb$_{18}$Te$_{20}$ high figure of merit thermoelectric alloy [3]. Crystalline size is one of the crucial parameters which affect the thermoelectric properties. In order to investigate the size effects we have ball milled AgSbTe$_{2}$ up to 4 hrs and measured the thermoelectric figure of merit, Seebeck co-efficient and thermal conductivity from 10K to 350 K for different milled samples. The results will be presented in detail. [1]. D.T. Morielli et al., Phys.Rev.Lett., 101 (2008) 035901 [2]. K. Wojciechowski et al., J. Phys.Chem.Solids., 69 (2008) 2748 [3]. K.F. Hsu et al., Science 303 (2004) 818 [Preview Abstract] |
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C1.00111: Enhanced Thermoelectric Figure-of-Merit in p-type Nanostructured Bismuth Antimony Tellurium Alloys Made from Elemental Chunks Yi Ma, Qing Hao, Bed Poudel, Yucheng Lan, Bo Yu, Dezhi Wang, Gang Chen, Zhifeng Ren In this study, we use the ball milling and hot press technique to make nanostructured bulk bismuth antimony telluride from elemental chunks of bismuth, antimony, and tellurium. We show that a peak ZT of about 1.3 in the temperature range of 75 and 100 \r{ }C has been achieved. The ZT improvement is caused mostly by the lower thermal conductivity. Transmission electron microscopy observations of the microstructures suggest that the lower thermal conductivity is mainly due to the increased phonon scattering from the increased grain boundaries of the nanograins, precipitates, nanodots, and defects. [Preview Abstract] |
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C1.00112: Thermoelectric properties of Yb$_{14}$MnSb$_{11}$ from first-principles J.-H. Song, M. Kim, A.J. Freeman The complex Zintl compound, Yb$_{14}$MnSb$_{11}$, has been recently given much attention as a high-performance thermoelectric due to its nearly twice the figure of metrit ($zT$) of p-type SiGe at high temperatures ( $>$ 900K)\footnote{S. R. Brown et al., Chem. Mater. {\bf 18}, 1873 (2006)}. Its high $zT$ can be attributed to low lattice thermal conductivity combined with a large Seebeck coefficient ($S$) and high electrical conductivity ($\sigma$) at high temperatures. To understand the thermoelectric properties of Yb$_{14}$MnSb$_{11}$ and to find possible improvements for thermoelectric performance, we have investigated its electronic structures and electrical transport properties ($S$,$\sigma$) using the highly precise FLAPW method\footnote{Wimmer, Krakauer, Weinert, Freeman, Phys. Rev. B {\bf 24}, 864 (1981)} with the local spin density approximation (LSDA) and LSDA+U\footnote{Shick et al, Phys. Rev. B {\bf 60}, 10763, (1999)} methods. We have found significantly different spin moments of Mn between the LSDA and the LSDA+U methods. Also, we determined the anisotropy of the conductivity. The linear temperature behavior of the Seebeck coefficients will be discussed from and related to the electronic structures. [Preview Abstract] |
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C1.00113: Terahertz mixing in AlGaAs/GaAs 2DEG hot-electron microbolometers at liquid nitrogen temperatures Kai Wang, Rahul Ramaswamy, Matthew Bell, Andrei Sergeev, Aleksandr Verevkin, Gottfried Strasser, Vladimir Mitin, Darold Wobschall We investigate THz mixing based on electron heating of two-dimensional electron gas (2DEG) in semiconductor mirobolometers. The 2DEG microbolometers were fabricated from AlGaAs/GaAs heterostructures and have dimensions of 3 - 20$\mu$m between the Ohmic contacts and 50µm in width. Significant efforts were made to get low Ohmic contact resistance for effective coupling to the THz antenna and to the intermediate frequency amplifier. We investigate mixing at subTHz and THz frequencies. In the sub-THz range, a W-band Gunn diode operating at 82 GHz was used as a local oscillator. In the THz range we employ a Quantum Cascade Laser (QCL). The QCL is positioned in close proximity at different locations to optimize electromagnetic coupling. Experiments at sub-THz and THz frequencies give consistent data, which provide evidence that electron-heating is the major mechanism of mixing. Mixing experiments allow us to evaluate the mixer gain bandwidth and conversion loss. The results show that a heterodyne receiver, which combines AlGaAs/GaAs 2DEG hot- electron mixer with a QCL as the local oscillator, has great prospects for THz sensing with high spectral resolution and wide spectral bandwidth. [Preview Abstract] |
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C1.00114: Design and operating regimes of quantum-dot photodetectors for room temperature operation Li-Hsin Chien, Andrei Sergeev, Vladimir Mitin To optimize quantum dot photodetectors for room temperature operation, we develop a detailed model of kinetic and transport processes in quantum dot structures. The model takes into account electron-phonon and electron-electron interactions in quantum dots and in the inter-dot space. We also consider formation of potential barriers around dots due to electrons captured into dots. Monte-Carlo method is used to investigate effects of the electric field on electron kinetics and transport. Results of our simulations demonstrate that electron capture process can be substantially suppressed due to barriers and specific operating regimes. Design and operating regimes provide wide possibilities for manageable (adaptive) kinetics of photoelectrons, which in turn allows significant improvements in responsivity (photoconductive gain) and noise characteristics (detectivity) of photodetectors. [Preview Abstract] |
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C1.00115: Polarization dynamics within the polarization-switching hysteresis loop of VCSELs Jin-Ing Tsai, Wang-Chuang Kuo, Chuan-Pi Hsu, Da-Long Cheng, Tsu-Chiang Yen In the L-I curve of some VCSELs, distinct polarization switchings (PS) with a hysteresis loop are observed. In this research, PS at the center of the hysteresis loop was conducted by a manipulation of the operation conditions, enabling the polarization dynamics within the loop to be investigated. Experimental results revealed that the temporal behaviors of PS were different at the two ends of the PS hysteresis loop. A set of rate equations based on a linear gain model was employed to understand the polarization dynamics involved. Simulations indicated that the polarization dynamics could be attributed to the variation of the polarization-resolved gains within the PS hysteresis loop. More investigated results will be presented in the report. [Preview Abstract] |
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C1.00116: Negative index of photonic crystal infiltrated with functional materials Ryotaro Ozaki, Hiroshi Moritake, Katsumi Yoshino, Anvar Zakhidov We study 2D or 3D photonic crystals infiltrated with functional materials such as liquid crystal, or a highly polarizable medium. Liquid crystal molecular orientations in photonic crystals strongly influence the light propagation. We reveal that the negative index of the photonic crystal depends on the liquid crystal molecules, which can be tuned by external electrical field or temperature. On the other hand, we also study negative index of photonic crystal with a highly polarizable medium having a frequency dependence of permittivity. Around anomalous dispersion frequency range, the photonic crystal with a highly polarizable medium shows unique characteristics due to coupling with polariton. [Preview Abstract] |
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C1.00117: First-principles study of atomic and electronic structures of coumarin dyes adsorbed on titania surface Hiroyoshi Momida, Takahisa Ohno The coumarin dyes are good photo-sensitizers for the dye-sensitized solar cell due to the wide absorption energy range of the visible light and the fast photo-induced charge injection from the dyes to the titania. The dyes are adsorbed on the Ti sites via the carboxyl group, but detailed adsorbed structures and effect on the electronic structures are unknown. We performed the first-principles calculations of the coumarin343 and NKX2311 dyes adsorbed on the rutile titania (110) for three types of the contact structures. We found that the bidentate type is energetically more stable than the ester-like and molecular types. The HOMO-LUMO gap of the NKX2311 is smaller than that of the coumarin343, consistent with the experiments. This work was partly supported by the RISS project in IT program and a Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese Government. [Preview Abstract] |
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C1.00118: ABSTRACT WITHDRAWN |
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C1.00119: Coiled-Coil Helix-Bundle Peptide-Polymer Conjugates Jessica Shu, Cen Tan, Yu-Ja Huang, Ting Xu Peptide-polymer conjugates have the potential to combine the advantages of synthetic polymers and peptides and may lead to hierarchically ordered, functional soft materials. Maintaining the structure and function of the peptides upon polymer conjugation is essential. Here, we present a solution study of three families of peptide-polymer conjugates to systematically investigate the effect of conjugated polymer on the peptide's secondary and tertiary structures using a photoactive, heme-binding 4-helix bundle. In particular, we focused on the effect of the peptide-polymer conjugate's architecture (side conjugation versus end conjugation) and the hydrophobicity of the synthetic polymer (polystyrene versus poly(ethylene glycol)). Upon attachment of polymer to the peptide N-terminus, the secondary structure was destabilized and the functionality within the bundle was inhibited. The effect was less dramatic with PEG conjugation in comparison to the hydrophobic PS. Upon attachment of PEG to the exterior of the coiled-coil helix bundle, the peptide secondary and tertiary structures were stabilized, and the functionality within the bundle was preserved. [Preview Abstract] |
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C1.00120: COMPLEX STRUCTURED MATERIALS |
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C1.00121: Anisotropical glassy properties--a theoretical model Dragos-Victor Anghel, Dmitry Churochkin We apply the model introduced in Phys. Rev. B {\bf 75}, 064202 (2007), to calculate the anisotropy effects in the interaction of two level systems with phonons and elastic waves in disordered crystals. In this model, the interaction strength depends on the orientation of the TLS with respect to the strain field through a $6\times6$ symmetric tensor of deformation potential parameters, $[R]$. The structure of $[R]$ is similar to the structure of the tensor of elastic stifness constants, in the sense that they are determined by the same symmetry transformations. In this way, we emphasize the anisotropy of the interaction of elastic waves with the ensemble of two-level systems in disordered crystals. We also point to the fact that the ratio $\gamma_l/\gamma_t$ has a much broader range of allowed values in disordered crystals than in isotropic solids. \\[4pt] {\bf Related publications:}\\ [0pt] [1] D. V. Anghel and D. Churochkin, Europhys. Lett. {\bf 83}, 56004 (2008).\\[0pt] [2] D. V. Anghel and D. Churochkin, Phys. Rev. B {\bf 78}, 094202 (2008). [Preview Abstract] |
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C1.00122: Brillouin light scattering measurements of high modulus glasses produced by physical vapor deposition Kenneth L. Kearns, Tim Still, George Fytas, M. D. Ediger Physical vapor deposition was used to create low enthalpy, high density glasses of indomethacin (IMC). Brillouin light scattering was employed to measure the longitudinal and transverse sound velocities of the stable vapor-deposited glass, supercooled liquid, and the ordinary glass formed from cooling the liquid. Both Young and shear high frequency moduli were approximately 20{\%} greater for the vapor-deposited sample as compared to the ordinary glass. The isothermal transformation of the high modulus glass to the supercooled liquid was 10,000 times slower than the structural relaxation time of the supercooled liquid at T$_{g}$+10 K. Additionally, the spectrum for both phonon polarizations broadens during the isothermal transformation, which suggests that the stable vapor-deposited glass and supercooled liquid coexist for long periods of time at a single temperature. [Preview Abstract] |
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C1.00123: Kinetics of Gold Nanoparticle Formation Ashley Cetnar, Sreeram Cingarapu, Kenneth Klabunde My objective was to understand the chemical details of an important method of producing monodisperse nanoparticles. The nanoparticles synthesized are gold ligated by thiol ligands. The nanoparticles average 5 nanometers in diameter with about 5000 gold atoms and 600 thiol ligands per particle. The two methods used to prepare the particles are the solvated metal atom dispersion method and the inverse micelle method. Both processes break the gold into nanoparticles and are ligated to protect the particles from aggregation. After the nanoparticles are produced they are made monodisperse by digestive ripening. Digestive ripening occurs when the polydispersed product is refluxed over time. During this illusive procedure the multi-sized particles all become uniform in size. During reflux, the samples are analyzed by UV spectroscopy. The spectroscopy reveals a plasmon emitted from the nanoparticles at 530 nm from a standard sample of 1:30 gold to ligand ratio. During the reflux procedure, the gold Plasmon peak narrows and the peak becomes steeper. Over time, the peak of the Plasmon seems to be red shifted. As the amount of ligand was varied the gold plasmon appeared to shift. [Preview Abstract] |
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C1.00124: Atomistic Mechanism of Catalyzed Growth of Silicon Nanowire Seunghwa Ryu, Wei Cai Understanding the growth mechanism of semiconductor nanowire(NW) from catalyzed droplet is important for better control of the shape and growth speed of NWs by chemical vapor deposition through the Vapor-Liquid-Solid (VLS) process. To accurately describe the interatomic interaction between gold and silicon atoms, we developed a Au-Si binary potential based on modified embedded-atoms method (MEAM), which is benchmarked against the experimental binary phase diagram and mixing enthalpy. Advanced sampling method is employed to obtain the critical island at the liquid(Si Au alloy) - solid(silicon nanowire) interface. The dependence of the nucleation rate of the critical island on temperature and Si supersaturation is compared with experimentally observed NW growth rate and conditions of growth anormally such as kinking. [Preview Abstract] |
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C1.00125: Self-Assembly of CdSe and PbS/PbSe Quantum Dots on Gold and other Surfaces Using Dithiol Functionalization Jeffrey Schwartz, Miaoxin Zhou, Anvar Zakhidov CdSe and PbS/PbSe quantum dots were deposited onto gold surfaces functionalized with self-assembled monolayers of dithiol molecules. Separately, quantum dots were treated in solution with dithiols to create linked quantum dot chains and then deposited onto gold and other surfaces. Analysis of the samples via atomic force microscopy and scanning tunneling microscopy was performed in order to characterize the samples and determine the ordering and level of coverage of the quantum dots on the substrate surface. We show that using benzenedithiols allows for increased electrical conductivity of self-assembled quantum dot layers and found the optimal conditions for maximum coverage and best ordering. This research is done with the intention of using linked, ordered, quantum dot chains in polymer solar cell devices, and embedding quantum dots inside opals and inverse opals to create negative index materials. [Preview Abstract] |
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C1.00126: Energetic and structural analysis of 102-atom Pd-Pt nanoparticles Rafael Pacheco-Contreras, Alvaro Arteaga-Guerrero, Dora Julia Borbon-Gonzalez, Alvaro Posada-Amarillas, J. Christian Schoen, Roy L. Johnston We present an extensive study of the structural and energetic changes of 102-atom \textit{Pd}$_{m}$\textit{Pt}$_{102-m}$ nanoparticles as a function of composition $m$, where the interatomic interactions are modeled with the many-body Gupta potential. The minimum energy structures are obtained through a genetic algorithm. The excess energy is calculated, as well as the pair distribution function $g(r)$. The radial distribution of the atoms is computed for each composition; the result indicates a multi-layer segregation for some compositions, with a shell growth sequence as follows: a core with a small number of Pd atoms is followed by an intermediate shell of Pt atoms and the external shell consists of Pd atoms. A region where Pd and Pt atoms are mixed is observed between the outermost and intermediate shells. Furthermore, the pure \textit{Pd}$_{102}$ and \textit{Pt}$_{102}$ nanoparticles have the same structure, while a variety of different structures are observed for the bimetallic clusters. [Preview Abstract] |
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C1.00127: Electronic Structure Models of Phosphorus Delta-Doped Silicon Oliver Warschkow, Damien J. Carter, Nigel A. Marks, David R. McKenzie We report a full density functional theory treatment of phosphorus delta-doped silicon. A particular difficulty of this system is associated with the large delocalization lenghts of donor electrons in the host. To this end, we use large asymmetric unit cells with up to 800 atoms, and we obtain first-principles doping potentials, band energies and donor electron distributions. We additionally examine the electronic effects of overlapping doping potentials when two delta-doped planes are bought into proximity. [Preview Abstract] |
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C1.00128: Experimental and theoretical spectroscopic studies of dye modification in synthetic Maya Blue pigment Layra Reza, Felicia Manciu, Alejandra Ramirez, Russell Chianelli Maya pigments are hybrid organic/inorganic materials with multiple technology applications that possess unprecedented stability with respect to harsh environment conditions. In this investigation, we address the question of how the organic indigo dye modifies as it binds to the inorganic palygorskite clay to form a pigment similar to \textit{Maya Blue }after a heating treatment is applied. Both infrared and Raman spectroscopic data demonstrate the disappearance of nitrogen-hydrogen (N-H) bonding, as the indigo molecule incorporates into the inorganic palygorskite material. This effect suggests a transformation of the dye from indigo to dehydroindigo. Furthermore, the Raman and infrared absorption results demonstrate partial elimination of the selection rules for the centrosymmetric indigo, which provides further evidence for this conversion. Theoretical spectroscopic studies are also addressed in this investigation to confirm the transformation of the dye into dehydroindigo. [Preview Abstract] |
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C1.00129: Spectroscopic study of thioindigo-mineral composite William Durrer, Felicia Manciu, Alejandra Ramirez, Jayesh Govani, Russell Chianelli We report in this study structural changes taking place for the thioindigo-clay mixture in forming a pigment similar to Maya Blue. Different proportions of dye concentrations relative to that of the mineral, as well as different heating times, were applied in pigment synthesis and the outcomes were investigated using FT-IR and FT-Raman spectroscopy. For the pigment samples, the FT-IR peaks at 1627 cm$^{-1}$ are attributed to a downshifted C=O stretching mode of thioindigo due to dye-clay interaction. This interpretation is corroborated by FT-Raman C=O peaks with 14~cm$^{-1}$ shifts to lower frequency for the pigment relative to thioindigo alone. Additional Raman scattering between 550~cm$^{-1}$ and 650~cm$^{-1}$ also suggests dye-clay interaction through metal-oxygen bonding. We thus consider the possibility of hydrogen bonding between silanol and carbonyl dominating at lower dye concentration, with mostly metal-oxygen bonding at higher dye concentration. [Preview Abstract] |
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C1.00130: Inverse magnetoelectric effects in a bilayer of ferrite and graded piezoelectric Vladimir Petrov, Gopalan Srinivasan Magnetoelectric (ME) effects in a piezoelectric-magnetostrictive composite are mediated by mechanical stress. An applied electric field, for example, will result in piezoelectric strain in the composite and will lead to shift in ferromagnetic resonance (FMR) in the ferrite. This work is on modeling of magnetoelectric interactions under FMR in a bilayer of ferrite and functionally graded piezoelectric. We show that an enhancement of the strength of ME interaction at FMR is possible with the use of piezoelectric coefficient-graded ferroelectric with the grading axis perpendicular to the sample plane. In this case, the thickness dependence of the piezoelectric coefficients leads to an additional bending strain, resulting in an increase in the FMR line shift. Expressions have been obtained for the electrically induced magnetic resonance line shift, taking into account the effect of grading and substrate clamping. The obtained results are applied to the cases of single crystal yttrium iron garnet (YIG) and graded lead magnesium niobate-lead titanate (PMN-PT). A 40 {\%} increase in the shift of FMR line is predicted for graded systems compared to homogeneous piezoelectric composition. [Preview Abstract] |
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C1.00131: Microwave Magnetoelectric Interactions in Ferrite-Piezoelectric Bilayers Alexander Tatarenko, Vikas Mathe, Gopalan Srinivasan The measurement of the strength of microwave magnetoelectric (ME) interactions through ferromagnetic resonance (FMR) in bilayers of single crystal ferrite-piezoelectric oxides is reported. An electric field E produces a mechanical deformation in the piezoelectric phase, resulting in a shift in the resonance frequency for the ferrite. The strength of ME coupling is obtained from data on frequency shift vs $E$. Studies were performed on bilayers with single crystal yttrium iron garnet (YIG) films or single crystal nickel zinc ferrite and single crystal lead zirconium niobate-lead titanate (PZN-PT) or polycrystalline lead zirconate titanate (PZT). The samples were positioned in a microstripline-alumina ground plane structure. Resonance profiles were with a vector network analyzer obtained for $E$ = 0-8 kV/cm for in-plane magnetic fields $H$. Important results are as follows. (i) The ME coupling in the bilayers is stronger in bilayers with PZT than for PZN-PT. (ii) The coupling is a factor of 2 stronger in samples with nickel zinc ferrite than for YIG. The bilayers are potentially useful for E-tunable microwave resonators, filters and phase shifters. [Preview Abstract] |
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C1.00132: Magnetic field gradient induced magnetoelectric response of piezoelectric-magnetostrictive laminates Gopalan Srinivasan, Vladimir Petrov Magnetoelectric (ME) effects in a piezoelectric-magnetostrictive composite are mediated by the mechanical stress. The ME coupling in composites when subjected to a bias magnetic field and an ac magnetic field leads to an induced voltage that is directly proportional to the applied ac magnetic field amplitude. We discuss here the theory of ME interactions in a piezoelectric-magnetostrictive laminate which is subjected to a non-uniform bias magnetic field. The model predicts that the induced ME voltage will include an additional term which is proportional to the field gradient provided that the gradient direction is perpendicular to the laminate plane. The supplementary term in the ME voltage can be attributed to flexural deformations due to stress irregularity in the magnetostrictive component. As an example, the gradient magnetic field induced ME effect is considered for a bilayer of Terfenol-D and lead zirconate titanate. The ME voltage coefficient at electromechanical resonance is expected to exceed the low-frequency value by two orders of magnitude. [Preview Abstract] |
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C1.00133: Controlling the percolation behavior of conductor-insulator composites by changing the granular size of insulators Kazuhito Shida, Ryoji Sahara, Hiroshi Mizuseki, Yoshiyuki Kawazoe The critical behavior of percolation model does not depend on the detail of the embedding lattice. This fact can be a hard obstacle when one attempt to modulate and control the characteristics of the composite materials because the limit of modulation is limited by the percolation threshold, as in the case of substitution of expensive conductor materials by inexpensive insulator materials. Many attempts to solve this problem by changing the sizes and aspect ratios of conductor particles, expecting their effect in enhancing conduction as a ``bridge'' is not working well. We report our attempt to realize the same goal by introducing size differences in the insulator particles, not conductor particles. The effective transition point observed is actually lowered to 0.52 by this modulation from about 0.59 of conventional site percolation model (2D). The statistical nature of this novel model, in particular the optimum design of insulator particle size distribution, is a completely new and interesting theoretical problem. Moreover, this is considered to be a promising technique to reduce the amount of expensive conductor, for example the Indium in typical transparent conductor film. [Preview Abstract] |
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C1.00134: Medium-range Order in Periodic Mesoporous Silica Ella Wan, Kuangmin Li, Gang Chen Periodic mesoporous materials contain ordered pores with diameters between 2 and 50 nm. In spite of their ordered pore structure, most periodic mesoporous materials do not possess crystalline pore walls, and the atomistic origin of the uncrystallizable pore walls has been elusive. It is believed that the medium-range structure in such materials holds the key to the answer. To understand the medium-range order in periodic mesoporous materials, we select periodic mesoporous silica as a model system for this study. SBA-15 of various pore sizes (5-15 nm) have been synthesized through a self-assembly process using triblock copolymers as the structure-directing agents. X-ray scattering was used to characterize the materials. Pore widths and pore thicknesses of SBA-15 were measured by small-angle x-ray scattering, and the medium-range structure was characterized by wide-angle x-ray scattering. Effects of periodic pore structure and temperature on the medium-range order of amorphous pore walls have been identified. Our study provides atomic insights into the origin of uncrystallizable pore walls of periodic mesoporous materials in general. [Preview Abstract] |
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C1.00135: Fullerene-Polyhedral Oligosilsesquioxane Organic-Inorganic Hybrids and Applications as a Nanolayered Supercapacitor Yingfeng Tu, Chun Ye, Wenbin Zhang, Chi-Chun Tsai, Bin Sun, Xiaohong Li, Stephen Z. D. Cheng Fullerenes and polyhedral oligomeric silsesquioxane (POSS) organic-inorganic hybrid material was synthesized by esterification of methano[60]fullerene carboxylic acid (MFCA) with POSS-OH. The chemical structure was characterized and proven by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), SEC and UV-Vis spectroscopy. The material has high solubility (more than 10{\%}) in solvents like toluene, THF, chloroform and hexane. The material has high thermal stability: only 1{\%} of total mass lost at 350 \r{ }C and 50{\%} at 800 \r{ }C. At high concentrations, the solution of fullerene-POSS can absorb nearly the full spectra of the UV-Vis region (200 nm-700 nm). Crystals can be grown from chloroform solution, and the crystal structure was determined by transmission electron microscopy (TEM) and x-ray diffraction as an orthorhombic structure with a = 2.10 nm, b = 1.06 nm and c = 3.71 nm. This indicates a bilayer structure. The alternating layered structure of fullerene (conductive) and POSS (insulating) in the crystal can be used for applications such as supercapacitors. [Preview Abstract] |
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C1.00136: Electronic properties of a coupled polyacetylene chain Raimundo Costa, Celio Muniz We study a coupled polyacetylene chain using a theoretical field formalism and verify that this structure presents a gap in its band structure. This energy gap is calculated in terms of a quantized effective mass that depends on the coupling between the polyacetylene chains. As the coupling decreases the gap vanishes and we can restore the previous results of one single polyacetylene chain. We show that there is a chiral broken symmetry. Electrons propagating in one direction are more energetic than electrons propagating in the other direction of the chain. A formalism is developed to show that there is a particle oscillation phenomenon analogous to Bloch oscillations. The conductivity of the system is also calculated. [Preview Abstract] |
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C1.00137: Energy level curvatures, parametric motion of electron spectra in carbon nanotubes Isa Zharekeshev We examine scaling properties of statistical spectral measures of single-walled nanotubes in the frame of a standard tight-binding model for modified quasi one-dimensional disordered systems. Numerical-scaling analysis is performed for the energy correlation function, the spectral factor and the distributions of the level curvatures and velocities. Non-analyticity at the zero velocities and curvatures is found, which can be lifted by applying a moderate magnetic field. In the limit of weak disorder and at B=0 the level curvature distribution does not entirely obey Wigner-Dyson statistics, but is rather a non-trivial combination of the GOEs distributions depending of the aspect ration of the modelled nanotube. At strong disorder the curvature distribution deviates from the conventional log-normal statistics. The results are verified on the double-wall carbon nanotubes. Similar applications for graphene structures are considered. [Preview Abstract] |
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C1.00138: The nearly free electron like superatom states in fullerenes and nanotubes Jin Zhao, Min Feng, Hrvoje Petek Motivated by the discovery of the superatom states of C$_{60}$ molecules,$^{1}$ by DFT calculations we investigate their origin and the factors that influence their energy and wave function hybridization into nearly-free electron bands in molecular solids. We show that the superatom states are derived from the universal image potential states of molecular sheets by rolling and wrapping them into 0D fullerenes. Unlike the well-known $\pi $ orbitals, superatom orbitals hybridize more extensively among the neighboring molecules to form bands with nearly free-electron dispersion. The prospect of exploiting the strong intermolecular coupling to achieve metal-like conduction in applications may be attained by lowering the energy of superatom states from 3.5 eV, for single chemisorbed C$_{60}$ molecules, to proximity of the Fermi level; therefore, we study how the superatom state energies depend on factors such as the aggregation into 1D - 3D solids, their cage size, and exo and endohedral doping by metal atoms. We also study the superatom states of 1D nanotubes. \\[3pt] [1] Min Feng, Jin Zhao, Hrvoje Petek \textit{Science}, \textbf{320},359, 2008. [Preview Abstract] |
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C1.00139: Effect of Helical Perturbation on Exciton Binding Energy in Semiconducting Carbon Nanotubes Benjamin Tayo, Slava Rotkin Exciton binding energy in the presence of an external DNA-induced helical potential is studied. Exciton energies are obtained by solving the Bethe-Salpeter equation within the tight-binding approximation. The quasi-particle wavefunctions and energies which enter the Bethe-Salpeter equation are ``dressed" by the one-electron helical potential. This external potential, produced by helical DNA-wrapping, is modelled by applying a perturbation operator of the Coulomb interaction which breaks both translational and rotational symmetry. This lowering of symmetry induced by DNA-wrapping has far-reaching effects: the DNA changes the band gap of the nanotube thus modulating its electronic and optical properties. For instance, the helical perturbation uplifts the degeneracy on the angular momentum quantum number $m$. The role of these effects for an exciton is elucidated. [Preview Abstract] |
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C1.00140: Intersection of two nanotubes: density of states modulated by plasmon beatings with period governed by Luttinger-liquid parameter Vagharsh Mkhitaryan, Yuan Fang, Jordan Gerton, Eugene Mishchenko, Mikhail Raikh We study theoretically the plasmon scattering at the intersection of two metallic carbon nanotubes. We demonstrate that for a small angle of crossing, $\theta \ll 1$, the transmission coefficient is an {\em oscillatory} function of $\lambda/\theta$, where $\lambda$ is the interaction parameter of the Luttinger liquid in an individual nanotube. We calculate the tunnel density of states, $\nu(\omega,x)$, as a function of energy, $\omega$, and distance, $x$, from the intersection. In contrast to a single nanotube, we find that, in the geometry of crossed nanotubes, conventional ``rapid'' oscillations in $\nu(\omega,x)$ due to the plasmon scattering acquire an aperiodic ``slow-breathing'' envelope which has $\lambda/\theta$ nodes. [Preview Abstract] |
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C1.00141: First principles study of energetic interaction of a carbon chain inside carbon nanotubes Luis Aguilera, Alejandro Tapia, Romeo De Coss Recently has been reported a new type of one-dimensional carbon nanostructure. Carbon nanowires formed by a linear carbon-atom chain inside a carbon-nanotube have been observed using high-resolution transmission electron microscopy (HRTEM). In the present work, we have studied the energetic interaction and atomics forces inside of the (5,5) and (8,0) carbon nanowires, using the Density Functional Theory. The calculations were performed by the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange- correlation potential. Analyzing the energetic interaction inside the carbon nanowires, we found that the linear carbon chain obtains a preferential position inside of the carbon nanowires. [Preview Abstract] |
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C1.00142: Physisorption of Nucleobases on C(9,1) and C(6,5) Single-Wall Carbon Nanotubes: A Density Functional Theory Study Brahim Akdim, Ruth Pachter Selective enrichment of single-wall carbon nanotubes (SWCNTs) of a specific chirality by single-stranded DNA sequences has been shown experimentally by Zheng et al. [JACS 2007, 129, 6084], where a larger enrichment of C(6,5) as compared to C(9,1), which are SWCNTs of the same diameter but different chirality, was demonstrated with alternating guanine and thymine (GT) bases. In this work, we report density functional (DFT) calculations of (G) and (T) nucleobase adsorption on C(6,5) and C(9,1) SWCNTs, in order to gain an understanding of the selective sorting, specifically regarding adsorption characteristics, interface energetics, and electronic structures, as dependent on the tube chirality, also including specifically an empirical dispersion correction in the DFT functional. [Preview Abstract] |
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C1.00143: Novel One-Dimensional Organometallic Half Metals: Vanadium-Cyclopentadienyl, Vanadium-Cyclopentadienyl-Benzene, and Vanadium-Anthracene Wires Lu Wang, Zixing Cai, Junyu Wang, Jing Lu, Guangfu Luo, Lin Lai, Jing Zhou, Rui Qin, Zhengxiang Gao, Dapeng Yu, Guangping Li, Wai Ning Mei, Stefano Sanvito By using the density functional theory, we find that organometallic multidecker sandwich clusters V2$n$+1Cp2$n$+2, V$n$(FeCp2)$n$+1 (Cp = cyclopentadienyl), and V2$n$Ant$n$+1 (Ant = anthracene) may have linear structures, and their total magnetic moments generally increase with the cluster size. The one-dimensional (VCp)$\infty $, (VBzVCp)$\infty $ (Bz = benzene), and (V2Ant)$\infty $ wires are predicted to be ferromagnetic half-metals, while the one-dimensional (VCpFeCp)$\infty $ wire is a ferromagnetic semiconductor. The spin transportation calculations show that the finite V2$n$+1Cp2$n$+2 and V$n$(FeCp2)$n$+1 sandwich clusters coupled to gold electrodes are nearly perfect spin-filters. [Preview Abstract] |
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C1.00144: A Hybrid Density Functional Study Of Pure Ge And GeC Nanotubes: Zigzag Configuration Somilkumar J. Rathi, Asok K. Ray Ab initio calculations within the framework of hybrid density functional theory and finite cluster approximation have been performed for the electronic and geometric structures of pure zigzag Ge and three different types of zigzag germanium carbide nanotubes from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. A detailed stability investigation of the topologically similar nanotubes with dependence of the electronic band gaps on the respective tube diameters, energy density of states, and dipole moments have been carried out for all the tubes. Using Mulliken charge analysis charge density distribution along the tube lengths is calculated. In depth structural analysis of the structure and molecular orbitals are also reported. From our results it is clear that type I zigzag nanotubes are the most stable structures. For pure Ge, type II, and type III GeC nanotubes the chemical bonding have mixed ionic-covalent character, while for type I GeC tubes are ionic in nature. A wide spectrum of band gap values is also obtained for these nanotubes. This present study also opens up the possibilities for numerous applications of hybrid Ge based nanotubes. [Preview Abstract] |
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C1.00145: Deposition of Carbon Nanotube Networks for Electronics Applications Garrett Wadsworth, Tetyana Ignatova, Slava Rotkin The development of a simple though reliable deposition technique for Carbon Nanotube Networks on substrates would advance the production of working Carbon Nanotubes (CNT) field effect transistors and other electronic devices immeasurably. Our investigation of different methods and processes which would be able to reliably create conductive networks of CNTs was in the effort to achieve this goal. Samples were prepared using different stabilizing solutions such as aqueous Sodium Cholate and Dichloromethane along with several processes of physical application to create a network on various substrates. Characterization using several instruments, including a Keithley Semiconductor Characterization Station for transport measurements, SEM, and AFM was performed to gauge their conductivity and the relation to the sample morphology. The most consistent deposition of CNTs on SiO2/Si, SiN/Si and glass substrates occurs when using aqueous Sodium Cholate as the stabilizing solution, etching using a strong acid and rinsing to remove Cholate crystals. [Preview Abstract] |
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C1.00146: Solution processed large area field effect transistors from dielectrophoreticaly aligned arrays of single-walled carbon nanotubes Eliot Silbar, Paul Stokes, Yashira M. Zayas-Gonzalez, Saiful I. Khondaker Solution processed electronic devices have attracted tremendous attention because of their ease of processablity, low cost of fabrication, and their ability to cover large areas. Over the last few decades, a tremendous amount of effort has been dedicated to improve device performance of solution processed organic field effect transistors (FETs). However, despite all these efforts, typical field effect mobilities for these devices are usually on the order of $\sim $ 0.1 cm$^{2}$/Vs, and can very rarely reach $\sim $ 1.0 cm$^{2}$/Vs. We demonstrate solution processable large area field effect transistors (FETs) from aligned single-walled carbon nanotubes (SWNTs) arrays. Commercially available, surfactant free SWNTs suspended in aqueous solution were aligned between source and drain electrodes using AC dielectrophoresis. After removing the metallic nanotubes using electrical breakdown, the devices displayed on-off ratios up to 10$^{4}$. The devices showed p-type FET behavior with maximum field effect mobility of 27.1 cm$^{2}$/Vs, two orders of magnitude higher than solution processed organic FET devices. [Preview Abstract] |
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C1.00147: Energy transfer between Rear Earth ions and Carbon Nanotubes. Tetyana Ignatova, Hikmat Najafov, Slava V. Rotkin We investigate a potentiality of rare earth (RE) ions for the sensibilization of the carbon nanotubes (NT) luminescence via the resonance-type energy transfer expected from the appreciable spectral overlap between the RE emission and the short-wavelength fraction of the NT absorption. RE spectroscopy combined with the time-resolved study of the excited states following the 20ps laser excitation was used to determine the transfer rate through the shortening of the RE luminescence decay time. In this study we mainly focus on the time-resolved spectroscopy of selectively excited Tb$^{3+}$ and Eu$^{3+}$ ions in water solution containing a high concentration of DNA-wrapped NT showed a clear sign of transfer from RE to NT. We propose that the electrostatic attraction between negatively charged DNA phosphate groups and positively charged RE ions (Tb$^{3+}$ and Eu$^{3+})$ in water solution resulted in RE-DNA-NT complex formation with a suitable inter-species spacing for the energy transfer from RE to NT as well as the appreciable spectral overlap. The transfer has been confirmed by small ($<$10{\%}) but systematic shortening of the RE emission in water solution containing DNA-wrapped NT. [Preview Abstract] |
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C1.00148: Optoelectronic Characterization of Nafion-gated Nanotube FETs Happiness Munedzimwe, Slava V. Rotkin Optoelectronic probing is a routine way of characterizing standard semiconductor devices. For Carbon Nanotubes Field Effect Transistors (CNT FETs) made on silicon, however, it is a challenge to distinguish between intrinsic and ambient/substrate effects. Photo voltages at the Si-SiO2 interface often dominate the characterization. Back gated FETs systems also exhibit very high gating voltages. Ionomeric substrates allow higher gating efficiencies and at lower voltages. We report significant transconductance and photo modulation at gate voltages peaking around 5V with Nafion-117 ionomer as substrate which is ten times less than for typical Si systems. We use a generic back-gated FET geometry for characterizing gating performance and the trapping processes at the Nafion --CNT layer interface. Typical signal rise and decay times are of the orders 10 s and 100 s respectively, consistent with charge trapping inside the ionomeric polymer. The close similarity between electrostatic gating and photo-gating signal profiles makes the latter a plausible explanation for photo-conductance characterization mechanism in our samples. [Preview Abstract] |
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C1.00149: Catalytic behavior of Graphene/CNT composites in DSCs Josef Velten, Anvar Zakhidov, Dillip Panda, Lynn Dennay, Attila Mozer, David Officer This presentation demonstrates the replacement of the Pt used in the counter electrode of a dye sensitized solar cell (DSC) by a nanocomposite of carbon nanotube with grapheme layers. The I/I$_{3}^{-}$ redox reaction of such DSC was studied using a composite of graphene flakes (obtained by reduction of grapheme oxide) with either single wall or multiwall carbon nanotube sheets. This nanocomposite was deposited onto FTO coated glass and this electrode showed improved catalytic behavior beyond the use of carbon nanotubes alone for the charge transfer redox reaction. This paper also compares the use of the CNT/Gr composite counterelectrode with the standard Pt counterelectrode. The details of increased catalytic activity of Gr/CNT was studied by impedance spectroscopy and the origin of the enhanced electron transfer at the Gr interface is discussed in terms of local states at atomic edges. [Preview Abstract] |
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C1.00150: Thermal Properties of Carbon Nanotube and Nanofiber Nanopapers: Finite Element Analysis Lawrenzo D. Moses, Alper Buldum Carbon nanotube and nanofiber nanopapers are promising candidates as electronic thermal management materials. Here we present finite element method calculations of nanotube-nanotube, nanofiber-nanofiber junctions and extended two dimensional structures (nanopapers) containing these junctions. In the studies of individual junctions, different nanotube/nanofiber diameters, size of contact area and effects of fusing are considered. In the studies of nanopapers, different morphologies, effects of junction-junction separation are considered and thermal transport through multiple layers are studied. [Preview Abstract] |
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C1.00151: Combined transport and Raman measurements on individual carbon nanotubes Markus Ahlskog, Olli Herranen, Jyri Rintala, Andreas Johansson, Mika Pettersson Combined techniques for measurement of structural, transport, and spectroscopic properties of individual carbon nanotubes are very important for current progress in the physics of these materials. We have measured the Raman spectra of individual single walled nanotubes that are electrically contacted with lithographically fabricated microelectrodes on Si/SiO substrates. The G-band of the Raman spectra have characteristic features for metallic and semiconducting tubes that we are able to discern. This conclusion is confirmed by transport measurements that unambiguously distinguish between the two types of tubes. [Preview Abstract] |
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C1.00152: Contact Resistance, Electrical Breakdown and Temperature-Dependent Conductance of Multi-Walled Carbon Nanotubes Xiangyu Chen, Deji Akinwande, H.-S. Philip Wong Contact resistance has always been one of the major issues for applications of carbon nanotubes such as interconnects for VLSI chips, etc. In order to study the physics of contact between carbon nanotubes and metal, the temperature dependence of contact resistance between carbon nanotube and different metals (Cr/Au, Pd, Ti/Au, etc.) in an extended temperature range (4K to 400K) are explored. These data provide insight into the carrier transport between metal and carbon nanotubes. In addition, the temperature coefficient of the resistivity of multi-walled carbon nanotubes (MWCNT) of different lengths in the temperature range from 4K to 400K are measured and compared with theoretical calculations. By studying the temperature-dependent conductance, we are able to understand carrier transport in MWCNTs at low temperatures. The electrical breakdown behavior of MWCNT is also studied. Information from shell-by-shell breakdown provides insight about the critical current density and inter-shell conductance at different temperatures. [Preview Abstract] |
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C1.00153: Quantized Conductance and Residual Resistance in Nanowires Charles Milner, Woo-Joong Kim, Steve Lamoreaux Conductance in nanowires is quantized in units of G$_{0}$ = 2e$^{2}$/h. Nanowires can be formed by momentary contact between the ends of macroscopic metallic wires. During the final stage of their rupture, the conductance of the wires drops in a stepwise fashion. However, these steps do not necessarily fall on integer multiples of G$_{0}$, because of a possible presence of residual resistance in the system. Using gold, we have observed the characteristic steps of quantized conductance. We have also found evidence of residual resistance. Looking forward, we plan to increase the precision of our conductance statistics by implementing automated data acquisition in order to explore the origin of residual resistance in different metallic wires, such as copper and silver. By examining the sample dependence of quantized conductance, we hope to find particular characteristics in metals which give rise to residual resistance. We hypothesize that surface potential is one such characteristic. [Preview Abstract] |
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C1.00154: Electronic Transport Properties on CNT-Metal NanoWire Junctions Sungjong Woo, Young-Kyun Kwon In the devices using carbon nanotube(CNT), the contact property between CNT and metal nodes such as contact resistance is very important. The nanofabrication technology has now begun to get the experimental control of the junction at nanoscale. Using Density Functional Theory(DFT), we have calculated stable junction structures numerically between CNT and metal nanowires(MNW) such as gold. With the stable structures we have found, the transport properties are caculated using non-equilibrium Green's function method. Different junction structures and their stabilities will be presented. The $I$-$V$ characteristics depending on different junctions and CNT chiralities will also be discussed. [Preview Abstract] |
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C1.00155: Electronic properties of multiwall carbon nanotubes studied by rotation driven by AC electric fields D. L. Fan, Frank Q. Zhu, Robert Cammarata, C. L. Chien We have studied the electronic properties of multiwall carbon nanotubes (MWCNT) using the frequency dependent rotation driven by AC electric fields. The rotation angle, speed, and chirality of MWCNT can be precisely controlled by the strength and frequency of the AC electric field. From the rotation characteristics, the imaginary part of the Clausius-Mossotti factor, which depends on the material, the geometry, and the AC frequency, has been determined from 0.05 to 1MHz. This work demonstrates a non-contact and non-destructive method for assessing the properties of nanotubes and other nanoentities. The rotation of MWCNT can also be exploited in nanooelectromechanical system (NEMS) with MWCNT acting as the rotating elements. [Preview Abstract] |
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C1.00156: Conductance and elastic modulus of a strained carbon nanotube Feras Alzubi, Ronald Cosby A first principles atomistic calculation of the electrical conductance for a strained, single-wall metallic carbon nanotube segment containing forty eight atoms and placed between copper electrodes is reported. Density functional theory and a non-equilibrium Green's function technique, encoded in a commercial software package, are used to calculate the electronic structure and current-voltage characteristics for small strains. A monotonic decrease in conductance with strain is predicted. Using force-strain data, a modified Young's modulus is computed for isolated, stretched nanotube segments containing up to 192 atoms. The computational methods, parameters, Poisson ratios, area selections, and results are described. [Preview Abstract] |
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C1.00157: Electronic and mechanical properties of phosphorus and phosphorus-nitrogen doped carbon nanotubes E. Cruz-Silva, F. Lopez-Urias, E. Munoz-Sandoval, B.G. Sumpter, H. Terrones, J.-C. Charlier, V. Meunier, M. Terrones Carbon Nanotubes have high potential for new materials based on their unique electronic and mechanical properties. They have found use in several fields, including composite materials, electronic nano-devices, catalysis, and energy storage, among others. Doping of nanotubes by exohedral or endohedral methods has been found to substantially modify their electronic structure, as well as their chemical reactivity. In this work, we present a density functional theory study of the electronic and mechanical properties of phosphorus and phosphorus-nitrogen substitutionally doped carbon nanotubes. It is found that doping with these atoms create localized states which modifies electron transport properties. The effects on mechanical properties will also be presented. These new doped nanotubes could have new applications in composite materials or in applications such as gas sensing or molecular detection. [Preview Abstract] |
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C1.00158: Development of Glucose Sensors by Modified Carbon Nanotube Arrays Jason Moscatello, Archana Pandey, Abhishek Prasad, Yoke Khin Yap In 2007 the CDC estimates 7.8{\%} of the US population had diabetes, and the percentage is rising [1]. Such numbers lead to a large demand for highly selective, sensitive glucose sensors. We have used vertically-aligned multiwalled carbon nanotube (VA-MWCNT) arrays [2] to fabricate glucose sensors. VA-MWCNTs were embedded in PMMA and polished to expose the tips. The tips were functionalized by carboxyl groups, then modified by immobilization of glucose oxidase. Initial results on sensors of this type were previously reported [3], but we have further characterized to include lowest detection limits, enzyme lifetime, and performance stability. Comprehensive electrochemical data will be presented along with Raman, IR, and SEM. 1. National Diabetes Fact Sheet, Centers for Disease Control and Prevention, U.S. Department of Health (2007) 2. J. Menda et al., Appl. Phys. Lett., 87, 173106-3 (2005) 3. Y. Lin, F. Lu, Y. Tu, Z. Ren, Nano Lett., 4, 191-195 (2004) [Preview Abstract] |
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C1.00159: Structure of the Solid Ink-sticks Jung-Il Lee, Keun Hwa Chae, Jong Han Song, Yeonhee Lee, Jae Pyung Ahn, Kyung Tae Hong, Man-Ho Kim, Andrew Jackson Traditional solid ink-sticks have been mainly used for calligraphy and oriental painting in East Asian countries. The ink-sticks used to be made from soot (or carbon black) and animal glue using their own family recipes at each country. We investigated the physical structure of the ink-sticks from micron to nanometer using ultra small angle neutron scattering (USANS) and SANS together. Differences in the structures of the ink-sticks collected from different countries will be discussed. *The authors, JIL {\&} MHK acknowledge support in part by the KIST (2V01331 {\&} 2V01344). [Preview Abstract] |
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C1.00160: Anisotropic etching of graphene sheets Anthony Mendez, Brian Standley, Marc Bockrath One challenge in the development of graphene nanoribbon transistors and graphene devices in general is the minimization of edge-induced disorder. We have discovered a simple etching process which may help address this challenge. Preliminary inspection of our etched graphene sheets reveals faceting of the edges and occasionally even hexagonal holes. We will present an atomic force microscopy study with the aim of determining the smoothness of the edges and their orientation relative to the crystal lattice. [Preview Abstract] |
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C1.00161: Heat Conduction in Graphene Flakes of Arbitrary Geometry Samia Subrina, Dmitri Kotchetkov, Alexander Balandin It was reported that the values of the room temperature thermal conductivity of graphene exceed those of carbon nanotubes [1-2]. The measurements of the thermal conductivity of graphene utilized a technique where the excitation laser initiated a heat wave. The data extraction procedure assumed plane heat waves. Realistic graphene flakes have variations in their width, and the heat wave front may deviate from the plane wave depending on the geometry of the flake. We report a numerical study of heat propagation in graphene flakes of arbitrary geometry. The thermal conduction was simulated using the finite element method. It was found that both the shape of the flake and the temperature distribution in the hot spot affect the extracted values. At the same time, for the flakes with the relatively constant width and the hot spot of the size comparable to the flake width, the thermal conductivity obtained within the simple plane-wave approximation give close values to our simulations. [1] A.A. Balandin, et al., Nano Letters, 8, 902 (2008) [2] S. Ghosh, et al., Appl. Phys. Lett., 92, 151911 (2008). [Preview Abstract] |
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C1.00162: Magnetic impurities in Graphene: Electronic structure and magnetic interaction Mohammad Sherafati, B. R. K. Nanda, S. Satpathy From density functional calculations using the LAPW method, we study the electronic structure of graphene in the presence of magnetic impurities and the interaction between the impurities mediated by the graphene electrons. The 3d transition metal impurities are considered. The results are interpreted in terms of the RKKY interaction and the Anderson impurity model. [Preview Abstract] |
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C1.00163: Normal-Metal/Graphene/Superconductor Tunnel Junctions Nan Sun, Kristof Tahy, Debdeep Jena, Huili Xing, Steven Ruggiero We report on progress with lateral tunneling in N/G/S (Normal-metal/Graphene/Superconductor) tunnel junctions. Our primary approach is the study of systems of the form: Au/Graphene/Nb where lateral tunneling occurs across graphene bridges. Gates are also provided for Fermi-level adjustments in the standard ``FET'' format. Samples are created by e-beam lithography on electronic-grade oxidized Si substrates, using commercially prepared graphene flakes. Raman scattering is used to verify the single-layer nature of samples under study. We discuss the current status of studies designed to observe predicted oscillations in the tunnel conductance of samples with the above-described geometry, associated with Klein tunneling in the graphene films and Andreev reflections at graphene interfaces. [Preview Abstract] |
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C1.00164: Work of an Energetic Charged Particle Penetrating Graphene V. Fessatidis, N.J.M. Horing The energy loss of a fast charged particle probe incident on a two-dimensional graphene sheet is examined here. The fast particle motion is taken to be perpendicular to the graphene sheet, which is considered to be in the degenerate limit of zero temperature. The response dynamics of the graphene layer are described in the random phase approximation and the energy loss for particle motion perpendicular to the graphene layer is calculated as a function of the velocity of the charged particle. [Preview Abstract] |
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C1.00165: Water adsorption on a titanium-graphene surface with high metal density Gerardo J. Vazquez, Eduardo Rangel, Gregorio Ruiz-Chavarria, Fernando Maga\~na Density functional theory and molecular dynamics were used to study the adsorption of a water molecule on a graphene layer modified with titanium at high metal coverage, with the \textit{Ti} atoms located above the centers of the carbon hexagons. Two stable configurations for the titanium-graphene sheet were considered. One with one titanium atom per eight carbon atoms and the other with one \textit{Ti} atom per two $C$ atoms. We found that the water molecule is adsorbed on both configurations, but it is dissociated in two different ways forming $H, O$ and \textit{HO} when the interaction is with the second configuration. [Preview Abstract] |
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C1.00166: Possible nano-spintronics devices with graphene as electron wave guides Koichi Kusakabe Another application of graphene to semiconductor spintronics devices is proposed theoretically. We have designed possible methods for fabrication of nano-scale device structures utilizing graphene as electron wave guides. Important techniques should be 1) formation of strong covalent bonding between a part of substrate and graphene, 2) creation of nano-sized superstructure with sharp edges inducing the grapheme edge states[1] by controlling interface between external electrodes and graphene, and 3) creation of nano-sized quantum structures based on the spinodal nano-decomposition. Several test simulations on the electronic states of proposed structures and theoretical estimation of functionality of graphene as an electron wave guide for semiconductor spintronics devices are presented. [1] M. Fujita, K. Wakabayashi, K. Nakada and K. Kusakabe, J. Phys. Soc. Jpn. 65, 1920 (1996). [Preview Abstract] |
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C1.00167: Effect of metal contacts on photocurrents in graphene transistors Roksana Golizadeh Mojarad, Fengnian Xia, Thomas Mueller, Marcus Freitag, Yu-ming Lin, Phaedon Avouris We present theoretical explanation of photocurrent in graphene and investigate the effect of contact induced states on in-plan electric field in graphene. Contact induced states are similar to the well-known metal induced gap states (MIGS) in metal-semiconductor Schottky junctions, which typically penetrate a few atomic lengths into the semiconductor, while the depth of penetration decreases with increasing band gap. However, in graphene we find that these states penetrate a much longer distance of the order of the width of the contacts. [Preview Abstract] |
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C1.00168: Micro-Raman imaging spectroscopy of suspended graphene J. R. Simpson, A. R. Hight Walker The recent observation\footnote{K. I. Bolotin \textit{et al.}, Solid State Commun. \textbf{146}, 351 (2008).} of ultrahigh mobility, $>200,000\,\mathrm{cm^2 V^{-1} s^{-1}}$, in suspended and annealed graphene underscores the importance of environmental effects on graphene electronic properties. We compare the Raman spectra of graphene and chemically modified graphite oxide both in contact with and suspended above substrate surfaces. Graphene samples were prepared using micromechanical cleavage and chemically modified\footnote{J. T. Robinson \textit{et al.}, Nano Lett. \textbf{8}, 3441 (2008).} graphite flakes on silicon substrates with a thin, $\approx 300\,$nm, silicon oxide coating. Reactive ion etching patterns the substrates with circular holes, approximately $3-7\,\mu$m in diameter, etched through the oxide layer. We present spatially-resolved Raman spectra obtained in a scanning, confocal microscope configuration using 632.8\,nm and 514.5\,nm laser excitation. [Preview Abstract] |
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C1.00169: Intrinsic and extrinsic temperature dependences of Raman spectra of graphene Daner Abdula, Taner Ozel, Kwangu Kang, David G. Cahill, Moonsub Shim Implementation of single-layer graphene (SLG) into next-generation electronics is of high interest due to unprecedented transport capabilities. Therefore, the importance of SLG doping and vibrational band structure is pronounced, both of which can be characterized with Raman spectroscopy. This work offers insights on the temperature dependent behavior of energy and linewidth of E$_{2G}$ G-band and A$_1$' 2D-band Raman spectral features of intrinsic and air-exposed SLG. Mechanically exfoliated graphene in air exhibits a G-band linewidth that increases with temperature between 298K and 573K but shows an opposite trend after annealing under Ar. The opposing temperature dependences are considered within the context of Kohn anomaly induced phonon softening and broadening. The primary cause of the changes in E$_{2G}$ phonon energy and the electron-phonon coupling is attributed to ambient O$_2$ shifting the Fermi level away from the Dirac point. Our results emphasize the need to consider sample environment when investigating electronic and vibrational properties of graphene as well as when they are utilized, for example, in devices where SLG would undergo lithographic processing or even be operated in contact with various materials that may compromise its supposed high performance. [Preview Abstract] |
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C1.00170: Conductance gaps modulation by periodic perturbations in graphene nanoribbons M. Pacheco, L. Rosales, Z. Barticevic, A. Leon, A. Latge, P. Orellana Recently we have shown that the quantum conductance of a single molecule absorbed to the GNR shows the presence of Fano antiresonances at the energy levels of the molecule, suggesting that the GNR can be used as a spectrometer sensor [1]. When groups of molecules are attached, forming a periodic-like structure the conductance of the system presents forbidden minibands. Here we present a theoretical study of the electronic and transport properties of periodic perturbations on graphene nanoribbons. We study super-lattices formed by linear organic molecules side-attached at the ribbon edges and also by periodic structures of antidots in the GNR. The electronic properties of the systems are studied by using first principle calculations (LSDA), and tight binding Hamiltonian models. The quantum conductance is calculated in the Landauer formalism, with real-space renormalization techniques to obtain the Green functions. A series of well defined gaps on the conductance as a function of the Fermi energy are observed. This behavior depends on the period and topology of the perturbations and on the aspect ratio of the system. Conductance gap modulations can be obtained, suggesting new applications in graphene based nano-devices. [1] L.Rosales et al.,Nanotechnology 19,0665402 (2008). [Preview Abstract] |
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C1.00171: Spin Dependent Transport in Graphene Nano Ribbon Devices Satofumi Souma, Matsuto Ogawa, Takahiro Yamamoto, Kazuyuki Watanabe Graphene is now one of the promising materials for future nanoelectronics. Especially graphene nanoribbon is attracting great attention since it possesses finite bandgap opening depending on the ribbon width and the transport orientation with respect to the graphene lattice. Another interesting property seen in graphene nanoribbon is the appearance of the ``edge-spin'' polarization at the edges of the zigzag-edged graphene nanoribbon. Recently it has been shown that such edge- spin polarization can be electrically controlled to induce the half-metallic band structure in such structures, meaning the electrical controllability of the spin current in such material. Therefore, toward the realization of the graphene nanoribbon spintronics, it is now important to study the spin- dependent transport characteristics in realistic device structure based on zigzag graphene nanoribbon. Here we present our numerical study of spin transport in zigzag-edged graphene nanoribbon transistor structures [1] using spin-density functional tight-binding method. Special attention is paid to the influence of edge roughness and electrostatic doping on the spin polarization and the spin current. [1] S.Souma, M.Ogawa, T.Yamamoto, K.Watanabe, J.Comp. Electron. 7, 390 (2008). [Preview Abstract] |
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C1.00172: Influence of an electric-field on electronic properties of few-layer armchair graphene nanoribbons Y.-C. Huang, H.-C. Chung In the presence of an electric field, the low-energy electronic properties of AB-stacked few-layer armchair graphene nanoribbons (AGNRs) are studied by using the tight-binding model. They are strongly dependent on the geometric structures (the interlayer interactions, the ribbon width $N_y$, and the ribbon number $N_z$) and the field strength. The interlayer interactions significantly affect density of states (DOS), energy gap ($E_g$), band structure, and free carriers. DOS exhibits many special structures, including plateau, discontinuities, and divergent peaks. The effective electric field modifies the energy dispersions, alters the subband spacing, changes the subband curvature, produces the new edge state, switches the band gap, and causes the metal- semiconductor (or semiconductor-metal) transitions. In gapless AGNR, electric fields not only lifts the degeneracy of subbands at $E_F$ but also induces an energy gap. $E_g$ is dependent on the ribbon width, and the field strength. The semiconductor- metal (or semiconductor-metal) transitions occur in AGNRs in the increase in electric fields. Due to electric fields, the above-mentioned effects are completely reflected in the features of DOS, such as the generation of special structures, the shift of peak position, the change in peak height, and the alternation of band gap. The predicted electronic properties could be examined by the experimental measurements on absorption spectra and transport properties. [Preview Abstract] |
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C1.00173: Low-energy Landau levels of AB-stacked zigzag graphene ribbons Yuan-Cheng Huang The low energy bands of AB-stacked zigzag graphene ribbons in the presence of a uniform perpendicular magnetic field are investigated by the Peierls coupling tight-binding model. They are dominated by the $\bf B$-field strength, the interlayer interactions, and the ribbon width. Many dispersionless Landau levels and parabolic energy bands exist along $k_x$ and $k_z$ directions, respectively. The former are doubly degenerate, while state degeneracy is absent for the latter. The occupied valence bands are asymmetric to the unoccupied conduction bands about the Fermi level. Such features are directly reflected in density of states. DOS exhibits a lot of asymmetric prominent peaks because of 1D parabolic bands. The predicted magnetoelectronic properties could be examined by the experimental measurements on transport conductance and absorption spectra. [Preview Abstract] |
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C1.00174: Quasiparticles for quantum dot array in graphene and the associated Magnetoplasmons Godfrey Gumbs, Oleg Berman, Pedro Echenique We calculate the low-frequency magnetoplasmon excitation spectrum for a square array of quantum dots on a two-dimensional (2D) graphene layer. The confining potential is linear in the displacement from the center of the quantum dot. Consequently, the corresponding Klein-Gordon equation may be solved analytically for the single-particle eigenstates since they are given by a simple harmonic oscillator operator. The electron eigenstates in a magnetic field and confining potential are mapped onto a 2D plane of electron-hole pairs in an effective magnetic field without any confinement. The tight-binding model for the array of quantum dots leads to a wavefunction with inter-dot mixing of the quantum numbers associated with an isolated quantum dot. It is verified that our tight-binding wave function obeys the Bloch-Peierls condition in the Landau gauge, For chosen confinement, magnetic field, wave vector and frequency, we plot the dispersion equation as a function of the period $d$ of the lattice. We obtain those values of $d$ which yield collective plasma excitations. For the allowed transitions between the valence and conduction bands in our calculations, we obtain plasmons when $d < 100 {\AA} $. [Preview Abstract] |
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C1.00175: Temperature Programmed Desorption Study of Graphene Oxide Nicholas Clark, Daniel Field, Simona Rieman, Carl Ventrice, Inhwa Jung, Dongxing Yang, Richard Piner, Rodney Ruoff Graphene oxide is an electrical insulator that shows potential for use in nanoscale electronic devices. An understanding of the thermal stability of graphene oxide sheets is important since the electrical, chemical, and mechanical properties of graphene oxide will change as it is reduced at elevated temperatures. In this study, graphene oxide films were grown by deposition of an aqueous solution of graphene oxide onto oxygen plasma cleaned silicon nitride on silicon substrates. The thermal stability of these films was studied by temperature programmed desorption under ultra-high vacuum conditions up to 350 $^{\circ}$C. The primary decomposition components of the films are H$_{2}$O, CO$_{2}$ and CO. Desorption of these components starts at $\sim $70 $^{\circ}$C and is completed by $\sim $150$^{\circ}$C. Coverage dependent measurements indicate that the desorption kinetics are second order. An activation energy of 162 meV for CO$_{2}$ desorption has been determined. [Preview Abstract] |
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C1.00176: Structural and electronic characterization of epitaxial graphene on SiC (0001) using scanning tunneling microscopy/spectroscopy David Torrance, Nikhil Sharma, Phillip First Epitaxial graphene exhibits high-quality crystallinity and is compatible with current industrial fabrication methods, which makes it a strong candidate for future electronic devices. One important and contested aspect of this material system is the interface region between graphene and SiC, and how this reconstruction alters the growth rate, structure, and electronic properties of graphene films. We have investigated epitaxial graphene on SiC (0001) in the very early stages of ultra-high vacuum growth using scanning tunneling microscopy/spectroscopy (STM/STS). Topographical maps of monolayer graphene islands formed in the initial stages of epitaxial growth will be presented along with STS measurements of these features and the surrounding interfacial reconstruction. We further discuss transitions between regions of different structure. [Preview Abstract] |
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C1.00177: Real-Time Path Integral Study of Electron Transport in Molecular Wires: A Constant Current Formulation and the Importance of Dissipative Processes Roberto Lambert, Ke Dong, Nancy Makri We report the results of real-time path integral calculations to study electron transport in molecular-wire models. The molecular wire system is modeled by a multi-site one-electron tight-binding Hamiltonian connected to two metal electrodes and coupled to a bath mimicking the dissipative effects of molecular vibrations. In order to maintain a steady current flow, we introduce a simple recharging model in which electrons are injected from the donor electron as needed to replenish charge lost to the acceptor, maintaining a constant electron population within the wire. Using real-time path-integral techniques, we study the conductance of the molecular wire model as a function of wire length, with emphasis on the effects of its dependence on dissipation. [Preview Abstract] |
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C1.00178: Synthesis and spectroscopic characterization of cadmium sulfide nanowires Narayanan Kuthirummal, Jason Reppert, Brian Diehl, Apparao Rao Pulsed laser vaporization method has been used for preparing cadmium sulfide (CdS) nanowires of 50 -- 100 nm in diameter. The morphology and crystallinity of as-prepared CdS nanowires are studied by means of X-ray diffraction, scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). Excellent ordering of the lattice planes perpendicular to the [001] plane has been observed. Photoacoustic (PA), UV-Vis, Raman, and photoluminescence spectroscopy have been used to measure the optical properties. PA spectra yielded a steeper absorption edge for as-prepared CdS nanowires when compared to the conventional optical absorption spectrum. The increased steepness might be attributed to the well-ordered structure and size distribution. The data shows that PA spectroscopy is an excellent technique to investigate opaque and highly light scattering samples. Raman data suggests increased exciton-LO phonon coupling in CdS nanowires. The appearance of a narrow photoluminescence peak at 491 nm (FWHM of 9 nm) and the absence of emission above 500 nm demonstrate the high quality of nanowires. [Preview Abstract] |
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C1.00179: Confocal Raman microscopy of one dimensional ZnO nanostructures Srikanth Singamaneni, Maneesh Gupta, Rusen Yang, Zhong Wang, Vladimir Tsukruk ZnO nanostructures with various shapes (vertically aligned nanorods, nanobelts, nanohelixes, nanorings) have been synthesized using both vapor phase and solution growth methods. In the simplest example of a nanobelt, the fast growth direction can be either (2$\overline 1 \overline 1 $0) or (01$\overline 1 $0) or (0001). Here, we show that confocal Raman microscopy can be employed as a fast and nondestructive analytical technique to identify the crystal planes and reveal the relative orientation of the ZnO nanostructure. Various features of the Raman spectrum of ZnO nanostructures (presence of the A$_{1}$(TO) mode, width of the E$_{2}$ mode) were found to be sensitive to relative orientation of the incident source laser and the crystal plane. Furthermore, owing to the optical anisotropy of ZnO, Raman scattering from the substrate is modulated (either enhanced or suppressed with respect to the background) depending on the polarization of the incident light with respect to orientation of the nanobelt. The results presented here describe a novel method to nondestructively identify the growth, relative orientation, and the waveguiding properties of the ZnO nanostructures. [Preview Abstract] |
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C1.00180: Characterization of SiC nanowires obtained from carbon black powder Monika Wieligor, T. W. Zerda SiC nanowires were obtained by a reaction between vapor silicon and carbon black powder in vacuum at 1200oC. Their structures and properties were studied using X-ray diffraction, high resolution transmission microscopy, HRTEM, and Raman scattering techniques. We show that diameter of sintered nanowires depends on carbon black grade and its history of thermal treatment. SiC nanowires of diameter as small as 10 nm were obtained from graphitized furnace carbon blacks. Chemical composition of nanowires was similar for all samples, but concentration of structural defects varied and depended on carbon black surface properties and surface morphology. Stacking faults and twins dislocations were observed in all specimens and characterized by HRTEM, X-ray diffraction, and Raman spectroscopy. [Preview Abstract] |
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C1.00181: Parallel Tandems of Dye Sensitized Solar Cells with CNT Collector Josef Velten, Chao-Chen Yuan, Anvar Zakhidov In this presentation, we demonstrate the fabrication of monolithic parallel tandem dye sensitized solar cells using a semitransparent layer of carbon nanotubes. Each DSC sub-cell has titania photoelectrode with two different dyes: N 719 and N 749, which absorb light in different parts of solar spectrum. This layer of carbon nanotubes laminated on highly porous polymeric Millipore filter acts as both the collector of charge carrier and as the catalyst of the I/I$_{3}^{-}$ redox reaction that completes the function of the cell, overall allowing easier fabrication for tandem solar cell devices, with a potential for creating flexible devices in the future. The parallel tandem shows the total photocurrent which is nearly the sum of two I$_{sc}$ currents of constituent cells, and total Voc, which is average of two Voc, while conventional in-series DSC tandems show the lowest V$_{oc}$ and slightly increased I$_{sc}$[1]. Thus the higher efficiency can be achieved in parallel DSC tandems, and we discuss the physical reasons for this effect. [1] Yanagida, et.al. J. of Photochemistry and Photobiology A: Chemistry Volume 164, Issues 1-3, 1 June 2004, Pages 33-39 [Preview Abstract] |
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C1.00182: Chaotic Electronic Transport in Nanocluster Wires M.S. Fairbanks, T.P. Martin, C.A. Marlow, B.C. Scannell, S.A. Brown, R.P. Taylor Electronic circuits featuring nanoscale devices are highly topical due to their potential for exhibiting novel device functionality and fundamental solid-state physics. Circuits based on nanoclusters are particularly appealing because they ``self-assemble'' [1]. Here we develop a theoretical transport model for nanowires formed from nanoclusters. The wire width varies along the wire's length, creating an array of connected cavities. The wire walls reflect electron trajectories through material-induced chaotic scatterers within each cavity. We discuss how the chaotic properties can be engineered to increase the conductivity's sensitivity to electric and magnetic fields for use as novel sensors. [1] For example, J. G. Partridge, et al., Microelectronic Engineering 83, 1460 (2006). [Preview Abstract] |
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C1.00183: Unusual Conductance in Cumulene Molecular Wires Jariyanee Prasongkit, Anton Grigoriev, G\"{o}ran Wendin , Rajeev Ahuja We report current-voltage curves and conductance of cumulene molecular wire suspended between Au(111) surfaces via thiolate bonds with full self-consistent { \it ab initio} calculation under external bias. The conductance of cumulene wires shows oscillatory behavior depending on the number of carbon atoms. Among all conjugated oligomers, we find that odd-number cumulene wires yield the highest conductance and present ballistic-like transport behavior. The reason has been traced to two factors: high density of state at the Fermi level, and the alignment of molecular orbital closed to Fermi level. Since the conductance depends weakly on applied bias, and the current voltage characteristic is linear under bias region -0.9 to 0.9 V, odd-number cumulene wire is a possible candidate as a near- perfect, ballistic one-dimensional molecular wire. [Preview Abstract] |
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C1.00184: QUANTUM FLUIDS AND SOLIDS |
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C1.00185: Critical temperature of extremely confined bosons P. Salas, M. de Llano, M. Fortes, F.J. Sevilla, M.A. Solis The critical BEC temperature $T_{c}$\ of an ideal boson gas inside a layered structure simulated by a Kronig-Penney-like trapping potential is found to {\it decrease} as the separation between planes decrease to the order of the thermal wavelength $\lambda _{0}\equiv h/\sqrt{2\pi mk_{B}T_0}$ of the free boson gas at its critical BEC temperature $T_{0}$ [1], where $m$ is the boson mass. However, when the plane separation is less than $\lambda _{0}$, $T_{c}$ increases to nearly $T_{0}$. This phenomenon could be present in cuprate superconductors and explain why their transition temperatures increases as a function of pressure. [1] P. Salas, M. Fortes, M. de Llano, F.J. Sevilla and M.A. Sol\'{\i}s, {\it ``Thermodynamic properties of bosons among Kronig-Penney layers,''} to be published. We acknowledge the partial support from grant PAPIIT IN1114708. [Preview Abstract] |
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C1.00186: NANOTECHNOLOGY/BIONANOTECHNOLOGY |
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C1.00187: Silicon nanowires under high pressure Yuejian Wang Silicon nanowires (Si NWs), one-dimensional single crystalline, have recently drawn extensive attention, thanks to their robust applications in electrical and optical devices as well as in the strengthening of diamond/SiC superhard composites. Here, we conducted high-pressure synchrotron diffraction experiments in a diamond anvil cell to study phase transitions and compressibility of Si NWs. Our results revealed that the onset pressure for the Si I-II transformation in Si NWs is approximately 2.0 GPa lower than previously determined values for bulk Si, a trend that is consistent with the analysis of misfit in strain energy. The bulk modulus of Si-I NWs derived from the pressure-volume measurements is 123 GPa, which is comparable to that of Si-V NWs but 25{\%} larger than the reported values for bulk silicon. The reduced compressibility in Si NWs indicates that the unique wire-like structure in nanoscale plays vital roles in the elastic behavior of condensed matter.. [Preview Abstract] |
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C1.00188: Improved Synthesis of Aligned Carbon Nanotube Arrays for Optical Applications Trilochan Paudel, Yantao Gao, Yucheng Lan, Gregs Macmohan, Krzysztof Kempa, Michael Naughton, Zhifeng Ren Vertically aligned carbon nanotubes were grown on the high temperature glass (Aluminosilicate, Corning 1737) substrates with improved characteristics compared to previous attempts. The glass substrates were first coated with a buffer layer of either Chromium or Titanium, thick enough to facilitate CNT growth, but thin enough as to be largely transparent. On the top of the buffer layer, a monolayer of polystyrene spheres was deposited with close compaction, and then a Nickel catalyst film was evaporated. The polystyrene spheres were then removed to obtain honeycomb Ni patterns. On top of the Ni patterns, vertically aligned carbon nanotubes were grown by the direct current plasma enhanced chemical vapor deposition (dc PECVD). These aligned carbon nanotubes, which can range in height from 0.5 to 10 microns, and in diameter from 50 to 350 nm, can then be coated with various dielectrics to function as components in optical waveguides, including solar cells. [Preview Abstract] |
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C1.00189: Enhancement of LED Backlight by Metallic Nanostructures Y.D. Yao, J.K. Wu, C.Y. Hsu, S.Y. Hsu, P.K. Wei, D.H. Wei, M.D. Chou, C.N. Mo Metallic nanostructures with different size on ITO coated glass substrates have been fabricated by using metal thin film dewetting, electron beam lithography, and nanosphere lithography techniques for studying the light guide in a display system. The increase of extraction efficiency is based on scattering light from the trapped photons. With Ag and Au nanostructures in peripheral area of emitting region on the ITO coated glass substrates, the external quantum efficiency of devices increases by roughly 14 {\%} and with a 100 nm-width and 450 nm-period metallic nanowire structures, the light extraction can enhance up to 40 {\%} from the glass substrate. We demonstrated that with a proper metallic nanostructure in the backlight system of a LED device, the extraction efficiency could be efficiently enhanced. [Preview Abstract] |
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C1.00190: Modified Electric Force Microscopy combined with Atomic Force Microscopy Electrostatic Nanolithography Sergei Lyuksyutov A hybrid method, combining electrostatic nanolithography with modified electric force microscopy was used to characterize and study surface electric charging of high molecular weight (850000 mw and 110000 mw) polymethyl methacryalate and polystyrene films. Experimental protocol to manipulate an atomic force microscope tip included 1) Displacement of the vibrating tip to the level when the vibration amplitude largely damped; 2) Tip retraction at the distance varied between 1 to 100 nm with positive or negative tip bias. A modified Electric force microscopy maps electric charge distribution and its sign on the sample surfaces. Stable surface deformation related to nanoscale mass transport was associated with electric breakdown and negative surface charging, while a temporary viscoelastic surface deformation followed by surface relaxation was due to positive surface charging. [Preview Abstract] |
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C1.00191: A Novel Carbon Nanotube Network and Aptamer Based Biosensor Y. Al-Titi, W.G. Matthews A carbon nanotube network field effect transistor (CNTN-FET) based biosensor for the detection of Tenascin C will be presented. The device consisted of CVD-grown CNTNs incorporated into FETs coupled with surface bound DNA aptamers. The aptamer conjugated FET provides highly selective and sensitive detection of protein concentrations. The sidewalls of the CNTs initially were functionalized with a short oligonucleotide which has the dual functions of blocking non-specific binding and serving as a tether for the addition of another DNA strand. Specific detection was accomplished through hybridization of an aptamer for Tenascin C to which the complementary strand of our blocking sequence was added to the 5' end. IV curves and conductance versus time were collected, demonstrating detection of each of the two DNA strands and the protein Tenascin C. The protein produced an undetectable signal in the absence of the aptamer, even at higher concentrations. Confirmation of adsorption of the oligonucleotide, hybridization of the aptamer, and binding of Tenascin C were each confirmed through fluorescence microscopy. The resulting device is an important step toward low cost, label-free biosensors. [Preview Abstract] |
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C1.00192: Detection of $\alpha $-fetoprotein in human serum using carbon nanotube transistor Hye-Mi So, Dong-Won Park, Seong-Kyu Lee, Beom Soo Kim, Hyunju Chang, Jeong-O Lee We have fabricated antibody-coated carbon nanotube field effect transistor (CNT-FET) sensor for the detection of $\alpha $-fetoprotein (AFP), single chain glycoprotein of 70 kDa that is normally expressed in the fetal liver, in human serum. The AFP-specific antibodies were immobilized on CNT with linker molecule such as pyrenebutyric acid N-hydroxysuccinimide ester. To prevent nonspecific adsorption of antigen, we performed blocking procedure using bovine serum albumin (BSA). Antibody-antigen binding was determined by measuring electrical conductance change of FET and took an average of thereshold voltage change before and after binding. Also we checked concentration-dependent conductance change in human serum using both p-type SWNT-FETs and n-type SWNT-FETs. [Preview Abstract] |
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C1.00193: Wrapping of a single bacterium with Functionalized - Chemically Modified Graphene (FCMG) sheets via highly specific protein-cell wall interaction Nihar Mohanty, Vikas Berry Graphene has recently generated a lot of interest due to its unique structural and electrical properties. It's micro-scale area and sub-nano-scale thickness coupled with ballistic electronic transport at room temperature, low Johnston noise and low charge scattering, have made it a gold mine for novel applications. Since its discovery in 2004, there have been a plethora of studies on characterizing its unique physical, chemical and electrical properties of graphene as well as on integrating it with various physical/chemical systems to utilize these properties. But there have been limited or no studies on the integration of graphene with living microorganisms or mammalian cells. Here we describe the novel wrapping of a single live bacterium (\textit{Bacillus cereus}) with a chemically modified graphene sheet functionalized with the protein Concanavalin-A (Con-A) via the highly specific Con-A - Teichoic acid interaction. We are investigating the structural and the electrical properties of these novel bacteria-FCMG ensembles. Further, we are also interested in characterizing this wrapping process in detail by studying the kinetics and the mechanism of action of bacterial-wrapping via 3D modelling. This is a first step towards the live-bio-nano-integration of graphene which would open up avenues for applications as diverse as bio-batteries using the \textit{Geobacter} to recombinant enzyme compartmentalization. [Preview Abstract] |
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C1.00194: Mechanical Properties of Bacteriophage P2 Capsid Van Chien Bui, Kyoung Jin Kim, Seong Soo Choi The mechanical properties of bacteriophage P2 capsids have been examined by nanoindentation technique by means of a tip of an atomic force microscope (AFM). Studies have been carried out on fully filled and 2/3 filled capsids containing dsDNA genomes. The phage sample was prepared on a copper grid with support film through a specific procedure for the transmission electron microscopy observation, and on pure glass substrate for AFM measurements. In order to get the quantitative information of the capsid elasticity, the force curves between the AFM tip and the phage capsids have been measured. The contact region of the force curve in approach mode has been used for the calculation of the Young's moduli as well as the internal pressures of the capsids. Using the continuum theory of elasticity for thin homogeneous shells we deduced the Young's moduli of fully filled and 2/3 filled phage capsids of 1.17 $\pm $ 0.10 GPa and 0.87 $\pm $ 0.10 GPa, respectively. Analysis of the force curves also showed that fully filled capsid stores higher internal pressure than 2/3 filled capsid does. The detailed explanation for the calculation of the Young's modulus and internal pressure will be discussed. [Preview Abstract] |
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C1.00195: FLUIDS AND SOFT MATTER |
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C1.00196: ABSTRACT WITHDRAWN |
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C1.00197: Aggregation and shear flow in a latex Suresh Ahuja A latex when subjected to shear can exhibit Newtonian or a non-Newtonian flow and a yield stress depending on inter-particle forces. Under dynamic deformation, elastic modulus shows a plateau as the shearing frequency is decreased. Acrylic latex was made under varying processing conditions, which resulted in differences in yield stress, elastic modulus and non-Newtonian behavior. The elastic modulus showed linear fit to yield stress and exponential fit to particle size of latex. The results are compared with non-linear elastic model that predict power law and exponential fits. The model uses microscopic statistical mechanical theory, which describes glassy dynamics based on a non-equilibrium free energy that incorporates local cage correlations and activated barrier- hopping processes. [Preview Abstract] |
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C1.00198: Computer Simulation of a Magnetized Two-Dimensional System Girija Dubey We performed extensive computer simulations on a two-dimensional electron system in a perpendicular magnetic field. The calculations cover the various values of the coupling parameters.The effect due to magnetic field is systematically studied as a function of coupling parameters for both static and dynamical properties. [Preview Abstract] |
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C1.00199: Dynamics of Nanoconfined Fluids measured by combined Force Microscopy and Fluorescence Correlation Spectroscopy Venkatesh Subba Rao, Mircea Pantea, Christopher Grabowski, Ashis Mukhopadhyay, Peter Hoffmann We present work performed on a model liquid, tetrakis(2-ethylhexoxy)silane (TEHOS), using Atomic Force microscopy (AFM) and Fluorescence Correlation Spectroscopy (FCS) to study its dynamical structure at the nanoscale. A novel homebuilt interferometer-based small amplitude AFM was used to measure directly the stiffness and damping coefficient of TEHOS film. Oscillations in stiffness and damping coefficient with period $\sim $1 nm (TEHOS molecular size) were observed. Translational diffusion in spin-coated TEHOS films was measured using Fluorescence Correlation Spectroscopy (FCS). Diffusion was found to be heterogeneous. Finally we present the ongoing work on an integrated platform of AFM and FCS to perform simultaneous measurements of nanoconfined fluids. Recent results using this new setup on a fluorescently labelled nanoparticle solution in confinement will be discussed. [Preview Abstract] |
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C1.00200: Cantilever mechanics and Atomic Force Microscopy study of TEHOS Shah Khan, Peter Hoffmann Properties of nanoconfined liquids have long been shown to be significantly different from the bulk, but the introduction of AFM has dramatically changed the pace of progress in this field. In this report, we present AFM study of a model liquid, tetrakis (2-ethylhexoxy) silane (TEHOS), using a state of the art small amplitude AFM. Besides calculating the stiffness of TEHOS, Derjaguin approximation has been used to calculate the size and sharpness of an unknown tip with the help of a standard spherical tip of precisely known diameter. Magnitude and oscillatory profiles of the force- versus- distance have been obtained using two different simultaneously measured sets of signals. Also, identical oscillating patterns of elastic modulus of TEHOS against the distance of approach have been obtained by complementary methods using the static deflection signal and the amplitude of the cantilever. [Preview Abstract] |
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C1.00201: Analysis of interactions between CNTs and LCs in a binary nematic mixture during Freedericksz transition in electric field Georgi Georgiev, Zarnab Iftikhar, Yaniel Cabrera, Peter Gati, Michael Mattera, Austin Potter, Peggy Cebe Making electro-optic cells by mixing them with organic liquid crystals shows a promise to allow alignment and orientation of the nanotubes using nematic coupling, surface anchoring, and electric and magnetic fields. This approach can be used to create electromechanical devices, for example a nanoswitch, and to position the carbon nanotubes in a particular 3D orientation. We chose 5CB as a liquid crystal because of its large dipole moments and birefringence, which are necessary for microscopic transmission ellipsometry; the method that we use to study the orientation of the carbon nanotubes as a function of the electric field. A downshift in the transition voltage for the carbon nanotube doped electro-optic cells was observed during the Freedericksz transition. [Preview Abstract] |
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C1.00202: Lithographic use of highly ordered toric focal conic domain (TFCD) in confined system Yun Ho Kim, Dong Ki Yoon, Hyeon Su Jeong, Jung Hyun Kim, Eun Kyung Yoon, Hee-Tae Jung Large area ordered structure by organic molecular soft building blocks is one of the most exciting interdisciplinary research areas in current materials science$^{1}$ and nanotechnology. To date, several distinct organic building blocks---including colloids, block copolymers and surfactants--- have been examined as potential materials for the creation of lithographic templates. Here we report that perfect ordered-arrays of toric focal conic domains (TFCDs) covering large areas can form by semi-fluorinated smectic liquid crystals (LCs). Combined with controlled geometry, i.e. microchannel, our smectic LC system exhibits high density of TFCDs that are arranged with remarkably high regularity. Direct visualization of the internal structure of TFCDs clearly verified that the smectic layers were aligned normal to the side walls and parallel to the top surface, and merge with the circular profile on the bottom wall surface. Moreover, we demonstrate the new concept of smectic LC lithography technique. Grown in microchannels from a mixture of LC molecules and fluorescent particles, TFCDs of the smectic LCs acted as a template, trapping particles in an ordered array. In addition to, the uniform radial director field of smectic LC molecule in TFCD is used as microlens for photolithographic process. The present findings pose new theoretical challenges and potentially open the way for lithographic applications based on smectic liquid crystalline materials. [Preview Abstract] |
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C1.00203: Miscibility behavior of blends of spiropyran chromophore and mesogenic diacrylate Harris Lam, Namil Kim, Thein Kyu The phase diagram of blends of photochromic molecule (spiropyran) and mesogenic diacrylate monomer (RM257) has been constructed experimentally and theoretically. The phase diagram involving solid-liquid phase transition has been investigated using differential scanning calorimetry (DSC) and subsequently the theoretical calculation was performed by self-consistently solving the combined free energies of Flory-Huggins (FH), Maier-Saupe (MS), and phase field (PF) theory. The simulated phase diagram composed of various coexistence regions involving single component mesophases (Cr$_{1}$, Cr$_{2}$, N$_{2})$ and several coexistence phases (Cr$_{1}$ + I$_{2}$, Cr$_{1}$ + N$_{2}$, Cr$_{1}$ + Cr$_{2})$ accorded well with the experimental results. These predicted coexistence regions have been further confirmed by conducting several temperature quench experiments into these coexistence gaps by means of optical microscopy (OM). The development of phase morphology will be discussed in relation to the phase diagram. [Preview Abstract] |
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C1.00204: Multiscale Dynamics of Pre-Transitional Fluctuations in the Isotropic Phase of a Lyotropic Liquid Crystal Mikhail Anisimov, Christopher Bertrand, Kirt Linegar, Andrei Kostko Using an improved static and dynamic light scattering technique, we have observed multiscale relaxation of the pre-transitional fluctuations in the isotropic phase of a cromolyn aqueous solution, a lyotropic liquid crystal where rods are formed by aggregates of disc-like molecules. We have detected the onset of cromolyn aggregation about 12 C above the transition temperature. The onset is manifested by the emergence of strong scattering due to the fluctuations of local anisotropy and by the split of the diffusion dynamics into two modes, one associated with the diffusion of the cromolyn monomers and the other one with the diffusion of the cromolyn aggregates. A third observed dynamic mode is associated with the pretransitional slowing down of the fluctuations of local anisotropy. This mode behaves differently in polarized and depolarized light scattering, due to a coupling between the fluctuations of anisotropy and velocity fluctuations. [Preview Abstract] |
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C1.00205: Phase equilibria of a polymer discotic liquid crystal mixture. Tsang-Min Huang, Thein Kyu Thermodynamic phase diagrams of a polymer dispersed liquid crystal (PDLC) containing a monomeric discotic liquid crystal (DLC) and a polymer have been established theoretically by combing Flory-Huggins theory for the free energy of mixing of isotropic phase and Chandrasekhar-Clark theory for the phase transition of hexagonal crystalline ordering of discotic liquid crystals. By varying interaction parameter of hexagonal columnar phase, columnar-isotropic and columnar-nematic-isotropic phase transitions can be predicted. The spinodal line of the columnar DLC/polymer will be calculated in conjunction with the conventional liquid-liquid spinodal. Effects of various molecular parameters on the columnar LC phase diagram will be discussed. [Preview Abstract] |
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C1.00206: Study of liquid crystal molecular dynamics algorithm Jones Tsz-Kai Wan Recent years have witnessed the growth in controlling liquid crystal (LC) alignment using patterned surfaces. Computer simulation of actual LC configurations that are due to different substrate surfaces is a useful tool to aid the design of practical LC cells. In liquid crystal simulations, one seeks for an optimal configuration of the LC director field n(r) that minimizes the total energy of the LC cell. For non-uniform substrate surfaces, the spatial variation of the LC is complicated and the minimization of the total energy is accomplished by advance numerical techniques like conjugate gradient (CG). In a recent work, the author proposed an efficient simulation scheme called liquid crystal molecular dynamics (LCMD), which is developed to determine liquid crystal configurations in complex physical environments. In this work, the author studies the limitation of such scheme and investigates how the simulation parameters can be tuned to achieve optimal performance. [Preview Abstract] |
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C1.00207: Atomistic DMD Simulations of Spontaneous Formation of Nematic and Smectic Phase in a Model Liquid Crystal Apichart Linhananta, Ian MacKay We present atomistic discontinuous molecular dynamics (DMD) simulations of the bulk liquid crystal phases of the molecular fluid 8CB. The model is based on previous DMD models of protein folding (A. Linhananta, J. Boer and Ian MacKay, \textit{J. Chem. Phys.}, 2005, \textbf{122}, 114901) in which all atoms including polar hydrogen, but not nonpolar hydrogen, are represented. Bonded pairs interact by infinite square well, while nonbonded atoms interact by hard-sphere square-well potentials. For the model 8CB, molecular parameters are scaled using AMBER and CHARMM force fields. The hard interaction potentials allow very rapid equilibration of ordered phases. Starting the DMD simulations from initial random states, without positional or orientation order, the 8CB systems spontaneously form ordered nematic and smectic phases. The simulations were performed in a 40 A X 40 A X 40 A box with 100 to 500 8CB molecules. At fixed temperature, as the density increases, the phase change from disorder to nematic to smectic. Finally a density-temperature phase diagram is presented. [Preview Abstract] |
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C1.00208: An improved differential effective medium model for the viscosity of hard sphere suspensions at arbitrary volume fractions. Carlos Mendoza, Ivan Santamaria-Holek We propose a simple and general model accounting for the dependence of the viscosity of a hard sphere suspension at arbitrary volume fractions. The model constitutes a continuum-medium description based on a recursive-differential method where correlations between the spheres are introduced through an effective volume fraction. In contrast to other differential methods, the introduction of the effective volume fraction as the integration variable implicitly considers interactions between the spheres of the same recursive stage. The final expression for the viscosity scales with this effective volume fraction which allows to construct a master curve that contains all the experimental situations considered. The agreement of our expression for the viscosity with experiments at low- and high-shear rates and in the high-frequency limit is remarkable for all volume fractions. [Preview Abstract] |
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C1.00209: Adsorption energy of nanoparticles at liquid/liquid interfaces Kan Du, E. Glogowski, T. Emrick, T. Russell, A. Dinsmore We investigated the adsorption energy of nanoparticles at liquid/liquid interfaces by measuring the change of interfacial tension during the self-assembly of nanoparticles at interfaces. The sessile-droplet and pendent-droplet methods were used to measure the interfacial tension of liquid-gallium/water and oil/water interfaces. Interfacial tensions were measured under different conditions, including the concentrations and sizes of nanoparticles, ligand composition, solution pH, and ionic strength. The measurements showed that interfacial tension can change by an amount ranging from 0.5 to 150 mN/m. From the change in interfacial tension, we obtain the adsorption energy per nanoparticle, which ranges from less than 10 $k_{B}T$ to more than 1000 $k_{B}T$. The results should contribute to the fabrication of membranes and other nano-composite materials by interfacial assembly. [Preview Abstract] |
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C1.00210: Controlling Stability and Rheology of Organic Foams Jamie Kropka, Mathew Celina It is often important to understand the stability and flow properties of polymeric foams in order to optimize industrial processing conditions or design new materials. The fact that foaming, polymerization and temperature rise are often coupled in these systems makes it difficult to even characterize existing materials, much less model behaviors to optimize formulations and processing conditions. To make progress in this area, we have developed model foaming systems that decouple these processes and allow us to characterize the physical properties of liquid foams. We are specifically interested in understanding the controlling factors of foam persistence, shear stability, and rheological behavior. We show both chemical (e.g., partial polymerization) and physical (e.g., particulate additives) means of tuning foam persistence as well as both small strain deformation flow and the less understood liquid-like flow at high applied stresses. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. [Preview Abstract] |
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C1.00211: Growth and self-assembly of water drops over evaporating polymer solutions Vivek Sharma, Mohan Srinivasarao Water drops that nucleate and grow over evaporating polymer solutions exhibit non-coalescence and pack like hard spheres. In this study, we elucidate how the creation and evolution of a population of close packed drops occur in response to the heat and mass fluxes involved in water droplet condensation and solvent evaporation. We describe a rich array of experimental observations about water droplet growth, noncoalescence and assembly that have not been reported in the published literature so far. The pursuit of perfect packing in growing, assembling water drops is qualitatively similar to colloidal crystallization. We examine the role of solvent and polymer in controlling the kinetics of growth and assembly of droplets, which eventually evaporate away, producing a polymer film with ordered array of pores. [Preview Abstract] |
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C1.00212: Molecular Dynamics of the Sedimentation of polydisperse colloids Manuel Valera, Athula Herat, Joseph Yarzebinski, Marisa Hicks We have performed molecular dynamics simulation on colloidal systems composed of~polydispersed hard spheres. The polydispersivity in the~systems had a Gaussian distribution~with a range of up to 10{\%}. ~We studied system where gravity plays a fundamental role. We show the sedimentation profiles and the effects on layering and crystallization for different values of the gravitational length, polidispersivity and area density of the system. [Preview Abstract] |
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C1.00213: Gradient Sensing in Reactive, Ternary Membranes Olga Kuksenok, Anna C. Balazs Using computer simulations, we investigate the behavior of reactive ternary ABC membranes that are subjected to an external, spatially nonuniform stimulus, which controls the rate of interconversion between the A and B components. We assume that A and B have different spontaneous curvatures. Furthermore, the C component is taken to be nonreactive and incompatible with both A and B. We find that a gradient in the applied stimulus causes the dynamic reconstruction of the membrane, with a preferential reorientation of the reactive AB domains along the gradient. In addition, the external gradient effectively controls the transport of the nonreactive C component within the membrane. The latter effect could potentially be exploited for cleaning the membrane of the nonreactive C impurities or for the targeted delivery of the C component to specific locations. [Preview Abstract] |
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C1.00214: Line Tension and the Nature of the Boundary in a Pure Model System Richelle Teeling, Pritam Mandal, Lu Zou, Andrew Bernoff, James Alexander, J. Adin Mann, Elizabeth Mann Insoluble 8CB (4-n-octyl-4 -cyanobiphenyl) layers at the air/water interface provide a well-controlled system on which to analyze the line tension and the nature of the boundary between quasi-two dimensional domains. The average molecular area was adjusted to monolayer liquid/gas or to monolayer/trilayer coexistence. In the first case, difference in dipole moment density leads to long-range repulsive forces which affect line tension and domain configuration. The symmetry of additional bilayers in the second system minimizes such effects, allowing a direct test of the effect of repulsive forces. The line tension of both systems was determined from the hydrodynamic relaxation of stretched domains, through quantitative comparisons with a numerically tractable hydrodynamic model for the relaxation. This research will give insight into similar system of lipids and proteins in biological membranes. [Preview Abstract] |
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C1.00215: Mesoscopic Simulations of Microfluidic Flow in Irregular Geometries Tyler N. Shendruk, Gary W. Slater Stochastic Rotation Dynamics, a particle-based model for mesoscopic fluid dynamics, is used to study two and three-dimensional flow in a variety of complex boundaries and for a range of low Reynolds numbers (between 10 and 200). The systems considered are of two types: they consist of either irregular geometries such as dimpled pipes or require adaptive boundary conditions such as particle impact on a solid boundary. We apply out techniques to microfluidic devices with complex channel walls such as those used for slalom chromatography and sinusoidal undulation surface patterning chromatography. Numerical results showing good agreement with experimental data and previous computational simulations are presented. [Preview Abstract] |
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C1.00216: Polymer Brushes Driven by Electro-Osmotic Flow in Nanoscale Channels Ibrahim Souki, Mohamed Laradji, P.B. Sunil Kumar Using systematic dissipative particle dynamics simulations, we investigated the flow of solvents in nanoscale channels, driven by wall grafted polyelectrolites , under the influence of an oscillating external electric field. Net flow of the fluid is observed when the external field is temporally asymmetric. We found that the flow rate is strongly affected by grafting density, chain length, field amplitude and period. In particular we can achieve an optimum flow rate for specific values of the parameters listed above. The details of polymer kinetics involved and their effect on net fluid flow will be presented. [Preview Abstract] |
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C1.00217: Guiding \textit{E.coli} to nanosensors Dong-Won Park, Hye-Mi So, Beom Soo Kim, Ki-jeong Kong, Hyunju Chang, Jeong-O Lee Electronic nanosensors based on nanomaterials such as carbon nanotubes and nanowires are expected to have ultimate sensitivity. However, as an inherent problem of nanosensors, they have extremely small sensor surface for reaction. Therefore, simple diffusion of target biomolecules is not enough for such nanosensors, and the problem is even more serious in the case of motile bacteria. Previously, we have shown that we could estimate the titer of \textit{E.coli} with arrays of single-walled carbon nanotube field effect transistors (SWNT-FET) combined with statistical method. Still, sensitivity of our method is inferior compared with incubation method, due to the limited sensor surface area. In this work, we actively guide \textit{E.coli} to the sensor surface using micro-fabricated channels. Arrow-shaped and funnel shaped microstructures were fabricated in the channel to guide \textit{E. coli} to the sensor surface, and we used green fluorescent protein expressed \textit{E.coli} to monitor the guiding of \textit{E.coli.} [Preview Abstract] |
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C1.00218: Hydrodynamic flow in a microchannel due to nanocapillary membrane electro-osmotic flow Jarrod Schiffbauer, Will Booth, Kathleen Kelly, Boyd Edwards, Aaron Timperman A model for hydrodynamic flow in a microchannel terminated by a nanocapillary membrane (NCM) is proposed in which the microchannel electric-double layer (EDL) is treated as a boundary-layer, providing a hydrodynamic slip-velocity at the channel wall, and the NCM electro-osmotic flow (EOF) is treated as fully-developed. Applied pressure gradients and the contribution of the microchannel EDL to both the net charge transport and the back-pressure on the NCM are neglected. The proposed coupling between the NCM EOF and microchannel hydrodynamic response is obtained by arguing that the steady-state Onsager symmetry between linear-response coefficients may be applied to the transient response of the microchannel. The resulting form of the Navier-Stokes equation in the microchannel possesses steady-state solutions that are compatible with parabolic and inverted-parabolic profiles observed in NCM sample concentration experiments. [Preview Abstract] |
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C1.00219: Measurements of Stopping Force on Ball on Impact with Granular Medium Joseph Amato, Laura Coyle, Michael Nitzberg We present direct measurements of the deceleration vs. time of a 3.8 cm diameter brass ball plunging into a loose granular bed of 400 - 600 $\mu $m glass beads. Data were obtained using an accelerometer chip housed within the ball. As suggested by Durian and co-workers, the measured force on the ball is well described by a velocity dependent force $\alpha v^2$ plus a separate depth dependent force $\beta (z+z_0 )$. For impact velocities in the range 1.3 -- 5.1 m/s, a single set of parameters $(\alpha ,\beta ,z_0 )$ fits all the data well, with the exception of the first few ms after impact, when the ball is only partially submerged in the granular matter. [Preview Abstract] |
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C1.00220: Fluidization of granular media wetted by liquid $^4$He Kai Huang, Masoud Sohaili, Matthias Schroeter, Stephan Herminghaus We explore experimentally the fluidization of vertically agitated
PMMA spheres wetted by liquid $^4$He at temperatures around the
$\lambda$ point. For wetting by normal fluid helium
($T>T_{\lambda}$), the critical acceleration for fluidization
($\Gamma_c$) shows a steep increase close to the saturation of the
vapor pressure in the sample cell. For superfluid helium
($T |
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C1.00221: Melting in a finite, two-dimensional Yukawa system T.E. Sheridan A complex (dusty) plasma disk is a two-dimensional system of monodisperse microspheres confined by a parabolic well and interacting through a Yukawa potential. (Complex plasma is an open, dissipative sytem.) Consequently, a complex plasma disk is a physical realization of a finite, two-dimensional Yukawa system. Recent experiments on a complex plasma disk with $n \approx 3900$ dust particles [T. E. Sheridan, {\it Phys. Plasmas} {\bf 15}, 103702 (2008)] indicate that the system melts via two second-order topological phase transitions. In the present work, we will model these experimental results using the Metropolis algorithm to generate ensembles of configurations consistent with a given thermodynamic temperature. Model results will be compared with experiment. In particular, we wish to determine the exponent characterizing the power law decay of the bond-orientational correlation function in the hexatic phase, which the experimental results indicate may be greater than that predicted by KTHNY theory. [Preview Abstract] |
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C1.00222: Percolation in Granular Material Mark Zimmerman, D.T. Jacobs Percolation was studied by measuring the resistance to the flow of electricity through a system of conducting and insulating spheres. The percolation threshold was measured on three different size systems by varying the number fraction of conducting spheres in the mixture of 3 mm diameter steel shot and glass spheres as well as 1 mm silver coated glass spheres and uncoated spheres. A dynamic pressure effect was observed in the random-packed system when using the less conducting steel shot but not with the silver coated spheres. Results have qualitative and quantitative similarities to published experimental and simulation work on comparable systems going from 2D to 3D. The percolation threshold observed will be discussed and compared to other experiments as well as simulations. We acknowledge support from NSF DMR-0649112. [Preview Abstract] |
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C1.00223: Self-Organized Criticality in a Bead Pile Mike Winters, D.T. Jacobs This experiment examined a conical bead pile and the distribution of avalanche sizes when using uniform 3mm zirconium spheres ("beads"). A 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 distribution could be compared to a power law description as predicted by self-organized criticality. We had found in an earlier experiment that glass beads dropped from a small height were consistent with a simple power-law, but if dropped from larger heights then a power-law times an exponential was needed. The zirconium beads sometimes had a distribution that deviated from a power-law times an exponential when the beads were dropped from larger heights, and occasionally the distribution showed a distinct enhancement of the probability for large avalanches when beads were dropped from smaller heights. Using data collected over many years, it was found that the density and type of bead did not appear to affect the avalanche distribution. We compare our experimental results to a numerical simulation. We acknowledge support from NSF DMR-0649112. [Preview Abstract] |
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C1.00224: The mussel thread cuticle, a biological granular composite coating Niels Holten-Andersen, Henrik Birkedal, Kaa Yee C. Lee, J. Herbert Waite The cuticle of mussel byssal threads is a peculiar natural granular composite coating that combines high extensibility with high stiffness and hardness. In this study fluorescence microscopy and elemental analysis were exploited to show that the 3, 4-dihydroxyphenyl-L-alanine (dopa) residues of mussel foot protein-1 co-localize with Fe and Ca distributions in the cuticle of \textit{Mytilus galloprovincials} mussel byssal threads. Removal of Fe and Ca from the cuticle by chelation results in a 50{\%} reduction in hardness. Dopa-metal complexes may be a significant source of stability as cross-links in the composite cuticles. [Preview Abstract] |
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C1.00225: Electron Shock Waves Propagating into a Pre-ionized Medium M. Hemmati, N. Rasul, R. Peden We employ a one dimensional, constant velocity, steady-state, three component fluid model to investigate breakdown waves propagating into an ionized medium. Assuming that electron gas partial pressure is much greater than that of the other species, we have been able to write down equations of conservation of the flux of mass, momentum and energy, plus the Poison's equation. The charge concentration ahead of the wave alters the set of fluid equations and also the boundary conditions at the shock front. The ionization rate is calculated by considering ionization from both random and directed electron motions. Integration of the set of electron-fluid dynamical equations for antiforce waves propagating into a pre-ionized medium through the dynamical transition region of the wave for two wave speeds and several current values ahead of the wave was successful. The results for both wave speed values and all current values ahead of the wave meet the expected physical conditions at the end of the sheath region. Calculation of the ionization rate through the sheath region shows that for high wave speeds and for all current values ahead of the shock front, as one approaches the trailing edge of the sheath, the ionization rate increases slightly. However, as the wave speed decreases, for all current values ahead of the shock front, the ionization rate essentially remains constant throughout the sheath region. [Preview Abstract] |
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C1.00226: Bubble Chains in Magnetic Fluids (Ferrofluids) Jong(James) Yoo, Philip Yecko, Wah-Keat Lee Direct numerical simulations are applied to the problem of dynamics of chain formation among small bubbles in a magnetic liquid (ferrofluid), coalescing at low Reynolds number due to magnetophoresis. Complementary experiments performed using high-intensity high-resolution X-ray images of air bubbles in ferrofluid have revealed that linear chains of several small bubbles are extremely common. In numerous applications of ferrofluids, the wanted or unwanted presence of bubbles and bubble chains in particular, is crucial to describing and predicting critical flow properties. In this study we examine the chain formation process between two and three identical bubbles, finding regimes of conditions within which chain formation is expected under a uniform applied magnetic field. We conjecture how these results can be extended to larger numbers of bubbles forming longer chains. Added mass plays a significant role in the magnetophoresis-driven dynamics. We therefore examine the role of the density ratio in the coalescence process among bubbles within the limits imposed by the volume of fluid (VOF) method that we use. [Preview Abstract] |
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C1.00227: Charge transport mechanism of ionic liquids at metallic interfaces Anatoli Serghei, Martin Tress, Joshua Rume, Friedrich Kremer A quantitative description is suggested for electrode polarization, an ubiquitous phenomenon which takes place at the interface between a metallic and an ionic conductor. Based on the fact that, due to Coulombic interactions, the ion mobility is drastically slowed down at the interfaces, this approach quantitatively describes the experimentally observed scaling laws and enables one to deduce -- by use of a novel formula -- the bulk conductivity of the ionic charge carriers under study. It allows furthermore a quantitative determination of the conductivity function of the ionic liquids in the interfacial regions and opens, by that, multiple perspectives in understanding the mechanisms of charge transport at interfaces. [Preview Abstract] |
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C1.00228: Exact thermodynamic calculation of a monatomic system and its ideal glass transition on a new recursive lattice formed by cubic units Ran Huang, Puru Gujrati A many-body Ising lattice model is used to represent monatomic systems and is solved exactly on a new recursive lattice with the aim to study the metastability in supercooled liquids and the ideal glass transition. Interactions between particles farther away than the nearest neighbor distance are taken into consideration. The Ising model is antiferromagnetic in nature so that its ordered phase represents an alloy-type crystal of alternating species (A-B or particle-void). The new recursive lattice appears quite reliable to represent a cubic lattice. Thermal properties including free energy, energy and entropy of the ideal crystal and supercooled liquid state of the model are calculated. The computation results show a first order melting and second order ideal glass transition (entropy crisis) in the supercooled liquid phase. The effects of different energy terms on the two transitions are studied. We also study the defects in the ideal glass, supercooled liquid and the crystal to support the theory that a glass can be treated as a highly defective crystal. [Preview Abstract] |
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C1.00229: Pattern formation in two-dimensional binary mixtures of colloids interacting via short-ranged interactions Carlos Mendoza, Erasmo Batta We report Monte Carlo simulations on the pattern formation in a binary mixture of colloidal particles interacting via short ranged potentials. Such potentials consist of a hard-core square-shoulder interaction if the particles are of the same type and of a hard-core square-well if they are of different type. For 50/50 mixtures, we find a rich variety of patterns that can be grouped mainly in alternate strips each one consisting of particles of the same type or aggregates that self-assembly in a regular square lattice. For mixtures in which the are more particles of one of the species then a phase separation is observed, one of the separated phases consists only of particles of the dominant type while the other is a mixture of both types of particles. [Preview Abstract] |
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C1.00230: ABSTRACT WITHDRAWN |
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C1.00231: Phase Separation in the Advective Cahn-Hilliard Equation with a Chaotic Flow Sohei Yasuda, Benjamin Vollmayr-Lee The phase separation between two immiscible liquids advected by a chaotic flow is studied by numerical simulations of the advective Cahn-Hilliard Equation. It has been shown that the competition between phase separation dynamics, which tends to grow domains, and chaotic flow, which tends to break up the domains, determines the length scale characterizing the domains in the steady state \footnote{L. O. Naraigh, J.-L. Thiffeault, Phys.\ Rev.\ E {\bf 75}, 016216 (2007).}. We extend this analysis to investigate the correlation between the local finite-time Lyapunov exponent field and the domain structure. In particular, we consider alternating sine flows and an alternating periodic vortex flow. We also investigate whether the steady state domain structure demonstrates any history dependence by studying both a initially mixed state and an initially phase separated state. A summary of our results is presented. [Preview Abstract] |
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C1.00232: Controlling Pattern Formation in Polymer and Nanoparticle Assemblies via Programmed Flow-coating Hyun Suk Kim, Mark McDonough, Sam Pendergraph, Alfred Crosby We have developed a novel flow-coating method for assembling periodic polymer and nanoparticle line patterns with controlled spacing and width of lines. In flow-coating, a dilute polymer and/or nanoparticle solution is held by capillary forces under a stationary knife blade fixed at gap height above a substrate fixed to a translating stage. Upon translating the substrate, spontaneous formation of convective polymer and nanoparticle assemblies occurs at the three-phase contact line of the meniscus. We demonstrate that the width and spacing of deposited lines can be controlled over a wide range by using programmed velocity profiles for the translating stage. Deposition of solutes is induced when contact lines are ``stick'' at slow or zero velocity, while limited deposition occurs during ``slip'' at high velocity. We investigate the effect of gap height, concentration, and velocity on the pattern formation This new method provides an easy, robust, and lithography-free method to control the deposition of line pattern of polymers and nanoparticles for various applications. [Preview Abstract] |
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C1.00233: Nonlinear I-V Characteristics of Nano-Pores: Depletion Layer Pattern Formation and Vortex Instability Gilad Yossifon, Hsueh-Chia Chang We report the first direct experimental proof for Rubinstein's instability [1] by using an applied AC electric field across a straight nano-slot, whose transverse dimension is at least 10 times larger than the depletion layer, EO convective flow is completely arrested and ion transport is dominated by diffusion and electro-migration. The ion flux dynamics is imaged using fluorescent dye molecules in combination with confocal microscopy, to understand the non-equilibrium phenomenon of over-limiting current density across a nanoporous membrane. With a slow AC field, an ion depletion front is generated intermittently from one end of the nano-slot and a vortex instability is found to arrest the self-similar diffusive front growth. This electrokinetic instability evolves into a stationary interfacial vortex array that specifies the over-limiting current, independent of external stirring or convective flow. [1] I. Rubinstein, E. Staude and O. Kedem, Desalination 69, 101 (1988). [Preview Abstract] |
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C1.00234: Transfer of colloidal particles using the reversible buckling patterns. Dong Choon Hyun, Unyong Jeong Buckling or wrinkling is a well-known phenomenon. It is realized by releasing strain applied to a hard film on an elastomer substrate. Strain engineering allows the buckling to have the highly ordered and regular wavy surfaces. The amplitude of the buckling can be reversibly tuned by a cycle of applying and releasing strain. This reversible nature of buckling was used to deposit the spherical colloids in the trenches of the wavy patterns and transfer the colloids to flat surfaces. The colloidal deposition and transfer was repeatedly carried out to fabricate identical patterns of colloidal assembly. In this presentation, we will demonstrate complex colloidal patterns (hydrogels colloids, silica, Au nanoparticles, magnetic nanoparticles) transferred from the buckled surfaces. [Preview Abstract] |
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C1.00235: DNA Linker Mediated Assembly of Colloidal Nanoparticles Huiming Xiong, Daniel van der Lelie, Oleg Gang When flexible ssDNA linkers are added to the mixture of two types of dispersed, ssDNAs capped gold nanocolloids which are mutually non-complementary but complementary to the respective ends of the linker DNA, a crystalline phase of body-centered-cubic unit cell forms. The phase diagram of DNA linker mediated nanoparticle assemblies has been experimentally investigated and constructed by using in-situ small angle x-ray scattering. The influence of linkage defects on crystalline structure was also examined. [Preview Abstract] |
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C1.00236: Birefringence Measurements of Spherulites formed in $\beta$-Lactoglobulin Eric Hardin, Brad Kirkwood, Jazmine Loman, Athula Herat, Rizwan Mahmood, Kristin Domike Many proteins have a propensity to aggregate into amyloid fibril containing spherulite-like structures. In some instances these spherulitic protein aggregates have been observed in people suffering from a number of neurodegenerative diseases, including Alzheimer's, Parkinson's, and Creutzfeldt-Jakob's. However, the exact role these aggregates play in the body, their internal structure, and the aggregation mechanism still remains a mystery. The model protein used in our study, $\beta$-lactoglobulin (BLG), produce spherulites under low pH and high temperature conditions. We report birefringence measurement on BLG using phase retardation method as a function of temperature. Birefringence ($\sim $0.0022 $\pm$ 0.0002) data suggest very weak ordering within the spherulites. These spherulites seem to disappear when we added an extensively studied thermotropic liquid crystal [4'-pentyl-4-cyanobiphenyl (5CB)] in $\beta $-Lactoglobulin + water+ hydrochloric acid. Our preliminary data suggests that the strong interaction energy between the two systems may lead to the destruction of spherulites. [Preview Abstract] |
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C1.00237: Solvation structure of ice-binding antifreeze proteins Hendrik Hansen-Goos, John Wettlaufer Antifreeze proteins (AFPs) can be found in organisms which survive at subzero temperatures. They were first discovered in polar fishes since the 1950's [1] and have been isolated meanwhile also from insects, plants, and bacteria. While AFPs shift the freezing point of water below the bulk melting point and hence can prevent recrystallization; the effect is non-colligative and there is a pronounced hysteresis between freezing and melting. For many AFPs it is generally accepted that they function through an irreversible binding to the ice-water interface which leads to a piecewise convex growth front with a lower nonequilibrium freezing point due to the Kelvin effect. \\ Recent molecular dynamics simulations of the AFP from {\it Choristoneura fumiferana} reveal that the solvation structures of water at ice-binding and non-ice-binding faces of the protein are crucial for understanding how the AFP binds to the ice surface and how it is protected from being overgrown [2]. We use density functional theory of classical fluids in order to assess the microscopic solvent structure in the vicinity of protein faces with different surface properties. With our method, binding energies of different protein faces to the water-ice-interface can be computed efficiently in a simplified model. \\ {[1]} Y. Yeh and R.E. Feeney, Chem. Rev. {\bf 96}, 601 (1996). \\ {[2]} D.R. Nutt and J.C. Smith, J. Am. Chem. Soc. {\bf 130}, 13066 (2008). [Preview Abstract] |
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C1.00238: Hovering of a free rigid pyramid in an oscillatory air flow Bin Liu, Brendan Folie, Annie Weathers, Jun Zhang, Stephen Childress We investigate the dynamics of free rigid bodies when moving in an oscillating background flow. Given a pyramid-shaped object, the fluid drag due to a downward flow and an upward flow around the body differ when the inertia of the air flow is relevant. We find that when the amplitude of the air flow is above a threshold, the net lift on the pyramid overcomes its weight. The body then starts to hover, despite the fact that the air flow has no upward or downward preference. The threshold amplitude of the oscillating air depends on the weight of the rigid object and its geometric anisotropy. We show that at a given frequency there is an optimal shape of the pyramid, such that hovering occurs at minimal amplitude of the flow. [Preview Abstract] |
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C1.00239: ABSTRACT WITHDRAWN |
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C1.00240: GENERAL PHYSICS |
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C1.00241: Mass, Energy, Space And Time System Theory---MEST A way to help our earth Dayong Cao There are two danger to our earth. The first, the sun will expand to devour our earth, for example, the ozonosphere of our earth is be broken; The second, the asteroid will impact near our earth. According to MEST, there is a interaction between Black hole (and Dark matter-energy) and Solar system. The orbit of Jupiter is a boundary of the interaction between Black hole (and Dark matter-energy) and Solar system. Because there are four terrestrial planets which is mass-energy center as solar system, and there are four or five Jovian planets which is gas (space-time) center as black hole system. According to MEST, dark matter-energy take the velocity of Jupiter gose up. So there are a lot of asteroids and dark matter-energy near the orbit of Jupiter-the boundary. Dark matter-energy can change the orbit of asteroid, and take it impacted near our earth. Because the Dark matter-energy will pressure the Solar system. It is a inverse process with sun's expandedness. So the ``two danger'' is from a new process of the balance system between Black hole (and Dark matter-energy) and Solar system. According to MEST, We need to find the right point for our earth in the ``new process of the balance system.'' [Preview Abstract] |
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C1.00242: On the Earthly Origin of the Penzias-Wilson Microwave Background Dmitri Rabounski, Larissa Borissova According to the experimental analysis conducted by P.-M. Robitaille, the 2.7K microwave background, first detected by Penzias and Wilson, is not of cosmic origin, but of the Earth, and is generated by oceanic water. With these we have two entire fields to consider (Robitaille, Progr. Phys., 2007, v.4, 74): (1) the Earth Microwave Background, the EMB, present with the 2.7K monopole and 3.5mK dipole components; (2) the weak (micro Kelvins) Intergalactic Microwave Background, the IMB, which is connected to the entire Metagalaxy. This conclusion meets our theory. First, the field density of the EMB, being inversely proportional to the field volume, should decrease with the cube of the distance from the Earth's surface, while its dipole anisotropy, which is due to the motion of the entire field in common with the Earth, is independent from altitude. Therefore the EMB monopole shouldn't be found at the 2nd Lagrange point (far distant from the Earth), while the dipole anisotropy remained the same that near he Earth. Second, Einstein's equations for commonly the EMB and the IMB are valid only if the Metagalaxy's entire space rotates, that permits some cosmological conclusions. [Preview Abstract] |
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C1.00243: PAW dataset library for the Quantum-Espresso package Rashid Hamdan, Chao Cao The frozen-core approximation is widely employed in plane-wave density functional theory calculations, because it can greatly reduce the required cut-off energy to achieve convergence. The commonly used ultra-soft pseudopotential method is one flavor of this approximation. Despite its advantages, the ultra-soft pseudopotentials are difficult to generate, and it is difficult to control the quality. It is also impossible to reconstruct the complete wave functions from the pseudopotential method calculations. The PAW method was developed to conquer these difficulties. We have constructed a set of soft, reliable PAW dataset library for the Quantum-Espresso package. The datasets were thoroughly tested, and the results were compared with VASP calculations. As a demonstration, we present the comparison with VASP calculations for Bromine doped graphite system and a comparison between the ultra-soft pseudopotential and PAW calculations of the recently discovered iron-based superconductor LaFeAsO compound. The PAW calculations yielded magnetic moment that is much closer to experimental value than the ultra-soft pseudopotential calculations. [Preview Abstract] |
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C1.00244: Green Energy - Fiction and Reality Lawrence Cranberg The term ``Green Energy'' has been popularized to refer to energy sources that do not depend on fossil fuels. The oldest truly ``green'' energy source is wood fuel derived by photosynthesis for thermal comfort in the cold season. Thermal energy from the combustion of wood for personal heating in our 41 million fireplaces has greatly declined, due to an ``Anti-fireplace Hoax'' (1) that fireplaces are ``energy counterproductive.'' Physicists have a special obligation to address the problem that our major true source of ``Green Energy'' is widely misrepresented and neglected. 1. L. Cranberg, The Physics Teacher, Letter, January,l989 [Preview Abstract] |
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C1.00245: Biothermophotonic evaluation of multilayered tissue structures. Anna Matvienko, Andreas Mandelis, Stephen Abrams Biothermophotonics is a novel non-invasive method for safe in vivo evaluation of thermal and optical properties of tissues. The method involves analysis of photothermal field induced in a sample by frequency-modulated laser excitation and following optical-to-thermal energy conversion. The theoretical model for fitting the properties of the sample features coupled diffuse-photon-density-wave and thermal-wave mathematical description. The sample is considered to be a multilayered one-dimensional structure. The best fits to the model are obtained with Simplex Downhill algorithm for multi-parameter minimization. The results demonstrated robustness of the algorithm and the capabilities of the method to simultaneously evaluate optical and thermal properties of multilayered tissue structures in vivo. [Preview Abstract] |
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C1.00246: STATISTICAL AND NONLINEAR PHYSICS |
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C1.00247: Excursion time distributions of heartbeat time series Israel Reyes-Ramirez, Lev Guzman-Vargas We present a study of heart interbeat time series based on excursion time distributions from healthy subjects and patients with heart failure. We describe some differences between these groups by means of the calculation of the characteristic time scale of the exponential distributions for stationary segments. We also compare day-night periods for both groups. In particular, we find that the characteristic time scale associated to the healthy group is slightly smaller than the heart failure group, indicating that large exrcursions are more probable under pathologic conditions. When day-night period are compared, we observe that night records lead to a smaller time constant than day records. Moreover, we simulate correlated noises with power spectrum of the form $S(f)\sim f^{-\beta}$ with $0<\beta<1$, to detect changes in the excursion time distributions with the presence of long-range correlations. Finally, we discuss our results in the context of heartbeat dynamics. [Preview Abstract] |
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C1.00248: Mittag-Leffler Correlated Noise and Anomalous Diffusion within a Single Protein Molecule Ke-Gang Wang, Daniel Vi\~nales, Marcelo Desp\'osito One of authors (Wang) studied the motion of a particle under the influence of a random force modeled as Gaussian colored noise with arbitrary correlation and with/without external force (Wang et al., Physica A \textbf{265, }341(1999)). The generalized Langevin equation, Generalized Fokker-Planck equation, and the variances of displacement, velocity and cross variance between displacement and velocity are obtained in that paper. Recently, Xie et al. (Phys. Rev. Letters. \textbf{93}, 180603 (2004), \textbf{94}, 198302 (2005)) applied the theory developed by Wang to explaining the anomalous diffusion within a single protein molecule. However, in this presentation, we will show that using Mittag-Leffler correlated noise and generalized Langevin equation can more accurately explain the experimental data of autocorrelation function of distance in a single protein molecule. [Preview Abstract] |
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C1.00249: Contact process with sublattice symmetry breaking Ronald Dickman, Marcelo Martins de Oliveira We study the phase diagram and scaling properties of a contact process with creation at first- and second-neighbor sites and inhibition at first-neighbors. Inhibition takes the form of an increased annihilation rate, proportional to the square of the number of occupied neighbors of a given site. The pair approximation predicts the existence of three phases, inactive (absorbing), active symmetric, and active asymmetric, the latter exhibiting distinct sublattice densities on a bipartite lattice. These phases are separated by continuous transitions in the space of control parameters; the phase diagram is reentrant. Monte Carlo simulations in two dimensions verify the existence of a phase with broken sublattice symmetry. The symmetric-asymmetric transition appears to belong to the Ising universality class, as expected from symmetry considerations. [Preview Abstract] |
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C1.00250: Weakly disordered absorbing-state phase transitions Jos\'e Hoyos The effects of quenched disorder on nonequilibrium phase transitions in the directed percolation universality class are revisited. Using a strong-disorder energy-space renormalization group, it is shown that for any amount of disorder the critical behavior is controlled by an infinite-randomness fixed point in the universality class of the random transverse-field Ising models. The experimental relevance of our results are discussed. [Preview Abstract] |
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C1.00251: Absorbing-state transitions on percolating lattices Man Young Lee, Thomas Vojta We study the nonequilibrium phase transitions of reaction-diffusion systems into absorbing states. In the presence of quenched disorder, i.e., spatial impurities or defects, the interplay between geometric and dynamical fluctuations leads to exotic behavior and ultraslow dynamics. Specifically, we investigate the contact process on a randomly diluted lattice. We find that the nonequilibrium phase transition across the percolation threshold of the lattice is characterized by unconventional activated (exponential) dynamical scaling and strong Griffiths effects. We calculate the critical behavior in two and three space dimensions, and we relate our results to the infinite-randomness fixed point in the disordered one-dimensional contact process. To confirm the universality of this exotic scaling scenario we also study generalizations of the contact process involving several absorbing states, and we support our calculations by Monte-Carlo simulations. [Preview Abstract] |
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C1.00252: Infinite-randomness critical point in the two-dimensional disordered contact process Adam Farquhar, Jason Mast, Thomas Vojta We study the nonequilibrium phase transition in the two-dimensional contact process on a randomly diluted lattice by means of large-scale Monte-Carlo simulations for times up to $10^{10}$ and system sizes up to $8000 \times 8000$ sites. Our data provide strong evidence for the transition being controlled by an exotic infinite-randomness critical point with activated (exponential) dynamical scaling. We calculate the critical exponents of the transition and find them to be universal, i.e., independent of disorder strength. The Griffiths region between the clean and the dirty critical points exhibits power-law dynamical scaling with continuously varying exponents. We discuss the generality of our findings and relate them to a broader theory of rare region effects at phase transitions with quenched disorder. Our results are of importance beyond absorbing state transitions because according to a strong-disorder renormalization group analysis, our transition belongs to the universality class of the two-dimensional random transverse-field Ising model. [Preview Abstract] |
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C1.00253: Efficiency, coherent transport and entropy fluctuations in a Brownian motor driven by time-dependent temperature Ronald Benjamin We investigate the transport and energetics of a Brownian motor driven by position dependent temperature. We found that coupling enhances the current as well as the efficiency. Novel features such as current reversal with respect to the coupling strenth and inertia of the Brownian particle is also observed. We also find that the total entropy production satisfies the fluctuation theorem in the steady state. [Preview Abstract] |
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C1.00254: Unified approach to the derivation of work theorems for equilibrium and steady-state, classical and quantum Hamiltonian systems Daniel Kosov, Maxim gelin The fluctuation theorems rigorously relate equilibrium ensemble properties of a dynamical system with its evolution under nonequilibrium conditions, beyond the domain of validity of the linear response theory. We present a unified and simple method for deriving work theorems for classical and quantum Hamiltonian systems, both under equilibrium conditions and in a steady state. We adopt the partitioning of the total Hamiltonian into the system part, the bath part, and their coupling. We rederive many equalities which are available in the literature and obtain a number of new equalities for nonequilibrium classical and quantum systems. Our results can be useful for determining partition functions and generalized free energies through simulations or measurements performed on nonequilibrium systems. We derive a semiclassical version of the work theorem and discuss the definition of semicalssical work operator. Phys.Rev. E 78, 011116 (2008) [Preview Abstract] |
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C1.00255: On the quantum master equations for BCS-type quasiparticles C.F. Huang, K.-N. Huang The quantum master equations are introduced for the density matrices of BCS-type quasiparticles, which may include both the particle-particle and particle-hole couplings. The constraints to relate the loss and gain factors are important to preserve the forms of the density matrices under such equations. These two factors describe not only the scattering where the number of quasiparticles are conserved, but also the creation and destruction of quasiparticles. The introduced equations can be reduced to the semiclassical master equations in the homogeneous limit. [Preview Abstract] |
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C1.00256: Obtaining the fractal dimensions and length distributions for the external hulls of Q-state Potts model clusters David Adams, Leonard Sander, Robert Ziff We obtain the fractal dimensions of the complete and external hulls of Q-state Potts model clusters. We grow percolation clusters (Q=1) using the Leath method. For Q$>$1 up to the upper critical dimension (Q=4), we grow Fortuin-Kasteleyn (FK) clusters using the Swendson-Wang method. Our results for fractal dimension for the complete and external hulls agree with the predictions of Duplantier. We also obtain the distribution of complete and external hull lengths and cluster height. For a given Q, the distributions for different size systems can be collapsed using scaling. The distributions of heights display simple exponential tails, which can be understood in terms of hull walks and the geometry of the system. [Preview Abstract] |
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C1.00257: Fractal structure of a solvable lattice model Kazuhiko Minami A fractal set which corresponds to the six-vertex model is introduced and a relationship between the free energy of the six-vertex model and the fractal dimension of the fractal set is formulated. It is pointed out that notions which correspond to the transfer matrix method and the n-equivalence relation in lattice theory have been introduced in the area of fractal geometry. These relations can be generalized to the case of the models suitable to the transfer matrix treatment. [1] K.Minami, An Equivalence Relation of Boundary/Initial Conditions and the Infinite Limit Properties, J. Phys. Soc. Jpn. 74 (2005) 1640. [2] K.Minami, The Free Energies of Six-Vertex Models and the n-Equivalence Relation, J. Math. Phys. 49 (2008) 033514. [3] K.Minami, Fractal structure of a solvable lattice model, cond-mat/0801.0186 [Preview Abstract] |
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C1.00258: The Role of Walls' Stochastic Forces in Statistical Mechanics -- Irreversibility and Transition from One Microstate to Large Number of Microstates Madhav Gautam, Puru Gujrati A statistical system, by definition, experiences uncontrollable stochastic interactions with the surrounding and allow for irreversibility.$^{(1)}$ A purely deterministic system will not show any irreversibility.$^{(2)}$ One can model the walls of the container containing a system to be the source of these stochastic impulses. We present the results of such stochastic walls' impulses on a single particle in a one-dimensional box of a fixed length. At each collision with the walls, the velocity changes due to stochastic impulses so that the velocity becomes unpredictable. After a long period of time, a single initial velocity results in a distribution of velocities. If the strength of the impulse is not too strong, the average kinetic energy reaches a finite limit, so that it can be used to define the temperature. \\[4pt] 1) ``Irreversibility, molecular Chaos, and A simple proof of the second law'' P.D.Gujrati, http://arxiv.org/abs/0803.1099 (arXiv:0803.1099) \\[0pt] 2) ``Poincare Recurrence, Zermelo's Second Law Paradox, and Probabilistic Origin in Statistical Mechanics'' P.D.Gujrati, http://arxiv.org/abs/0803.0983 (arXiv:0803.0983) [Preview Abstract] |
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C1.00259: Lack of Molecular Chaos and the Role of Stochasticity in Kac's \textit{Ring} Model Pradeep Fernando, Puru Gujrati The dynamics of a system can either be deterministic or stochastic. In deterministic dynamics, there is unique \textit{one-to-one }relationship between the initial state of the process and its evolution at a later time, while in stochastic process, there are several possible outcomes or evolved sates in future. Since the outcome is not certain, there are \textit{one-to-many} relationships between the current states and its evolution in future. We use simple \textit{Kac ring model} to demonstrate the properties of deterministic and stochastic dynamics. The results lead us to understand the following: 1) In deterministic dynamics, the memory of the initial state is never lost and therefore no equilibrium state will ever appear. Instead, the initial sate recurs eventually following Poincare Recurrence. In particular, molecular chaos assumption of Boltzmann cannot be justified. 2) In stochastic dynamics the system reaches equilibrium irrespective of the initial state. References: [1] P.D. Gujrati, Irreversibility, Molecular Chaos, and A Simple Proof of the Second Law, http://arxiv.org/abs/0803.1099 (arXiv:0803.1099) [2] P.D. Gujrati, Poincare Recurrence, Zermelo's Second Law Paradox, and Probabilistic Origin in Statistical Mechanics, http://arxiv.org/abs/0803.0983 (arXiv:0803.0983) [Preview Abstract] |
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C1.00260: Response of a simple dynamical network to stress or strain Nasrin Afzal, Michel Pleimling Motivated by a recent series of experiments that study the response of the cytoskeleton of living cells to mechanical forces, we study numerically a simple dynamical network where new links are formed and existing links are dissolved with probabilities that can depend on time. We thereby mimic mechanical stress and strain by protocols where we rapidly change the geometry of the network. Interestingly, the number of links in the network displays a nontrivial time dependence during these protocols. [Preview Abstract] |
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C1.00261: Node weight distribution and disparity of some bipartite networks Xiu-Lian Xu, Chun-Hua Fu, Da-Ren He We present an empirical investigation of 14 real world networks, which can be described by bipartite graphs. Each node is assigned a node weight, which denotes the obtained competition result. Firstly, empirically we observed that the total node weight distributions of all the systems may be fitted by shifted power law function form. The key parameters of the function can be used to describe the disparity. Secondly, a node weight disparity is defined for the same purpose. The empirical relationships between the parameters are obtained. The results show that the node weight distribution is very uneven. [Preview Abstract] |
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C1.00262: Properties of four real world collaboration--competition networks Chun-Hua Fu, Xiu-Lian Xu, Da-Ren He Our research group has empirically investigated 9 real world collaboration networks and 25 real world cooperation-competition networks. Among the 34 real world systems, all the 9 real world collaboration networks and 6 real world cooperation-competition networks show the unimodal act-size distribution and the shifted power law distribution of degree and act-degree. We have proposed a collaboration network evolution model for an explanation of the rules [1]. The other 14 real world cooperation-competition networks show that the act-size distributions are not unimodal; instead, they take qualitatively the same shifted power law forms as the degree and act-degree distributions. The properties of four systems (the main land movie film network, Beijing restaurant network, 2004 Olympic network, and Tao-Bao notebook computer sale network) are reported in detail as examples. Via a numerical simulation, we show that the new rule can still be explained by the above-mentioned model. [1] H. Chang, B. B. Su,\textit{ et al}. Phsica A, 2007, 383: 687-702. [Preview Abstract] |
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C1.00263: A model of the world languages distribution Ai-Xia Feng, Da-Ren He The world language distribution is described by a bipartite graph. One kind of nodes is the languages; the other is the countries where some languages are used. When interested in interactions between the languages, we project the bipartite graph onto the language nodes and obtain a unipartite graph. After investigating the node strength distribution of the unipartite network we realize that the language distribution shows a kind of duality property. Thus, we set up a model to interpret and explain the property. Also, we explained, by using the model, the empirical results about the clustering coefficient distribution and the average nearest neighbor strength distribution. [Preview Abstract] |
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C1.00264: Monte-Carlo simulations for two-stage percolation transition of the enhanced trees Takehisa Hasegawa, Tomoaki Nogawa We investigate the bond percolation problem on the enhanced
binary tree (EBT).
The EBT is given by adding intra-generation links to the binary
tree.
The EBT belongs to the class of {\it nonamenable graphs} (NAGs),
and percolations on NAGs are predicted to show two-stage
transition through three distinct phases
according to open bond probability $p$;
(i) {\it nonpercolating phase}: there is no infinite cluster for
$0 \le p |
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C1.00265: Interest rate change and Omori dynamics in the Stock Market Alexander Petersen, Fengzhong Wang, Shlomo Havlin, H. Eugene Stanley I present the behavior of U.S. markets on the day of U.S. Federal Open Market Commission (FOMC) meetings from the perspective of Statistical Physics. The announcement of key U.S. Federal Reserve rate changes causes a small financial shock, where the dynamics before and after the announcement can be described by an Omori law. We find that markets respond sharply to the news in a complex way reminiscent of physical earthquakes described by the Omori law, which describes the power-law relaxation of aftershocks following a singular perturbation. We find Omori laws in both the volatility of the price (also known as the absolute returns) and the volume traded, using 1-minute resolution financial time series. These results suggest that the perturbative response of the stock market is the same for both financial news and financial crises. The intraday response can be measured by the Omori power-law exponent $\Omega$, which has opposite sign before and after the announcement. We estimate the magnitude of news by relating $\Omega$ to the behavior of the U. S. Treasury Bill before and after FOMC announcements. [Preview Abstract] |
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C1.00266: Structure of correlations with partially surrogated price fluctuations Gyuchang Lim, Sooyong Kim, Ki-Ho Chang, Kyungsik Kim The well-known facts of financial markets support that the price fluctuation contains information about the complexity of interactions among market participants. In this work, we present a new surrogate method to find the dependency of higher- order correlations on the magnitude of price fluctuations. By sorting returns into several groups with respect to the level of fluctuations, we show that the large fluctuations characterize the structure of temporal correlations of a financial time series. In particular, by investigating the positive and negative parts separately, we confirm that risk-averse behavior of traders is explicitly observed in financial markets. [Preview Abstract] |
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C1.00267: Sediment transport dynamics of a river network in a long period Jie Huo, Rui Hao, Xu-Ming Wang A sediment transport model that connects a lower-water season to the higher-water season is suggested to study the dynamics in a long-term evolution process. The model is based on the feedback mechanism between sediment-carrying capacity of stream and erosion-deposition state of channels. It is checked by comparing the simulated results with the observed data of the Yellow River. The comparison can be conducted in two aspects. One is the comparison between the model results on every segment and the real results; the other is the estimation whether the variation trends of the calculated results are qualitatively in accordance with that occurred in the natural river network. The comparisons show that our model is reasonable. The detail of the dynamics manifests that the model can generate the general inherent characteristics of a real river network as it passes through a lower-water season to the higher-water season. This might provide us with a new visual angle for the researches in some related fields. [Preview Abstract] |
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C1.00268: Probing Localization in Scattering Systems via Fidelity Mei Chai Zheng, Joshua Bodyfelt, Ulrich Kuhl, Hans-Juergen Stoeckmann, Tsampikos Kottos Using scattering measurements from a microwave cavity filled with randomly distributed scatterers, we evaluate the scattering fidelity. We show that depending on the degree of localization inside the sample, the fidelity decay deviates from ``traditional'' Gaussian law, applied in the case of diffusive/chaotic cavities when small perturbations are involved. We instead show that for small displacements of one of the walls of the cavity, the fidelity decays in a novel way that reflects the degree of localization (or randomness) inside the cavity. The outcome of the experimental measurements are explained on the basis of a parametric Banded Random Matrix modeling which incoorporates localization phenomena. The theoretical results are in good agreement with those of the experiment. [Preview Abstract] |
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C1.00269: Experimental observation of soliton propagation and annihilation in a hydromechanical array of one-way coupled oscillators Patrick M. Odenthal, John F. Lindner, Kelly M. Patton, James C. Gallagher, Barbara J. Breen We have experimentally realized unidirectional or one-way coupling in a mechanical array by powering the coupling with flowing water. In cyclic arrays with an even number of elements, soliton-like waves spontaneously form but eventually annihilate in pairs, leaving a spatially alternating static attractor. In cyclic arrays with an odd number of elements, this alternating attractor is topologically impossible, and a single soliton always remains to propagate indefinitely. Our experiments with 14 and 15-element arrays highlight the dynamical importance of both noise and disorder and are further elucidated by our computer simulations. This work was supported in part by NSF DMR-0649112. [Preview Abstract] |
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C1.00270: Order and Chaos in the Two-Body Problem Jacob Lynn, Frank W. King, John F. Lindner We investigate a simple extension of the classical two-body problem involving the gravitational interaction of a point and a line segment. We find families of periodic orbits amidst chaotic orbits in both the parameter and initial condition spaces. We characterize the dynamics using animations, Poincare sections, distance metrics, power spectral densities, and Lyapunov exponents. This work was supported in part by NSF DMR-0649112. [Preview Abstract] |
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C1.00271: Simulation of the Dynamics of a Plane Pendulum with Positional Dependent Torque Todd McAlpine, Alison Huff We investigate the dynamics of a plane pendulum with positional dependent driving torque as would be produced by a horizontally directed force exerted on the pendulum bob. We compare and contrast this with the well known dynamics of a standard plane pendulum. In particular we compare the bifurcation diagrams of the two systems and look at the effects of the driving amplitude. [Preview Abstract] |
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C1.00272: SUPERCONDUCTIVITY |
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C1.00273: A Systematic Photoemission Study of the Fe(Te$_{1-x}$Se$_{x})$ Superconductor System YuQi Xia, N.L. Wang, Zahid Hasan We present a systematic photoemission study of the newly discovered superconducting class Fe(Te$_{1-x}$Se$_{x})$. By using a series of photon energies and scattering geometries we investigated the details of the quasiparticle dispersion, Fermi surface and the global band structure. Doping dependent phase diagram study into the superconducting regime would be reported. [Preview Abstract] |
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C1.00274: High energy anomaly in hole- and electron-doped cuprates B. Moritz, F. Schmitt, W. Meevasana, S. Johnston, E. M. Motoyama, M. Greven, D. H. Lu, C. Kim, R. T. Scalettar, Z.-X. Shen, T. P. Devereaux Recent ARPES experiments reveal the presence of a dispersion anomaly in the high $T_{c}$ cuprates. This universal anomaly appears at an energy of $\sim 300$ meV in hole-doped compounds, with a similar feature reported in the half-filled parent insulators. New experiments on Nd$_{2-x}$Ce$_{x}$CuO$_{4}$ also reveal an anomaly, but at a higher energy scale of $\sim 500$ - $600$ meV. A key question concerns the origin of this anomaly. Quantum Monte Carlo simulations of the single-band Hubbard model reveal qualitative and quantitative agreement with the dispersion anomaly throughout the doping spectrum. They demonstrate that strong correlations play a key role in the development of the anomaly as well as that of spectral weight transfers that accompany doping. [Preview Abstract] |
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C1.00275: Determination of the Eliashberg's Equations in the Superconductivity Post BCS Carlos Figueroa, Rene Betancourt, Lazaro Ferrer, Martin Molinar The Eliashberg theory was a significant advance with respect to the BCS Theory because of it extends the rank of application without changing its origin, which is based on the formation of Cooper pairs by the interaction electron phonon. It doesn't modify the essential characteristics of BCS theory but it includes more information about the subject. Another point to be considered is BCS theory works, better with the weak electron-phonon coupling superconductors as the aluminium (Al). As the coupling becomes strong the results show significant deviations as in the case of lead (Pb). The Eliashberg's equations make an extension to incorporate the strong electron-phonon interaction. This theory synthesizes the information in a expression known as Eliashberg's function, or effective spectral density. Using the last problem solutions it can be possible to recover the universal relation of the BCS, likewise, the deviation function and the isotope effect. No doubt, it is a qualitative jump in the knowledge of the conventional superconductor materials. [Preview Abstract] |
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C1.00276: Condensation of topological excitations in two coupled layers of Josephson junction arrays. Said Sakhi The phase diagram of two coupled layers of Josephson junction arrays (JJA) in the presence of charge and magnetic frustration is investigated. The quantum phase model of JJA is mapped in the self-dual limit into an Abelian gauge theory with Maxwell terms and a mixed Chern--Simons term. The low effective field theory is shown to be governed by complex fields associated with disordering caused by electric charges and magnetic charges minimally coupled to two gauge fields related to the currents of Cooper pairs and vortices. The condensation of disorder fields leads to a rich phase diagram with important features not attainable by standard mean field theories. In addition to insulating and superconducting phases, the bi-layer system displays interesting interplay between Hall quantization and interlayer coherence: Hall quantized states with and without interlayer coherence and interlayer coherent states without Hall quantization. S. Sakhi , \textit{Quantum disordering effects in bilayer Josephson junction arrays} , J. Phys. A: Math. Theor. 41 (2008) 085003. [Preview Abstract] |
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C1.00277: The Electronegativity Spectrum of Superconductors O. Paul Isikaku-Ironkwe In the experimental search for novel superconductors, the correlation of electronegativity with superconductivity has been a useful guide. Previous studies have identified the range of electronegativities for low and high Tc superconductors. A detailed spectrum plot of electronegativity versus transition temperature for all known superconductors has still not been published. Here we produce such a plot which includes electronegativities of the newly discovered iron-based pnictide superconductors. We analyze this spectrum plot and use it to predict the electronegativity of higher Tc superconductors. [Preview Abstract] |
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C1.00278: Experimental and Theoretical Investigation of High Temperature Superconductors Scott Dietrich The study includes ongoing physical measurements on High Temperature Superconducting (HTS) samples. A dual-coil apparatus, using BSCCO and YBCO samples, is used to measure the magnetic susceptibility, resistivity and other measurements of the samples. This allows for the inspection of the HTS material during its superconducting state, above the critical temperature and the region in between. Using this data, we hope to model the HTS material using a mathematically driven computer simulation. The simulation models the material as a matrix of Josephson Junctions and can apply the variables added in the lab, including electrical current, magnetic field, and temperature variation. The simulation aims at explaining the mechanisms behind high temperature superconductivity. Included in the program is the option to change lattice structures, giving the ability to explore theoretical HTS material compositions and preview their actions compared to the commonplace square lattice structures. [Preview Abstract] |
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C1.00279: Force analysis of a permanent magnet and a superconducting hollow cylinder Mohammed Alqadi The interaction between a cylindrical magnet and a superconducting hollow cylinder in the Meissner state was analyzed using dipole-dipole model. Analytical expression of the levitation force was derived as a function of the magnetic moment, radius of the magnet, radius and thickness of the superconductor sample. The obtained results show that there is strong dependent of the levitation force on the magnetic dipole orientation at a small magnet-superconductor distance. [Preview Abstract] |
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C1.00280: C-axis persistent current and Cooper-pair tunnelling through intrinsic Josephson junctions in a ring-shaped YBa$_2$Cu$_3$O$_{7-\delta}$ film Ahmad Mansour, Mohamed Saber, Kim Chow, Jan Jung We present the direct experimental observation of the temperature dependence of the persistent current I$_{cj}$ due to tunneling Cooper pairs along the c-axis intrinsic Josephson junctions integrated into YBa$_2$Cu$_3$O$_{7-\delta}$ ring-shaped thin films. The measured I$_{cj}$ exhibits a linear temperature dependence over a wide range of temperatures well below T$_c$. Similar behavior was observed in different samples, confirming the reproducibility of the fabrication technique and the reliability of the results. Our fabrication and measurement techniques which allowed us to observe ``pure'' Cooper pair tunneling persistent current are superior to other techniques that are unable to separate Cooper pair from quasi-particles tunneling currents. [Preview Abstract] |
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C1.00281: Probing KT transition using ac current Hengsong Zhang, Fulin Zuo We report studies of the Kosterlitz-Thouless (KT) transition in thin Tin films using an ac excitation current rather than the conventional dc current. The nonlinear dependence or power-law exponent of the voltage on current is probed by measuring the harmonic terms of the voltage signal. The voltage can in general be expressed as a sum of odd-powered current terms with the experimentally measured power exponent increasing with lowering temperature. The temperature and current dependence of the exponent have been studied and will be discussed in terms of vortex- antivortex pair and pair-pair interactions. [Preview Abstract] |
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C1.00282: Phase Separated Bose-Einstein Condensate for High Sensitivity Force Measurement Satyan Bhongale, Eddy Timmermans A trapped, phase separated, two component Bose-Einstein condensate (BEC) can be configured to give a single BEC bubble that floats freely in the surrounding BEC. We point out that this system gives a unique template to carry out mesoscopic quantum studies and to detect weak forces. We demonstrate the detection capabilities by proposing and studying a ``Quantum Level" for fundamental quantum fluctuation studies and for mapping the potential energy landscape near a surface with exquisite accuracy. We show that for typical (modest) values of currently available experimental parameters, the proposed device is sensitive to the variations in gravitational acceleration to 1 part in 10 billion. While such sensitivity is in the range of other available devices, for example torsion balance, the BEC device allows for measuring the gravitational acceleration on length scales of the order of a few microns. [Preview Abstract] |
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C1.00283: Definition of current density in presence of AC electric field Zhang Lei, Wang Jian Under time varying AC electric field, the transport problem becomes complicated due to the presence of displacement current. The conventional current density calculated by using the formula $J_{c}=\frac{e}{2m}[((p-eA)\psi)^{*}\psi- \psi^{*} ((p-eA )\psi)]$ is not conserved, which means $\nabla\cdot J_c(r,t)\neq 0$. In order to solve this problem, we will give a new definition of current density by using non-equilibrium Green's function which includes the contributions from the Coulomb interaction in low frequency limit. And we will show that the current calculated from the current density is conserved. [Preview Abstract] |
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C1.00284: The dynamic critical exponent in optimally doped Pr$_{1.85}$Ce$_{0.15}$CuO$_4$ as a function of film inhomoegneity R.A. Isaacs, J. B. Olson, J. Sousa, M. Salvaggio, M.C. Sullivan, R.L. Greene Scaling analysis of voltage vs.\ current isotherms is a good tool to study the normal-superconducting phase transition in cuprate conductors. This measurement has never been performed on the optimally doped cuprate conductor Pr$_{1.85}$Ce$_{0.15}$CuO$_4$. If we take the finite thickness of the films into account,\footnote{Sullivan \textit{et al.}, Phys. Rev B \textbf{69}, 214524 (2004)} we can find the critical isotherm and determine the dynamic critical exponent \textit{z} in our Pr$_{1.85}$Ce$_{0.15}$CuO$_4$ films. We find that the critical exponent varies as a function of transition width, from which we can infer the effect of sample inhomogeneity on the dynamic critical exponent. We present our results of the critical exponent as a function of sample inhomogeneity and compare it to the hole-doped cuprate YBa$_2$Cu$_3$O$_{7-\delta}$. [Preview Abstract] |
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C1.00285: A study of the critical current density in optimally-doped, thin-film cuprate superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ E.S. Backus, M. Lilly, M.C. Sullivan Scaling analysis of voltage vs. current isotherms has often been used to study the normal-superconducting phase transition in cuprate superconductors, though there is little consensus in the literature as to the values of the critical exponents for this phase transition. Studying the critical current will give us another way to examine the normal-superconducting phase transition, and perhaps rectify the lack of consensus regarding the critical exponents. We designed a photolithographic mask with several meander patterns to test, varying the lengths and thicknesses of the patterned wires. We conducted reverse-polarity measurements sent through the meander patterns of thin-films of the cuprate superconductor YBa$_2$Cu$_3$O$_{7-\delta}$. Because the critical current density in this material is so high, several extrinsic effects must be taken into consideration in order to avoid heating, including: determining the most effective number of measurements, the wait time between measurements, and the wait time between increments of temperature in order to reduce the error. I present my results as a plot of the critical current as a function of temperature in zero-field, and the critical exponent. [Preview Abstract] |
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C1.00286: Influence of diffusion-annealing time on the mechanical properties of bulk Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$O$_{y}$ superconductors diffusion-doped with Fe. Mustafa Akdogan, Ozgur Ozturk, Ersin Yucel, Erdal Bekiroglu, Mustafa Yilmazlar, Cabir Terzioglu In order to investigate the role of Fe doping and diffusion-annealing duration on the mechanical and superconducting properties of Bi-Pb-Sr-Ca-Cu-O, Bi$_{1.8}$Pb$_{0.35}$Sr$_{1.9}$Ca$_{2.1}$Cu$_{3}$O$_{y}$ superconductors were prepared by standard solid-state reaction methods. Doping of Bi-2223 was carried out by means of iron diffusion during sintering from an evaporated iron film on pellets. The investigations consist of SEM, dc resistivity and hardness measurements. These measurements indicated that the Fe doping and diffusion-annealing time increased the T$_{c}$, J$_{c}$, Vickers hardness (H$_{0})$, Young's modulus(E), yield strength(Y), fracture toughness(K$_{IC})$ values and improved the grain connectivity. The mechanical properties of the samples were found to be load dependent and on the diffusion-annealing time. In addition, we calculated the load independent H$_{0}$, E, Y, and K$_{IC}$ of the samples. Possible reasons for the observed improvements in the superconducting and mechanical properties due to Fe diffusion are discussed. [Preview Abstract] |
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C1.00287: Soft X-ray Imaging of Vortex Dynamics in Trilayer Pattered Magnetic Elements Brooke Mesler, Dong-Hyun Kim, Peter Fischer Soft X-ray microscopy provides element specific magnetic imaging with a spatial resolution down to 15nm. At XM-1, the full-field soft X-ray microscope at the Advanced Light Source in Berkeley, a stroboscopic pump and probe setup has been developed to study fast magnetization dynamics in ferromagnetic elements with a time resolution of 70ps which is set by the width of the X-ray pulses from the synchrotron. Previous studies of patterned permalloy elements have revealed complex magnetization dynamics. Results obtained with a 2$\mu$m x 4$\mu$m x 45nm rectangular permalloy sample exhibiting a seven domain Landau pattern reveal dynamics up to several nsec after the exciting magnetic field pulse. Domain wall motion, a gyrotropic vortex motion, and a coupling between vortices in the rectangular geometry are observed. On going studies of patterned trilayer elements, composed of magnetic permalloy and cobalt layers separated by a copper spacer layer, will probe the dynamics of the trilayer system. Of particular interest is observing how the coupling between the magnetic layers affects the vortex dynamics. [Preview Abstract] |
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C1.00288: Two dimensional magnetization mapping in exchange-coupled nanodot chain arrays using the magento-optic Kerr effect Sarah C. Hernandez, Jian Dou, Chengtao Yu, Michael J. Pechan, Liesl Folks, Jordan A. Katine, Matthew J. Carey Nanoscale permalloy dot arrays were fabricated with dot diameters of 300 nm, thicknesses of 40 nm, and coupled via permalloy bridges, with bridge widths ranging from zero to 60 nm. Magnetization reversal in this system was previously investigated with the field applied along and perpendicular to the coupling direction. Hysteresis loops reflect reversal by domain wall motion.\footnote{ S. C. Hernandez et al, (To be published in J. Appl. Phys.)} As a result of rotating the applied magnetic field relative to the sample's coupling direction, unusual hysteresis loops were observed. The magneto-optic response resulted in an asymmetric loop with one notable feature, an increase in coercivity with increasing bridge width. We will show that these curves arise from the second-order magneto-optic Kerr effect, where coherent rotation of magnetization plays an important role. This work is supported by US-Dept.of Energy at MU. [Preview Abstract] |
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C1.00289: Superconducting properties of tetragonal FeSe and FeTe Yoshikazu Mizuguchi, Yoshihiko Takano The discovery of LaFeAsO1-xFx superconductor triggered active studies on iron-based superconductors. Recently, superconductivity in tetragonal FeSe was reported. FeSe is the simplest-structured iron-based superconductor. We reported a huge enhancement of the transition temperature Tc under high pressure. The onset of Tc increased from 13 to 27 K at 1.48 GPa. FeSe undergoes a structural phase transition to orthorhombic around 70 K. A suppression of the structural phase transition will be a key to raise Tc in this system. Tetragonal FeTe has a structure very analogous to that of superconducting FeSe, however, does not show superconductivity, and undergoes a structural phase transition around 80 K. We synthesized S-substituted FeTe, FeTe1-xSx, and observed the suppression of the structural phase transition and superconductivity at low temperatures. Since FeTe1-xSx is composed of nontoxic elements, this compound is advantageous for applications. Here we report the pressure and the elementary substitution effects on FeSe, the pressure studies on FeTe, and the superconducting properties of FeTe1-xSx. [Preview Abstract] |
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C1.00290: Effects of sintering temperature on properties of Ti-sheathed, SiC-doped MgB2 superconducting wires Gan Liang, Hui Fang, Cad Hoyt, Samaresh Guchhait, John Markert Mono-core Ti-sheathed, silicon carbide (SiC) doped MgB$_{2}$ wires have been successfully fabricated by powder-in-tube method. The average size of the doped SiC nano particles is 20 nm and the doping level is 10 wt.{\%}. The wires were sintered for 30 minutes at five temperatures from 650 $^{o}$C to 800 $^{o}$C. Effects of sintering temperature on the phase composition, microstructure, and critical current density ($J$c) were studied by x-ray diffraction, scanning electron microscopy, and magnetization measurements. The results indicate that the Ti sheath does not react with the magnesium and boron, and the present wire rolling process can produce Ti-sheathed, SiC-doped MgB$_{2}$ wires with high critical current density. It is found that $J$c peaks up at sintering temperature of 800 $^{o}$C. This is in sharp contrast with the previously reported result (by other group) that the optimal $J$c was achieved at sintering temperature 650 $^{o}$C. The correlations between $J$c and the structural properties of the wires are discussed. [Preview Abstract] |
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C1.00291: Meissner effect in ensemble of slightly boron-doped carbon nanotubes J. Haruyama, N. Murata, J. Reppert, A. Rao, T. Koretsune, S. Saito The small mass of carbon can promote high transition temperature (T$_{c})$ in BCS-type superconductivity (SC). Recently, new carbon-based superconductors with order of T$_{c}$ of $\sim $10K [1, 2] were discovered and higher T$_{c}$ has been expected. In particular, the SC in a carbon nanotube (CNT) is attracting considerable attention [3]. We reported that entirely end-bonded multi-walled CNTs, in which Luttinger liquid was suppressed, could show SC with T$_{c}$ = 12K, previously [4]. In contrast, it had problem in reproducibility, because correlation with carrier doping was not clarified. Moreover, none has succeeded substitutional carrier doping into CNTs and also revealed the correlation with SC. Here, we report on the Meissner effect with T$_{c}$=12K found in thin films consisting of boron-doped single-walled CNTs [5]. We reveal that boron concentration $<$ 1.5 at.{\%} in the CNTs and those highly homogeneous assembling to thin films are favorite to yield evident Meissner effect. This can be understood by better alignment of E$_{F}$ to van Hove singularity in density of states. [1] T. E. Weller et al., \textit{Nature Physics} 1, 39 (2005), [2] E. A. Ekimov et al., \textit{Nature} 428, 542 (2004), [3] M. Kociak et al., \textit{Phys. Rev. Lett.} 86, 2416 (2001), [4] I. Takesue, J.Haruyama, et al., \textit{Phys. Rev. Lett.} 96, 057001(2006), [5] N.Murata, J.Haruyama, et al., \textit{Phys.Rev.Lett.} 101, 027002 (2008) [Preview Abstract] |
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C1.00292: Coexistence between magnetism and superconductivity in the HgMn$_{0.3}$Pb$_{2}$ compound Ausdinir Danilo Bortolozo, Erika Carlina A. Santana, Carlos Alberto M. dos Santos, Antonio Jefferson S. Machado In this work will be show the influence Mn doping in the HgPb$_{2}$ phase. The HgMn$_{0.3}$Pb$_{2}$ phase is investigated by x-ray diffraction, magnetic and electrical resistivity measurements. Polycrystalline samples with HgMn$_{0.3}$Pb$_{2}$ nominal compositions were prepared by solid state reaction. X-ray powder diffractograms suggest that all peaks can be indexed with the tetragonal phase of AuCu prototype. The R(T) data for the HgMn$_{0.3}$Pb$_{2}$ composition reveals superconductor behavior below 5.9K. The careful analysis of M(T) data reveals magnetic ordering close to 45K with saturation around the superconducting transition. The Mn doping in the HgPb$_{2}$ phase suggests the magnetic ordering it is occurring in the specific plane occupied by Mn atoms. The M(H) data show typical type-II superconductor which we estimate the H$_{C1}$ approximately 240 Oe. This work, report by first time the coexistence between magnetism and superconductivity in an AuCu prototype compound [Preview Abstract] |
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C1.00293: Designing Superconductors with Periodic Table-based Maps and Material Databases O. Paul Isikaku-Ironkwe, Alex Animalu One of the grand challenges of superconductivity science is achieving a paradigm shift from discovery by serendipity to discovery by design. Empirical and heuristic rules have been a useful bridge in this desired direction. Many early superconductors were discovered by this method and by seredipity. DFT-based \textit{ab initio} methods have often ignored empirical and experimental data. Here we propose that by using Periodic Table-based maps such as electronegativity spectrum maps, valence electron spectrum maps and atomic number spectrum maps for binary systems, A$_{x}$B$_{y}$, combined with data-mining of experimental material databases we can ``reverse-engineer'' many known superconductors. We demonstrate the power of this technique by predicting new and novel superconductors without recourse to DFT calculations. [Preview Abstract] |
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C1.00294: Microscopic transport in indium oxide thin films near the superconductor-insulator quantum phase transition Minsoo Kim, Tailung Wu, Zhenzhong Shi, Adam Stabile, G. Sambandamurthy We present results from low temperature ($T$) and high magnetic field ($B$) transport measurements on disordered thin films of amorphous indium oxide. Two-dimensional (2D) indium oxide films can be driven between insulating and superconducting ground states by controlled tuning of either the intrinsic disorder or external $B$. We have grown these films with hitherto unachieved control of their structure and property and patterned into Hall bars and nanowires using standard nanolithographic techniques for transport measurements. Here we present the results of a study of the resistance behavior in these films in the 1D and also in the 1D-2D crossover regimes when the ground state in the $T$ = 0 limit is tuned from an insulator to a superconductor. Our efforts are aimed at achieving, for the first time, a continuously tunable 1D superconductor. [Preview Abstract] |
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C1.00295: The Superconducting Transition in Al Nanowires Paul Aliotta, John Free, Robert Westervelt Strong evidence for macroscopic quantum tunneling has been presented in Al wires with diameters less than 10 nm [1], which is much lower than the material's coherence length. We have investigated the superconducting transition and evidence for macroscopic quantum tunneling in Al nanowires with diameters ranging from 10 to 40nm. We will present data for these wires. \\[3pt] [1] F. Altomare, Phys. Rev. Lett. \textbf{97}, 017001 (2006). [Preview Abstract] |
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C1.00296: Pressure effects on superconductivity and magnetism in FeSe$_{0.88}$ and FeSe$_{1-x}$Te$_{x}$ Chien-Lung Huang, Chi-Chie Chou, Kuo-Feng Tseng, Yi-Lin Huang, Fong-Chi Hsu, Kuo-Wei Yeh, Mau-Kuen Wu, Hung-Duen Yang We have performed the pressure ($P)$ dependence of ac, dc susceptibility and resistivity measurements on iron chalcogenides FeSe$_{0.88}$, FeSe$_{0.5}$Te$_{0.5}$, FeTe and FeTe$_{0.9}$. The superconducting transition temperature ($T_{c})$ of FeSe$_{0.88}$ is found to increase with $P$ linearly at a rate of d$T_{c}$/d$P \sim $ 3.09$\times $10$^{-2}$ K/kbar, while the $T_{c}$ of FeSe$_{0.5}$Te$_{0.5}$ increases nonlinearly with an initial rate of 1.47K/kbar then saturates at $P \sim $ 18 kbar. Such the enhancement of $T_{c}$ might be attributed to an increase of density of states. There is no indication of superconductivity observed in FeTe and FeTe$_{0.9}$, which is inconsistent with the result of theoretical calculation, and it might be due to the existence of long range magnetic spin coupling that inhibits the formation of superconductivity mediated by spin fluctuations, which is applied to describe the mechanism in Fe-based superconductors. [Preview Abstract] |
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C1.00297: ABSTRACT HAS BEEN MOVED TO S1.00263 |
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C1.00298: Superconductivity in (La,Y)FeAs(O,F) pncitides Matteo Tropeano, Carlo Ferdeghini, Carlo Fanciulli, Alberto Martinelli, Andrea Palenzona, Marina Putti, Roberta Cimberle, Fabio Canepa The structural, magnetic and resistive properties of (La$_{1-x}$Y$_{x})$FeAs(O$_{0.85}$F$_{0.15})$ (x $\le $ 0.7) compounds prepared at normal pressure were investigated. Substituting La with Y decreases the ionic size at the rare earth site, determining a progressive decrease of both cell edges; as a result a notable increase of the superconductive transition temperature is observed. In particular T$_{C}$ increases with Y content, up to a maximum value of 39.8 K for x = 0.5, followed by the a slight decrease for x = 0.7 (T$_{C}$ = 35.9 K). The resistivity curve of the corresponding undoped compound, (La$_{0.5}$Y$_{0.5})$FeAsO, exhibits the typical bump related to the SDW onset; the first derivative curves for (La$_{0.5}$Y$_{0.5})$FeAsO and LaFeAsO are almost superposed around T$_{SDW}$. [Preview Abstract] |
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