Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session C1: Poster Session I |
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Room: Baltimore Convention Center Exhibit Hall 2:00pm - 5:00pm (DPOLY session: 11:15am - 2:15pm) |
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C1.00001: DPOLY POSTER SESSION I |
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C1.00002: A Multi-Sample Melt Micro-Rheometer Kalman Migler, Anthony Bur We have developed a multi-sample melt micro-rheometer (M3R) based on pressure driven channel flow and designed for simultaneous measurement of multiple polymer melts. The required sample size is less than 100 mg. The driving force for the rheometer is pressurized gas from a nitrogen tank that forces polymer melt into a slit. The melt flow is monitored using a video camera that views the flow front through a sapphire window. The device contains no moving parts and no gaskets or O-rings. Measurements of polyethylene and polycarbonate are presented. [Preview Abstract] |
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C1.00003: Collection of an electrospinning jet Tao Han, Darrell Reneker Electrospinning [1, 2] of polymer nanofibers involves an electrically driven bending instability of the elongating jet. If the jet is collected on a stationary surface immediately before or after the bending instability occurs, the jet buckles as it stops. Bending and buckling are distinct phenomena. The determination of the behavior of the jet path in the vicinity of the onset of the first bending instability is important for the orderly collection of the nanofiber. Precise adjustment of the fluid flow, the electrical current, and the shape of the region from which the jet issued, produced a very stable jet which was observed with a high frame rate, short exposure time camera. The fluid jet and the resulting nanofibers were collected on a solid, electrically conducting substrate which was moved laterally, and simultaneously, away from the tip. This collected material preserved a record of the straight segment and the bending and buckling instabilities with a minimum of overlapping. The occurrence of a second bending instability was sometimes observed in the dry fiber. 1. Doshi, J.; Reneker, D.H., \textit{Journal of Electrostatics}; \textbf{35}, 151, \textbf{1995} 2. Reneker, D.H. ;Yarin,A.L.Fong, H.; Koombhongse, S., \textit {Journal of Applied Physics}, \textbf{87}, 4531, \textbf{2000} [Preview Abstract] |
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C1.00004: Electrospun Nanofiber Yarn Sphurti Doiphode, Darrell Reneker Electrospinning creates an electrically charged jet of polymer solution or melt, which elongates dries and solidifies to give very long fibers with nanometer-scale diameters [1]. The yarn manufacturing method [2,3] involves collecting the electrically charged fibers between two parallel and electrically grounded collector surfaces separated by a distance commensurate with the diameter of the loops formed by the electrically driven bending instability [1]. One of the collector surfaces is rotated around its axis at an appropriate rate to twist the fibers into a nanofiber yarn. The yarn was extended, for example by translating the other collector away from the rotating collector. Properties such as yarn diameter, fiber count, and twist per unit length were controlled by changing the rotation rate of the disk. It appears that yarns of nanofibers can be produced from all polymer solutions that can be electrospun. \newline \newline References: \newline [1] Reneker, D.H.; Yarin, A.L.; Fong, H. Koombhongse, S. \textit{J. App. Phys.} 87, 2000, 4531. \newline [2] Dalton, P. D.; Klee, D.; M\"{o}ller, M. \textit{Polymer} 46(3), 2005, 611. \newline [3] Dzenis, Y. \textit{Private communication}. [Preview Abstract] |
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C1.00005: Branching in electrospinning of nanofibers A. L. Yarin, W. Kataphinan, D. H. Reneker, Z. Zhong . A sequence of secondary jet branches sometimes emanates from the electrically charged primary fluid jet during electrospinning experiments. This process was observed during the electrospinning of solutions of polycaprolactone dissolved in acetone [1]. Branching occurred both in the straight segment of the jet and after the onset of the bending instability. Jets with larger diameters, associated with higher voltages, tend to have more branches. Stereographic, stopped motion images of the path of the jet showed that the branches grow in all azimuthal directions around the jet with a smaller component of their growth along the direction of the applied electric field. An electrohydrodynamical model of the branching process showed that the surface of a conducting fluid jet can acquire complicated static equilibrium undulations which become unstable and are capable of transforming into branches. 1. Yarin, A. L.; Kataphinan, W.; Reneker, D. H. \textit{J. App. Phys., }98, 2005, 064501. [Preview Abstract] |
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C1.00006: Developments of Novel Polymer Electrolyte Fuel Cell Membranes Tomomi Irita, Masahiro Kondo, Hirokazu Aoyama, Thomas Russell Perfluorinated polymer electrolyte membranes (PEM), such as Nafion, are considered to be the most promising candidate for the development of the next generation fuel cell technology. The key technological challenges facing PEMs are their performance, durability and cost. In this research, the polymer electrolyte emulsions (PEE) were obtained by a simple hydrolysis reaction of the precursor polymer emulsion. PEMs are obtained by solvent casting the PEE. The PEE obtained here has a very low viscosity even at high solution concentrations. Using high concentration emulsions greatly reduces the amount of the waste, which makes this technology superior to the conventional ones. Casting conditions were optimized to enhance the mechanical properties, e.g. the tensile strength and viscoelastic properties, of the membrane. The PEMs obtained possessed better ionic conductivity than Nafion while their mechanical properties are comparable. Finally, the cost evaluation for this process was conducted and it was shown that the contribution to the cost reduction becomes bigger. (This research was sponsored by New Energy and Industrial Technology Development Organization, Japan) [Preview Abstract] |
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C1.00007: ABSTRACT WITHDRAWN |
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C1.00008: Non-halogen Flame retardant High Impact Polystyrene Composites Miriam Rafailovich, Mayu Si, Jonathan Sokolov, Joshia Otaigbe, Vladimir E. Yudin In recent years, driven by the health issues and the incurred banning policy of bromine compounds, it is a great demand to find an alternate to replace brominated compounds in polymer flame retardant industry. High impact polystyrene (HIPS), a popular materials widely used for electrical appliances and electronic instruments, attracts extensive attention for its dominant flame retardant agent, decabromodiphenyl ether. Here we propose a novel idea to prepare non-halogen HIPS self-extinguishing composites based on the combination of phosphorus compounds and clay. The combustion behavior was thoroughly investigated by UL 94 V-0, LOI, and cone calorimeter measurements. The addition of Cloisite 20A dramatically decreases the value of LOI and the resulted HIPS composites could not pass UL 94 V-0. On the other hand, the introduction of thermal stable clay significantly increases the value of LOI and the corresponding HIPS composites can successfully self-extinguish. These results strongly demonstrate that the thermal stability of clay is the key factor to determine the final flame retardant performance. The synergy between the clay and phosphorus compounds is further studied. [Preview Abstract] |
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C1.00009: An ``Alternating-Curvature'' Model for the Nanometer-scale Structure of the Nafion Ionomer, Based on Backbone Properties Detected by NMR Klaus Schmidt-Rohr, Q. Chen The perfluorinated ionomer, Nafion, which consists of a (-CF$_{2}$-)$_{n}$ backbone and charged side branches, is useful as a proton exchange membrane in H$_{2}$/O$_{2}$ fuel cells. A modified model of the nanometer-scale structure of hydrated Nafion will be presented. It features hydrated ionic clusters familiar from some previous models, but is based most prominently on pronounced backbone rigidity between branch points and limited orientational correlation of local chain axes. These features have been revealed by solid-state NMR measurements, which take advantage of fast rotations of the backbones around their local axes. The resulting alternating curvature of the backbones towards the hydrated clusters also better satisfies the requirement of dense space filling in solids. Simulations based on this ``alternating curvature'' model reproduce orientational correlation data from NMR, as well as scattering features such as the ionomer peak and the I(q) $\sim $ 1/q power law at small q values, which can be attributed to modulated cylinders resulting from the chain stiffness. The shortcomings of previous models, including Gierke's cluster model and more recent lamellar or bundle models, in matching all requirements imposed by the experimental data will be discussed. [Preview Abstract] |
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C1.00010: Dynamics of Sulfonated Polystyrene Copolymers and Ionomers using Broadband Dielectric Spectroscopy Pornpen Atorngitjawat, James Runt The dynamics of sulfonated polystyrene (SPS) copolymers in acid and neutralized forms were investigated using broadband dielectric relaxation spectroscopy. SPS copolymers were synthesized by sulfonation of a monodisperse polystyrene to 1 and 7 mol {\%}. Neutralization was achieved by exchanging the protons of the acid functionality with Na, Cs and Zn cations. Multiple relaxation processes were observed above the glass transition temperature of the neutralized and unneutralized materials. For the unneutralized copolymers, a `chemical relaxation' was observed at temperatures above the segmental process, arising from the presence of hydrogen bonding. For the ionomers, a Maxwell-Wagner-Sillars process was observed due to the presence of ionic clusters. The `chemical relaxation' followed Arrhenius behavior and its relaxation strength decreased significantly with increasing temperature. The relaxation times of the MWS process of all ionomers followed a VFT form. A local relaxation in the glassy state was observed for unneutalized copolymers and ionomers neutralized with monovalent cations, while it was suppressed for ionomers neutralized with divalent cations. [Preview Abstract] |
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C1.00011: Molecular Dynamics Simulations of Polyelectrolyte Adsorption at Oppositely Charged Surfaces Jan-Michael Carrillo, Andrey Dobrynin We have performed molecular dynamics simulations of polyelectrolyte adsorption at oppositely charged surface from dilute polyelectrolyte solutions. In our simulations polyelectrolytes are modeled by chains of charged Lennard-Jones particles with explicit counterions. We have studied the effects of surface charge density, surface charge distribution, solvent quality for the polymer backbone, strength of the electrostatic and short-range interactions on the polymer surface coverage and thickness of the adsorbed layer. We have observed surface undercharging by adsorbing polyelectrolyte in most systems except for systems with low surface charge densities. This undercharging is due to partial screening of the surface charge by surface counterions however this effect is negligible at low surface charge densities. Surface overcharging was also observed for the so-called ``salt-free'' systems in which only counterions necessary for neutralization of the charge difference between surface charge and polyelectrolytes were kept in the system. Hydrophobic polyelectrolytes cover higher percentage of the adsorbing surface forming a thinner polymeric layer in comparison with those observed in the systems with hydrophilic polyelectrolytes. However, the polymer surface coverage is close for both these systems. [Preview Abstract] |
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C1.00012: Molecular Dynamics Simulations of Polyelectrolyte-Polyampholyte Complexes. Effect of Solvent Quality and Salt Concentration. Junhwan Jeon, Andrey Dobrynin Using molecular dynamics simulations we have studied complexation in polyelectrolyte-polyampholyte mixtures in poor solvent conditions for the polyelectrolyte backbone. In a poor solvent a polyelectrolyte form a necklace-like structure. Upon forming a complex with both random and diblock polyampholytes a polyelectrolyte chain changes its necklace conformation by forming one huge bead. The collapse of the polyelectrolyte chain occurs due to neutralization of the polyelectrolyte charge by polyampholytes. In the case of the random polyampholyte the more positively charged sections of the chain adsorb on the surface of the globular bead while more negatively charged chain sections form loops surrounding the collapsed core of the aggregate. In the case of diblock polyampholyte the positively charged block and a part of the negatively charged block wraps around the collapsed polyelectrolyte with a substantial section of the negatively charged block sticking out from the collapsed center of the aggregate. These structures appear as a result of optimization of the net electrostatic energy of the complex and short-range attractive interactions between monomers of the polyelectrolyte chain. [Preview Abstract] |
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C1.00013: Surface Treatment for Improved Mobility in Poly(3-hexylthiophene) Thin-Film Transistors Adrian Southard, Michael Fuhrer Thin films of poly(3-hexylthiophene), an organic semiconductor, were spin-coated from chloroform onto a self-assembled monolayer of octyltrichlorosilane (2 nm thick) and yielded an order of magnitude higher field-effect mobility than similar films deposited directly onto the SiO$_{2}$/Si substrate. Mobility was measured using the polymer as the conducting channel of a field-effect transistor with Au top contacts as the source and drain electrodes and the doped silicon as a gate. The higher mobility is presumed to be due to the increased order of the semiconducting layer. Evidence for this ordering and the effect of other self-assembled monolayers will be discussed along with the effect of various contact geometries. This work was supported by the Laboratory for Physical Sciences. [Preview Abstract] |
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C1.00014: Age old antipodes united: stable \emph{and} low-work-function surfaces are generic M.A. Uijttewaal, G.A. de Wijs, R.A. de Groot Both a low work function and a stable surface are crucial for the application of cathodes in \emph{e.g.} microwave ovens, organic photoconductors and displays as CRTs and OLEDs. Until recently they were considered antipodes. In previous work[1] we showed a stable low-work-function surface to be realised for the compound BaAl$_4$ and even predicted that stable, low-work-function surfaces would be generic for metals with polar surfaces. Now, \emph{ab initio} calculations confirm the prediction for the compounds CaAl$_4$, BaAuIn$_3$ and LaB$_6$.\newline \newline [1] M.A.~Uijttewaal, G.A.~de~Wijs, R.A.~de~Groot, R.~Coehoorn, V.~van~Elsbergen, and C.~H.~L.~Weijtens, \emph{Chem. Mater.} \textbf{17}, 3879 (2005) [Preview Abstract] |
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C1.00015: Effects of Local Dielectric Property on the Chain Conformation Distribution of Poly (vinylidene fluoride-hexafluoropropylene) Copolymers. Guolin Wu, Suriyakala Ramalingam, Shaw Ling Hsu Poly(vinylidene fluoride) (PVdF) is a well known polymer possessing various polymorphic structures. Local dielectric property is known to affect the relative amount of polymorphic phases. The copolymer of PVdF and hexafluoropropylene units is especially fascinating. In this copolymer, changes in structure need to consider both localized dielectric property and steric effects of the comonomer units. The copolymer structure possesses smaller remnant polarization and fewer polar crystalline states in comparison to the homopolymer. Solution NMR studies reveal that the relative population of various rotational isomeric states has been changed in comparison to the homopolymer. This change in single chain structure obviously propagates into the condensed state yielding polar structure, that is, $\beta $ and $\gamma $ phases. NMR, Raman spectroscopy, wide-angle X-ray diffraction, and calorimetric methods were utilized in these studies. The steric effects of the comonomer units driving away from the $\beta $ phase have also been established. [Preview Abstract] |
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C1.00016: The Effects of Surface Interactions and Confinement on the Melting Point of Semi-crystalline Polymer Thin Films Yantian Wang, Miriam Rafailovich, Jonathan Sokolov, Dilip Gersappe, Ashish Bakshi, Rajesh Atluri, Tohru Araki, Ying Zou, Harald Ade, David Lewis Kilcoyne, Gad Marom, Arnold Lustiger A decrease in melting temperature for semi-crystalline polyethylene thin films in the vicinity of a substrate was observed. The depression in the melting point increases with increasing surface interaction. The biggest T$_{m}$ depression is 38$^{\circ}$C. We propose a model where the depression is attributed to the attractive force between the substrate and the polymer chains which competes with the ordering force among the polymer chains. In order to determine the universality of the effect, experiments were conducted on other polymers, i.e. polycaprolactone and poly(ethylene oxide) where similar results were obtained. The effects of confinement were then studied by crystallizing the films on patterned surfaces where the dimensionality of the patterns was continuously varied for nanometer to micron scale. [Preview Abstract] |
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C1.00017: Oriented Lamellar Structure and Pore Formation Mechanism in CSX-Processed Porous High-Density Polyethylene Shujun Chen, Samuel P. Gido, Souvik Nandi, H. Henning Winter Characterization of pore structure and pore wall crystal structure was performed on porous high-density polyethylene (HDPE) using SEM, TEM, and electron diffraction. The porous HDPE material was obtained through crystallization from swollen crosslinked polyethylene gels (CSX process) in supercritical propane. SEM showed an open pore structure of micron-sized pores, large void fraction and surface area, as well as thin yet rigid pore walls, making this material a good candidate for a variety of applications. TEM revealed oriented lamellar structure in the pore walls which was much different from structures found in typical bulk HDPE as well as that of the crosslinked HDPE before CSX processing. Electron diffraction results confirmed the presence of oriented lamellar stacking. Based on this oriented lamellar structure, possible mechanisms for crystallization and pore formation in the CSX process are suggested. [Preview Abstract] |
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C1.00018: Melting Point Measurement of Polycaprolactone Thin Films Clive Li, Victor Wang, Jonathan Sokolov, Miriam Rafailovich We investigated the melting point of Polycaprolactone (PCL) thin films as a function of film thickness by using three different techniques, namely, Shear Modulation Force Microscopy (SMFM) technique, Atomic Force Microscopy (AFM) topographic technique, and optical birefringence technique which consisted of laser, polarizers, photoelasitc modulator (PEM), and a lock- in amplifier. The optical and the AFM topography results show PCL to behave similarly for film thicknesses of 215.8 and 37.0 nm, both melting around 331 - 335 K. However, the SMFM show an approximate 8 K decrease in melting point, suggesting that the polymer may get softer at this lower temperature before it changes in structure for 37.0 nm PCL films. Possible explanations for the differences are discussed. [Preview Abstract] |
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C1.00019: Effects of Residual Crystallinity on the Crystallization Behavior of Random Polypropylene-Polyethylene Copolymer Samuel Amanuel, Xiaofeng Chen, Rahmi Ozisik, Sanford S. Sternstein Differential scanning calorimeter measurements revealed that blends of isotactic polypropylene and random polypropylene- polyethylene copolymer have two separate melting peaks, with a peak at 45 $^{o}$C attributed to the copolymer and another peak at 160 $^{o}$C attributed to the homopolymer. Annealing at temperatures below and above the melting of the homopolymer, 145 $^{o}$C and 200 $^{o}$C, resulted in changes of the melting temperature and melting enthalpy of the copolymer. This suggests that the crystallization behavior of the copolymer has been influenced by the residual crystallinity of the homopolymer. Furthermore, this crystalline memory has significant influence on the aging process of the blend. For instance, dynamic measurements, at room temperature, revealed that samples annealed at 120 $^{o}$C have lower shear storage modulus compared to those that were annealed at 200 $^{o}$C. Although physical aging increases the storage modulus in both cases, the rate at which it changes is also dependent on the presence of residual crystallinity. [Preview Abstract] |
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C1.00020: Disk, Cylinders, Stack-of-Disks, and Vesicles Morphologies from Amphiphilic Block Copolymer Solution-State Assemblies Zhibin Li, Zhiyun Chen, Honggang Cui, Kelly Hales, Kai Qi, Karen Wooley, Darrin Pochan Disk formation has been examined through self-assembly of poly(acrylic acid)-$b$-poly(methyl acrylate)-$b$-polystyrene (PAA-$b$-PMA-$b$-PS) amphiphilic triblock copolymer with polyelectrolyte PAA as corona block and organic diamines as counterions in water/THF solvent mixtures. It was found that by using the same triblock copolymer but varying the type and amount of diamines, disk or cylindrical micelles could be selectively formed and intermediate structures between discs and cylinders were observed. Under certain solution conditions, disks were prefer to stacking together to form stack-of-disks, and stack-of-disks could also transfer to organized rods by increasing the counterion concentration. Discs within the stacks could be uniform in size, and organized rods had the same geometry while they changed from stack-of-disks. It was interesting to see the long range (microns) interactions between discs or organized-rods. By using diblock (PAA-$b$-PS) copolymer analogues, vesicles were obtained with the presence of diamine counterions. The stability of disc vs. vesicle will also be discussed, and the experimental results will be used to compare with the theoretical predictions. The system was investigated by means of transmission electron microscopy, cryogenic transmission electron microscopy, DLS and SANS. [Preview Abstract] |
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C1.00021: Nanoporous Membrane with Ultrahigh Selectivity and Flux Suitable for Filtration of Viruses Jin Kon Kim, Seung Yun Yang, In Cheol Ryu, Sung Key Jang, Thomas P. Russell We introduce a new double layered nanoporous membrane suitable for virus filtration. One layer is an 80 nm thick film having cylindrical pores with diameters of 15 nm and a narrow pore size distribution. This layer is prepared by using a thin film of the mixture of a block copolymer and a homopolymer, and mainly acts to separate viruses. The support layer is a conventional micro-filtration membrane with a broad pore size distribution. This asymmetric membrane showed very high selectivity and flux for the separation of human rhinovirus type 14 which has a diameter of $\sim$ 30 nm and is a major pathogen of the common cold in humans. [Preview Abstract] |
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C1.00022: Effect of Selective Solvent on the Morphological Phase Behavior of PS-b-PEO Prachur Bhargava, Xiaoliang Zheng , Yingfeng Tu, Stephen Z.D. Cheng Amphiphilic block copolymers with glassy cores can be self -assembled in solution to form various nanoscale morphologies by using a two solvent process. In the first step the block copolymer is dissolved in a common solvent and then a selective solvent for one of the blocks is added to induce micellization. We have used this method to obtain nanoscale morphologies for PS-b-PEO. We have used DMF as the common solvent and have investigated two selective solvents for PEO, water and acetonitrile. The morphologies obtained by using both these selective solvents are similar. Spheres, rods/worm and vesicles can be obtained by varying only the solvent composition in both the systems. However a `worm network' can be obtained only by using water as a selective solvent. Also in case of water all the morphologies can be obtained in a very narrow range of water content while in case of acetonitrile the morphologies can be obtained only in a broad range of acetonitrile content. The difference in the behavior with water and acetonitrile can be attributed to their solubility parameters which affects the polymer solvent interaction parameter $\chi $. [Preview Abstract] |
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C1.00023: Effect of Annealing Temperature on the Surface Composition of Block Copolymers with Semifluorinated Side Chains K.E. Sohn, A. Hexemer, S. Krishnan, M. Paik, C.K. Ober, E.J. Kramer, D. Fischer The effect of the annealing temperature on the surface composition and orientation of semifluorinated side chains in styrene-isoprene based block copolymers has been studied using NEXAFS spectroscopy, angle resolved XPS, and AFM. Annealing brings the fluorogroups to the surface due to their lower surface energy, resulting in a decrease in styrene content at the surface. NEXAFS experiments on samples annealed in high vacuum and slowly cooled show orientation of the CF$_2$ helix of fluorinated side chains as characterized by a helix orientational order parameter, S$_{helix}$, (relative to the surface normal) that is increased by annealing at the optimum temperatuer. NEXAFS measurements during heating in-situ heating reveal how the orientation progresses at the annealing temperature. [Preview Abstract] |
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C1.00024: Polystyrene Freeze Dried from Dilute Solution:\^{E} Tg Depression and Residual Solvent Wei Zheng, Sindee Simon The calorimetric glass transition temperature, Tg, was measured for both linear and cyclic polystyrenes freeze-dried from dilute solution in benzene for concentrations of 0.10{\%}, 0.05{\%} and 0.02{\%} polymer by weight. Upon freeze-drying, Tg was found to be depressed by 4 to 15 K depending on the sample, solvent concentration, and freezing conditions. Annealing under vacuum (0.05 torr) at moderate temperatures, 40 to 140$^{\circ}$ C, resulted in the shifts of Tg back to its bulk value and was accompanied by a decrease in sample weight. The observed weight loss is presumably due to residual solvent. The amount of solvent present in the original freeze-dried samples was determined from the weight loss observed after annealing under vacuum (0.05 torr) for one hour at 100$^{\circ}$ C and one hour at 140$^{\circ}$ C. The calorimetric glass temperature was measured as a function of the fraction of the residual solvent. A linear correlation was found between the Tg depression and the residual solvent concentration, in agreement with data in the literature. In addition, the structure of the freeze-dried polystyrene was examined using Fourier transform infrared spectroscopy. Results show that the recovery of Tg is not due to the structure change during annealing. We conclude that the residual solvent has a significant effect on the Tg depression observed for polymers freeze-dried from dilute solution; no depression or even a slight increase in Tg was observed in the absence of residual solvent. [Preview Abstract] |
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C1.00025: Enthalpy Recovery of Polymeric Glasses: Is the Theoretical Limiting Liquid Line Reached? Qingxiu Li, Sindee Simon Glasses are inherently non-equilibrium materials, and consequently, their properties evolve toward equilibrium in a process known as structural recovery or physical aging. Recently, several authors have suggested that the equilibrium liquid line is not reached even when properties have ceased to evolve. In this work, we present measurements of the enthalpy recovery of polystyrene (PS) at temperatures ranging from the vicinity of glass transition temperature to 10\r{ }C below Tg (90\r{ }C), for aging times up to 200 days. The results are analyzed in the context of the TNM model of structural recovery. In addition, we analyze data in the literature to determine whether enthalpy recovery ceases prior to the material reaching the equilibrium liquid line obtained by extrapolation of the liquid line above Tg. The results suggest that, in fact, the liquid enthalpy line is reached at temperatures below Tg when equilibrium is reached, i.e., when properties cease to evolve. [Preview Abstract] |
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C1.00026: Universal Aspects of Macromolecules in Polymer Blends, Solutions, and Supercritical Mixtures Yuri Melnichenko, George Wignall, Dietmar Schwahn ?We demonstrate that macromolecules in miscible polymer blends may behave as poor, theta and good polymeric solvents for each other. We construct a conceptual phase diagram, indicating the range of validity of the random phase approximation, outside of which molecules contract or expand beyond their unperturbed dimensions, contrary to common assumptions. Similarly, the concentration fluctuation correlation length collapses onto a master curve for polymeric, liquid and supercritical solvents, indicating that macromolecules behave universally in these media over a wide range of thermodynamic variables. [Preview Abstract] |
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C1.00027: Associative polymers bridging between layers of multilamellar vesicles. Seo Choi, Surita Bhatia Multilamellar vesicles can be found in a variety of pharmaceutical formulations, personal care products, and home care products. Hydrophobically modified associative polymers are often used to stabilize the vesicles or to control the rheological properties of these formulations. The hydrophobic groups are expected to insert themselves into the vesicle bilayers. Recent experimental work shows that hydrophobically modified polymers may from bridges between vesicles or may bridge between layers of a single vesicle. The latter configuration forces an interlayer spacing roughly equal to the radius of gyration of the backbone between associative groups. We have performed simple mean-field calculations on ideal telechelic associative polymers between concentric spherical surfaces. We find that the free energy per chain has an attractive minimum when the layer spacing is approximately $N^{1/2}l$, which is consistent with experimental results. The depth of the minimum depends on both chain length and curvature, and as expected when the curvature becomes small, the result for telechelic chains between flat surfaces is recovered. [Preview Abstract] |
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C1.00028: Synthesis and characterization of thermoreversible hydrogels from associating polymers Jun Jiang, Chunhua Li, Michael Rubinstein, Ralph Colby, Daniel Cohn, Miriam Rafailovich, Jonathan Sokolov Multiblock copolymers of poly(ethylene oxide)$_{99}$-poly(propylene oxide)$_{69}$-poly(ethylene oxide)$_{99}$ were synthesized by coupling with hexamethylene diisocyanate (HDI). The rheological, morphological and structural properties of the gel were characterized as a function of temperature, composition and block number. Mixtures of multiblock and single block copolymers were also studied. Using neutron scattering we found that a large degree of alignment could be induced in the single block gel, but no order could be found in the multi-block or homopolymer multiblock mixture. The yield strain in samples with 3.2 of multiblocks was nearly an order of magnitude higher than the single bock gel. This was interpreted in terms of an ordered layered state of micelles being formed by steady shear. A model based on the competition between forming non-interacting micelles and forming bridges will be presented. [Preview Abstract] |
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C1.00029: Design, Synthesis, and Evaluation of Non-Porous, Hydrophilic Membranes Sadie White, Michael Fryd, Bradford Wayland, Russell Composto, Karen Winey The use of membranes in biological sciences, electrochemistry, and separation technologies is widely expanding. In this investigation, the water flux and filtration capacities of polyacrylamide-based hydrogel membranes were studied under gravity- and forced filtration processes. The crosslinked membranes were prepared via room-temperature aqueous free radical polymerization, initiated with ammonium persulfate. The crosslinker hydrophilicity and concentration (between 0.5 and 10 mole percent), as well as the membrane thickness, were varied to determine the dependence of gel swelling and water flux on these factors. Suspensions of narrowly-dispersed pigment particles (with a diameter of approximately 200 nanometers) were analyzed with light scattering before and after filtration to determine how effectively the membranes remove particulate matter in this size range. Ongoing work will broaden the investigation to include similar water throughput and filtration studies on crosslinked poly(acrylic acid) membranes. [Preview Abstract] |
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C1.00030: Small angle neutron scattering study to determine the structure of high strength hydrogels. Taiki Tominaga, Vijay R. Tirumala, Eric K. Lin, Wen-li Wu, Jian Ping Gong, Hidemitsu Furukawa, Yoshihito Osada Hydrogels are swollen polymer networks containing more than 90{\%} water. Most hydrogels, however, are mechanically too weak to be used as load bearing devices. Gong \textit{et al.} have overcome this problem by synthesizing hydrogels with a double network (DN) structure. Modifying the polyelectrolyte network structure by polymerization of high molecular weight uncharged polymer \textit{in situ}, resulted in orders of magnitude increase in their load bearing ability. Despite 90{\%} water, these tough gels exhibit a fracture stress of 170 kg/cm$^2$, similar to that of articular cartilage found in the bone-joints of human body. In this work, we determined the structure of DN-gels using small angle neutron scattering. Structural origins for high toughness found in DN-gels were then examined by comparing the structure of DN-gels with that of pure polyelectrolyte network and polyacrylamide solution. [Preview Abstract] |
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C1.00031: Quantitative analysis of interfacial reaction and interfacial thickness by FTIR and Ellipsometry. Manoranjan Prusty, Han Goossens, Gert de Wit, Piet Lemstra, Matrin Van Duin We have studied the development of interface and also interfacial reaction in Polyethylene-co-methacrylic-acid (PE-co-MA) and Styreneacrylonitrile-oxazoline (SAN-Oxaz) bilayer film. The interfacial reaction was studied in-line at different temperatures for the bilayer sample. A decrease in oxazoline and increase in amide and ester was observed. The intensity of amide I was found to have a plateau at higher time indicating that the reaction is diffusion limited. The growth of interface was also studied with the ellipsometer. The retardation, $\Delta $ and reflection ratio, tan$\psi $ data were recorded for the bilayer sample at three angles of incidence (60\r{ }, 70\r{ } and 80\r{ }) and at different temperatures. These data were fitted according to a 4-layer model. The time variations of interfacial thickness in SAN-Oxaz/PE-co-MA bilayer was found to increase with time and finally go to a plateau at higher temperatures. [Preview Abstract] |
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C1.00032: Confinement Effects on the Phase Separation of Polymer Dispersed Liquid Crystals Jianfeng Xia, Jun Wang, Zhiqun Lin, Feng Qiu, Yuliang Yang The phase separation kinetics of polymer dispersed liquid crystals (PDLC) confined between two parallel, smooth walls are numerically studied for the first time. The time evolution of two order parameters (i.e., composition order parameter, \textit{$\phi $} and orientational order parameter, $Q)$ are calculated by solving coupled time-dependent Ginzburg--Landau (TDGL) model C equations. The external confinement is found to accelerate the ordering of LC. The results presented in the study may provide insights into the experiments on the control of LC domain morphology under nanoscopic confinement. [Preview Abstract] |
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C1.00033: Crystallization of Ethylene Vinyl Acetate (EVA) and Polyethylene (PE) /deuterated Polystyrene (dPS) Blends in Supercritical Carbon Dioxide (scCO$_{2})$ Christopher Pynn, Payvand Ahdout , John Jerome, Yantian Wang, Vladimir Zaitsev, Johnathan Soklov, Miriam Rafailovich, Steven Schwarz Thin films of EVA or PE and dPS were spun cast onto Si wafers and crystallized in supercritical carbon dioxide at pressures and temperatures corresponding to the density fluctuation ridge$^{1}$ or thermally annealed using standard protocols. The morphology composition and melting points of the films were studied using scanning force microscopy and imaging time-of-flight secondary ion mass spectrometry as function of film thickness and homopolymer concentration. The results showed that exposure to scCO$_{2}$ produced highly crystalline films. Furthermore, in contrast to the thermally annealed films, the homopolymer was fully incorporated into the crystalline phase. The surface morphology of the films after crystallization showed either island or hole structure, depending on the relation between the film thickness and the lamellar height. Supported in part by the NSF-MRSEC program and by a grant from the SRC-NYS consortium. \newline Reference: $^{1 }$Koga T., Seo Y.S., Shin K., Zhang Y., Rafailovich M., Sokolov J., B. Chu, Satija, S.K. \underline {Macromolecules}. Vol. 36. 2003: 5236- 5243. [Preview Abstract] |
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C1.00034: Phase structures of block copolymers blended with small molecules Kishore Tenneti, Xiaofang Chen, Christopher Li, Xinhua Wan, Qi-Feng Zhou, Igors Sics, Benjamin Hsiao We report our observations on the influence of blending small molecules on the phase structures of a block copolymer (BCP) system. Poly(styrene-b-4vinyl pyridine) (PS-b-P4VP) BCP was blended with 4-(3,4,5-tris(alkyloxy)benzoyloxy)phenyl 4- hydroxyphenyl isophthalate (BCLCn where n = 6-16) small molecule in different weight ratios. The terminal hydroxyl group of the BCLC is expected to form hydrogen bonding with the P4VP and thus alter the phase structure of the BCP. Thermal analysis, X-ray analysis and transmission electron microscopy were conducted and it was observed that BCLCs with n = 6 and 8 did not have any influence on the BCP morphology and those with n = 14 and 16 have phase separated. There was a substantial decrease in the d-spacing of BCPs blended with BCLCs with n = 10 and 12 and a bilayer structure was evident. [Preview Abstract] |
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C1.00035: Structure and Nanomechanical Properties of Well-aligned Electrospun PS/MWCNT Composite Nanofibers Yuan Ji, Shouren Ge, Jaseung Koo, Bingquan Li, Batya Herzberg, Toby Klein, Jonathan Sokolov, Miriam Rafailovich Carboxyl-functionalized multi-wall carbon nanotubes (MWCNT) were incorporated into polystyrene/DMF solutions and electrospun to form PS/MWCNT composite nanofibers. The nanofibers were spun onto a high speed rotator where they became well aligned. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the surface morphology and interior structure of the electrospun nanofibers. A three-point bending test, using atomic force microscopy (AFM), was utilized to measure the Young's moduli of the nanofibers as a function of fiber diameter and MWCNT concentration. Shear modulation force microscopy (SMFM) was employed to measure the surface glass transition temperature of the composite nanofiber. The existence of MWCNT enhanced the Young's moduli of fibers and increased the glass transition temperature by nearly 10 degrees. Supported by NSF-MRSEC. [Preview Abstract] |
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C1.00036: Spherical nanoparticle ordering in block copolymer systems John Papalia, Mary Galvin In recent years, nanoparticles and self-assembled systems have both been areas of extensive research. Our work combines the unique properties of both fields into a single system by investigating the ordering of nanoparticles in block copolymers (BCPs). Balazs et al. put forth an expansive set of theories which predict the behavior of hard nanoparticle inclusions in BCP systems. These composites combine the natural drive of the BCPs to self-assemble with the physical properties of the particles, yielding complex systems. Our goal is to methodically investigate the theories via model experimental systems. Silica nanoparticles ($<$25nm have been incorporated into the styrene phase of a polystyrene-b-poly(ethylene-co-propylene) BCP. Parameters such as particle size, surfactant coverage, and particle volume fraction are varied in a controlled fashion with their effects on particle ordering studied. Results show surfactant use is almost mandatory to provide the particles with the energetic advantage needed to integrate them into the BCPs. Integrated particles show definitive ordering within discrete BCP domains. Our current and future systems seek to further investigate these results and trends. The combination of these result sets, along with experimentation related to domain size, will aid the design of multi-size particle systems potentially suited for improved photonic devices or nano-scale waveguides. [Preview Abstract] |
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C1.00037: Dependence of Tg Upon Fiber Orientation in Epoxy-Matrix Composites Kristy Visconti, Patrick Burton, John D. McCoy Epoxy-matrix glass-fiber reinforced composites were tested using a Rheometrics RMS to investigate the dynamic complex shear modulus. The samples were constructed from woven prepreg tape with all layers layed-up at a single weave orientation. Rectangular samples were cut at various angles relative to the fiber direction. The material was found to be rheologically simple. Consequently, a single master curve was constructed for each sample orientation. From this master curve the corresponding shift factors were extracted and plotted against temperature. The WLF equation was used to estimate the glass transition temperature, Tg. An apparent shift in the glass transition temperature was observed as the orientation of the fiber weave relative to the torsional axis was varied. [Preview Abstract] |
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C1.00038: One Dimensional Nanocomposites Nikhil Sharma, Darrin Pochan Tailoring the structure of hybrid materials at the nano-scale in order to enhance their properties could produce advanced materials with remarkable attributes and poses significant research challenges. One- dimensional nanoparticle assemblies are an interesting class of materials that may provide an insight into the fundamentals of quantum mechanics of nanomaterials and have potential applications as sensors, in drug-delivery, and in the conduction of novel signals such as phonons and spin states. Experimental work with electrospinning of polyethylene oxide fibers with inorganic particles (silica and iron) is underway that utilizes a coaxial capillary electrospinning apparatus for the formation of one- dimensional assemblies of nanoparticles. The effect of change in solution concentrations and relative flow rates in internal and external channels of the coaxial electrospinning apparatus on the inter-particle distance are being investigated. [Preview Abstract] |
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C1.00039: Structure, Morphology and Properties of Carbon Nanotube Containing Polymeric Materials Lingyu Li, Steve Kodjie, Christopher Li Carbon nanotubes (CNTs) are considered an ideal reinforcing fillers in polymer nanocomposites because of their high aspect ratio, nanosize diameter, very low density and excellent physical properties (such as extremely high mechanical strength, high electrical and thermal conductivity),. However, in order to achieve homogeneous dispersion of CNTs without damaging their extraordinary properties, non-covalent functionalization is an essential step. Our study of functionalization of CNTs via controlled polymer crystallization method has resulted in the formation of ``nano hybrid shish-kebab'' (NHSK), which is CNT periodically decorated with polymer lamellar crystals. By tuning the experimental parameters such as concentration of polymer and crystallization temperature, hybrid polymer spherulite with CNT inside was achieved. This can be considered as CNT reinforced composite with ideally controlled CNT dispersion. Both Nylon 6, 6 and PE were used as the matrix materials. Excellent dispersion of CNTs in polymer matrix was achieved and the nanocomposites showed improved thermal stability. [Preview Abstract] |
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C1.00040: Organic Photonic Crystal Lasers from Holographic Polymer Dispersed liquid Crystals (H-PDLCs) Timothy Bunning, Rachel Jakubiak, Dean Brown, Richard Vaia, Pamela Lloyd, Vincent Tondiglia, Lalgudi Natarajan, Richard Sutherland Holographic polymerization of liquid crystal containing photopolymerizable resins enables one-step, rapid formation of multi-phase structures that exhibit partial photonic band gaps. These holographic polymer dispersed liquid crystals (H-PDLCs) provide a versatile platform for diffractive optical elements because the structures are not limited by multi-phase equilibrium but are controlled by the interference of multiple lasers at discrete angles. Incorporation of laser dyes into H-PDLCs form 1-D and 2-D optically pumped distributed feedback lasers. Linewidths as narrow as 1.8 nm are observed with laser thresholds below 1 mJ/cm$^{2}$ in 2-D columnar structures compared to 9 nm and 25 mJ/cm$^{2}$ exhibited by 1-D H-PDLC Bragg stack lasers. In the 2-D lattices the energy of the laser action can be tuned within the gain spectrum of the lasing medium by an applied electric field. [Preview Abstract] |
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C1.00041: Single-layer white-light polymeric luminescent film by plasma polymerization for light emitting diodes Chun-Chih Chang, Yi-Hsing Chang, Ying-Chu Chen, Arnold Chang-Mou Yang, Kuo-Chu Hwang Efficient white polymeric light-emitting diodes (PLED) were fabricated with a single active layer consisted of three-dimentional crosslinking $\pi $-conjugated system by plasma polymerization from conjugated monomers. As indicated by the FTIR, XPS UV-vis and PL spectra, the plasma polymer chains were constructed by various chromophores including naphthalene, phenyl, polyene and alkyl groups. Upon optical excitation, the light emission was characterized with a broad peak (FMHW $\sim $ 100 nm) located at 430 nm. In a PLED device, however, the energy transfer by Foster processes (FRET) between multiple host-guest pairs give rise to white emission located in CIE coordinates of (0.3439, 0.3369). This result illustrated the feasibility of large area contour coating of single-layer white-light luminescent polymers for LEDs by simple plasma polymerization methods. This work is supported by National Science Council of Taiwan. [Preview Abstract] |
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C1.00042: Evaporation induced hierarchical structure formation using diblock copolymers Suck Won Hong, Jun Xu, Zhiqun Lin We present a study of the formation of the hierarchically ordered structures produced from the combination of two self-assembling processes on different length scales, i.e., the dynamic self-assembly via irreversible solvent evaporation in restricted geometries at the microscopic scale and the spontaneous self-assembly of diblock copolymer (e.g., PS-b-PMMA) at the nanoscale. This approach utilizes concurrent self-assemblies as a means to organize unique nanomaterials into spatially ordered structures. [Preview Abstract] |
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C1.00043: A Unique Two-Stage Dewetting of Ultrathin Films of Entangled Chains Solution-Cast on a Deformable Surface Tony Ming-Hsun Yang, S.Y. Hou, Arnold Chang-Mou Yang, F.C. Chang, C.F. Wang Stability of polystyrene (PS) thin films (200k$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $M$_{w}\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $2M, 20 nm$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $h$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $80 nm) on a deformable surface of low energy at 170 ${^\circ}$C was investigated. A unique two-stage dewetting process was discovered and the magnitude of total forces driving the dewetting was determined from the strong substrate interaction. The film dewet by first nucleating small holes which grew rapidly but subsequently ran into a complete rest. Additional annealing of more than 4.5 hours, however, induced a second stage dewetting initiated from the intact region. The newly initiated holes were characterized with fingers growth that broke down into tiny droplets concurrent to holes expansion. The dewetting force was estimated to be around 0.036 N/m and decrease with aging time. Substrate interactions appeared to have a significant effect of increasing surface energy, hampering the rate of dewetting.~This work is supported by Air Force (AFOSR-04-4074) and National Science Council of Taiwan. [Preview Abstract] |
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C1.00044: Investigation of atomic force microscopic image resolution of organic molecules Masanori Harada, Masaru Tsukada, Naruo Sasaki We simulated atomic force microscopic images of organic molecules using MM3 force field. Especially we investigated how higher the resolution of images can change using single atom tip compared with realistic tip model. This investigation was motivated by the fact that the resolution of the AFM images of organic molecules is not as good as the images of inorganic surfaces. The difference of the image resolutions can be seen for different element atom, which means using different van der Waals parameter. We also investigated the relation between resolution and mobility of molecules. [Preview Abstract] |
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C1.00045: Surface Plasmon Resonance Studies of Hydroxypropyl Xylan Self-Assembly on Cellulose Daniel A. Drazenovich, Abdulaziz Kaya, Alan R. Esker, Wolfgang G. Glasser Wood is a multiphase material consisting of cellulose crystals embedded within a non-crystalline hetereopolysaccharide (hemicellulose) and lignin rich phase. The hierarchial arrangement of these three chief components in wood produces excellent properties like resistance to fracture and toughness. Through the study of self-assembly of hemicellulose onto a model cellulose surface, further insight into the interactions between hemicelluloses and cellulose can be gained. In our study, we used xylans with different degrees of substitution of hydroxypropyl groups. Surface plasmon resonance measurements (SPR) probe the self-assembly behavior of hydroxypropyl xylans (HPX) onto a cellulose coated gold surface. In addition, tensiometry provides the critical aggregation concentration (CAC) of different HPX samples. CAC results can be correlated to adsorption observed by SPR. Increasing the degree of hydroxypropyl substitution decreases the CAC and increases adsorption onto cellulose surfaces. [Preview Abstract] |
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C1.00046: Microfluidic interfacial tensiometry Jai Pathak, Steven Hudson, Joao Cabral A microfluidic instrument to measure interfacial tension of multicomponent immiscible liquids is reported. The instrument measures deformation and retraction dynamics of drops under extensional flow, and is accurate within a few percent. Binary and ternary mixtures have been examined. Surfactant transport phenomena and the effects of viscosity ratio and bounded flow have also been explored. [Preview Abstract] |
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C1.00047: The Effect of Humidity on the Ordering of Block Copolymer Thin Films Joona Bang, Bumjoon J. Kim, Thomas P. Russell, Edward J. Kramer, Craig J. Hawker Solvent cast diblock/triblock copolymer films of poly(styrene-$b$-ethylene oxide) (PS-PEO) and poly(styrene-$b$-methyl methacrylate-$b$-ethylene oxide) (PS-PMMA-PEO), with cylindrical microdomains of PEO or PMMA-PEO, have a high degree of long-range lateral order after solvent annealing. Relative humidity of the vapor during the solvent annealing has been shown to play an important role in achieving this order yet the origin of the humidity effect is has been the subject of debate. This work focuses on understanding the role of humidity on the ordering of block copolymer thin films. We find that PS-PMMA-PEO triblock copolymers that show a lamellar morphology in bulk develop a hexagonal array of PMMA-PEO domains on the film surface after solvent annealing in a humid environment. To study the effect of humidity further, hydrophilic nanoparticles, such as PEO-coated gold nanoparticles and PEO-star polymers, were incorporated into nonhydrophilic block copolymers, i.e., poly(styrene-$b$-methyl methacrylate) (PS-PMMA) diblock copolymers that exhibit PMMA cylinders. By controlling the relative humidity and the volume fraction of hydrophilic nanoparticles, it was found that lateral ordering of these PS-PMMA diblock copolymers can also be achieved. The thin film morphologies were investigated in detail using AFM, GISAXS, and TEM. [Preview Abstract] |
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C1.00048: Surface Modification Using Photo-Crosslinkable Random Copolymers Joonwon Bae, Joona Bang, Peter Lowenhielm, Christian Spiessberger, Thomas P. Russell, Craig J. Hawker We recently reported that poly(styrene-$r$-methyl methacrylate) (PS-$r$-PMMA) random copolymers containing benzocyclobutene (BCB) group can be used to modify the surface effectively by thermal crosslinking. It was demonstrated that this method is simple, rapid, and robust, and can be applied to various surfaces. However, it requires the large amount of heat for processing, and the BCB monomer itself involves a hard chemistry. An alternative way that can replace BCB with easier chemistry and lower cost, if possible, is highly desirable. We introduce the new functional group, azide group, which can be crosslinked simply by UV irradiation, for this purpose. PS-$r$-PMMA random copolymers, containing various amounts of azide groups, were synthesized via controlled living-radical polymerization. It was demonstrated that even after 1 minute of the UV irradiation can crosslink the materials effectively, so that they can be used as crosslinked random copolymer mat to control the surface energy. However, it was observed that the longer irradiation time causes the damages on the surface due to the other side reactions. Depending on the UV intensity, the UV irradiation time, and the amount of azide group, the effective processing window that leads to the crosslinking without any surface damages was optimized. [Preview Abstract] |
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C1.00049: Mean-field Description of Spinodal Growth of Surface Waves on Rupturing Films Yong Jian Wang, Ophelia K.C. Tsui We examine the extent to which the mean-field theory is applicable to the description of the experimentally observed growth of surface waves on a rupturing polystyrene film coated on an oxide-covered silicon that is known to be spinodal unstable. We find that good agreement between theory and experiment is obtainable if corrections due to non-linear effects and stochastic thermal fluctuations are considered. [Preview Abstract] |
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C1.00050: The Interface between Two Incompatible Polymers in Density Fluctuating Supercritical Carbon Dioxide J.S. Koo, T. Koga, M. Rafailovich, J. Sokolov The X-ray reflectivity was used to investigate an effect of CO$_{2}$ sorption on interface between two immiscible polymers, polystyrene (PS) and poly(methylmethacrylate) (PMMA). Thin films of PS and PMMA were spun cast onto Si wafers and the interfacial width was measured as a function of the film thickness of both PS and PMMA layers. The samples were then exposed CO$_{2}$ gas at pressures and temperature corresponding to the density fluctuation ridge (1). The relative dilation of the two layers and the change in the interfacial width was then determined. The results showed that the dilation was nearly independent of the PMMA film thickness, and maximal at thickness less than 3Rg of the PS layers. The interfacial width in all cases was almost twice as large after exposure. These results will be interpreted in terms of the interfacial reduction induced by the CO$_{2}$ and capillary wave theory. (1) Koga, T. \textit{et al. Phys. Rev. Lett. }\textbf{2002}, $89$, 125506 ; Koga, T. \textit{et al. Macromolecules }\textbf{2003}, $36$, 5236. [Preview Abstract] |
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C1.00051: Trisilanolphenyl-POSS as an Adhesion Promoter Sarah Huffer, Ufuk Karabiyik, Alan Esker Polyhedral oligomeric silsesquioxanes (POSS) have been an innovative research area for over twenty years. Potential aerospace applications include space-survivable coatings and ablative insulation. Recent studies showed that trisilanol-POSS derivatives form monolayers at the air/water interface. The purpose of this study was to improve adhesion between ceramics and metals and metals and polymers by preparing multilayer films at various pH values and metal ion concentrations using trisilanolphenyl-POSS (TPP). Multilayer systems were created by spincoating polystyrene, using the Langmuir-Blodgett technique for TPP, and physical vapor deposition of aluminum oxide. The resulting films were characterized for quality and stability using atomic force microscopy, optical microscopy, X-ray photoelectric spectroscopy, and dewetting experiments. Initial experiments demonstrated that TPP-aluminum ion complexes facilitated smooth aluminum oxide film formation on silicon wafers while TPP alone yielded a blistered aluminum oxide surface. [Preview Abstract] |
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C1.00052: Interface Behavior in Diblock Copolymer Brushes Gokce Ugur, Bulent Akgun, William J. Brittain, Mark D. Foster, Xuefa Li, Dong Ryeol Lee, Jin Wang A polymer brush is an assembly of polymer chains with one end tethered to a surface or an interface with a tethering density high enough that the polymer chains are forced to stretch away from the substrate. This stretching of polymer chains along the direction normal to surface is different from the typical behavior of flexible chains. The study of surface and interface properties of polymer brushes is important for their use in nano-scale applications. We investigated the surface and interface structure of polystyrene-b-polymethylacrylate (PS-$b$-PMA) diblock copolymer brushes that have been synthesized using atom transfer radical polymerization (ATRP). Grazing incidence small angle X-ray scattering (GISAXS) was used to probe the structure of the surface as well as the buried interfaces of the brushes. It showed that there are lateral correlations inside the brush and that the spacing of these structures is on the order of the top layer thickness of the brush. Analysis of the GISAXS data provides information for values of the in-plane scattering vector that are larger than those accessible using a conventional transverse scan. [Preview Abstract] |
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C1.00053: Exciton Emission in PTCDA Thin Films under Uniaxial Pressure A. DeSilva, V.R. Gangilenka, H.P. Wagner, R.E. Tallman, B.A. Weinstein, R. Scholz We study the strain dependent photoluminescence (PL) of a 90 nm thick polycrystalline PTCDA film on Si(001) between 20 and 300 K. Uniaxial pressure up to 1 kbar is applied along the molecular stacking direction using a home made pressure cell. With increasing pressure we find a quenching of the total PL intensity which is mainly attributed to the creation of defects. At low temperature the charge transfer exciton emission (CT2) gains intensity relative to the Frenkel exciton emission. Furthermore the CT2 transition reveals a shift to lower energies by approximately 5 meV. At room temperature the PL is dominated by the excimer transition which shows a redshift of 5 meV at highest uniaxial pressure. The increase of the CT2 transition at low temperature and the redshift of the emission bands are attributed to an increased exciton trapping probability and enhanced binding energy with reduced distance between stacked molecules. [Preview Abstract] |
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C1.00054: Evidence for Capillary Contributions to Gecko Adhesion from Single Spatula Nanomechanical Measurements Gerrit Huber, Stanislav Gorb, Eduard Arzt, Ralph Spolenak, Klaus Mecke, Hubert Mantz, Karin Jacobs The hairy attachment system on a gecko’s toes, consisting of one billion spatulae in the case of Gekko gecko allows it to adhere to nearly all surface topographies. The mechanistic basis for gecko adhesion has been intensely investigated, but the lowest hierarchical level, that of the spatula, has become experimentally accessible only recently. This study details measurements of the adhesion force exerted by a single gecko spatula for various atmospheric conditions and surface chemistries. Through judicious choice and modification of substrates, the short- and long-range adhesive forces are separated. In contrast to previous work, our measurements clearly show that humidity contributes significantly to gecko adhesion on a nanoscopic level. These findings are crucial for the development of artificial biomimetic attachment systems. [Preview Abstract] |
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C1.00055: The Influence of Stereoerrors on the Crystallization of Isotactic Polypropylene Xiaofeng Chen, Sanat K. Kumar, Rahmi Ozisik Crystallization behavior of four isotactic polypropylenes (iPP) with stereoerrors was studied by Monte Carlo simulation. All systems were equilibrated above the melting temperature (T$_{m}$) and then cooled systematically to temperatures below the T$_{m}$. The conformations of the iPP chains were analyzed to characterize the crystallinity development in each system. The probability of helix formation, the average length of helices, and the fraction of repeat units involved in helical structures all increased as temperature decreased. As expected, the stereoregular iPP had the longest helical structures and the highest overall crystallinity compared to the other systems with stereoerrors. The overall crystallinity decreased with increasing number of stereoerrors. The influence of stereoerrors on the ability of iPP repeat units participation in helical structures was also investigated. The results showed that the stereoerrors can exist in helices but they strongly influence the ability of their neighbors to exist in helices. [Preview Abstract] |
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C1.00056: Investigation of the Structure and Dynamics of Polyethylene Nanocomposites Peter J. Dionne, Rahmi Ozisik, Catalin R. Picu The structure and dynamics of linear, monodisperse polyethylene (PE) melts (C$_{160}$H$_{322}$ and C$_{440}$H$_{882}$) containing homogenously distributed spherical nanoparticles were investigated. The PE chains were simulated using a coarse grained model and a Monte Carlo algorithm. Two variables were considered: (i) the wall-to-wall distance between particles (\textit{d}), and (ii) the interaction energy between monomers and particles. The various chain structures changed greatly with \textit{d} while the monomer-particle interaction had little effect. The average size, shape, and orientation of PE chains did not differ significantly from those of a neat melt. Bridge segments were more stretched relative to segments in the neat melt and the stretch increased with increasing \textit{d}. However, the number of bridge segments decreased markedly with increasing \textit{d}. Chain dynamics was monitored by computing the Rouse relaxation modes and the mean-square displacement of the center of mass. The dynamics were slowed by both geometric effects (confinement by fillers) and energetic effects (monomer-particle energetic interaction). [Preview Abstract] |
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C1.00057: Extensions of an analytical coarse-grained description for polymer liquids: thermodynamic determinations and an intermediate length-scale description Edward Sambriski, Marina Guenza We extend our previous analytical coarse-graining (CG) procedure \footnote{G. Yatsenko, E. J. Sambriski, and M. G. Guenza, J. Chem. Phys., \textbf{106,} 054907:1-12 (2005); G. Yatsenko, E. J. Sambriski, M. A. Nemirovskaya, and M. Guenza, Phys. Rev. Lett., \textbf{93,} 257803:1-4 (2004).}, which maps polymer liquids onto a system of interacting soft-colloidal particles. First, we present an optimized representation of the effective pair potential, $v_{cc}(r)$ [initially determined via the hypernetted-chain closure], by carrying out an interative predictor-corrector (PC) scheme. Then, we compare the thermodynamics obtained through the virial and compressibility routes, for which we observe an improvement in their consistency when using the PC result. Finally, we present an intermediate length-scale CG treatment for polymers by performing an analytical remapping of the chain onto ``blobs'' (monomer aggregates). The derived expression for the blob-blob total correlation function, $h_{bb}(r)$, is seen to be in agreement with data from united-atom molecular dynamics simulations. [Preview Abstract] |
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C1.00058: A Novel Approach for Understanding the Effect of Nano-Fillers on the Conformational Properties of a Polymer Matrix: Dimensions go up or down? Fatih M. Erguney, Wayne L. Mattice MC simulations of a polymer matrix composed of linear POE chains and nano-fillers were performed on a 2nnd lattice to reveal the change in the $<$s$^{2}>$ of matrix chains perturbed by nano fillers. Nano-fillers are obtained by the collapse of a desired number of linear chains by increasing the contribution of the attractive core of discretized intramolecular LJ potential. The resulting change in $<$s$^{2}>_{matrix}$ is case sensitive in such a way that it might either go up or down depending on the size of both species. It tends to increase in the presence of nano-fillers when both kinds are represented by a small number of beads. There's a peak point observed in this case after which the dimensions start to decrease as the filler fraction is further increased. The contraction of chains is also of concern provided that chains have a larger number of beads. On the contrary, there's no peak point observed in such a case, but a plateau region is acquired at high filler fraction. Magnitude of the change depends on several parameters like mobility and compactness of fillers. [Preview Abstract] |
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C1.00059: Density functional and molecular dynamics study of conducting polymers Y. Dai, E. Blaisten-Barojas Polypyrrole belongs to the important class of conducting polymers and is a good candidate for photonic devices and chemical sensors. In this work we performed electronic structure calculations of pyrrole oligomers containing 6 to18 rings at the density functional (DFT) level and searched for the charge distribution in the oxidized and neutral phases. The description of bipolaron given in terms of charge localization over domains along the pure polymer chain by semiempirical methods could only be confirmed by DFT studies in the oxidized phase when dopants are present. A model potential for polypyrrole was developed based on the first principles calculations of the structure and charge distribution. Several finite temperature and dynamical properties were studied with molecular dynamics. [Preview Abstract] |
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C1.00060: Structure and Spectra in Mutated Green Fluorescent Protein: A Combined Molecular Dynamics and QM/MM Study Soumya Patnaik, Steven Trohalaki, Ruth Pachter Recently, several Green Fluorescent Protein (GFP) mutants have been developed with red-shifted absorptions. The molecular structures of two such mutants with S65G and S65T mutations have been studied with an aim towards understanding the shift in their absorption spectra. A combined approach of molecular dynamics (MD) and Quantum Mechanics/Molecular Mechanics (QM/MM) has been used. Time dependent density functional theory (TDDFT) based absorption spectra calculations were found to be of excellent agreement with experimental data. These calculations were carried out on chromophore structures derived from QM/MM and MD studies, thus taking into account, both the effects of thermal fluctuations and the protein and solvent environment. In addition to providing information regarding the variation of the geometrical parameters due to temperature effects, the MD simulations also identify residues around the chromophore which are associated with conformational change on mutation. By using QM/MM to systematically analyze significant structural features that were identified by MD simulations, a detailed understanding of the energetics of the optimized chromophore conformations was achieved. [Preview Abstract] |
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C1.00061: Biodegradable Epoxy Networks Cured with Polypeptides Shigeo Nakamura, Edward J. Kramer Epoxy resins are used widely for adhesives as well as coatings. However, once cured they are usually highly cross-linked and are not biodegradable. To obtain potentially biodegradable polypeptides that can cure with epoxy resins and achieve as good properties as the conventional phenol novolac hardeners, poly(succinimide-co-tyrosine) was synthesized by thermal polycondensation of L-aspartic acid and L-tyrosine with phosphoric acid under reduced pressure. The tyrosine/succinimide ratio in the polypeptide was always lower than the tyrosine/(aspartic acid) feed ratio and was influenced by the synthesis conditions. Poly(succinimide-tyrosine- phenylalanine) was also synthesized from L-aspartic acid, L- tyrosine and L-phenylalanine. The thermal and mechanical properties of epoxy resins cured with these polypeptides are comparable to those of similar resins cured with conventional hardeners. In addition, enzymatic degradability tests showed that Chymotrypsin or Subtilisin A could cleave cured films in an alkaline borate buffer. [Preview Abstract] |
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C1.00062: A novel Generalized Langevin approach to bridge different timescales of relaxation in Protein Dynamics Esther Caballero Manrique, Jenelle Bray, Marina Guenza The derivation of a Generalized Langevin Equation (GLE) for the long-time dynamics of biological systems presents several challenges as hydrogen bonding, secondary and tertiary structure, Coulombic interactions, and hydrophobic effects come into play. Here we propose a novel GLE approach where the internal friction is explicitly included in the protein dynamics, allowing the distinction between hydrophobic and hydrophilic effects. The protein is described as a linear chain of beads (centered at the alpha carbons) that are connected by harmonic springs. Input for our theory is short time (ns) molecular dynamics simulations of a single protein (or complex) in solution, in this case the bacterial signal transduction protein CheY. Effective inter-bead potentials and local friction coefficients are obtained from the simulations. A comparison of the bond autocorrelation function predicted from the theory and calculated directly from the simulation affords the test of the theory in the short timescales (ns). In the long timescales (ms), the theory is tested against experimental NMR $\mbox{T}_1 $ relaxation values. Our results show a remarkable agreement in both cases, indicating that our GLE correctly bridges from the short- to the long-time scale of protein dynamics. [Preview Abstract] |
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C1.00063: Quantitative prediction for two-dimensional bacterial genomic displays Jean-Francois Mercier, Christine Kingsburry, B\'en\'edicte Lafay, Gary W. Slater Two-dimensional bacterial genomic display (2DBGD) is a simple technique that allows one to directly compare complete genomes of closely related bacteria. It consists of two phases. First, polyacrylamide gel electrophoresis (PAGE) is used to separate the DNA fragments resulting from the restriction of the genome by appropriate enzymes according to their size. Then, temperature gradient gel electrophoresis (TGGE) is used in the second dimension to separate the fragments according to their sequence composition. After these two steps, the whole bacterial genome is displayed as clouds of spots on a two-dimensional surface. 2DBGD has been successfully used to distinguish between strains of bacterial species. Unfortunately, this empirical technique remains highly qualitative. We have developed a model to predict the location of DNA spots, as a function of the DNA sequence, the gel electrophoresis and TGGE conditions and the nature of the restriction enzymes used. This model can be used to easily optimize the procedure for the type of bacteria being analyzed. [Preview Abstract] |
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C1.00064: Osmotic Pressure induced by Poly(ethylene glycol) at High Salt Concentrations Sungkyun Sohn, Helmut Strey, Sam Gido The osmotic pressure method is one of the most effective tools that can be used in controlling self-assembly of polymers in solution, especially of water-soluble biopolymers. This study investigated if there is a noticeable synergistic osmotic pressure increase between co-existing polymeric osmolyte and salt when extremely highly concentrated salt molecules are present both at sample subphase and stressing subphase. PEG 8,000 and LiBr were chosen as osmolyte and salt, respectively, since this model system can be directly applied to the case of silk protein self-assembly, where hydrogen bonding plays a major role. In addition to the conventional methods for measuring osmotic pressure, such as membrane osmometry, vapor pressure osmometry, and ultracentrifuge, an `equilibration method' that measures osmotic pressure relative to a reference with known osmotic pressure, was introduced. PEG 400 solution was chosen as the reference for this method. Osmotic pressure of aqueous LiBr solution up to 2.75M was measured and it was found that the synergistic effect was insignificant up to this salt concentration. Solution parameters and Arrhenius kinetics based on time-temperature relationship during the equilibration process were derived as well. [Preview Abstract] |
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C1.00065: The Effect of Polymer-Clay Nano-Composites on Human Dermal Fibroblasts Lourdes Collazo, Hilana Lewkowitz-Shpuntoff, Mary Catherine Wen, Miriam Rafailovich The effect of polymer-clay nano-composites on the proliferation of Human Dermal Fibroblasts (HDF) as a function of clay content was investigated. Polybutadiene with different clay concentrations were spun cast on glass substrates. HDF cells were cultured on these substrates and growth curves were generated for a period of 2 weeks.The results show that the optimal growth occurred on Polybutadiene films with nano-composites that consisted of 90\% polymer and 10\% clay. The relative modulus of these polymer-clay nano-composites films were measured by Scanning Modulus Force Microscopy (SMFM) 1 and showed a linear increase with clay concentration, indicating that the nano-composites became harder with increased clay concentration.Confocal microscopy revealed that the morphology of the F-Actin fibrils is a function of the matrix modulus. In addition more focal adhesion points were found on the harder substrates. This adaptation of normal fibroblasts will be compared to cancer fibroblasts as well as protein distribution by western blotting. Reference: Shouren Ge et al. PRL (2000) 85(11) 2340-2343 [Preview Abstract] |
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C1.00066: Receptor/Ligand Interactions at an Oil/Water Interface Daniel Carvajal, Chi-Yang Chao, Kenneth Shull The strength of the interaction between biotin and avidin has sparked major research interests as the system serves as a vehicle for both targeted drug delivery and the simulation of surface recognition processes. Interfacial tension measurements (IFT) using R-PEO-biotin$^{1}$ were used to obtain dynamic information on the avidin-biotin interaction. Real time IFT data was gathered from the liquid-liquid interface by monitoring the shape of the drop via a drop shape analysis (DSA) instrument. A drop, containing dissolved R-PEO-biotin block copolymers in an ``oil like'' phase, was formed in an immiscible embedding ``water like'' phase. The block copolymers were specially designed to segregate to the liquid-liquid interface and cover the drop surface. By adding avidin to the surrounding water phase, changes in the drop shape provided dynamic data on the avidin-biotin interaction, as avidin binds to biotin only at the drop surface. This is the first study to show that DSA can be applied to the dynamic study of the interaction between avidin and biotin. $^{1}$Biotin-functionalized block copolymers with a hydrophobic aliphatic block and a hydrophilic PEO block [Preview Abstract] |
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C1.00067: Theoretical Comparative Study of the Structure, Dynamics and Electronic Properties of Five Ally Molecules: Allicin, Methyl Propyl Disulfide (MPD), Allyl Methyl Sulfide (AMS), S-allyl cysteine (SAC) and S-allyl mercaptocysteine (SAMC) Emine Deniz Calisir , Sakir Erkoc, Handan Yildirim , Abdelkader Kara, Talat S. Rahman, Mahmut Selvi, Figen Erkoc The structural, dynamics and electronic properties of five allyl molecules have been investigated theoretically by performing semi-empirical molecular orbital (AM1 and PM3), ab-initio (RHF) and density functional theory calculations. The geometry of the molecules have been optimized, the vibrational spectra and the electronic properties of the molecules have been calculated in their ground states in gas phase. For each molecule, we found that the optimized geometries resulting from calculations based on the three levels of accuracy, to be very similar. However, we found that an accurate description of the vibrational properties of these molecules necessitates calculations at the ab-initio level. The electronic structures of these molecules were performed at the DFT level, resulting in an accurate description of the HOMO-LUMO gap and the local charges. [Preview Abstract] |
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C1.00068: Spheres-to-vesicles morphological transition in polymer micelles Zhijun Hu, Alain Jonas, Jean-Fran\c{c}ois Gohy Self-assembly of block copolymers in solution and the resultant nano-objects such as spheres, rods, and vesicles, have been the focus of much interest during the last 20 years. The ability to tune the micellar morphology and trigger the morphological transitions still remains a central challenge in this field. Here we present the possibility to control the micellar morphologies in poly(styrene)-\textit{block}-poly(4-vinylpyridine)/surfactant complexes by dilution, which is believed to be due to the changes of order in the insoluble blocks. These complexes, that form spherical micelles at a concentration of 1 g/L, rearrange into vesicles when the solutions are diluted, as confirmed by combined dynamic light scattering, atomic force microscopy and transmission electron microscopy investigations. This morphological transition can be further used as a tool to encapsulate molecules of interest in the interior of block copolymer vesicles. [Preview Abstract] |
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C1.00069: Osmotic Pressure Measurements of the Order Disorder Transition in Acrylic Triblock Copolymer Gels Rafael E. Bras, Kenneth R. Shull Semi-dilute solutions of PMMA-PnBA-PMMA triblock co-polymers in alcohols are excellent binder materials for a novel ceramics processing method, thermo-reversible gel casting. Processing methods based on this technology offer a low cost alternative to traditional slip and gel casting techniques. The rapid transition of these gels from freely flowing liquids to elastic solids has been attributed to the aggregation of the PMMA endblocks to form small spherical domains. We have recently begun to examine the order disorder transition of the PMMA endblocks with vapor pressure osmometry. This technique measures osmotic pressure by monitoring the equilibrium temperature of a solution droplet relative to the temperature of a pure solvent droplet. Measurements of solutions consisting of 15 vol {\%} acrylic triblock copolymer in butanol show a significant drop in osmotic pressure between 80 and 85 \r{ }C. This result indicates that the relaxation times of the ordered gels can be quite low, so that the order-disorder transition of the triblock copolymer occurs at temperatures higher than the rheologically determined gelation temperature of about 65 \r{ }C. [Preview Abstract] |
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C1.00070: Scaling of Avrami Kinetics of Growing Anisotropic Grains Samuel Gido, Ashoutosh Panday The kinetics of phase transformations proceeding by nucleation and growth are commonly modeled with the Avrami equation. In its most general form, the Avrami equation is expressed as V(t) = 1- exp [-V$_{e}$(t)], where V(t) and V$_{e}$(t) denote actual volume transformed and \textit{extended} volume respectively, as a function of time t. The extended volume, V$_{e}$(t) is the imaginary volume of all the grains if they did not stop at impingement and grew into one another. We report an observation about the growth of anisotropic grains obtained through simulations. We have found that for both simultaneous and continuous nucleation of elliptical grains, of aspect ratio L, the extended volume is reduced by a factor of L$^{1/2}$ in random orientation as compared to unidirectional orientation. In other words, V$_{e}$(t), $_{random}$ = [ V$_{e}$(t), $_{unidirectional }$] / L$^{1/2 }$. [Preview Abstract] |
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C1.00071: Block Copolymer Nanotemplates for Biomolecular Arrays Jung Hyun Park, Yale E. Goldman, Russell J. Composto The controlled positioning of biomolecules on surfaces is important for applications such as high-throughput proteomic arrays as well as fundamental biological research. However, the development of biomolecule arrays requires well-ordered nanosize platforms. The perpendicular lamellar structure of diblock copolymer films deposited on silicon substrates is a good candidate as a nanotemplate because of their spatial dimensions and orientation. Using scanning probe microscopy, a nearly symmetric poly(styrene-b-methyl methacrylate) P(S-b-MMA) diblock copolymer spin coated on silicon and annealed at 175\r{ }C for 2 days exhibits a perpendicular lamellar morphology with a periodicity of 70nm. To further constrain biomolecules or proteins, topographical variations were etched into the film by exposure to UV radiation for varying times. This exposure was found to preferentially etch the MMA phase resulting in ``trenches'' of MMA stripes separated by hills of PS. Studies are underway to investigate the controlled attachment of biomolecules on both the perpendicular lamellar morphology and the same morphology with trenches. [Preview Abstract] |
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C1.00072: X-ray Photon Correlation Spectroscopy Studies of Dynamics in a Polymer Bicontinuous Microemulsion Kristin Brinker, Wesley Burghardt, Simon Mochrie Polymer bicontinuous microemulsions are ternary blends of otherwise immiscible homopolymers that are compatibilized with their corresponding diblock copolymer, leading to an equilibrium spongy interconnected morphology with domain sizes typically on the order of 10 - 100 nm. Recent research has demonstrated that the dynamics of this interconnected structure leads to rich and complicated linear and nonlinear viscoelastic behavior. Direct probing of the equilibrium dynamics of order parameter fluctuations within bicontinuous microemulsion phases has been achieved using dynamic light scattering; however, the range of accessible scattering vector in light scattering is poorly matched to the intrinsic length scale of the microemulsion morphology. Here we report experiments using small-angle X-ray Photon Correlation Spectroscopy, performed using facilties at Sector 8 of the Advanced Photon Source, to make direct measurements of the dynamic structure factor in a polystyrene- polyisoprene microemulsion sample in the vicinity of the Teubner-Strey scattering peak associated with the dominant length scale of the bicontinuous phase. [Preview Abstract] |
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C1.00073: Morphology of Fluorinated and Sulfonated diblock Copolymers Tomonori Hosoda, Sam Gido, Tianzi Huang, Jimmy Mays We have studied the micro-phase separation of Fluorinated and Sulfonated diblock Copolymers. The polymer was synthesized by post-polymerization fluorination and sulfonation of PI-b-PS diblocks. THF containing different weight fraction of water was used as solvents for the diblock copolymers to solution casting films. From the dry THF, we obtained a coexistence morphology of well-ordered lamella and cylinders. As the water content in the solvent was increased, the morphology changed from well-ordered to disordered. In addition, it was to be found that thermal annealing at 120C of the well ordered samples caused the morphology become disordered. The progressive disordering of the structure upon annealing was directly observed with TEM and SAXS. The results are very different the usual behavior or uncharged diblock copolymers in which annealing generally results in improvements in long range order. The disordering upon annealing may be the result of ion cluster formation which interferes with the normal block copolymer morphology. [Preview Abstract] |
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C1.00074: Stereocomplex Formation in Incompatible Racemic Chiral Polylactide Block Copolymers Lu Sun, Lei Zhu Stereocomplexes in incompatible racemic chiral polylactide (PLA) block copolymers have not been widely studied. In this work, we synthesized PLLA and PDLA containing block copolymers by ring opening polymerization of L- and D-lactides from hydroxyl-terminated hydrophilic [poly(ethylene oxide) (PEO)] and hydrophobic [poly(ethylene-\textit{co}-1,2-butylene) (PEB)] oligomers, respectively. Two samples PEO-$b$-PLLA (2,000-5,400) and PEB-$b$-PDLA (4,200-5,400) were chosen. The stereocomplexes were cast from equal molar blends of above two block copolymers in chloroform solution, followed by two different thermal treatments before stereocomplex formation; The blend was either heated to 250 \r{ }C and quickly quench to 160 \r{ }C or heated to 250 \r{ }C for 15 min and quench to 160 \r{ }C for stereocomplex crystal growth. Before the formation of stereocomplexes, lamellar and cylindrical morphologies were observed in blends for the first and second thermal treatments, respectively, as evidenced by small-angle X-ray scattering (SAXS). After complete crystal growth, the 100{\%} stereocomplexes was confirmed by differential scanning calorimetry and wide-angle X-ray diffraction (WAXD). The morphologies of stereocomplexes grown from these two pre-existing microphases (lamellar vs. cylindrical) were studied by time-resolved SAXS and transmission electron microscopy (TEM). [Preview Abstract] |
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C1.00075: Effect of local point group symmetry on self-assembly in thin films of block copolymers on topographically patterned substrates. Ion Bita, Joel Kang, Karl Berggren, Edwin Thomas We have investigated the self-assembly of a diblock copolymer with spherical morphology on novel topographically patterned substrates. Poly(styrene)-b-poly(ferrocenyldimethylsilane), PS-$b$-PFS, was spin casted to form thin films with a PFS monolayer of spheres morphology. Topographically patterned silicon substrates were fabricated by both electron-beam and interference lithographies. To vary the local point group symmetry, a number of topographical patterns were designed and fabricated. Quasiperiodic arrays of posts allows access to multiple types of local symmetries with the average distance between posts an order of magnitude or more larger than the BCP period. Results for controlling long-range correlations of the BCP morphology and local 4-, 6-, 8-, and 12-fold rotational symmetries will be presented. [Preview Abstract] |
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C1.00076: Spectroscopy of the Primary Photoexcitation and the Origin of the Photocurrent in Rubrene Single Crystals Hikmat Najafov, Ivan Biaggio, Vitaly Podzorov, Matt Calhoun, Michael Gershenson By studying and correlating the photoexcitation spectra of several observables connected with excitons and charge transport we are able to gain new insights into the nature of the primary photoexcitation in organic molecular crystals. By simultaneously measuring the excitation spectra of the transient luminescence and of the transient photoconductivity after picosecond pulsed excitation in rubrene single crystals we show that free excitons are photoexcited starting at photon energies larger than 2.0 eV. We observed a competition between photoexcitation of free excitons and photoexcitation into vibronic excited states that subsequently decay into free carriers, while self-trapped molecular excitons are instead formed predominantly through the free exciton. At photon energies smaller than 2.25 eV free charge carriers are only created through a long-lived intermediate state with a lifetime of up to 0.1 ms and no free carriers appear during the exciton lifetime. [Preview Abstract] |
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C1.00077: Exciton Dissociation by a Static Electric Field Followed by Nano-scale Charge Transport in PPV Polymer HIkmat Najafov, Ivan Biaggio, Ta-Ko Chuang, Miltiadis K. Hatalis The nature of the photoinduced generation of charge carriers in conjugated polymers is still the subject of an intense discussion. We investigate the main question of weather photoexcitation results in localized excitons or directly leads to mobile charge carriers by simultaneously studying the electric field dependence of the photoluminescence and the photoinduced charge-transport in a phenyl-substituted PPV derivative. We show that charge-carriers are created indirectly through field-induced ionization of excitons, and by quantitatively estimating the amount of carriers created by ionization of the exciton we identify a free-carrier mobility larger than $\sim $3.0$\times $10$^{-6 }$cm$^{2}$V$^{-1}$s$^{-1}$ that is valid for transport over a few nm during an apparent free-carrier lifetime of $\sim $50 ns. The time-dynamics of the photoluminescence and its temperature-quenching behavior indicate the presence of two species of excitons, which can be interpreted as intra-chain and inter-chain excitons. [Preview Abstract] |
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C1.00078: Temperature Dependent Electroluminescence of Alq$_{3}$ Based OLEDs Ajith DeSilva, H. P. Wagner, R. A. Jones, W. Li, A. Stekl The temperature dependent I-V characteristics and electroluminescence (EL) of an ITO/PEDOT/NPD/Alq$_{3}$/LiF--Al OLED is investigated. The I-V measurements reveal a trap charge limited current behavior with characteristic trap energy of 53 meV. The EL of the device is compared with the photoluminescence (PL) of a 50 nm thick Alq$_{3}$ film on Si (001) in the range from 10 to 320 K. The EL efficiency of the device shows similar temperature dependence as the PL intensity obtained from the Alq$_{3}$ film. The OLED brightness saturates at 10,000 cd/m$^{2}$ (T = 300 K; V = 15 V). For a constant forward bias (8 V) the maximum EL efficiency of the device is 2.2 cd/A obtained at 180 K. The maximum PL efficiency of the Alq$_{3}$ film is observed at the same temperature (180 K). Furthermore, both the EL and PL spectra reveal a maximum redshift at 180 K which is tentatively attributed to the formation of self-trapped excitons within the Alq$_{3 }$layer. [Preview Abstract] |
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C1.00079: Multiplicative luminescence enhancement induced by chain relaxation in ultrathin films of a conjugated polymer (MEH-PPV) Chih-Wei Yang, Juo-Huei Jou, Arnold Chang-Mou Yang A surprising multiplication of light-emitting efficiency was observed in dewetting process of the conjugated luminescent polymer of poly (2-methoxy- 5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV). The luminescent efficiency increased with the dewetting process and became about six-fold when the polymer film ruptured into tiny droplets. This enhancement appeared to be related to the carrier transport mechanisms and the motions of polymer chains. The effects of inter-molecular energy transport and molecular deformation of polymer chains were studied by examining the emission behavior in liquid and solid solutions. It was found that the molecular movements during stretching in the glassy state were quite different from that in the dewetting process. The latter was dominated by disengagement of inter-molecular entanglements while the former was strongly influenced by trapping mechanisms of chain entanglements due to rapid local molecular strains. This work is supported by National Science Council of Taiwan. [Preview Abstract] |
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C1.00080: How Fast Should Polymer/Drug Nanocrystal Dispersions Be Frozen? Jonghwi Lee, Chul Ho Park Recent advances in nanoparticle technologies have significantly enhanced the oral and parenteral delivery of poorly water-soluble active pharmaceutical ingredients (APIs). However, reports have been limited on the various drying procedures to convert a liquid nanocrystal dispersions into solid dosage forms. The solid dosage form should consist of nanocrystals that can readily reconstitute into their original size upon dissolution in water. Herein, the freeze drying process of nanocrystal dispersions was examined at varying freezing rates (speed of freezing interface). As freezing rate decreases, more particle-particle aggregation developed. A critical freezing rate, below which the dried nanocrystals cannot be re-dispersed, was identified based on the plot of the particle size of reconstituted nanocrystals versus freezing rate. Freeze drying at a freezing rate near the critical value produces dry powders of bimodal particle size distribution after re-dispersion. In addition, API concentration was found to significantly affect the critical freezing rate and therefore the re-dispersibility of dry powders. The concept of critical freezing rate is critical for the development of solid dosage forms of liquid nanocrystal dispersions. [1] J. Lee, Drug nano- and microparticles processed into solid dosage forms: physical properties, J. Pharm. Sci., 92(10) (2003) 2057-2068. [Preview Abstract] |
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C1.00081: Equilibrium interactions and phase behavior of nanoparticles in solutions of adsorbing polymers Megha Surve, Victor Pryamitsyn, Venkat Ganesan We present the polymer mediated pair-interaction potentials, phase and percolation behavior of nanoparticles in presence of adsorbing polymers. We propose a ``saturable'' adsorption model to capture the effect of the finite surface saturation capacity for adsorption, and use polymer self-consistent field theory in combination with a McMillan-Mayer framework to compute the pair interaction potentials. Our results demonstrate novel size effects that distinguish the adsorption characteristics of nanoparticles from that of larger particles. Specifically, we predict that the nanoparticle regime is characterized by a significant adsorbance of polymers, distributed predominantly in the form of tails. We also demonstrate that an interplay between the surface saturation, polymer-to-particle size ratios and the polymer concentrations governs the overall effective interactions between nanoparticles in presence of adsorbing polymer. Our results show that the percolation threshold for smaller particles are significantly smaller (and overall correspond only to a few volume percent) compared to that of the larger particles. Further, with a decrease in the size of the particles, we also predict a considerable increase in the miscibility of the polymer-particle mixtures. The importance of surface saturation considerations is highlighted by comparing our results with the previous approaches. [Preview Abstract] |
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C1.00082: How do colloidal particles rotate? New Materials and New Physics Liang Hong, Stephen Anthony, Huilin Tu, Steve Granick Surface modification of colloidal particles to a Janus (asymmetric) chemical composition affords an opportunity to measure the rotational dynamics of colloidal particles in suspension as well as at interfaces. Using a metal deposition technique, we make particles half-covered by metal, and generate geometrically symmetric but chemically and fluorescently asymmetric materials. The rotational dynamics of single colloidal particles as well as rod-like structures have been measured utilizing imaging and tracking techniques. Increasing the concentration of polyelectrolytes in the solution results in the retardation of the rotational diffusion of single colloidal particles. This decrease, however, is not proportional to the viscosity of the solution. Moreover, we formed a metal-welded rod-like tetramer with this approach; for the first time, the rotational dynamics along the long-axis is measured. Research in progress includes chemical modification of the metal surface to form new colloid based materials and Brownian dynamics studies of these new materials. [Preview Abstract] |
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C1.00083: The Prospects of Nanorods as Blending Agents in Immiscible Binary Polymer Blends Michael J. A. Hore, Mohamed Laradji Systematic, large scale dissipative particle dynamics computer simulations performed in three dimensions indicate that the dynamics of phase separation of polymer blends containing rigid nanorods can be substantially slower than that of a pure binary blend, and that the dynamics depend greatly on the aspect ratio, i.e length/diameter, of the nanoparticles. When compared with spherical nanoparticles, it is also found that nanorods with the same volume fraction, or same surface area, are more effective in slowing down the dynamics of the blend -- an indication that the anisotropy of the nanoparticles plays an important role in the phase separation kinetics. For a given volume fraction of rods, the domain growth exponent decreases (and growth may become non-algebraic) as the aspect ratio of the rods is increased. Growth is also slowed as the volume fraction of the nanorods is increased for a given aspect ratio. Additionally, it is found that the effect of lengthwise polydisperse rods is similar to that of monodisperse rods with a length equal to the mean length of the polydisperse rods. In cases with high aspect ratio rods or high volume fractions of rods, systems often proceed to micro-phase separated states -- results not seen for nanospheres. The upshot of these results is that nanorods may potentially be used as effective emulsifiers of immiscible binary polymer blends. The thermodynamic stability of these micro-phase separated states will be discussed. [Preview Abstract] |
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C1.00084: Adhesion and Release Mechanisms for Nanoimprint Lithography Douglas Holmes, John Whang, Edwin Chan, Alfred Crosby Nanoimprint lithography is a leading candidate for fabricating next generation devices with features smaller than 50nm. A fundamental challenge with this emerging technology is the generation of defects during the release of the template from the cured polymer pattern. This release process is dependent not only on the surface energetics of the template and the cured polymer, but also on the local mechanical properties of both materials -- similar to the propagation of a crack at an interface. Here we present results on the investigation of adhesion and release properties of several polydimethylsiloxane-based polymer templates using UV-based imprint lithography techniques. We demonstrate that the framework of fracture mechanics and the theory of Johnson, Kendall, and Roberts (JKR) allows the separation of bulk and interfacial contributions to the overall release process. This decoupling of material properties guides the future development of both templates and imprintable resists for the success of nanoimprint lithography. [Preview Abstract] |
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C1.00085: Nanotransfer printing for patterning conductive copper features Kimberly Dickey, Yangming Sun, Yueh Lin Loo The drive for low-cost electronics creates a need for new techniques to directly and inexpensively pattern copper features in the 1-100$\mu $m range. We have developed a solventless, additive approach for printing permanent, conductive copper features at ambient conditions. Our technique is analogous to previously established nanotransfer printing (nTP) procedures for patterning gold with one marked difference. When copper is deposited onto a poly(dimethylsiloxane), PDMS, stamp, residual oligomers from the stamp penetrate between copper grains. This penetration disrupts the conductive pathway between copper grains; the printed copper patterns are electrically insulating as a consequence. This phenomenon is not observed with nanotransfer printing of gold features. A simple modification to the patterning procedure -- leaching the PDMS stamps in boiling toluene for 2-3 days to remove uncrosslinked oligomers -- results in printed copper patterns that are electrically conductive, with an average resistivity of 31$\mu $ohms-cm. [Preview Abstract] |
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C1.00086: Surface grafting of carbon nanotubes with conjugated polybenzoxazole polymer Chih-Wei Lin, Jen-You Lin, Arnold Chang-Mou Yang, Chen-Chi M. Ma Surface-grafted carbon nanotubes impart extraordinary mechanical reinforcement to the polymer nanocomposites but considerably reduce the superior electrical conductivity of the neat carbon nanotubes. The conjugated polymer of polybenzoxaole (PBO) for grafting carbon nanotube therefore is very interesting as it may warrant reinforcement of both electrical and mechanical performances. The PBO-grafted carbon nanotubes was obtained from graft polymerization on nanotubes of polyhydroxyamide (PHA), the precursor of PBO, via condensation of 2,2'-bis(3-amino-4- hydroxyphenyl)-hexafluropropane (BisPF$_{6})$ and isophthaloyl chloride (IC) at low temperatures. The microstructure of the hybrid nanocomposites was investigated by FTIR, SEM, and TEM. The PBO/MWNT nanocomposites demonstrated excellence electronic (resistivity 0.374 $\Omega $-cm) and thermal (decomposition temperature 590 ${^\circ}$C) properties. This work is supported by Air Force (AFOSR-04-4074) and National Science Council of Taiwan. [Preview Abstract] |
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C1.00087: Modification of Nanocomposite POSS-PMMA Surfaces by Exposure to Reactive Oxygen. Rebekah Esmaili, Jacob Forstater, Brian H. Augustine, Wm. Christopher Hughes Thin films of the nanocomposite copolymer polymethylmethacrylate-polyhedral oligomeric silsequixane (PMMA-POSS) have been deposited onto glass and polymeric substrates and modified by exposure to reactive oxygen. The source of the oxygen was either a remote capacitively coupled plasma or UV-generated ozone. A change from hydrophobic to hydrophilic was observed after exposure to oxygen for time periods greater than 20 seconds. This change was quantified by measuring water contact angles on the surface which varied from greater than 90\r{ } before plasma exposure to less than 10\r{ } afterwards. A model for this behavior in which the isobutyl groups around the POSS cage are selectively removed by the oxygen plasma leaving a SiOx-rich surface is proposed. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) data were performed to test this model and show that the number of isobutyl groups on the surface does decrease with exposure time. Ongoing experiments involving the effect of oxygen exposure on the electro-osmotic flow in microfluidic structures which incorporate these films will be discussed. [Preview Abstract] |
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C1.00088: Polypeptide-Based Silicate Layered Nanocomposite: Effect of Poly(L-lysine) Secondary Conformation on Physical Properties of the Hybrid Rohan Hule, Jeffrey Thompson, Timothy Deming, Darrin Pochan The formation of nanocomposites from poly(L-lysine) (PLL) as the matrix and reinforced by Na$^{+}$- MMT clay is discussed. By varying solution conditions such as pH, temperature and concentration in the presence of MMT, the secondary conformation of PLL was controllably altered into $\alpha $-helical, $\beta $-sheet and random coil. Investigations were made into the PLL secondary conformation using FTIR, XRD and Circular Dichroism (CD). CD and FTIR revealed a strong propensity to fold into $\beta $-sheet when cast as films, irrespective of the initial secondary structure in solution. Two principles were observed for nanocomposite behavior: better mechanical properties at high molecular weight and controllable secondary structure at low molecular weight. Local morphology, observed using TEM and XRD confirmed the coexistence of intercalated and exfoliated MMT platelets over a wide range of compositions. Nanocomposite material properties relative to the secondary conformation of the matrix revealed significant enhancement in composite elastic modulus over neat polypeptides, with values comparable to traditional engineering polymers. [Preview Abstract] |
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C1.00089: Oriented Mesoporous Inorganic Thin Films Using Laterally Confined Swellable Block Copolymer Templates. Se Gyu Jang, Edward J. Kramer, Seung-Man Yang The control of grain orientation and long-range ordering of mesoporous inorganic materials produced by a sol-gel reaction of an inorganic precursor in self-assembling amphiphilic template systems have been limited due to the restrictions both on the time-scale and conditions for processing imposed by network formation of the inorganic component. Our goal is to form ordered mesoporous inorganic thin films by starting with a crosslinkable block copolymer template with long range order. A cylindrical poly(styrene-2-vinylpyridine) (PS-P2VP) diblock copolymer with Mn = 32.7 kg/mol and f$_{PS}$ = 0.21 was spin-cast onto a set of 30 nm high and 2000 nm wide SiOx channels on Si substrates produced by optical lithography. An ordered PS-P2VP monolayer$^{1}$ is achieved via slow cooling after heating above its bulk order-disorder transition temperature (212 °C), measured by small angle X-ray scattering. Hybrid inorganic/organic structures are fabricated by incorporation of inorganic precursor into the chemical cross-linked P2VP matrix.$^{2}$ Cylindrical pores within the inorganic matrix are then obtained by removal of the organic component using UV-ozone treatment. $^{1}$M.R.Hammond, E. Cochran, G.H. Fredrickson, E.J. Kramer Macromolecules \textbf{38} 6575 (2005). $^{2}$R.C. Hayward, B.F. Chmelka, E.J. Kramer Macromolecules \textbf{38} 7768 (2005). [Preview Abstract] |
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C1.00090: Chemical composition effects on the crazing of PS-PMMA block copolymers Won Kim, Junwon Han, Hoichang Yang, Chang Ryu Using a large scale separation technique adopting interaction chromatography, we have fractionated as-synthesized PS-PMMA block copolymers in terms of the average chemical composition difference, while maintaining the same average molecular weight. Copper grid technique with optical, atomic force and transmission electron microscopy has been employed for the fracture study to reveal how the composition-dependent morphology affect the crazing of the glassy-glassy block copolymers, while maintaining the same level of Chi*N. In addition, we study how the thermal annealing affects the median strains for crazing and catastrophic failure. [Preview Abstract] |
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C1.00091: Impact of Nanotube Addition on Stress Recovery of Thermoplastic Elastomer Nanocomposites. Daniel Powers, Max Alexander, Richard Vaia, Michael Arlen, Hilmar Koerner Recent extension of polymer nanocomposite concepts to shape memory polymers has demonstrated potential to substantially improve recovery stress and provide novel triggering options, while still maintaining large deformations. One such example is multi wall carbon nanotubes (MWCNT)s in thermoplastic polyurethane (PU), where the MWCNTs increase modulus and modify strain induced crystallization leading to improved strain set and recovery force relative to unfilled PU as well as conventionally-filled PU. The impact of MWCNT alignment on the stress recovery rate depends on MWCNT concentration and the procedure used to `set' the deformation. Differences in response time upon shape recovery are observed whether the nanocomposites are `set' above the melting point of soft segment crystallites or at room temperature (RT). A detailed dynamic mechanical analysis protocol reveals that recovery rate and shape fixity are increasing as a function of MWCNT volume fraction and that RT processed nanocomposites show overall superior results. Recovery times can be described with a modification of the Kohlrausch-Williams-Watt equation, indicating a contribution from elasticity of the carbon nanotubes or chain scission of the matrix PU. [Preview Abstract] |
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C1.00092: Long DNA Molecules at Liquid-Solid Interfaces Vladimir Samuilov, B. Li, J. Sokolov, M. Rafailovich, B. Chu The electrophoresis of long DNA molecules was studied using a newly developed method of electrophoresis on flat surfaces [1] in the regime of strong electrostatic interaction. The mobility of lambda- DNA molecules on this surface was found to scale as the square root of the persistent length with the ionic strength at high buffer. This experimental result indicates that at high buffer concentration the separation mechanism of solid-liquid interface electrophoresis is expected to be due to surface friction rather than biased reptation [2-4]. At low buffer concentrations the DNA chains are stretched .The electric double layer is responsible for a velocity profile of the electroosmotic flow. The net electrophoretic mobility of longer DNA, being trapped closer to the surface as found to be higher then for the shorter ones in the electric field. \newline [1]. N. Pernodet, V. Samuilov, K. Shin, et al. Physical Review Letters, 85 (2000) 5651-5654. \newline [2] Y.-S. Seo, V.A. Samuilov, J. Sokolov, et al. Electrophoresis, 23 (2002) 2618-2625. \newline [3] Y.-S. Seo, H.. Luo, V. A. Samuilov, et al. DNA Electrophoresis on nanopatterned surfaces, Nano Letters, 4, 2004, 659-664. [Preview Abstract] |
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C1.00093: Closed-Loop Phase Behavior: Is it Universal Phenomenon for Block Copolymers with Lower Critical Transition Temperature? Jin Kon Kim, Chaoxu Li, Dong Hyun Lee A closed-loop phase behaviour was found for Polystyrene-block- poly(n-pentyl methacrylate) (PS-PnPMA) copolymer having a weak interaction between two segments. On the other hand, PS-block- poly(n-butyl methacrylate) (PS-PnBMA) exhibited only lower disordered-to-ordered transition (LDOT). Then, a question might be raised: Is it possible that PS-PnBMA has the closed-loop phase behaviour, although the upper ordered-to-disordered transition (UODT) could not be detected in the experimentally accessible temperature. In this study, we clearly demonstrate that PS-PnBMA exhibits the closed-loop phase behaviour, where both LODT and UODT were measured at experimentally accessible temperatures (100 $\sim$ 280$^{\circ}$C) by using special solvents. [Preview Abstract] |
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C1.00094: Acoustic modes and elastic properties of polymeric nanostructures Ryan D. Hartschuh, A. Kisliuk, A.P. Sokolov, V. Novikov, P.R. Heyliger, C.M. Flannery, W.L. Johnson, C.L. Soles, W.-l. Wu Very few experimental techniques exist to quantify the mechanical properties of nanoscale photoresist structures. This inadequacy is going to become increasingly important as the rigidity of such structures is expected to change as the feature sizes approach the characteristic dimensions of the macromolecules and size-dependent material properties begin to compromise device fabrication and performance. Phonon spectra of polymeric linear nanostructures have been characterized using Brillouin light scattering. In addition to phonon modes similar to those present in uniform thin films, the phonon spectra of the nanolines reveal a new mode with a lower frequency that depends on the width of the nanolines. Classic wave theory and finite element analysis were combined to identify this new mode as a flexural vibration of the nanolines. Analysis of the phonon spectra gave estimates of elastic constants in the nanostructures and indicated that there is no significant deviation from bulk mechanical properties and no mechanical anisotropy in structures as small as 88 nm. [Preview Abstract] |
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C1.00095: Polymeric Micro/Nanostructures Fabricated through a Novel Method with Optical Microscopy Chao-Min Cheng, Bin Li, Philip LeDuc We present a technique for building three-dimensional structures using optical methods with photocuring chemistry. This method merges an optics-based approach with chemical restructuring through the transition of materials from distinct phases. By activating a photocurable material in combination with controlling the intensity distributions that are inherent in optical patterns, in-situ fabrication of three-dimensional polymeric microstructures is demonstrated. Furthermore, polymeric nanostructures can be also obtained based on this method through combining this technique with Al2O3 nanopores. This experimentally simple approach combined with thermal control can create complex shapes including curved and asymmetric profiles. This method has potential applications in a variety of fields including optical technique, micro/nanoelectromechanical systems and microfluidics. [Preview Abstract] |
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C1.00096: Nanoparticle arrays controlled by polymeric ligands Chun-Kwei Wu, Jeffrey T. Koberstein Ligand chemistry on nanoparticles plays an important role in applying their unique properties to the real world. The original capping ligands on nanoparticles, i.e. oleic acid, limit their compatibility with some bulk materials of interest and can restrict some potential applications. We have successfully exchanged the original oleic acid ligands on $\gamma $-Fe$_{2}$O$_{3}$ nanoparticles with $\omega $-poly(dimethylsiloxane) (PDMS). A high grafting density of PDMS on iron oxide nanoparticles has been achieved by this ``grafting to'' method. Fe$_{2}$O$_{3}$ nanoparticles with PDMS ligands self-assemble with hexagonal packing when deposited on substrates. The interparticle spacing can be controlled by varying the molecular weight of the PDMS. The PDMS-modified Fe$_{2}$O$_{3}$ nanoparticles are totally compatible with bulk PDMS allowing nanocomposites to be formed. The PDMS components in resultant thin films can subsequently be converted to silicon oxide by room temperature UV/ozone treatment to fabricate Fe$_{2}$O$_{3}$-silica composite thin films. The use of such nanocomposite films in gas separation and catalyst membranes is being studied. [Preview Abstract] |
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C1.00097: Crosslinked nanoparticle assemblies at liquid-liquid interfaces Ravisubhash Tangirala, Habib Skaff, Yao Lin, Thomas Russell, Todd Emrick The assembly of nanoparticles at the interface of immiscible fluids holds promise for the preparation of new materials that benefit from both the physical properties of the nanoparticles and the chemistry associated with the ligands. The weak confinement of nanoparticles to the liquid-liquid interface enables the formation of particle-based assemblies that possess unique features relative to assemblies of micron-scale particles. Crosslinking of nanoparticles at a liquid-liquid interface lends greater stability to the interfacial assembly, leading to ultrathin nanoparticle-based capsules which possess mechanical integrity even after removal of the interface. Norbornene-functionalized CdSe/ZnS core/shell quantum dots are used in this study to afford facile capsule visualization by fluorescence confocal microscopy, as well as ease of crosslinking in mild conditions by means of ring-opening metathesis polymerization (ROMP) using a unique amphiphilic ruthenium benzylidene metathesis catalyst. The crosslinked capsules display a size-selective encapsulation capability, dictated by the interstitial spaces between the nanoparticles. The porosity of the capsules can be further tuned by the addition of small amounts of uncrosslinkable nanoparticles prior to crosslinking. [Preview Abstract] |
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C1.00098: Gold nanoparticle self-assembly and gold patterning using thin film polymer blend templates. Ranjan D. Deshmukh, Russell J. Composto In this study we have used thin films of polymer blend of Poly(methyl methacryalate), PMMA, and Poly(styrene-ran-acrylonitrile), SAN, as templates for patterning gold as well as gold nanoparticles on silicon substrate. PMMA/SAN phase separate above lower critical solution temperature, LCST, and form cylindrical and bi-continuous morphologies in 50/50 and 70/30 blend compositions. Selectively etching out PMMA phase by UV and acetic acid treatment results in a template, which is used for patterning. Gold is sputtered on these templates followed by removal of SAN in a solvent, leaving gold patterns on the substrate. Unique cylindrical island-like and bi-continuous patterns were observed by AFM. We also selectively patterned the etched region (PMMA) with a self-assembled monolayer, SAM, of 3-aminopropyl-triethoxysilane, APTES, followed by SAN removal and coating the exposed region with 3-mercaptopropyl-trimethoxysilane, MPTMS. Further, deposition of colloidal citrate-stabilized gold nanoparticles resulted in the selective deposition of gold nanoparticles on APTES (island-like and bi-continuous patterns), because of the charge-charge interactions between nanoparticles and SAM. [Preview Abstract] |
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C1.00099: Organometallic Polymer-Derived Catalyst Dispersion Effects on SWNT Growth Sarah Lastella, Pulickel M. Ajayan, Chang Y. Ryu, David Rider, Ian Manners Catalyst formation kinetics of a ferrocene-containing homopolymer, polyferrocenylethylmethylsilane or PFEMS, is investigated as it relates to the catalysis of single walled carbon nanotubes (SWNTs) and is compared with that of the corresponding diblock copolymer, poly(styrene-b-ferrocenylethylmethylsilane) or PS-b-PFEMS. The polystyrene blocks in the PS-b-PFEMS form a matrix to uniformly disperse discrete nanoscale iron domains that enhance the uniformity of nanotube diameters compared to the homopolymer. PFEMS homopolymer contains 23 percent iron by weight, while PS-b-PFEMS with a 25 vol percent PFEMS is only 6 percent iron, respectively. It is concluded that iron present in a block copolymer film is two times more active than a PFEMS film, and in turn, leaves a lower iron density on the substrate surface relative to its nanotube yield. [Preview Abstract] |
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C1.00100: BIOLOGICAL PHYSICS POSTER SESSION |
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C1.00101: Elastic and osmotic properties of articular cartilage David Lin, Emilios Dimitriadis, Iren Horkayne-Szakaly, Ferenc Horkay The pathophysiology of osteoarthritis involves cellular and biochemical processes linked to mechanical stress. A better understanding of the mechanism of these processes and how they cause changes in the composition, macro- and micro-structure, and mechanical properties of cartilage is necessary for developing effective preventative and treatment strategies. In this study, elastic and osmotic swelling properties of tissue-engineered cartilage were explored using atomic force microscopy (AFM) and a tissue osmometer. AFM was also used to image the surface of the specimens while chemical composition was determined by biochemical analysis. Estimation of the Young's moduli of the tissue from AFM force-indentation data was performed using an optimization approach to fit appropriate models to the data. Force-indentation data were acquired both with sharp, pyramidal and with microspherical probes. The procedure has been validated by making measurements on model gel systems of known elastic properties. This approach is presented as a robust method of optimally extracting Young's moduli of soft, crosslinked materials from AFM data. Gross inhomogeneities at different scales in the cartilage tissue are manifested in the high degree of variance in local Young's moduli values obtained from both AFM and osmotic swelling data. These findings suggest that the mechanical properties of cartilage are affected by the local macromolecular composition. [Preview Abstract] |
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C1.00102: The Influence of Environment Geometry on Injury Outcome: II. Lumbosacral Spine Saami J. Shaibani It is widely agreed that the type of motor vehicle in which an occupant is situated can sometimes make a noticeable difference in injury potential even when the insult suffered is the same. A simple example might be the same occupant being in a sports car as opposed to a minivan, but such anecdotal experience does not usually help to distinguish the effect of particular features within the same category of vehicle. Other research has addressed the role of environment geometry in neck injury,[1] and this paper adopts the same methodology for the low back. The heights, lengths and angles of the seat cushion and seat back (including head rest) are all examined as descriptors of passenger compartment geometry, and any changes caused by these are determined. Useful results are feasible with the large patient population available even if clear patterns in these are not always present. As in earlier work, there is still the option of finding individual outcomes on a case-by-case basis. \newline [1] The influence of environment geometry on injury outcome: I. Cervical spine, Bull Am Phys Soc, in press (2006). [Preview Abstract] |
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C1.00103: Analysis of a 2D simulation model of biofilms with autonomous cells Anand Bhandar, Yergou Tatek, Gary Slater Biofilms are substances consisting of a large number of microorganisms that grow on surfaces in contact with liquids. They can be found growing in water pipes, on surgical instruments or on tooth surfaces. Mathematical models have been used for the last three decades in order to improve our understanding of their growth and behavior. We have designed and implemented a new Monte Carlo model based on the life of autonomous cells and investigated the static and dynamic characteristics of the resulting bacterial populations. Each cell is modeled as an autonomous agent whose behavior is controlled by thermodynamic parameters, mechanical properties, physiological rules and environmental conditions. In the 2D version studied, a cell is represented by a closed chain of self-avoiding beads linked together using the bond fluctuation algorithm. The cell is controlled both by the rigidity of its membrane and a pressure difference. The model is complemented by key features such as the processes of cell division, growth and death, attractive interactions between the cell and the surface, and the explicit presence of nutrient diffusion. Tuning model parameters leads to the growth and maturation of various types of biofilms. Typical colonies incorporating these and other important characteristics of biofilms such as the exopolymeric substance (EPS), metabolism and waste production, cell motility and chemotaxy, and cell mutation will be presented. [Preview Abstract] |
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C1.00104: A physiologically-based spatiotemporal model of fMRI hemodynamic responses. Jackie Huber, Peter Drysdale, Peter Robinson A 3D cerebrovascular model is developed to describe the spatiotemporal Blood Oxygen Level Dependent (BOLD) functional MRI (fMRI) response. Modelling spatial effects is particularly important as technology improves, shrinking image voxels and thereby increasing voxel interdependence. Specifically, poroelastic theory, originally developed in geophysics, is used to model the brain tissue and vasculature as a porous continuum. The model yields equations describing conservation of mass, momentum, and deoxyhemoglobin, plus the effect of neuronal activity on blood flow. The equations reproduce existing, non-spatial, hemodynamic models in the relevant limit. Imposition of continuity of flow between adjacent points enables potential investigation of spatial phenomena such as `blood steal' which has been proposed to account for negative BOLD signals abutting sites of positive BOLD responses. This model will enable future study of spatiotemporal relationships between stimuli and experimental fMRI BOLD responses. [Preview Abstract] |
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C1.00105: BOLD Responses to Stimuli: Dependence on Frequency, Stimulus form, Amplitude, and Repetition Rate. Peter Robinson, Peter Drysdale, Helena Van der Merwe, Elizabeth Kyriakou, Michelle Rigozzi, Biljana Germanoska, Christopher Rennie A quantitative theory is developed for the relationship between stimulus and the resulting Blood Oxygen Level Dependent (BOLD) functional MRI signal in the brain. The relationship of stimuli to neuronal activity during evoked responses is inferred from recent physiology-based modeling of evoked response potentials (ERPs). A hemodynamic model is then used to calculate the BOLD response to neuronal activity. The predicted response is analyzed vs. form, frequency, and amplitude of stimulus. The BOLD frequency response is very nearly linear in the parameter ranges of interest, with the form of a low-pass filter with a weak resonance at 0.07 Hz. For short stimuli, the response is closely proportional to the time-integrated stimulus-evoked activity, rather than the peak amplitude, as often assumed. There can thus be widely differing proportionalities between BOLD and peak activity, a likely reason for the weak expected correlation between ERPs and BOLD. [Preview Abstract] |
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C1.00106: Measurement of the Mechanical Properties of Intact Collagen Fibrils H. Mercedes, A. Heim, W.G. Matthews, T. Koob Motivated by the genetic disorder Ehlers-Danlos syndrome (EDS), in which proper collagen synthesis is interrupted, we are investigating the structural and mechanical properties of collagen fibrils. The fibrous glycoprotein collagen is the most abundant protein found in the human body and plays a key role in the extracellular matrix of the connective tissue, the properties of which are altered in EDS. We have selected as our model system the collagen fibrils of the sea cucumber dermis, a naturally mutable tissue. This system allows us to work with native fibrils which have their proteoglycan complement intact, something that is not possible with reconstituted mammalian collagen fibrils. Using atomic force microscopy, we measure, as a function of the concentration of divalent cations, the fibril diameter, its response to force loading, and the changes in its rigidity. Through these experiments, we will shed light on the mechanisms which control the properties of the sea cucumber dermis and hope to help explain the altered connective tissue extracellular matrix properties associated with EDS. [Preview Abstract] |
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C1.00107: Design and use of an artificial capillary in the study of metastatic cell adhesion Adam Rafi, Rebecca Boren, August Heim, William G. Matthews To improve the quality of life of patients with cancer, treatments will need to both minimize existing tumors and reduce the metastasis of cancer cells. The effectiveness of potential treatments on existing tumors can be directly probed, but anti-metastasis treatments are difficult to quantify. Therefore, a detailed understanding of the metastatic process is required for drug design. Details of the metastatic deposition of tumor cells in the circulatory system are not well understood. We are investigating the binding of tumor cells to an artificial endothelium. The model system allows for control over molecular composition at the interface, presenting the proteoglycans (PGs) found in the glycocalyx to tumor cells under shear flow conditions. Whether rolling or static adhesion is preferred, as well as what mechanical properties of the interaction between the cells and the PGs are important is to be determined. The outcomes of these experiments will help guide the search for pharmaceuticals that can disrupt the metastatic process at the endothelial adhesion step. [Preview Abstract] |
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C1.00108: Study of Native Type I Collagen Fibrils August Heim Presented in this work is direct imaging and force microscopy of native, intact type I collagen fibrils extracted from the sea cucumber \textit{Cucumaria frondosa} dermis with affiliated proteoglycan molecules. The prototypical collagen fibril structure is well conserved through higher mammalian species and presents a model for study of the mechanical properties of the primary individual components of the dermis and skeletal ligature. Common practice is to use reconstituted fibrils which lack the precise conformal structure and affiliated proteoglycans. We have performed force microscopy to probe the mechanical properties of native fibrils and extract the elastic modulus under natural conditions. This knowledge is combined transmission and atomic force imaging, in conjunction with applied computation models, to demonstrate an inherent semitubular structure of these fibrils. [Preview Abstract] |
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C1.00109: Conformational analysis of tripeptides: a molecular dynamics study of rigid and non-rigid tripeptides John Shibata, Mark Mochel Molecular dynamics simulations have been performed on different tripeptides classified as structurally rigid and non-rigid (1). The simulations were run using the OPLS-AA force field (2) with and without explicit solvent. Two modeling programs, Tinker (3) and Macromodel (4), were used to simulate the dynamics. The accessible conformations were analyzed using Ramachandran plots of the dihedral angles. The results of this study are compared to the rigidity classification scheme (1), and differences in the results using explicit solvent and a continuum solvent model are noted. (1) Anishetty, S., Pennathur, G., Anishetty, R. BMC Structural Biology \textbf{2}:9 (2002). Available from http://www.biomedcentral.com/1472-6807/2/9. (2) Jorgensen, W. L., Maxwell, D. S., Tirado-Rives, J. J. Am. Chem. Soc. \textbf{118}, 11225 (1996). (3) Dudek, M. J., Ramnarayan, K., Ponder, J. W. J. Comput. Chem. \textbf{19}, 548 (1996). Available from http://dasher.wustl.edu/tinker. (4) Mohamadi, F., Richards, N. G. J., Guida, W. C., Liskamp, R., Lipton, M., Caufield, C., Chang, G., Hendrickson, T., Still, W. C. J. Comput. Chem. \textbf{11}, 440 (1990). [Preview Abstract] |
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C1.00110: Examination of the Interface Formed from Protein Interactions in Gels Perumal Ramasamy, Lisa M. Miller, M. Raafat El-Maghrabi , Miriam Rafailovich Understanding the interaction of proteins with one another in confined environments serves as an important step for developing faster protein separation methods. To understand protein–protein interaction of oppositely charged proteins, fluorescently-labeled Albumin and poly-L-Lysine were subjected to electrophoresis in Agarose gels, in which the cationic albumin and the anionic poly-lysine were allowed to migrate towards each other and interact. Confocal microscopy was used to image the fluorescently-tagged proteins in the gel. The secondary structure of the proteins was studied using FTIR microspectroscopic imaging. Results showed that sharp interfaces were formed where the proteins met. Protein-protein interactions were observed through fluorescence quenching. The migration of the interface in the gel was found to be dependent upon the relative concentration of the proteins. The structure of the proteins at the interface, the fluorescent intensity modifications, and the mobility of the interface for different pore sizes are currently under investigation. [Preview Abstract] |
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C1.00111: Simple Model for Phase Diagram of Lysozyme as a Function of Salt Type and Salt Concentration Nathaniel Wentzel, James D. Gunton The liquid-liquid phase separation curves for lysozyme are known to depend on the salt type and salt concentration. For the case of monovalent cations, the cloud point temperature typically increases with increasing salt concentration, for fixed lysozyme concentration. For the case of divalent cations, however, a maximum in the cloud point temperature is observed that has been interpreted as being due to ion binding to the protein surface and subsequent water structuring. In this paper we use a simple square well model due to Grigsby et al (Biophys. Chem. 91, 231 (2001)), whose well depth depends on salt type and salt concentration, to determine the phase diagram for both monovalent and divalent cations. The phase diagrams are calculated using standard Monte Carlo simulations and compared with known experimental results. [Preview Abstract] |
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C1.00112: Computationally Efficient Method of Simulating Creation of Electropores John Neu, Wanda Krassowska Electroporation, in which electric pulses create transient pores in the cell membrane, is an important technique for drug and DNA delivery. Electroporation kinetics is described by an advection-diffusion boundary value problem. This problem must be solved numerically with very small time and space steps, in order to resolve very fast processes occurring during pore creation. This study derives a reduced description of the pore creation transient. This description consists of a single integrodifferential equation for the transmembrane voltage V(t) and collateral formulas for computing the number of pores and the distribution of their radii from V(t). For pulse strengths corresponding to those used in drug and DNA delivery, relative differences in predictions of the reduced versus original problem are: voltage V(t), below 1{\%}; number of pores, below 10{\%}; pore radii, below 6{\%}. Computational efficiency increases with the number of pores and thus with the pulse strength. For the strongest pulses, the run time of the reduced problem was below 1{\%} of the original one. Such time savings can bridge the gap between problems that can be simulated on today's computers and problems that are of practical importance. [Preview Abstract] |
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C1.00113: Hydrophobic Mismatch and Phase Transition in a Membrane Composed by a Mixture of Linear and Bola Phospholipids Gabriel Longo, Igal Szleifer Archeobacteria are microorganisms that can survive and proliferate in extreme habitats, such as high salt concentration environments, anaerobic conditions, and high or low temperatures. A membrane composed of bolaform phospholipids is what gives these unique survival qualities to the bacteria. The nature and composition of this membrane has not yet been elucidated. In this work, a membrane composed by a mixture of linear and bola phospholipids is studied using a molecular theory. The effect of changing the fraction of bolaform phospholipids, as well as the length of the hydrocarbon chain of the linear lipid are studied. A phase separation in the mixture between a thin bola rich membrane and a thick linear rich membrane is found. The thin membrane is mainly composed by ``spanning'' bola molecules whose polar heads are in opposed hydrophilic regions of the membrane. The phase separation is only present when the hydrocarbon chains of both molecular species have comparable sizes. The driving force for the phase separation is the size matching between the hydrophobic chains of the linear phospholipid and the spanning bola lipid. [Preview Abstract] |
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C1.00114: Renormalized Elasiticity of Lipid Membranes with Adsorbed Polymers Joel D. Revalee, Mohamed Laradji Renormalized elastic moduli of self-assembled lipid membranes, with anchored polymers that interact attractively with the membrane, are determined by means of large scale dissipative particle dynamics simulations. We show that the effective surface tension and the bending modulus of the membrane behave non-monotonically with the molecular weight or/and polymer coverage. At low molecular weight or grafting densities, the surface tension increases, while the bending modulus decreases, with increasing molecular weight or grafting density of the polymer chains. However, at high molecular weight or grafting densities, when the polymers are in the brush regime, we found that the surface tension decreases while the bending modulus increases with increasing grafting density or molecular weight of the polymers. We will also present results on the pearling instability of the lipid membrane due to grafted polymers. [Preview Abstract] |
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C1.00115: On the Registry of Lipid Domains in Multicomponent Lipid Membranes Clayton H. Davis, Mohamed Laradji Recent experiments on multicomponent lipid vesicles, composed of a saturated lipid, unsaturated lipid and cholesterol, have shown that the liquid-ordered domains in the two leaflets of the bilayer are in strong registry [1,2]. In order to understand the reasons behind this domain registry, we propose a simple lattice model, where the two leaflets are represented by two spin-half Ising surfaces, where the up and down spins represent the saturated and unsaturated lipids, respectively. Since lipid flip-flops are very rare events, spins in the two Ising lattices are only allowed to diffuse within each leaflet through spin-exchange Kawasaki dynamics. In addition each lattice point can also be occupied by a cholesterol particle which is allowed to both diffuse within each lattice and flip-flop between the two lattices. We found that registration can occur even for small concentrations of cholesterol. We will discuss the effects of cholesterol saturation and intra-layer and inter-layer lipid-cholesterol interaction on domains registration. [1] S.L. Veatch and S.L. Keller, Phys. Rev. Lett. 89, 268101 (2002) [2] T. Beaumgart, S.T. Hess, and W.W. Webb, Nature 425 (2003) [Preview Abstract] |
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C1.00116: Cubic Phase Formation in Peptide/Lipid Systems Brandon Scuffins, Beth Cunningham, David Wolfe Previous studies have shown that the phenomena of spontaneous membrane self-assembly can be used to incorporate membrane peptides into lipid bilayers. Once a peptide is incorporated in these peptide/lipid systems they may then be crystallized through the process of \textit{in meso} crystallization. In this study, we used x-ray diffraction and $^{31}$P NMR to show that a system of dioloeoylphosphatidylethanolamine (DOPE), monoolein (MO), and DOPE with polyethylene glycol covalently attached to the headgroup (PEG-lipid) can create a system with a higher concentration of peptide incorporated into the cubic phase then previously reported. We have observed that DOPE:MO:PEG-lipid at a molar ratio of 97.5:100:2.5 naturally forms the Im3m cubic phase at room temperature. Furthermore, we found that the DOPE:MO:PEG-lipid system can incorporate a concentration of up to 25 mole {\%} peptide at room temperature. Preliminary results indicate that the lipid/peptide system requires a stable cubic phase for peptide crystallization to occur. [Preview Abstract] |
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C1.00117: Conformational Change in Fibrinogen on Langmuir Blodgett Clay Monolayer J.S. Koo, T. Koga, M. Rafailovich, J. Sokolov We have studied the adsorption of the plasma protein, fibrinogen, on two different clay monolayers. Surface pressure-molecular area ($\pi -A)$ isotherm measurements, atomic force microscopy (AFM), X-ray reflectivity and grazing incident X-ray diffraction (GID) were used to characterized formation of organo-clay and sodium clay monolayers. These clays serve as model hydrophobic and hydrophilic surfaces, respectively. The overall conformational structure of fibrinogen is dramatically different on organo-clay and sodium clay surfaces. On the sodium clay surface, individual fibrinogen molecules appear globular in shape whereas, on orgno-clay, the trinodular structure is most commonly observed. Time dependent studies were also conducted. The results show that uniform multilayer formation occurred only on the hydrophobic surfaces. Fibrillar fibrinogen structures are observed over their uniform bilayers$.$ Non-uniform adsorption occurred on the hydrophilic surfaces. [Preview Abstract] |
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C1.00118: pH-dependent conformational changes of diphtheria toxin adsorbed to lipid monolayers by neutron and X-ray reflection Michael Kent, Hyun Yim, Sushil Satija, Ivan Kuzmenko Several important bacterial toxins, such as diphtheria, tetanus, and botulinum, invade cells through a process of high affinity binding, internalization via endosome formation, and subsequent membrane penetration of the catalytic domain activated by a pH drop in the endosome. These toxins are composed of three domains: a binding domain, a translocation domain, and an enzyme. The translocation process is not well understood with regard to the detailed conformational changes that occur at each step, To address this, we performed neutron reflectivity measurements for diphtheria toxin bound to lipid monolayers as a function of pH. While the final membrane inserted conformation will not be reproduced with the present monolayer system, important insights can still be gained into several intermediate stages. In particular, we show that no adsorption occurs at pH = 7.6, but strong adsorption occurs over at a pH range from 6.5 to 6.0. Following binding, at least two stages of conformational change occur, as the thickness increases from pH 6.3 to 5.3 and then decreases from pH 5.3 to 4.5. In addition, the dimension of the adsorbed layer substantially exceeds that of the largest dimension in the crystal structure of monomeric diphtheria, suggesting that the toxin may be present as multimers. [Preview Abstract] |
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C1.00119: Topology based theory of helix-coil transition Kingshuk Ghosh, Ken Dill We revisit the problem of helix-coil transition. We propose a new theory based on topology, significantly different from Zimm-Bragg theory. Our model predicts the cooperativity and is in excellent agreement with available experimental data. The model can be extended to study the thermodynamics of other structures as well. It also provides a framework to understand the kinetics of formation for different structures. [Preview Abstract] |
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C1.00120: An Inside Look at Traube's Rule: A Molecular Dynamics Study Allison Dickey, Roland Faller According to Traube's Rule [1], the alcohol concentration required to maintain the interfacial tension ($\gamma$) of a bilayer is reduced by a factor of three for each additional CH$_2$ group that is added to the alkyl chain of the alcohol. Recent experimental work confirmed that Traube’s Rule applies to 1-stearoyl, 2-oleoyl phosphatidylcholine (SOPC) lipid bilayers that are exposed to alcohol solutions of methanol, ethanol, propanol, and butanol [2]. To examine the molecular mechanisms leading to Traube’s Rule, we use molecular dynamics simulations to study the interactions between a dipalmitoylphsphatidylcholine (DPPC) bilayer and ethanol, propanol, and butanol solutions. We first examine how the bilayer structure variation depends on alcohol chain length via the area per lipid headgroup, lipid chain disorder, and electron distribution functions. We also study the alcohol dynamics within the bilayer by monitoring the time length, number, and location of hydrogen bonds. Lipid mean squared displacements are also calculated to determine the extent to which lipid mobility is affected by alcohols. \newline \newline [1] I. Traube Liebigs Annalen (1891)\newline [2] H. Ly, M. Longo Biophys J (2004) [Preview Abstract] |
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C1.00121: Optimum pH for protein-protein complexes. Petras Kundrotas, Emil Alexov The structure and function of proteins are influenced by external parameters such as pH of the environment. The pH at which proteins are most stable is the optimum pH of stability and the pH at which the binding affinity of protein-protein complexes is maximal is called optimum pH of the complexes. Therefore it is plausible to suggest that two proteins forming a complex in a particular environment should have their optimum pH's correlated as well as they should be correlated with the optimum pH of the complex. In order to test this hypothesis, we have calculated the pH dependencies of electrostatic folding free energy and total net charge for a set of 60 protein complexes previously used for protein-protein docking benchmark. The calculations have been performed for the entire complex and for each individual molecule separately. It was shown that there exists a clear correlation between optimum pH of the complex and optimum pH's of its components. In addition, the correlations between the net charges of the individual molecules and between the charges of the interfaces were also studied. The above findings could be used as additional criteria in evaluating models of protein-protein complexes. [Preview Abstract] |
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C1.00122: Excited state of peptide nanorings Tetsuo Yamada, Hiroshi Miyazaki, Hajime Okamoto, Kyozaburo Takeda Peptide nanorings (PNRs) has a closed ring form composed of alternating D- and L-$\alpha $-amino acid residues. Much interest has been attracted owing to their function as a selective ion receptor. Here, based on \textit{ab initio} molecular orbital theory, the excited as well as the ground state structures have been theoretically studied and discussed how the photo-excitation changes the ion-capturing ability with regarding on the two ring skeletons of Extended (E)- and Bound (B)-type PNR geometries. Because the HOMO-LUMO transition is optically allowed, we took into account this single excitation via the unrestricted Hartree-Fock (UHF/6-31G**) calculations. Our results reveal that the HOMO-LUMO single electron transition expands the bore of E-type PNR while narrows that of B-type one. This \textit{ad hoc} treatment, however, causes an overestimation, because the electronic states both near the HOMO and LUMO are \textit{pseudo}-degenerated. An inclusion of other configurations due to the single electron excitation (CIS) relaxes the above geometrical changes predicted by the UHF HOMO-LUMO single excitation. Thus, the ring molecular geometry in the first optical excitation is rather indistinguishable compared with that in the ground state. [Preview Abstract] |
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C1.00123: Free energy versus potential energy landscapes of drug-like molecules Yonas Abraham, Rebecca Harris, Philip S. Hammond, Jeffrey D. Schmitt To gain information about molecular shape tendencies, the life science community has traditionally focused primarily on conformational search methodologies that explore the Potential Energy Surface (PES). The output of these methods is a collation of so-called minimum energy conformers. In our effort to gain more insight into molecular shape and overall behavior, we have used both PES conformational search techniques and {\em ab initio} molecular dynamics to study a set of neuronal nicotinic receptor (NNR) ligands that possess a non-trivial structure-affinity relationship. This latter method, properly executed, provides the free energy landscape. In this poster we show the sometimes dramatic difference in predicted behavior between these two methods. Significantly, conformers predicted to be highly populated in one method are disallowed in the other method. This work constitutes our first exploration into the use of an {\em ab initio} derived free energy landscape to better understand small molecules of biological interest. [Preview Abstract] |
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C1.00124: Surface Charge Method Calculation of Biomolecular Electrostatic Force with Application to a Model System Timothy Doerr, Yi-Kuo Yu Due to the presence of ions, a high dielectric constant solvent (water with $\varepsilon=80$), and significant charges and polarizabilities associated with many biomolecules, electrostatic forces play a crucial role in biomolecular interactions. It is particularly important to adequately account for the effects of the solvent. The surface charge method presented here has been applied to a system of an arbitrary number of charged dielectric spheres embedded in an infinite dielectric medium (the solvent). The surface charge method allows calculation (to any accuracy desired) of the energy and the various forces using only matrix inversion. The energy and forces are relatively insensitive to the value chosen for the dielectric constant inside the spheres. For the special case of two isolated charged dielectric spheres in an infinite medium, the results are not obvious: The repulsive force for like-charged spheres is strengthened (compared to point charges in the solvent medium) at short distances, while the attractive force for oppositely-charged spheres is to a lesser degree weakened at short distances. In the limit that the charges associated with a biomolecule are point-like, the excess repulsion and suppressed attraction found here might play a role in minimizing the effect of energetic traps. [Preview Abstract] |
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C1.00125: Gamma Oscillations and Visual Binding Peter A. Robinson, Jong Won Kim At the root of visual perception is the mechanism the brain uses to analyze features in a scene and bind related ones together. Experiments show this process is linked to oscillations of brain activity in the 30-100 Hz gamma band. Oscillations at different sites have correlation functions (CFs) that often peak at zero lag, implying simultaneous firing, even when conduction delays are large. CFs are strongest between cells stimulated by related features. Gamma oscillations are studied here by modeling mm-scale patchy interconnections in the visual cortex. Resulting predictions for gamma responses to stimuli account for numerous experimental findings, including why oscillations and zero-lag synchrony are associated, observed connections with feature preferences, the shape of the zero-lag peak, and variations of CFs with attention. Gamma waves are found to obey the Schroedinger equation, opening the possibility of cortical analogs of quantum phenomena. Gamma instabilities are tied to observations of gamma activity linked to seizures and hallucinations. [Preview Abstract] |
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C1.00126: Experimental Study of the Dynamics of Foraging Ants J. I. Walker, R. P. Fetzner, G. W. Baxter We study the search paths of foraging ants in order to describe their behavior mathematically. Ants have become popular as simple agents in models of artificial life. Here, the ant is presented the problem of finding food when no food cues are present. In this experiment, individual ants (Formicinae lasius flavus) are allowed to forage on a two-dimensional textured surface in the absence of a food source. The position of the ant as a function of time is determined with a high resolution digital camera. The scaling properties of the resulting foraging paths compare favorably with those of certain types of random walk. [Preview Abstract] |
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C1.00127: Coarse-grained dynamics of alignment in animal group models Sung Joon Moon, Simon Levin, Yannis Kevrekidis Coordinated motion in animal groups, such as bird flocks and fish schools, and their models gives rise to remarkable coherent structures. Using equation-free computational tools we explore the coarse-grained dynamics of a model for the orientational movement decision in animal groups, consisting of a small number of informed "leaders" and a large number of uninformed, nonidentical ``followers.'' The direction in which each group member is headed is characterized by a phase angle of a limit-cycle oscillator, whose dynamics are nonlinearly coupled with those of all the other group members. We identify a small number of proper coarse-grained variables (using uncertainty quantification methods) that describe the collective dynamics, and perform coarse projective integration and equation-free bifurcation analysis of the coarse-grained model behavior in these variables. [Preview Abstract] |
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C1.00128: Assigning p-values to complex biological systems Natalie Arkus, Michael Brenner Models of complex biological systems with many free parameters do not describe a unique data set, nor is a data set uniquely described by one of them. Their conclusions may therefore not reveal an underlying biological phenomenon, but rather be model or parameter specific. We propose a method of assigning p-values to these models and their conclusions. As an example, we consider feedback and open loop models of the e. coli heat shock response system. We determine to what degree properties associated with the feedback loops are a result of the loops themselves or of the model and its specific parameter regime. [Preview Abstract] |
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C1.00129: Applications of non-equilibrium thermodynamics to signaling and metabolic pathways Dawei Hu, Ensheng Liu, Jian-Min Yuan Signaling transduction pathways play important roles in regulating cell functions, such as growth, differentiation, and apoptosis. Metabolic pathways, on the other hand, generate many metabolites utilized by human body. Abnormal regulations of the enzymes and metabolites associated with these pathways may be related to diseases. In view of their importance, we are interested in applying non-equilibrium thermodynamics to investigate the properties and dynamic behaviors of these two types of pathways. The systems of concentration are the MAPK, coupled MAPK-PI3K, and insulin metabolic pathways. In the case of signaling pathways we study the properties of thermodynamic variables, such as the affinities and fluxes of individual reaction steps, as affected by the perturbations of rate constants, protein-protein interactions, and cross talks. In the case of metabolic pathways, we study the system dynamics, the stability of steady states, and the flux-affinity relations as functions of constant inputs and outputs as well as the parameters of feedback loops. Our goals are to shed light on the design principles of the biological pathways and to rank the most vulnerable nodes of these pathways. [Preview Abstract] |
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C1.00130: Discovering Fuzzy Motifs in Yeast Genome through a generalized REDUCE algorithm Xing Zheng, Caiyi Lang, Weiqun Peng, Chen Zeng Chromatin immunoprecipitation followed by cDNA microarray hybridization (ChIP-on-Chip) has become a popular procedure for studying genome-wide protein-DNA interactions and transcription regulation. We present here a fuzzy REDUCE computational method on the genes subgroup significantly associated with each of 203 DNA-binding transcriptional regulators, based on the model in which upstream motifs contribute additively to the logRatio of chip fluorescent intensities between the enriched sample and the control sample. Statistically significant motifs are deduced from the analysis of publicly available ChIP data for Saccharomyces cerevisiae and compared to the motifs obtained using other approaches. Interactions and formations of multi-transcription activation complex are discussed. [Preview Abstract] |
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C1.00131: Recovery of Elasticity of Aged Human Epithelial Cells \textit{In-Vitro} Igor Sokolov, Swaminathan Iyer, Craig Woodworth We recently found a considerable increase in rigidity of human epithelial cells during ageing \textit{in-vitro}. This is important because the loss in elasticity of epithelial tissues with ageing contributes to many human diseases. We also found that cultured cells had three distinct regions of rigidity, and that the increase in rigidity correlated with an increase in density of cytoskeletal fibres. However, it was not clear which type of fibre was important. Atomic Force Microscopy (AFM) and imunofluorescence microscopy were used in this study to characterize aging human epithelial cells in vitro, both before and after treatment with cytochalasin B. We found that the fibres associated with increased rigidity were mostly F-actin microfilaments. Furthermore, using cytochalasin B, a chemical that inhibits polymerization of F-actin, we restored the rigidity of old cells to the young level in all three areas of rigidity simultaneously. In conclusion, these results clarify how the cell mechanics changes during aging \textit{in vitro}, and they may be relevant for treatment of age-related~loss of elasticity in epithelial tissues. The trials of this new treatment are in progress. [Preview Abstract] |
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C1.00132: The Effect of Polybutadiene Polymer on Cell Aging In Vitro. Ying Liu, Lourdes Collazo, Miriam Rafailovich, Jonathan Sokolov Cell experimentation often undergoes several weeks of culturing. The most common problem that scientists face is the variability of cell behavior due to subculturing. Most cells have a limited lifespan in vitro, changing their cell characteristic after just a few passages. Here we focus on the changes in cell function with passage. We used human CRF31 dermal fibroblasts initially cultured from lower passages (P11) to higher passages (P20) at a density of 5000/cm2. We first generated a series of cell growth curves for the different passages. We observed that as cell passage number increased, cell proliferation decreased significantly. Western Blot analysis indicated that the composition of the extracellular matrix proteins changed with increasing passage. The effect of these changes on migration and actin production will be presented. [Preview Abstract] |
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C1.00133: Regulation of an Actin Spring Barney Tam, Jennifer Shin, Ricardo Brau, Matthew Lang, L. Mahadevan, Paul Matsudaira To produce motion, cells rely on the conversion of potential energy into mechanical work. One such example is the dramatic process involving the acrosome reaction of \textit{Limulus} sperm, whereby a 60 $\mu $m-long bundle of actin filaments straightens from a coiled conformation to extend out of the cell in five seconds. This cellular engine and the motion it produces represent a third type of actin-based motility fundamentally different from polymerization or myosin-driven processes. The motive force for this extension originates from stored elastic energy in the overtwisted, pre-formed coil---much like a compressed mechanical spring. When the actin bundle untwists, this energy is converted to mechanical work powering the extension. We report on experiments probing the regulation of this actin spring by extracellular calcium. We find that extracellular calcium needs to be present for the spring to activate, and that calcium regulates the velocity of the extension. [Preview Abstract] |
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C1.00134: Radiation Hazard from Galactic Cosmic Rays Ashraf Farahat Space radiation is a major hazard to astronauts in long-duration human space explosion. Astronauts are exposed to an enormous amount of radiation during their missions away from the Earth in outer space. Deep space is a rich environment of protons, gamma rays and cosmic rays. A healthy 40 years old man staying on Earth away from large doses of radiation stands a 20{\%} chance of dying from cancer. If the same person travels into a 3- year Mars mission, the added risk should increase by 19{\%}. This indicates that there is 39{\%} chance of having cancer after he comes back to Earth. Female astronaut chances to get cancer is even almost double the above percentage. The greatest threat to astronauts en route to the red planet is galactic cosmic rays (GCR). GCRs penetrate through the skin of spaceships and people like tiny firearm bullets, breaking the strands of DNA molecules, damaging genes, and killing cells. Understanding the nature of the GCRs, their effect on biological cells, and their interactions with different shielding materials is the key point to shield against them in long space missions. In this paper we will present a model to evaluate the biological effects of GCRs and suggestion different ways to shield against them. [Preview Abstract] |
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C1.00135: A Comparative Study of Different Monte Carlo Modeling Techniques for Proton Dose in Biological Materials Dan Fry, Wilfred Sewchand, John O'Connell We have performed a comparison of the Monte Carlo simulation tools SRIM, PTRAN, and GEANT 4.7.0. The comparative parameters were chosen according to the degree of flexibility, ability to handle complex simulation geometries and physical processes modeled. Proton depth-doses in water have been compared with experimental measurements at 72 MeV, 110 MeV 158.5 MeV and 250 MeV. At the lowest incident proton energy all tools are in agreement with measurement. With increasing energy, SRIM underestimates the entrance and plateau dose. PTRAN and GEANT consistently predict the measured depth-dose over all energies simulated. Comparison was also done by simulating the depth-dose distribution in aluminum, tissue equivalent plastic (A-150) and graphite. The entrance ($D_{0}$) and peak doses ($D_{m}$), and the FWHM $\sigma_{50}$ were simulated with both SRIM and GEANT at incident proton energies of 70 MeV, 100 MeV, 150 MeV, 200 MeV and 250 MeV. Comparison was made with the extended PTRAN-X code results of Palmans {\it et al.} (Phys. Med. Biol., 42, 1175, 1997). Neither SRIM nor GEANT are in agreement with PTRAN-X. Differences range from a few to over 100$\%$. [Preview Abstract] |
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C1.00136: M\"{o}ssbauer Spectroscopy on Compounds of Biomedical Interests F. Oliver, N. Ewing, E. Hoffman, A. Kinyua, F. Oladeinde, A. Murdock M\"{o}ssbauer spectroscopy (nuclear gamma resonance spectroscopy)$^{1}$ has been used in our laboratory for many biomedical applications. This presentation will demonstrate uses of M\"{o}ssbauer spectroscopy to obtain qualitative and quantitative information about the electronic and magnetic properties of various systems. Information is obtained related to the electronic spin, electric quadrupole interaction, and magnetic hyperfine interactions. This technique has a very broad spectrum of applications, most of them in solid state physics and chemistry. Experiments may be done using transmission or backscattering geometry. For the past fifteen years we have successfully applied this technique to investigate materials of biomedical interest. Materials investigated include porphyrins containing europium$^{2}$, plants, over the counter medicines, hemoglobin, and ion implanted implant materials. Results of these experiments and other possible applications will be reported. 1. Leopold May, An Introduction to M\"{o}ssbauer Spectroscopy, Plenum Press Z(1971). 2. Oliver, et al., Inorganica Chimica Acta, Vol. 186, 119 (1991). * Partially supported by NIH, ** Partially supported by NSF-SEM program. [Preview Abstract] |
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C1.00137: Chlorophyll-a self-assembly: A low temperature STM investigation Violeta Iancu, Saw-Wai Hla We investigate self-assembly of chlorophyll-a molecules on a Au(111) surface by using a low temperature scanning tunneling microscope (LT-STM) at 4.6 K. Chlorophyll-a is a vital resource for the sustenance of life on Earth and responsible for the green color in plant leaves. Chlorophyll-a forms hexagonal close-packed structures that grow epitaxially on Au(111). The STM images show the detailed structure of the self-assembled molecular (SAM) layer where the molecules are positioned in pairs with the heads facing each other. Within a single row along the long-molecular axis direction, the molecules are assembled in an alternating head-tail-tail-head arrangement. The tunneling spectroscopy of single chlorophyll-a molecules inside this SAM layer reveals that their lowest unoccupied molecular orbital (LUMO) is located at 2.8eV above the Au(111) Fermi level. This investigation provides detailed structural and electronic properties of self-assembled chlorophyll-a and may be useful for the development of bio-molecular electronic devices. This work is supported by a US-DOE grant, DE-FG02-02ER46012 and Ohio University Nanobio Technology Initiative program BNNT [Preview Abstract] |
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C1.00138: A statistical model for bacterial speciation triggered by lateral gene transfer Sunjeet Sidhu, Wequin Peng The process of bacterial speciation has been a major unresolved issue in the study of bacterial evolution. It has been proposed that lateral gene transfer and homologous recombination play critical and complementary roles in speciation.{\footnote{ J. G. Lawrence, Theor. Popul. Biol. {\bf 61}, 449(2002).}} We introduce a statistical model, of a population, for the evolution under lateral gene transfer and local homologous recombination. We examine the evolutionary dynamics and its dependence on various evolutionary operators. [Preview Abstract] |
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C1.00139: Three Laws in Darwinian Evolutionary Theory Ping Ao Recent works to formulate laws in Darwinian evolutionary dynamics will be discussed. Specifically, three laws which form a consistent mathematical framework for the evolutionary dynamics in biology will be spelt out. The second law is most quantitative and is explicitly expressed in the unique form of a stochastic differential equation. Salient features of Darwinian evolutionary dynamics are captured by this law: the probabilistic nature of evolution, ascendancy, and the adaptive landscape. Four dynamical elements are introduced in this formulation: the ascendant matrix, the transverse matrix, the Wright evolutionary potential, and the stochastic drive. The first law may be regarded as a special case of the second law. It gives the reference point to discuss the evolutionary dynamics. The third law describes the relationship between the focused level of description to its lower and higher ones, and defines the dichotomy of deterministic and stochastic drives. It is an acknowledgement of the hierarchical structure in biology. A new interpretation of Fisher's fundamental theorem of natural selection is provided in terms of the F-Theorem. \newline \newline Ref. \newline P. Ao, Physics of Life Reviews 2 (2005) 117-156. [Preview Abstract] |
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C1.00140: Impact of Stability on Random and Small-World Brain Networks Richard Gray, Peter Robinson, Candy Fung The dynamics and stability of networks of brain components are studied to determine the role stability plays in constraining the network structure of the brain. The linear stability of a brain network is determined from a physiologically based continuum model of the brain's electrical activity. If instabilities correspond to neurological disorders such as seizures, stability is an important constraint on network structure and, hence, brain physiology and anatomy. Results for random brain networks and small-world networks are presented, showing that stability sharply constrains random network structure to satisfy $npg < 1$, where $n$ is the number of components, $p$ the probability of connection, and $g$ the connection gain. In contrast, small-world networks have a stability boundary independent of $n$ with a connectivity similar to experimentally determined cortical networks. Implications of these results to brain structure and its evolution are made, along with comparisons with cortical connection networks. [Preview Abstract] |
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C1.00141: Large-scale simulation of the primary visual cortex Jim Wielaard, Paul Sajda We have developed a large-scale computational model of a 4x4 $mm^{2}$ patch of a primary visual cortex (V1) input layer. The model is constructed from basic established anatomical and physiological data. Based on numerical simulations with this model we are able to suggest neural mechanisms for a wide variety of classical response properties of V1, as well as for a number of extraclassical receptive field phenomena. The nature of our model is such that we are able to address stationary as well as dynamical behaviour of V1, both on the single cell level and on a population level of up to about $10^5$ cells. [Preview Abstract] |
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C1.00142: Comparative Genomic Study of Plant Putative Glutamate Receptors Yoshihisa Ishizuka, Mimmie Huang, Sheri Church, Frank Turano, Weiqun Peng Glutamate receptors are ion channels that were first discovered in vertebrates and found to play a vital role in the mediation of signal transmission in the central nervous system. Recently, sequence homologs of these receptors were found in Arabidopsis, which was a surprise, as plants do not have a true nervous system. These putative glutamate receptors (GLRs) have been shown to play a critical physiological role in the regulation of carbon and nitrogen metabolism in Arabidopsis. However, their functions at the molecular and biochemical levels are not known. The newly completed genome of a second plant, rice, presents an opportunity to investigate the functions of the GLRs via a comparative genomic approach. Using phylogenetic and bioinformatics analysis, we identify the important residues, functional specificity, and potentially interacting sites and domains. [Preview Abstract] |
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C1.00143: Modeling phototaxis in complex networks Olga Kuksenok, Anna C. Balazs Phototaxis is the movement of organisms towards or away from light. It is one of the most important photo-biological processes, which in turn are responsible for light reception and the use of photons as a source of information. We briefly review current models of phototaxis of biological organisms and we develop a simple, minimal model for synthetic microscale units that can undergo phototactic motion. We then use this model to simulate the collective motion of such photosensitive artificial objects within a complex network, which is illuminated in a non-uniform manner by an external light. [Preview Abstract] |
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C1.00144: Energy Flow Analysis of Photoactive Yellow Protein Takakazu Ishikura, Kazutomo Kawaguchi, Hiroshi Watanabe, Takahisa Yamato The signal transduction of photosensory receptors is intimately related to the energy relaxation associated with the relevant functional motion. To understand this energy conversion process, it is useful to analyse the energy flux vector field in a polypeptide chain matrix. Recently, we developed a new formalism for energy flux, $J_{AB}$, between two different sites A and B in a protein. Flexibility is one of the attractive points of this method, namely, sites A/B can be consisted of an atom or any groups of atoms. In addition, huge computation resource is not required for this method. Since this method is based on the linear response theory, the energy flux, $J_{AB}$, can be obtained from a classical molecular dynamics simulation trajectory. We can define energy conductivity between the sites A and B in terms of the time-correlation function of $J_{AB}$. This quantity corresponds to the transport coefficient of heat and potential energy, representing the strength of the direct energetic coupling between the two sites. We applied this method to a photosensory receptor, photoactive yellow protein (PYP). We calculated the energy conductivity between the chromophore and the surrounding amino acid residues, Tyr42, Glu46, Thr50, Arg52, and Tyr98. As a result, we observed the values of energy conductivity decreased in this order. We will discuss the possibility of finding energy transfer pathway in PYP with this method. [Preview Abstract] |
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C1.00145: IRMPD Spectroscopic Analysis of Peptides and Oligosaccharides Using FTICR With Mid-Infrared Free-Electron Laser Kazuhiko Fukui, Katsutoshi Takahashi The fragmentation in gas-phase peptides and oligosaccharides has been investigated by using electrospray ionization (ESI) Fourier-Transform Ion Cyclotron Resonance (FTICR) mass spectrometry (MS) with a laser cleavage infrared multiphoton dissociation (IRMPD) technique. In order to cleave the ionized sample introduced in the FTICR cell, an infrared free electron laser (FEL) is used for the technique of IRMPD as a tunable infrared light source. The gas-phase infrared spectra of protonated peptides (Angiotensin II, Substance P) and sodiated ologosaccharide (Sialyl Lewis X) are obtained in the range from 5.7 $\mu $m to 9.5 $\mu $m. The results of the IRMPD spectra of the peptides show that the peaks for the photoproducts are observed as y/b type fragment ions in the IR range from 5.7 $\mu $m to 7.5 $\mu $m, corresponding to the cleavage of backbone in the parent amino acid sequence, while the spectra of the oligosaccharide have the peaks for the B/Y type in the range from 7.1 $\mu $m to 9.3 $\mu $m. [Preview Abstract] |
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C1.00146: Divergence of protein structure in solvent from that in X-ray quality crystals: probing the local environment of Chl $a$ in the cytochrome $b_{6}f$ complexes by ultrafast spectroscopy Sergei Savikhin, Naranbaatar Dashdorj, Hanyoup Kim, John Schaibley, Huamin Zhang, Jiusheng Yan, Eiki Yamashita, William Cramer The cytochrome $b_{6}f$ complex in oxygenic photosynthesis mediates electron transfer between the reaction centers of photosystems I and II, and coupled proton translocation across the membrane. High-resolution X-ray crystallographic structures of the $b_{6}f$ complex show a single chlorophyll $a $(Chl $a)$ molecule as an intrinsic component of the complex. Using ultrafast optical spectroscopy, we have shown that the excited state lifetime of the Chl $a$ in dissolved complex is unusually short ($\sim $200 ps) and attributed the observed quenching to the electron transfer exchange with a nearby amino acid. Similar optical time resolved experiments performed on single crystals of the$ b_{6}f$ complex reveal significant changes in the lifetime of the excited state and suggest structural dissimilarities between the complexes within crystals and in solvents. The extent of the structural variations is discussed and modeled using molecular dynamic simulation methods (NSF MCB-0516939, NIH GM-38323). [Preview Abstract] |
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C1.00147: Raman study of CaDNA films as a function of water content and excess CaCl$_{2}$ concentration: Stability of the B conformation. Megan Schwenker, Robert Marlowe, Scott Lee, Allan Rupprecht Highly oriented, wet-spun films of CaDNA expand in the direction perpendicular to the helical axis as the hydration of the film is increased. CaDNA films with a high CaCl$_{2}$ content show an unexpected shrinkage at a relative humidity of about 93$\%$. We have performed Raman experiments on CaDNA films as a function of both water content and excess CaCl$_{2}$ concentration in order to determine if this unexpected shrinkage might be related to a conformational transition of the DNA molecules. We find that the DNA molecules remain in the B conformation for all salt contents down to a relative humidity of 59$\%$. [Preview Abstract] |
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C1.00148: High pressure mid-infrared study of deoxyadenosine Scott Lee, Ian Lawson, Lauren Lettress, Anthony Anderson Crystalline deoxyadenosine has been studied via infrared spectroscopy at room temperatures up to about 10 GPa of pressure. Samples, typically 250 microns in diameter and roughly 25 microns in thickness, were loaded into a piston-cylinder type diamond anvil cell supplied by Diacell Ltd. and fitted with type IIa diamonds. To avoid saturation of strongly absorbing modes, the deoxyadenosine sample was diluted with KBr powder, which also served as an isotropic pressure-transmitting medium. A number of changes in the infrared spectra are noted near 2 GPa, suggesting a phase transition. [Preview Abstract] |
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C1.00149: Multivariate statistical analysis of Raman spectra to distinguish normal, tumor, lymph nodes and mastitis in mouse mammary tissues H. Dai, J.S. Thakur, G.K. Serhatkulu, A.K. Pandya, G. W. Auner, R. Naik, D. C. Freeman, V.M. Naik, A. Cao, M.D. Klein, R. Rabah Raman spectra ( $>$ 680) of normal mammary gland, malignant mammary gland tumors, and lymph node tissues from mice injected with 4T1 tumor cells have been recorded using 785 nm excitation laser. The state of the tissues was confirmed by standard pathological tests. The multivariate statistical analysis methods (principle component analysis and discriminant functional analysis) have been used to categorize the Raman spectra. The statistical algorithms based on the Raman spectral peak heights, clearly separated tissues into six distinct classes, including mastitis, which is clearly separated from normal and tumor. This study suggests that the Raman spectroscopy can possibly perform a real-time analysis of the human mammary tissues for the detection of cancer. [Preview Abstract] |
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C1.00150: Influence of Temperature and Hydration on Protein dynamics J.H. Roh, J.E. Curtis, S. Azzam, V.N. Novikov, I. Peral, Z. Chowdhuri, V. Garcia-Sakai, R.B. Gregory, A.P. Sokolov Protein dynamics and function are strongly influenced by temperature and hydration. Dynamic transition is believed to be closely related to onset of protein function since protein function activates at dynamic transition temperature, $T_{d}$. However, understanding of correlation between protein dynamics and function and of microscopic mechanism of the dynamics activated above $T_{d}$ is sill a subject of discussion. We used neutron and light scattering measurements to study temperature and hydration dependence of protein-lysozyme dynamics in the frequency range from 100 MHz to 1 THz. Our detailed analyses of protein dynamics provide i) two onsets of anharmonicity: methyl group rotation that activates regardless of hydration at 100 K and slow relaxation process that appears only in wet proteins at 200 K, ii) slow relaxation process is the mode that activates dynamic transition and enzymatic activity, and iii) temperature dependence of slow relaxation process exhibits Arrhenius-like behavior at $T \quad >$ $T_{d}$. [Preview Abstract] |
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C1.00151: A new Monte Carlo approach for exact calculation of polymer translocation time through a channel Michel G. Gauthier, Gary W. Slater Molecular Dynamics simulations are useful to study the impact of hydrodynamic interactions on the translocation process, but this technique requires large computer resources (both time and memory) which limit the size of the systems that we can study. We propose a new Monte Carlo algorithm that integrates various effects such entropic forces, external force fields frictional effects, and polymer-channel interactions. Our novel approach allows us to study the polymer as a single Brownian particle diffusing on a one-dimensional lattice in a non-constant force field. The calculation technique we suggest gives us the exact value of the translocation time via the resolution of a simple system of linear equations. This Monte Carlo approach can be used to obtain scaling laws of polymer translocation through a channel much faster than by using fluctuating-bond simulation models. [Preview Abstract] |
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C1.00152: Kinetics of Protein Adsorption at liquid/solid interfaces Markus Bellion, Ludger Santen, Armin Nagel, Hubert Mantz, Anthony Quinn, Karin Jacobs Protein adsorption processes are of crucial importance in many biomedical processes. From a physical point of view these processes raise a number of challenging questions, e.g.: How does the surface influence the conformation of proteins at the surface? What are the characteristics of the protein film at the liquid/solid interface? In this work we investigate the adsorption kinetics of salivary proteins on different kinds of surfaces in a liquid environment. The adsorbed protein layers are analyzed by means of ellipsometry, plasmon resonance, and SPM. It turns out that the adsorbed amount of proteins is sensitive to the long ranged interactions of the solid surface. The experimental data are compared to extensive Monte Carlo simulation of a colloidal protein model. The Monte Carlo results strongly suggest that induced conformal changes lead to the experimentally observed three step kinetics of amylase. [Preview Abstract] |
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C1.00153: CHEMICAL PHYSICS POSTER SESSION |
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C1.00154: Thermally activated escape rate for a Brownian particle in a tilted periodic potential for all values of the dissipation: classical and quantum regimes William Coffey, Yuri Kalmykov, Sergey Titov, B. Mulligan The translational Brownian motion of a particle in a tilted periodic potential is considered. The classical and semiclassical escape rates of a particle out of the well are estimated both numerically and analytically. In order to accomplish this, the continued-fraction method of solving classical Fokker--Planck equations is adapted to treat quantum master equations of the Caldeira--Leggett type using the phase-space (Wigner) representation of the quantum density matrix as suggested by Garcia-Palacios [J. Phys. A: Math. Gen. \textbf{37, }10735 (2004)]. The numerical escape rates are compared with those obtained in the context of the Kramers theory of the escape rate of a Brownian particle from a potential well as extended by Mel'nikov [Physica A \textbf{130}, 606 (1985); Phys. Rep. \textbf{209}, 1 (1991).] and Rips and Pollak [Phys. Rev. A\textbf{ 41}, 5366 (1990)] for all values of the dissipation including the very low damping, very high damping, and turnover regimes. It is shown that in the low temperature limit, the universal expressions for the escape rate provide a good estimate of escape rates both in classical and quantum regimes. [Preview Abstract] |
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C1.00155: Nonequilibrium phase transition of a model of diffusion, aggregation and fragmentation on complex networks Yup Kim, Sungmin Lee, Sungchul Kwon We investigate condensation phase transitions of symmetric conserved-mass aggregation (SCA) model on random networks (RNs) and scale-free networks (SFNs) of degree distribution $P(k) \sim k^{-\gamma}$. In SCA model, masses diffuse with unite rate, and unit mass chips off from mass with rate $\omega$. The dynamics conserves total mass density $\rho$. In the steady state, on RNs and SFNs of $\gamma>3$ for $\omega \neq \infty$, we numerically show that SCA model undergoes the same type condensation transitions as those in regular lattice. However the critical line $\rho_c (\omega)$ depends on network structures. On SFNs of $\gamma \leq 3$, the fluid phase of exponential mass distribution completely disappears and no phase transitions occurs. Instead, the condensation with exponentially decaying background mass distribution always takes place for any non- zero density. For the existence of the condensed phase for $\gamma \leq 3$ at the zero density limit, we investigate one lamb-lion problem on RNs and SFNs. We numerically show that a lamb survives indefinitely with finite survival probability on RNs and SFNs of $\gamma >3$, and dies out exponentially on SFNs of $\gamma \leq 3$. The finite life time of a lamb on SFNs of $\gamma \leq 3$ ensures the existence of the condensation at the zero density limit on SFNs of $\gamma \leq 3$. At $\omega = \infty$, we numerically confirm that complete condensation takes place for any $\rho > 0$ on RNs. [Preview Abstract] |
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C1.00156: Adsorption on an Equilateral Triangular Terrace Three Atomic Sites in Width: Application to Chemisorption of CO on Pt(112). Alain Phares, David Grumbine, Jr., Francis Wunderlich The study of monomer adsorption on equilateral triangular terraces three atomic sites in width is presented. Adsorbate-substrate interactions at the terrace edges differ from those at bulk sites. Adsorbate-adsorbate interactions up to second neighbors are included. Phase diagrams for all possible interactions whether attractive or repulsive are obtained at low temperature. The effect of increasing temperature is also investigated. Results of the model are applied to chemisorption of CO on Pt(112). [Preview Abstract] |
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C1.00157: Single Walled Carbon Nanotubes as Macroscopic Surfactant Molecules Erik K. Hobbie, Barry J. Bauer Single-walled carbon nanotubes (SWNTs) are made hydrophyllic through coating and wrapping with short segments of single-stranded DNA (ssDNA) containing alternating guanine (G) and thymine (T) units. Small-angle neutron scattering (SANS) measurements on dilute to semi-dilute aqueous suspensions of these colloidal SWNTs raise interesting questions about the degree of nanotube dispersion, with power-law exponents suggestive of weak attractive interactions.~ The SWNT-ssDNA complexes also act as nanoparticle surfactant, stabilizing the interface between water and toluene, for example. We exploit this to make hydrophillic cross-linked polymer particles coated and stabilized by the ssDNA-SWNT complex. Near-infrared fluorescence microscopy demonstrates the band-gap fluorescence of these SWNT-coated particles, suggesting potential routes to novel platforms and applications.~ Light scattering and optical microscopy from index-matched suspensions of the SWNT-coated colloids are compared with similar measurements on colloids made with conventional surfactants. [Preview Abstract] |
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C1.00158: Rotational Energy Exchange in Molecule-Surface Collisions Hailemariam Ambaye, Joseph Manson A theoretical approach that combines classical mechanics for treating translational and rotational degrees of freedom and quantum mechanics for describing the excitation of internal molecular modes is applied to the scattering of diatomic molecules from metal surfaces. Calculations are carried out for determining the extent of energy transfer to the rotational degrees of freedom of the projectile molecule. For the case of observed spectra of intensity versus final rotational energy, quantitative agreement with available experimental data for the scattering of NO and N$_2$ from close packed metal surfaces is obtained. It is shown that such measurements can be used to determine the average rotational energy of the incident molecular beam. Measurements of the exchange of energy between translational and rotational degrees of freedom upon collision are also well described by calculations for these same systems. [Preview Abstract] |
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C1.00159: Understandings of Formation of N-Ntrosoamine in Smoke. Yi-Lei Zhao, Carlos Gonzalez, Manuel Marquez Formation of N-nitrosoamine compounds is highly concerned in combustion and past-combustion. In chemical laboratory, nitrosylation of amine toward N-nitrosoamine generally requires nitrosonium donor and acidic condition. Recently, an unexpected reaction was observed to be relevant to nitrogen dioxide, a common component of past-combustion gas; an alternative non-ionic pathway must lead to the rapid nitrosylation. Here, we proposed a radical mechanism, by which amino-radical is formed by H-abstraction of nitrogen dioxide, followed by radical scavenging with nitric oxide. Relatively low activation energy of 10-11 kcal/mol (ca., CBS-QB3) of the radical mechanism rationalized the feasibility of N-nitrosoamine formation in colloids after combustion of bio-materials. Acid-catalyzed nitrosylation in aqueous solution was also computed. [Preview Abstract] |
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C1.00160: Classical nucleation theory based method for computing the crystal-melt interfacial free energy Xian-Ming Bai, Mo Li The crystal-melt interfacial free energy is a fundamental thermodynamic parameter governing phase transformations. It is very weak and extremely difficult to obtain experimentally. Here we present a simple approach, which is based on classical nucleation theory, for calculating the solid-liquid interfacial free energy. Using molecular-dynamics simulations, we construct spherical crystal nuclei embedded in the supercooled liquids to create an ideal model of homogeneous nucleation. The interfacial free energy is extracted by fitting the relation between the critical nucleus size and the reciprocal of the critical undercooling temperature. The orientationally averaged interfacial free energy is found to be 0.301 with errors of 0.002 (in standard LJ unit). The temperature dependence of interfacial free energy is also obtained in this work. We find that the interfacial free energy increases slightly with increasing temperature. The positive temperature coefficient of interfacial free energy is in good agreement with Spaepen's analysis [Solid State Phys. \textbf{47}, FS181, (1994)] and Turnbull's empirical estimation [J. Appl. Phys. \textbf{21}, 1022 (1950)]. [Preview Abstract] |
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C1.00161: Polarization Model for the Hydration Forces. Oscar Calvo, Marian Manciu, Eli Ruckenstein The interactions between hydrophilic surfaces in water cannot be always explained on the basis of the traditional DLVO theory, and an additional repulsion, the ``hydration force'' is sometimes required to accommodate the experimental data. While this force is in general associated with the organization of water in the vicinity of the surface, different models for the hydration were typically required to explain different experiments. We will show that the polarization model for the double layer/ hydration, which account for the correlations between neighboring dipoles, is consistent with a number of experiments, such as (i) the repulsion almost independent of the electrolyte concentration between neutral lipid bilayers, with a short decay length ($\sim $2{\AA}), (ii) the repulsion between weakly charged mica surfaces, with a longer decay length ($\sim $10 {\AA}), exhibiting not only a dependence on the ionic strength, but also strong ion specific effects. (iii) the repulsion between silica surfaces. It is shown that, for a particular structuring of water in the vicinity of a flat surface (in ice-like layers)., the polarization model leads to an oscillatory behavior of the polarization and a non-local dependence on the local electric field, as suggested by Molecular Dynamics simulations. [Preview Abstract] |
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C1.00162: A particle-based simulation technique for fluid flow: applications to binary mixtures, microemulsions and colloids Erkan Tuzel, Thomas Ihle, Guoai Pan, Daniel Kroll Particle-based simulation techniques provide an attractive alternative to traditional methods for the coarse-grained modeling of a fluctuating solvent. A particularly appealing algorithm was introduced by Malevanets and Kapral[1]. The algorithm has been successfully applied to study the behavior of polymer solutions, colloids and vesicles in shear flow. We present generalizations of this algorithm to fluids with non-ideal equations of state and binary mixtures with a miscibility gap[2]. We show the thermodynamic consistency of the model by measuring the pressure and density fluctuations and compare with analytical results. Results for the demixing of a binary mixture are presented such as the phase diagram and measurements of interface fluctuations and the surface tension of a droplet as well as the coarsening of domains during spinodal decomposition. Preliminary results for the lowering of the surface tension in microemulsions and the onset of emulsification are presented. Furthermore, colloids are included in the solvent and results for colloidal suspensions driven by external forces will be shown. [1] A. Malevanets, R. Kapral, J. Chem. Phys. 110, 8605 (1999) . [2] T. Ihle, E. Tuzel, D. M. Kroll, cond-mat/0509631. [Preview Abstract] |
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C1.00163: Thermodynamic Investigation of Ar, CH$_{4}$, and D$_{2}$O$_{ }$Adsorption on ZnO surfaces Sami Chanaa, M. Farinelli, A. Freitag, M. Ross, John Z. Larese ZnO nanoparticles of different shape and exposed crystal face have raised considerable interest in the recent past, because their potential use for electronic and photonic devices, etc. Understanding the relationship between the macroscopic particle shape and the surface morphology, structure and polarity will play a crucial role in developing technologically useful devices. Using a recently developed synthetic method we have been able to produce large quantities of high quality pure and doped ZnO nanomaterial with shapes including plates, nanowires and tetrapods as observed by TEM. High resolution adsorption isotherms were used to investigate the interaction of the nanoparticle surfaces with different probe molecules. The shape of the resulting adsorption isotherms varies as the distribution of nanoparticle shapes and surfaces used as substrate is changed. Results of thermodynamic investigation of argon and methane adsorption below the respective triple points show the formation of 3 distinct adsobate layers before the onset of bulk adsorbate formation. D$_{2}$O isotherms show weak evidence of different mono and multi layer capacities depending on previous exposure of the nanoparticle surface to UV radiation. [Preview Abstract] |
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C1.00164: The non-dominance of counterions in the spherical electrical double layer: an integral equation and simulational study Enrique Gonz\'alez-Tovar, Iv\'an Guerrero-Garc\'{\i}a, Mart\'{\i}n Ch\'avez-P\'aez The ionic cloud around a charged colloid (or electrode) immersed in an electrolyte is known as the electrical double layer (EDL). An important amount of theoretical and simulational work in this topic has been done in the frame of the restricted primitive model (RPM) of an electrolyte, in which the ionic size correlations are taken into account considering equal-sized ions. Ionic size asymmetry, on the other hand, has been explored to much less extent. One possible explanation to this can be found in the common belief that counterions dominate the EDL, i.e., that away from the zero-charge point the properties of the EDL are essentially equal for size-symmetric and size-asymmetric electrolytes if the counterions are the same in both cases. Recent developments, however, clearly show that size asymmetry can induce dramatic effects on the structure and properties of EDLs. In the present work we report Monte Carlo simulations and theroretical results that exhibit that the counterions not always rule the properties of the EDL, e.g. the ionic size asymmetry enhances the phenomenon of charge reversal (i.e., the overcompensation of the bare charge of the macroion) and the screening due to the electrolyte. Additionally, we find that the predictions of the HNC/HNC and HNC/MSA integral equations are in good agreement with simulations in a wide range of conditions. [Preview Abstract] |
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C1.00165: Optical detection of sub-micron and nanoscale particles in liquids Subechhya Pradhan, Matthew McGrath, Tobias Hertel We discuss a scheme for detection of submicron and nanoscale particles using light scattering in combination with lock-in filtering for increased sensitivity and signal-to-noise ratio. In this experiment, suspended submicron and nanoscale particles flow downstream a microfluidic cell until they enter the detection volume where particles are subjected to forced oscillatory motion perpendicular to the flow direction. Scattered light can then be detected in the forward direction by a position sensitive detector or in backscattering geometry using an interferometric confocal setup. The signal to noise ratio is improved over previous experiments making use of low pass filtering by lock-in amplification. We explore the potential of this technique for nanoparticle detection in liquid environment and present preliminary results on the detection of low and high index spherical particles such as polystyrene beads or colloidal gold as well as of high aspect ratio particles such as carbon nanotubes and tobacco mosaic virus. [Preview Abstract] |
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C1.00166: Coexistence curve of a near-critical, eight-arm star polystyrene in methylcyclohexane Mark Wellons, Mark Lightfoot, D.T. Jacobs The coexistence curve of eight-arm star polystyrene in methylcyclohexane has been measured and used to determine the coexistence curve amplitude B. An automated measurement of the minimum deviated angle in each phase provides the refractive index and thus the composition in each phase. By exploring temperatures from a few milliKelvins to two Kelvin below the critical temperature, the shape of the coexistence curve is determined and compared to a simple power law of amplitude B and exponent $\beta $. The exponent should be independent of molecular weight while the amplitude should vary as a power-law in molecular weight. We report the results of one molecular weight (228,000) and compare them to published values for a smaller molecular weight (74,000) and to the results for a linear polystyrene in the same solvent. We acknowledge the support from the donors of the American Chemical Society Petroleum Research Fund. [Preview Abstract] |
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C1.00167: Investigation of Gas Phase Gold Oxide Cations Towards the Oxidation of CO Nelly Moore, Grant Johnson, A. Welford Castleman, Jr. Studies are underway in our laboratory aimed at providing information to aid in the design of more efficient and selective catalysts. Gas phase metal oxide cluster studies are becoming a valuable complementary technique to surface methods for elucidating the mechanistic details and active sites of catalytic systems. It is our present goal to uncover possible species responsible for the increased activity and selectivity of gold oxide catalysts utilizing gas phase studies. To gain insight into the bonding properties and structures of gold oxide clusters, collision induced dissociation experiments were undertaken. In addition, reactivity studies of gold oxide clusters with CO provided information into different reaction pathways based on size, stoichiometry, and charge state. Reactions of gold oxide cations with CO were explored and compared to anionic cluster reactions previously conducted in our laboratory. These studies have provided evidence of various reaction mechanisms including oxidation, replacement, and association which will be presented. [Preview Abstract] |
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C1.00168: Stern-Gerlach molecular beam deflection studies of magnetic sandwich clusters Mark Knickelbein, Ken Miyajima, Atsushi Nakajima Stern-Gerlach studies of transition metal-benzene [M$_{n}$(bz)$_{m}$] and lanthanide-cyclooctatetarene [Ln$_{n}$(COT)$_{m}$] sandwich clusters and related sandwich compounds have identified several systems that are ferromagnetically ordered. Such ordered organometallic systems are promising candidates as building blocks for spintronic and information storage applications: their quasi-one-dimensional molecular structures introduce the spatial anisotropy required for magnetic bistability. Magnetic moment measurements of representative magnetically ordered M$_{n}$(bz)$_{m}$ (M=Sc and V) and Ln$_{n}$(COT)$_{m}$ (Ln=Eu, Tb, Ho) systems will be presented. [Preview Abstract] |
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C1.00169: Reactivity of Size-Selected Gas-Phase Transition Metal Sulfide Clusters with CO and NH$_{3}$ James Lightstone, Melissa Patterson, Michael White Our current focus has been the production of early transition metal sulfide and carbide clusters for reactivity studies in both the gas-phase and deposited on well defined surfaces. The transition metal sulfides are particularly interesting due to their catalytic properties and their ability to form fullerene-like nanostructures that reflect the S-M-S layered structure of the bulk material. Gas-phase M$_{x}$S$_{y}^{+}$ clusters (M=Mo, Nb, Ta, W) were produced in a cluster deposition apparatus by reactive sputtering via a magnetron cluster source. Mass spectroscopy results show that Mo, Ta, and W preferentially produce clusters of similar stoichiometry (x/y = 2/6, 3/7, 4/6, 5/7, and 6/8) while all the metals are found to form the ``magic'' cluster, M$_{4}$S$_{6}^{+}$. Several prominent M$_{x}$S$_{y}^{+}$ clusters in the mass spectra were size-selected and reacted with CO and NH$_{3}$ in a hexapole collision cell. In general, CO adsorbs sequentially on exposed metal sites, while the results for NH$_{3}$ appear to suggest the formation of solvation shells. These results and how they may relate to cluster structure and reactivity will be discussed. In addition, we will discuss current progress towards deposition of these nanomaterials on well-defined substrates. [Preview Abstract] |
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C1.00170: Simulations of vapor water clusters at vapor-liquid equilibrium Kim Bolton, Peter Ahlstrom, Erik Johansson, Arne Rosen Clustering of water molecules is important, for example, in the nucleation of water drops and in the penetration of water into hydrophobic polymers where water trees can be formed. Monte Carlo methods have been used to study the clustering of water under vapour-liquid equilibrium conditions between 300 and 600 K. The number of clusters, as well as the cluster size, increases with increasing temperature. In addition, due to entropic effects, the percentage of clusters that have linear (or open) topologies increases with temperature and dominate over the minimum-energy cyclic topologies at the temperatures studied here. [Preview Abstract] |
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C1.00171: An Atom in a Golden Ring: M@Au$_{6 }$(M = Ti, V, Cr) Kiran Boggavarapu, Xi Li, Li-Feng Cui, Lai-Sheng Wang The electronic structure and magnetic properties in a series of transition metal doped Au clusters, MAu$_{6}^{-}$ (M = Ti, V, Cr), are investigated experimentally using photoelectron spectroscopy (PES) and density functional calculations. PES features due to the impurity atoms and the Au$_{6}$ host are clearly observed. It is found that all the MAu$_{6}^{-}$ and MAu$_{6}$ clusters possess a planar structure, in which the transition metal atom is located in the center of an Au$_{6}$ ring and carries large magnetic moments (2, 3, and 4 $\mu _{b}$ for MAu$_{6}$, M = Ti, V, and Cr, respectively). [Preview Abstract] |
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C1.00172: Small Metallized Carbon Clusters. A. Patrick, P. Williams, E. Blaisten-Barojas Studies of carbon clusters with 1-4 Ca atoms metallized with Li and Be were performed within the density functional theory approach (DFT). Structures of the ground state and first 3 or 4 excited states where systematically calculated for C$_{m}$Li$_{n}$ and C$_{m}$Be$_{n }$with $n$, $m$=1, 2, 3, and 4. Several of these clusters have ground states of high multiplicity, which make them interesting for magnetic applications. Overall, most stable structures are either linear or planar in the ground state for the smaller clusters, whereas larger clusters acquire 3D structures. Charge transfer in these compounds is notorious, showing no indication of covalent bonding. Calculations were done with DFT the gradient corrections and large basis sets, and compared for several excited states with CASSCF calculations. [Preview Abstract] |
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C1.00173: ABSTRACT WITHDRAWN |
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C1.00174: Size-Evolution of the Structural and Energy Characteristics of Magnesium Clusters Paulo H. Acioli, Julius Jellinek The most fascinating and important from the applied point of view attribute of the cluster phase of matter is the unique and often unexpected variation of properties with the cluster size. The structural forms, electronic properties, nature and strength of bonding, and other physical characteristics all change as the clusters grow. The rate of change in different properties is, however, nonuniform and element/material dependent. The goal of this study is to investigate and characterize qualitatively and quantitatively the size evolution of the structural and energy characteristics of magnesium clusters. These include the transition from a tetrahedral- to pentagonal- to capped trigonal prism-based motif as the energetically most preferred one. The analysis will include also the higher energy isomers of the clusters and will address the issue of the transition to the bulk lattice. [Preview Abstract] |
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C1.00175: Catalytic water formation on free platinum and palladium clusters Mats Andersson, Arne Rosen A pulsed beam of neutral metal clusters is generated with a laser vaporization source. The cluster beam passes through two reaction cells, in which the clusters make from less than one up to a few collisions with the reactive molecules. The clusters are detected with laser ionization and time-of-flight mass spectrometry. By measuring the abundance of pure clusters and reaction products as a function of reaction cell pressure, the reaction probability in a cluster-molecule collision can be determined. Platinum clusters with more than 6 atoms form stable reaction products with both oxygen and hydrogen. When the clusters first react with oxygen and then with hydrogen we measure a decreasing number of oxygen atoms adsorbed on the clusters as the number of cluster-hydrogen collisions is increased. The interpretation for this is that water molecules form on the clusters and desorb. The efficiency of the reaction is high on all cluster sizes measured (7-30 atoms), with only a weak size dependence. The water formation reaction also proceeds on palladium clusters in the same size range. [Preview Abstract] |
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C1.00176: Size, charge, and isomer specific vibrational spectroscopy of isolated metal clusters in the far infrared Andre Fielicke, Gert von Helden, Gerard Meijer, Christian Ratsch We report on the vibrational spectra of neutral and charged metal clusters in the far infrared. These spectra are obtained via far infrared resonance enhanced multiple photon dissociation (FIR-MPD) of the complexes of metal clusters with rare gas atoms. The experiments make use of the Free Electron Laser for Infrared eXperiments (FELIX) in Nieuwegein, The Netherlands, as an intense and widely tunable far-infrared radiation source. The measured FIR-MPD spectra of the complexes represent the infrared absorption spectra of the bare metal clusters. These spectra are unique for each cluster size and are true fingerprints of the cluster's structure. This FIR-MPD technique has been applied to cationic vanadium clusters and cationic and neutral niobium clusters containing 3 to more than 20 atoms. For smaller sized clusters ($n<$15), theoretical infrared spectra have been calculated using density functional theory and a comparison with the experimental spectra allows for the structure determination. [Preview Abstract] |
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C1.00177: Multiphoton control of an electrocyclic ring-opening Elizabeth Carroll, Brett Pearson, James White, Andrei Florean, Philip Bucksbaum, Roseanne Sension We have investigated optical control over the photoisomerization of 1,3-cyclohexadiene to 1,3,5-cis-hexatriene via multiphoton excitation. Sub-80fs pulses at 800nm were shaped with an acousto-optic modulator. A closed-loop genetic algorithm (GA) searched for optimal excitation pulses while the effectiveness of each pulse was evaluated using differential absorption of a time-delayed, broadband, ultraviolet probe pulse. Reaction products were subsequently identified in an ultraviolet spectrophotometer. The GA identified pulses that increased the formation of hexatriene by a factor of two over the transform-limited pulse. Detailed analysis of the pulses in the GA search set has identified negative quadratic spectral phase and cubic phase as important control parameters. Multiphoton control mechanisms will be discussed. [Preview Abstract] |
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C1.00178: Ultrafast Proton Transfer Driven by a Femtosecond Strong-Field Laser Pulse Alexei Markevitch, Dmitri Romanov, Stanley Smith, Robert Levis Kinetic energy distributions of protons ejected from a polyatomic molecule, anthraquinone, subjected to 60~fs, 800~nm laser pulses of intensity between 0.2 and 4.0x10\^{}14~W/cm\^{}2, reveal field-driven restructuring of the molecule (intramolecular proton migration) prior to its Coulomb explosion. Model calculations demonstrate that proton migrates into a field-dressed metastable potential energy minimum. Isomerization mediated by strong field is an important novel phenomenon in coupling of polyatomic molecules with intense laser pulses. [Preview Abstract] |
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C1.00179: Synthesis of anatase TiO$_{2}$ nanocrystals by low temperature sol-gel method modified with a hydrophobic ionic liquid Yen-Hui Liu, Chih-Wei Lin, Arnold Chang-Mou Yang, Min-Chao Chang, Hsin Shao, Chih-Jen Lin, Li-Jiaun Lin Anatase TiO$_{2}$ nanocrystals of uniform sizes were synthesized via low temperature sol-gel reaction of titanium tetraisopropoxide (TIP) with water in the presence of small amount of hydrophobic ionic liquid (IL) molecules. It was found that the IL molecules did not actively participate in precursor hydrolysis and TiO$_{2}$ nucleation. However, the IL molecules strongly screened the abundant remaining hydroxylic bonds on the surfaces of the primordial TiO$_{2}$ particles, giving rise to low temperature transition to anatase phase at 100 ${^\circ}$C and impeded inter-particle sintering. The former was believably induced by self-organization of the IL molecules that adsorbed on the hydroxylic bonds. This IL-modified sol-gel reaction resulted in uniform sized ($\sim $ 10 nm) anatase TiO$_{2}$ nanocrystalline particles, useful for high efficiency photo-catalytic applications. [Preview Abstract] |
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C1.00180: Semi-Classical Quantization of a [2] Rotaxane Karl Sohlberg, Ari Silver Rotaxanes show tantalizing potential for functional nanosystems. A [2]rotaxane is a molecular complex consisting a long dumbbell-shaped chain molecule, (called the shaft) which threads a ring molecule, typically a crown-ether or cyclodextrin. The chain component is terminated on each end by a bulky substituent to prevent unthreading of the ring. The components are therefore chemically independent but mechanically interlocked. When such complexes are synthesized with two inter-component binding stations, bistability results, hinting at potential for switching or data storage applications. We have investigated the quantum-mechanical eigenstates associated with the shuttling motion between these co-conformations. The state density is very high because nano-systems exist at the transition/interface between molecular systems, which are dominated by quantum phenomena, and macroscopic systems where matter is essentially continuous and classical physics provides the best description. We show that state density is \textit{highest} where quantum mechanical tunneling is most important. [Preview Abstract] |
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C1.00181: Single molecule fluorescence investigates the heterogeneity of liquid crystal matrix. Yu-Tsu Chuang, Jui-Hung Hsu Liquid crystals are attracted for their existence of unique meso-phase between solid state and liquid state. We perform the single-molecule (SM) fluorescence investigation on the thermotropic liquid crystal matrix. Using the nm size fluorescent quantum dots as a probe, it allows us to investigate the local structural and dynamic heterogeneity in the liquid crystal matrix. Controlling the temperature allows us to probe how the local behaviors differ at different meso-phases. Fluorescence correlation spectroscopy (FCS) as well as the intensity time trace analysis indicate the much more heterogeneity in the liquid crystal phase than the other phases. [Preview Abstract] |
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C1.00182: Synthesis and Characterization of Rectangular Palladium Nanoparticles. Yuan Sun, Lihua Zhang, Eli Sutter, Yimei Zhu, Miriam Rafailovich, Jonathan Sokolov The optical, magnetic and catalytic and electronic properties of nanoparticles are affected not only by their size, but also by their shape. We have used a mild reducing agent, ascorbic acid, in the presence of sodium citrate and a surfactant, cetyltrimethylammonium bromide, at ambient conditions to prepare colloidal rectangular palladium nanoparticles, including nanocubes and nanorods. Our procedure requires no seed-mediated growth or nanoporous template so that it is more practical for large-scale synthesis. Upon changing the concentration of sodium citrate from 0.2 $\times $ 10$^{-3}$ M to 1.0 $\times $ 10$^{-3}$ M, TEM measurements indicate that the average size of the nanocubes decreases slightly from 31.8 $\pm $ 3.2 nm to 29.4 $\pm $ 4.2 nm and the aspect ratio of the nanorods increases from 2.48 $\pm $ 1.42 to 3.94 $\pm $ 2.50. HRTEM images and diffraction patterns indicate that the particles are highly crystalline and have strong (100) faceting. Being exposed to air for $\sim $100 days, the particles are oxidized to form 2$\sim $4 nm-thick amorphous shells. [Preview Abstract] |
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C1.00183: Nucleation, composition and morphology of ALD HfO$_{2}$ films Justin C. Hackley, Theodosia Gougousi A hot wall Atomic Layer Deposition flow reactor equipped with a Quartz Crystal Microbalance (QCM) has been used in the development of a HfO$_{2}$ process from tetrakis-ethylmethylamino hafnium (TEMAH) and H$_{2}$O precursors. We have studied the nucleation, composition and morphology of HfO$_{2}$ films deposited on H- terminated Si, native oxide and SC1 chemical oxide. Ellipsometry and QCM measurements confirm linear growth of the films ($\sim $1.2{\AA}/cycle at 250\r{ }C). Similar incubation periods ($\sim $10 cycles) are found for depositions on the H-terminated Si and native oxide starting surfaces in agreement with recently published results.\footnote{ M.-T. Ho, Y. Wang, R. T. Brewer, L. S. Wielunski, Y. J. Chabal, N. Moumen, and M. Boleslawski, APL 87, 133103 2005} AFM measurements show rms roughness of the as deposited films below 4{\%} of the total film thickness. FTIR measurements show some OH and carbonate content in the films that are corroborated by XPS measurements. Rapid Thermal Anneal of the films in Ar (500 to 900\r{ }C, 2 min) results in the destabilization of the HfO$_{2}$/SiO$_{2}$ interface, increased rms roughness and crystallization of the film. FTIR and XPS analysis of the films annealed at 900\r{ }C in Ar confirm removal of the OH and carbonate species from the films. Finally, we present QCM measurements for the nucleation of HfO$_{2}$ films on Si and H-terminated surfaces. [Preview Abstract] |
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C1.00184: Ranked solutions to a class of combinatorial optimizations - with applications in mass spectrometry based peptide sequencing Timothy Doerr, Gelio Alves, Yi-Kuo Yu Typical combinatorial optimizations are NP-hard; however, for a particular class of cost functions the corresponding combinatorial optimizations can be solved in polynomial time. This suggests a way to efficiently find approximate solutions - - find a transformation that makes the cost function as similar as possible to that of the solvable class. After keeping many high-ranking solutions using the approximate cost function, one may then re-assess these solutions with the full cost function to find the best approximate solution. Under this approach, it is important to be able to assess the quality of the solutions obtained, {\em e.g.}, by finding the true ranking of $k$th best approximate solution when all possible solutions are considered exhaustively. To tackle this statistical issue, we provide a systematic method starting with a scaling function generated from the fininte number of high- ranking solutions followed by a {\em convergent} iterative mapping. This method, useful in a variant of the directed paths in random media problem proposed here, can also provide a statistical significance assessment for one of the most important {\em proteomic} tasks - - peptide sequencing using tandem mass spectrometry data. [Preview Abstract] |
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C1.00185: STATISTICAL AND NONLINEAR PHYSICS POSTER SESSION |
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C1.00186: Loschmidt echo decay in hard-disk billiards Arseni Goussev, Klaus Richter The Loschmidt echo (LE) quantifies the sensitivity of quantum dynamics to perturbations of system's Hamiltonian. In a chaotic system it is known to exhibit exponential time decay, for a certain range of perturbation strengths, with the decay rate given by the mean Lyapunov exponent of the counterpart classical system. This phenomenon makes the LE an attractive tool for quantifying {\it Quantum Chaos}. To date, all existing theories for the LE strongly rely on averaging over different realizations of the Hamiltonian and/or averaging over an ensemble of initial states. Thus, a theory for the LE in pure individual chaotic systems is needed. We attempt to fill in this gap by addressing the LE in pure open quantum hard-disk billiards. We find that in such systems the LE time decay is intimately connected to Lyapunov exponents as well as to quantities characterizing escape of classical trajectories from the system's chaotic repellor. Our theoretical findings are supported by results of numerical simulations. [Preview Abstract] |
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C1.00187: Random Walk Model with Waiting Times Depending on the Preceding Jump Length Vasily Zaburdaev In the present work the generalized continuous time random walk model with a coupled transition kernel is considered. The coupling occurs through the dependence of the waiting time probability distribution on the preceding jump length. The method, which involves the details of the microscopic distribution over the waiting times and arrival distances at a given point, is suggested for its description. In the particular case of coupling, when a waiting time is a simple function of a preceding jump length, a close analogy to the problem of a random walk with finite velocity is demonstrated. With its help an analytical solution for the generalized random walk model, including both effects (finite velocity and jump dependent waiting times) simultaneously, is found. Considered examples indicate a possibility to apply the developed approach to the biological problems where the random walk together with the recovery processes and the finite velocity are present, such as e.g. the foraging movements of animals or the motion of zooplankton. [Preview Abstract] |
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C1.00188: Diameter of Random Cluster Models D. W. Blair, J. Machta The diameter of critical clusters of the $q$-state Potts model in the random cluster representation is measured in numerical simulations. The diameter of a graph is the maximum over all pairs of connected sites of the minimum path length between the sites. Although the diameter of Fortuin-Kasteleyn clusters is not a thermodynamic quantity, it is expected to display power law critical behavior since the size of the largest cluster diverges at the critical point. The Swendsen-Wang algorithm is used for both for equilibrating the spin model and for identifying clusters. An efficient algorithm is employed to measure the diameter. The exponent characterizing the divergence of the diameter is obtained for $q=1$,2,3 and 4. The relation to other critical exponents is discussed. This work is supported by NSF (DMR-0242402). [Preview Abstract] |
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C1.00189: Empirical and model study on Travel-entering China Xue-Fang Han, Qi-Juan Chen, Hui Chang, Da-Ren He We have done an empirical investigation on the travel-entering China from abroad to 31 regions of Chinese Mainland in recent ten years, including the development of the traveler's number, the traveler's number distribution for the traveler's home regions, the traveler's number distribution for the traveler's destination regions in Chinese mainland, and so on. We also suggest a dynamic model for simulating the competition between the 31 regions in the traveling market by considering two main influence factors, the attracting factor of the travel destinations and the distance between the destination and the home regions of the travelers. The simulation results show a good agreement with the empirical data. We expect the model could suggest some advice and thoughts to the travel-entering management departments in China and may be also for other countries. [Preview Abstract] |
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C1.00190: An empirical and model study on automobile market in Taiwan Ji-Ying Tang, Rong Qiu, Yueping Zhou, Da-Ren He We have done an empirical investigation on automobile market in Taiwan including the development of the possession rate of the companies in the market from 1979 to 2003, the development of the largest possession rate, and so on. A dynamic model for describing the competition between the companies is suggested based on the empirical study. In the model each company is given a long-term competition factor (such as technology, capital and scale) and a short-term competition factor (such as management, service and advertisement). Then the companies play games in order to obtain more possession rate in the market under certain rules. Numerical simulation based on the model display a competition developing process, which qualitatively and quantitatively agree with our empirical investigation results. [Preview Abstract] |
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C1.00191: Stochastic Synchronization in Lattices of Model Neurons Andy Mueller, Klaus Lehnertz It has been shown recently that a wide class of uncoupled limit-cycle oscillators can be fully synchronized by a common weak additive white noise. We study the influence of noise on the dynamics of mutually uncoupled lattices that are composed of periodically spiking model neurons with an increasing complexity. In order to approximate characteristics of noise found in empirical data we use an Ornstein Uhlenbeck process (OUP) as the driving force. Varying the correlation time and the intensity of the OUP we study the time to full synchronization (ST) and the largest Lyapunov exponent (LLE) of the systems. For all investigated correlation times LLE is negative indicating the convergence of the trajectories of the systems. For a constant noise intensity we observe that both ST and LLE exhibit a minimum for a particular correlation time of the OUP. We discuss the possible relationship between the correlation time of the OUP and the time scales of the investigated systems. [Preview Abstract] |
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C1.00192: Score Statistics of Global Sequence Alignment and a Modified Directed Polymer Problem Mihaela Sardiu, Gelio Alves, Yi-Kuo Yu Sequence alignment is one of the most important bioinformatics tools for modern molecular biology. Using a variant of the directed path in random media model, we investigate the score statistics of global sequence alignment taking into account the compositional bias of the sequences compared. To accommodate the compositional bias, we introduce an extra parameter $p$ indicating the probability for positive matching scores to occur. When $p$ is large, the highest scoring point within a global alignment tends to be close to the end of both sequences, in which case we say the system percolates. By applying finite-size scaling theory on percolating probability functions of various sizes (sequence lengths), the critical $p$ at infinite size is obtained. For alignment of length $t$, the score fluctuation $\sim \chi t^{1/3}$ is confirmed via scaling of the alignment score. Using the Kolmogorov-Smirnov statistics test, we show that $\chi$ follows the Tracy-Widom distributions: Gaussian Orthogonal Ensemble for $p$ slightly larger than $p_c$ and Gaussian Unitary Ensemble for larger $p$. The possibility of characterizing score statistics for modest system size (sequence lengths), via proper reparametrization of alignment scores, is illustrated. [Preview Abstract] |
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C1.00193: Nonequilibrium phase transition on a randomly diluted lattice Man Young Lee, Thomas Vojta We show that the interplay between geometric criticality and dynamical fluctuations leads to a novel universality class of the contact process on a randomly diluted lattice. 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 also relate our results to the recently found infinite-randomness fixed point in the disordered one-dimensional contact process. [Preview Abstract] |
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C1.00194: Numerical Studies of the Edwards-Wilkinson interface equation: the influence of short-range time-correlated noise Mika Saukkonen, Teemu Laurila, Tapio Ala-Nissila We study the properties of the Edwards-Wilkinson equation with finite temporal correlations of duration $t_{d}$. Two limiting cases can be calculated analytically, namely, the thermal white noise limit, where $t_{d}\to 0$, and the purely columnar limit, when $t_{d}\to \infty$. The surface growth exponents are $\beta=1/4$ for the thermal white noise case and $\beta=3/4$ for the columnar noise case. Correspondingly, the rougness exponents are $\chi=1/2$ and $\chi=3/2$. We study the crossover scaling of the surface width and the dynamical structure factor between these two limits by introducing a scaling ansatz and numerically verifying it. Furthermore, we present results from a comparison between the time correlated case and the case with quenched noise, which has the same effective correlation length. The scaling behavior in these two cases is similar exept close to the pinning transition for the quenched noise case. [Preview Abstract] |
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C1.00195: A study of SOC models by the use of joint distributions Espen Jettestuen, Anders Malthe-S\orenssen, Jens Feder A precise characterization of scaling behavior is important for the further development of self-organized criticality. This has been achieved for models that display finite size scaling, but is lacking for systems that have more complicated scaling form. We propose that scaling of structures in joint probability densities can be used to identify the underlying structure in systems that show multi-scaling behavior. Here, we will study two simple models by the use of joint probability distributions. One is the BTW model that have multi-scaling behavior and the other is a randomized version of the Olami-Feder-Christensen earthquake model which has a simple finite size scaling form. We will also relate the scaling of the joint probability density to other well-known measures. [Preview Abstract] |
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C1.00196: Glassy dynamics in interface growth: aging, fluctuation disipation and thermal avalanches Jose J. Ramasco, Juan M. Lopez, Miguel A. Rodriguez In this work we study the KPZ interface growth equation subjected to both quenched and anealed disorder. We find that the interface dynamics shows a glassy behavior in the regime of low temperatures and low external force, a regime commonly known as creep in the superconductor literature. We also describe how the temperature affects to the avalanches in the front development. [Preview Abstract] |
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C1.00197: Delayed Feedback and Chaos on the Driven Diode-Terminated Transmission Line Vassili Demergis, Steven Anlage, Edward Ott, Thomas Antonsen, Alexander Glasser, Marshal Miller A simple model of a distributed, non-linear circuit that produces chaos at GHz frequencies is introduced and tested experimentally. The model circuit is a driven, diode-terminated transmission line with the transmission line impedance mismatched to that of the source. This model is motivated by the need to understand the mechanisms for RF upset in computer circuits. Experimental tests of the model were performed with driving frequencies of 10 MHz to 1.2 GHz, driving powers of -30 to +50 dBm, and delay times from 3 to 20 ns. Diode reverse recovery times (/tau/) ranged from 4 to 100 ns. Experimentally, it was found that chaotic behavior was strongly dependent on the reactance of the system as seen by the driving source, and influenced by an applied DC voltage-bias across the diode. In the experiments that showed period-doubling and / or chaos, the /tau/ was on the order of both the driving period and the delay time of the circuits. Comparisons between theory and experiment are in general agreement.Work supported by the DOD MURI AFOSR Grant F496200110374 and DURIP Grants FA95500410295, FA95500510240. [Preview Abstract] |
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C1.00198: Geometrically induced nonlinear dynamics in one-dimensional lattices Merle D. Hamilton, O.F. de Alcantara Bonfim We present a lattice model consisting of a single one-dimensional chain, where the masses are interconnected by linear springs and allowed to move in a horizontal direction only, as in a monorail. In the transverse direction each mass is also attached to two other linear springs, one on each side of the mass. The ends of these springs are kept at fixed positions. The nonlinearity in the model arises from the geometric constraints imposed on the motion of the masses, as well as from the configuration of the springs, where in the transverse direction the springs are either in the extended or compressed state depending on the position of the masses. Under these conditions we show that solitary waves are present in the system. In the long wavelength limit an analytic solution for these nonlinear waves is found. Numerical integrations of the equations of motion in the full system are also performed to analyze the conditions for the existence and stability of the nonlinear waves. [Preview Abstract] |
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C1.00199: Stochastic qualifyers of brain dynamics Jens Prusseit, Klaus Lehnertz Despite the fact that both linear and nonlinear analyses of EEG time series have provided valuable insights into the complex spatio-temporal dynamics of physiological and patho-physiological brain functions, these processes are far from being fully understood. We here investigate the applicability of a previously proposed analysis method to characterize EEG time series from epilepsy patients using concepts from the theory of Markov-processes. To estimate the coefficients of a corresponding Fokker-Planck equation we adopt the method of Siegert et al (Phys. Lett. A \textbf{243}, 275 (1998)) to the problem at hand. To check the validity of our approach we reconstruct the driving noise force via the associated Langevin equation and show that the noise is approximately delta-correlated and Gaussian. We then integrate our model to compare the stationary probability distribution function (PDF) as well as the conditional PDFs on different time scales with the PDFs derived from the EEG data. Applying the analysis method to long-lasting multichannel EEG recordings we discuss the possible relevance for diagnostic purposes. [Preview Abstract] |
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C1.00200: Berry curvature contributions to the density fluctuation spectrum of Bloch electrons M. J. Rave, W. C. Kerr Recent work has shown that the equations of motion (EOM) for semiclassical Bloch electrons must be modified in the presence of a non-zero Berry curvature [1]. These corrections to the EOM have implications for many physical quantities: effective mass, electron orbits in a magnetic field, de Haas-van Alphen oscillations, etc. In addition the Boltzmann transport equation is also modified with possible ramifications for calculations of transport phenomena. We investigate these issues for a gas of spinless Bloch electrons in an external electric field. We find modifications to the traditional dispersion relation for density fluctuations; in particular we find a shift in the plasma frequency and an anisotropic sound velocity. [1] M.-C. Chang and Q. Niu, Phys. Rev. B 53, 7010 (1996) [Preview Abstract] |
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C1.00201: Correlation functions and anisotropy in the XY model with a magnetic field Wei Zhang*, H.A. Fertig Recent studies have demonstrated that the classical XY model with a magnetic field has three phases: a linearly confined vortex-antivortex phase, a logarithmically (Log) confined phase, and a free vortex phase. We calculate correlation functions in this model by making use of duality transformations and numerical simulations. In all three phases, the order parameter is nonzero and $<\cos(\theta(r_1))\cos(\theta(r_2))> \rightarrow {\rm const.}$, for $|{\bf r}|=|{\bf r}_1-{\bf r}_2|\rightarrow \infty$, indicating true long range order, when the ordering field favors $\theta=0$. A renormalization group analysis suggests that the Log phase may be distinquished from the other two in the correlation function $C(r)=<\sin(\theta({\bf r}_1))\sin(\theta({\bf r}_2))>$, which is short-ranged with a correlation length that depends on the direction of ${\bf r}_1-{\bf r}_2$ with respect to the lattice axes. However, it is shown that a directional anisotropy also enters all the phases through a prefactor. Our numerical simulations support the existence of these anisotropies, but the the anisotropy in the prefactor is generically relatively strong while the correlation length anisotropy is rather weak, making it difficult to distinquish the different phases from these correlation functions.\\ ~*Present address: Department of Physics and Astronomy, Ohio University [Preview Abstract] |
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C1.00202: Emergent Structures in Dissipative Wave-Particle Systems Davit Sivil, Alfred Hubler We study the motion of a particle with mass m on a vibrated string of length L. We assume there is no friction force between the particle and the string. The string is sinusoidally forced at both ends. We find that the particle has attractors located at x=L/2 - $n\pi c/2 \omega$, where $\omega$ is the frequency of the waves on the string, and $n \in {\boldmath Z}$. We also study the same system with friction and multiple driving frequencies. We also compared our results with numerical simulations [Preview Abstract] |
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C1.00203: Scaling in a cellular automaton model of earthquake faults with long-range stress transfer Junchao Xia, Harvey Gould, M. Anghel, William Klein, John Rundle We present simulation data indicating that the scaling of earthquake events in models of faults with long-range stress transfer is composed of at least three distinct regions, corresponding to earthquakes with different underlying physical mechanisms. We discuss the interpretation of these events as fluctuations in the vicinity of a spinodal critical point. In addition to the scaling events, there are larger ``breakout'' events that do not scale. The nature of the stress density profile before an event is investigated and a possible way of predicting breakout events is discussed. [Preview Abstract] |
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C1.00204: Time-Evolution of the Wigner Function in Phase-Space using Finite Differences Shubhabrata Rath, Tomas Materdey Phase-space density holes are vortex-like nonlinear structures that have been observed in the magnetosphere. To study the time evolution of these structures we evolve the Wigner function in time by solving the quantum Vlasov equation using finite-differences. [Preview Abstract] |
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C1.00205: The Structural Database Nikolai Zarkevich, D.D. Johnson A Structural Database can be used as a universal tool for global accumulation and integration of structural and energy data from different methods, people, and places. It allows data mining and data validation by direct comparison of structural data from different sources. Being combined with multi-scale methods (e.g., ThermoToolkit), it can significantly reduce the cost of materials design. We exemplify these and other benefits of the Structural Database, and demonstrate its working prototype, available at http://data.mse.uiuc.edu. This database is a product of multi-disciplinary research involving Physics, Computer Science, and Materials Science and Engineering. [Preview Abstract] |
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C1.00206: Interacting Cracks in an Environmentally Assisted Fracture Artem Levandovsky, Anna Balazs We perform the study of environmentally assisted fracture within the framework of a lattice model. Formation of an ensemble of environmentally assisted microcracks, their coalescence and formation of crack ``avalanches'' lead to a very rich dynamical picture. Under specific condition crack healing can occur due to cohesive forces, which hold material together and tend to pull atoms together even if they are separated by a crack over several lattice units. We investigate the dynamical interplay between crack formation, arrest, healing and re-cracking. The goal here is to provide an understanding of the conditions leading to the phenomena of crack healing that happens along with the crack formation. We study the morphology of crack patterns with the intentions to establish a way to enhance the healing property of a material sample. [Preview Abstract] |
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C1.00207: Structure and Nonlinear dynamical response of Pinned Lattice systems: Application of the Phase Field Crystal Model to Pinned Lattices Mikko Karttunen, Cristian Achim, Ken Elder, Tapio Ala-Nissila, Enzo Granato, S.C. Ying We present analytic and numerical results for the structure and dynamics of a lattice system in 2D in the presence of a pinning potential. We employ a new approach via the Phase Field Crystal (PFC) model which describes phenomena on atomic length and diffusive time scales. It can be used for modeling elastic and plastic deformation, free surfaces and multiple crystal orientations in non-equilibrium processes, and enables access to time scales much longer than conventional atomic methods. The competition between the length scales associated with the intrinsic ordering and the pinning potential leads to commensurate-incommensurate transitions. The dynamical response of the system in the presence of a driving force has also been studied via the time dependent Landau Ginzberg equation. Dynamically induced phases, mobility thresholds and hysteresis behavior have been observed. We will discuss the application of this model to physical problems such as the I-V characteristics of 2-D vortex lattices and sliding friction in interfaces with boundary lubricants. [Preview Abstract] |
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C1.00208: Piconewton force measurement with a scanning tunneling microscope Kai-Felix Braun, Aparana Deshpande, Saw Hla The magnitude of force required to move a single atom across a crystal surface has been measured for the first time. During atomic manipulation experiments with a scanning tunneling microscope the tip heigth curve is recorded. Analysis of shape and period has yielded detailed knowledge about atomic movement while it is shown here that the amplitude of the manipulation curve is a measure of the interaction force between the microscopes tip and the manipulated atom on the surface. This interaction force has been measured for single Ag atoms on a Ag(111) substrate as a function of distance and amounts to several hundred piconewton. [Preview Abstract] |
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C1.00209: Theory of the Effects of Multiscale Surface Roughness and Stiffness on Static Friction Jeffrey Sokoloff It is shown on the basis of simple scaling arguments that an interface between two three dimensional elastic solids, consisting of completely flat disordered surfaces, which interact with interatomic hard core interactions, will be in a weak pinning regime, and hence exhibit negligibly small static friction. It is argued, however, that the presence of roughness on multiple length scales can lead to much larger friction (i.e., static friction coefficients not too much smaller than 1), as is characteristic of most solid surfaces. This approach suggests a possible way of understanding why coatings of materials with high elastic constants are often excellent lubricants. [Preview Abstract] |
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C1.00210: Electrospinning frozen in time Matija Crne, Jung Ok Park, Mohan Srinivasarao Electrospinning is known to produce microfibers with small diameter and/or high surface area. Often times, the high surface area of these fibers is associated with their surface structures, consisting of nanometer-sized holes, droplets, or microcups, whose formation depends on the spinning condition and the type of the solutions used. A mixture of isotactic and syndiotactic PMMA in dimethyl formamide was used in our study to produce helical microfibers by electrospinning at elevated temperatures. Rapid cooling during electrospinning allows for fast physical gelation to take place and trap helical microstructures arising from instabilities due to electrostatic, capillary and viscous forces. The formation of these helices was considered in terms of stability theory for electrically forced jets. [Preview Abstract] |
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C1.00211: Response to disturbance Wen-Xiu Wang, Dan Shen, Yu-Mei Jiang, Ying-Mei Wang, Da-Ren He, Pei-Pei Zhang, Yue He We suggest a new concept named response to disturbance for describing a character of dynamic systems. In relatively simple systems the evolution usually tends to a final state, which may be an equilibrium state, a periodic oscillating state, a quasi-periodic state, or a chaotic state. A disturbance, which always exists in practical systems, sometimes vanishes gradually and indicates the final state is stable, while it sometimes grows up very quickly and indicates the final state is unstable. However, in a relatively complex system disturbance may cause emergence of (may be a very large number of) new structures and very long evolution processes. So, we are trying to suggest a parameter with suitable function form so that the different responses to disturbance in different type of systems can be quantitatively distinguished. We hope that the parameter can be useful for understanding complexity of the practical systems. The details will be presented elsewhere. [Preview Abstract] |
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C1.00212: A model study on dyad act-degree distribution in some collaboration networks Yue-Ping Zhou, Hui Chang, Da-Ren He We (and cooperators) have suggested extending the conception collaboration network to some non-social networks, which have structures as sets of completed graphs [1]. A dyad is composed of two nodes, which are connected by one edge. In social network studies dyad often is considered as the basic units in networks. It should be more important in the extended collaboration networks. We suggest emphasizing the importance of dyad in organizing a network and studying the evolution of the extended collaboration networks by a dyad-act organizing model. The analytic and numeric studies of the model lead to a conclusion that most of the collaboration networks should show a dyad act-degree distribution (how many acts a dyad belongs to) between a power law and an exponential function, which can be described by a shifted power law. We have done an empirical study on dyad act-degree distribution in some collaboration networks. The results show good agreement with this conclusion. The details will be published elsewhere. \newline \newline [1] P-P Zhang, K. Chen et al., to appear on Physica A. [Preview Abstract] |
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C1.00213: Empirical study on dyad act-degree distribution in some collaboration networks Hui Chang, Pei-Pei Zhang, Yue He, Da-Ren He We (and cooperators) suggest studying the evolution of the extended collaboration networks by a dyad-act organizing model. The analytic and numeric studies of the model lead to a conclusion that most of the collaboration networks should show a dyad act-degree distribution (how many acts a dyad belongs to) between a power law and an exponential function, which can be described by a shifted power law. We have done an empirical study on dyad act-degree distribution in some collaboration networks. They are: the train networks in China, the bus network of Beijing, and traditional Chinese medical prescription formulation network. The results show good agreement with this conclusion. We also discuss what dyad act-degree implies in these networks and what are the possible applications of the study. The details will be published elsewhere. [Preview Abstract] |
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C1.00214: Empirical study on assortativity in some collaboration networks Bei-Bei Su, Hui Chang, Da-Ren He We (and cooperators) have suggested extending the conception collaboration network to some non-social networks, which have structures as sets of completed graphs [1]. In this view of point, we may divide practical networks into four groups: a) social collaboration networks, b) social non-collaboration networks, c) non-social collaboration networks, and d) non-social non-collaboration networks. We have done an empirical study on assortativity in some practical networks, which belong to the four groups. The results show that all the networks of a) and b) groups show positive assortativity, all the networks of d) group show negative assortativity. This is in agreement with the conclusion obtained by Newman [2]. However, for some of the networks belonging to group c), we obtained positive assortativity, but obtained negative one for other networks belonging to the same group. The details will be published elsewhere. Now we are trying to find the difference in the structure properties of these networks, which may be responsible for different sign of assortativity. [1] P-P Zhang, K. Chen et al., to appear on Physica A. [2] M. E. J. Newman, PRE 67, 026126 (2003). [Preview Abstract] |
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C1.00215: Dynamical Stochastic Processes of Returns in Financial Markets Kyungsik Kim, Soo Yong Kim , Gyuchang Lim, Junyuan Zhou, Seung-Min Yoon We show how the evolution of probability distribution functions of the returns from the tick data of the Korean treasury bond futures (KTB) and the S$\&$P $500$ stock index can be described by means of the Fokker-Planck equation. We derive the Fokker- Planck equation from the estimated Kramers-Moyal coefficients estimated directly from the empirical data. By analyzing the statistics of the returns, we present the quantitative deterministic and random influences on both financial time series, for which we can give a simple physical interpretation. Finally, we remark that the diffusion coefficient should be significantly considered to make a portfolio. [Preview Abstract] |
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C1.00216: ARTIFICIALLY STRUCTURED MATERIALS POSTER SESSION |
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C1.00217: Diffusion and binding of CO on Pt nanowires Nuri Oncel, Wouter J. van Beek, Jeroen Huijben, Harold J.W. Zandvliet, Bene Poelsema Room temperature scanning tunneling microscopy (STM) has been used to study the diffusion and binding of CO molecules on Pt nanowires. The perfectly straight Pt nanowires (with a cross-section of only one atom) are grown on Ge(001) surfaces. CO molecules bind on a bridge position of the Pt dimers and they are mobile at room temperature. The interaction between adsorbed CO molecules is strongly repulsive, which leads to low saturation coverage and ``restricted'' 1D Brownian motion along the nanowires. [Preview Abstract] |
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C1.00218: Phononic crystals for the mode conversion of elastic waves. Betsabe Manzanares-Martinez, Felipe Ramos-Mendieta We have studied theoretically the transmission of elastic waves in an Epoxy/Sn superlattice with Si and Epoxy as media of incidence and transmission, respectively. We found that this is a good system for conversion of the elastic mode polarization. Within some ranges of frequencies the incident longitudinal waves are converted to transverse waves with efficiency of 85{\%}. In order to understand this effect the polarization states of the sagittal bands need be considered. The modes of sagittal bands can be mainly transverse or mainly longitudinal. We found that as higher the density of transverse modes, higher the conversion. The effect depends strongly on the sound velocity of the medium of incidence - high velocity as possible is required. For calculations we also include absorption effects. [Preview Abstract] |
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C1.00219: X-ray Studies of Ultrathin Wires and Tubes in Nanoscale Confinement. Jonathan M. Logan, Oleg G. Shpyrko, Eric D. Isaacs, Rafael Jaramillo, Yejun Feng, Jeffrey W. Elam, David J. Cookson, Michael J. Pellin Nanoporous Anodized Aluminum Oxide (AAO) membranes are composed of self-assembled, densely packed, co-aligned cylindrical pores. The pore diameter of these membranes can be controllably reduced to as little as $\approx$1 nm through Atomic Layer Deposition (ALD) process. AAO pores have been used as templates for formation of metallic nanotubes and nanowires through ALD or thermal vapor deposition. These embedded structures have been characterized by small- and wide-angle x-ray scattering (SAXS, WAXS). The penetrating ability of x rays provides a non- destructive structural characterization technique for materials confined within AAO matrix, on both atomic (WAXS) and nanometer (SAXS) length scales. [Preview Abstract] |
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C1.00220: Electric Field Effects on Motion of a Charged Particle Through a Saddle Potential in a Magnetic Field V. Fessatidis, K. Sabeeh, N.J.M. Horing, M.L. Glasser Electron transmission through a quantum point contact (QPC) in the presence of both electric and magnetic fields is examined. The QPC is modeled as a saddle potential. The first part of the paper is devoted to deriving the relevant Green's function including the effects of arbitrarily time dependent electric and constant magnetic fields. The derivation is carried out using Schwinger's operator equation of motion approach. In the second part of the paper we apply it to determine transmission of the electron guiding center through the QPC in constant electric and magnetic fields. [Preview Abstract] |
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C1.00221: Hofstadter's butterfly with Rashba spin-orbit coupling Sukey Sosa y Silva Salgado, Fernando Rojas We study the energy spectrum of an electron in a two-dimensional periodic lattice in a perpendicular magnetic field in the tight-binding approximation including the Rashba spin-orbit coupling. We have investigated how the fractal spectrum known as Hofstadter’s butterfly is modified if one includes the spin-orbit coupling. We find a set of decoupled Harper-like equations for each spinor by restricting the Rashba coupling along one direction. We solve the set of equations and evaluate the energy spectrum for each spinor. In order to characterize the energy spectrum we calculate its fractal dimension, in particular, we analyze the capacity and the correlation dimension of each spin-subbands buttlerfly as a function of the spin-orbit coupling parameter and magnetic field. [Preview Abstract] |
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C1.00222: Ground state energy of an electron in a GaAs pillbox immersed in a GaAlAs substrate Gerardo Jorge Vazquez-Fonseca, Marcelo del Castillo-Mussot, Sandra Milena Ramos-Arteaga, Nelson Porras-Montenegro In this work we have studied the ground state energy behavior for a GaAs pillbox immersed in a system of GaAlAs as a function the thickness of the barrier potential when the length of the pillbox is fixed, as function the length of the pillbox when the thickness of the barriers remained constant, and as a function of the pillbox position in the host of GaAlAs. Also, we studied the behavior of the energy of the ground state in this system for different Al concentrations. It is important to stress that for small lengths of the pillbox the energy of the ground state as function de relative position to the barrier potential presents a similar behavior as the binding energy of a hydrogenic impurity in quantum wells, quantum wires and quantum dots. We also found that there are critical values of the pillbox length for which there are no bound states. [Preview Abstract] |
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C1.00223: Photoconductivity for an Array of Nanowires and Dots Paula Fekete, Godfrey Gumbs We present a model calculation for the photoconductivity of a two-dimensional electron gas in an ambient perpendicular magnetic field. An electrostatic modulation which produces quantum wires or dots is also applied. The system is then subjected to a weak radiation field. The Landau eigenstates in the periodically modulated system are first obtained numerically and then used in the Kubo formula to obtain the conductivity. We analyze the frequency-dependent transport coefficients for their dependence on frequency and strength of modulation. The calculation is restricted to the low-frequency regime where the system is assumed to be in or close to equilibrium. [Preview Abstract] |
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C1.00224: Dissipation Stabilized Superconductivity in Quantum Wires Henry Fu, Alexander Seidel, John Clarke, Dung-Hai Lee We present a theory of a superconducting wire dissipatively coupled to an environment. We show that due to the finite extent of the wire, in the absence of dissipation quantum phase slips always destroy superconductivity, even at zero temperature. Dissipation stabilizes the superconducting phase. We apply this theory to understand the ``anti-proximity effect'' recently seen by Tian et. al. [Phys. Rev. Lett. 95, 076802 (2005)] in Zinc nanowires. [Preview Abstract] |
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C1.00225: Readout of single spins via Fano resonances in quantum point contacts Lev Mourokh, Anatoly Smirnov, Vadim Puller, Jonathan Bird We examine the feasibility of performing single-spin readout in a small quantum dot (SQD), using a quantum point contact (QPC) that is coupled to it by a larger dot with a quasi-continuous spectrum. When the Fermi energy in the QPC is approximately equal to one of the discrete levels of the SQD, a Fano resonance is observed in its conductance. We propose a procedure that uses such Fano peaks to determine the spin projection of a single electron in the SQD, in the presence of an external magnetic field that causes Zeeman splitting of its levels. We also show that this structure can exhibit Rabi oscillations when subject to microwave irradiation. [Preview Abstract] |
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C1.00226: Fabrication of 3D-Ordered Nanoporous Gold for Chemical Sensors David Hung, Neepa Shah, Zhu Liu, Yaowu Hao, Peter Searson 3D ordered nanoporous materials provide high surface-to-volume ratio and controlled nano-scale periodic architecture, making them attractive for applications such as energy storage, catalysis, separations, chemical sensing, and tissue engineering. 3D-ordered nanoporous gold structures were fabricated by electrodeposition of gold into colloidal crystal templates formed by self-assembly. The structures are replicas of the colloidal crystal and have pore sizes and feature sizes that are dependent on the particle size. When the dimensions of a conductor are sufficiently small the resistance is dominated by surface scattering. A prototype chemical sensor was created exploiting this architecture. Molecules with sulfhydryl groups adsorb strongly to gold surfaces and can be monitored by the change in resistance. A resistance change of approximately 2 percent was achieved and a chemical sensor based on surface scattering has been demonstrated. [Preview Abstract] |
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C1.00227: Electronic and Magnetic Properties of Novel III-V-(M) Superlattices J. Rufinus We present the results of computational works on the electronic and magnetic properties of ``novel'' III-V-(M) (where M is transition metals) superlattice. The calculations were performed using ABINIT and Gaussian 03 codes. The objective of this work is to determine the possibility of ferromagnetism in this type of superlattice. [Preview Abstract] |
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C1.00228: Intersubband magnetophonon resonance in InAs/AlSb quantum cascade structures. Georgy Fedorov, Aaron Wade, Dmitry Smirnov, Roland Tessier, Alexei Baranov Application of an external magnetic field offers a sensitive experimental tool to study and control basic processes which determine the performance of quantum cascade lasers -- quantum confinement and intersubband relaxation. A strong magnetic field applied parallel to the confinement direction resonantly modulates the lifetime of the upper state of the laser transition, which is controlled by electron-optical phonon scattering. This effect of the intersubband magnetophonon resonance (ISMPR) allows for the investigation of the electronic structure and electron scattering mechanisms. We report on the observation of ISMPR in quantum cascade lasers based on InAs/AlSb heterostructures. Our experiments have been done under a magnetic field up to 33 T. We observe pronounced quantum oscillations in both the magnetoresistance and the intensity of the intersubband laser emission. Analysis of the obtained data is provided. [Preview Abstract] |
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C1.00229: Development of Low-Temperature Scanning Capacitance Microscopy for Measurement of Single Quantum Dots Guanglei Cheng, Jeremy Levy, Gilberto Medeiros-Ribeiro Self-assembled single quantum dots are widely considered to be leading candidates for spin-based quantum bits. The characterization of such systems requires local information about both charge and spin degrees of freedom as a function of temperature and magnetic field. We describe an extension of a working low-temperature AFM/optical microscope to enable scanning capacitance measurements of quantum dots. Our system relies on the sensitivity of a microwave resonator to perturbations from the scanning probe (similar to RCA's CED technology), using a quartz tuning fork with an etched tungsten tip. The expected sensitivity of the instrument (10$^{-21}$ F) is much below the capacitance of a single self-assembled quantum dot (10$^{-18}$ F). To measure the capacitance, we first use the AFM to locate a single quantum dot, and then collect local C-V information using the measured frequency shift of the resonator. [Preview Abstract] |
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C1.00230: ABSTRACT WITHDRAWN |
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C1.00231: Wigner Function for an Impurity in a Parabolic Quantum Dot Gary Snyder, Majd Mayassi, Praveen Nittala, Tomas Materdey High sensitivity of quantum dots with impurities can be linked with phase space high sensitivity to initial conditions. We present the Wigner function for an impurity in a parabolic quantum dot obtained from a variational wavefunction. [Preview Abstract] |
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C1.00232: Optical and phonon spectra of wurtzite ZnO quantum dots and nanocrystals Vladimir A. Fonoberov, Khan A. Alim, Alexander A. Balandin ZnO nanostructures have recently attracted attention due to the proposed optoelectronic and spintronic applications. Envisioned applications require accurate knowledge of exciton states and optical phonons. We report results of the investigation of wurtzite ZnO nanostructures with diameters from 2 nm to 20 nm (quantum dots to nanocrystals). The calculated size dependence of the exciton states and UV photoluminescence spectra of ZnO nanostructures is in agreement with the experimental data [1]. In addition, both interface and confined polar optical phonon modes in ZnO quantum dots and nanocrystals have been calculated and identified in the resonant and non-resonant Raman spectra [2]. It was found that the phonon confinement resulted in phonon frequency shifts of few cm$^{-1}$ in the non-resonant Raman spectra. We also show that UV laser excitation in resonant-Raman spectroscopy leads to large red shifts of phonon peaks (up to 14 cm$^{-1})$ due to heating. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center. [1] V.A. Fonoberov and A.A. Balandin, Appl. Phys. Lett. 85, 5971 (2004); [2] V.A. Fonoberov and A.A. Balandin, Phys. Rev. B 70, 233205 (2004); K.A. Alim, V.A. Fonoberov, and A.A. Balandin, Appl. Phys. Lett. 86, 053103 (2004). [Preview Abstract] |
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C1.00233: A Study Of CdSe/ZnS Core-Shell Quantum Dots For Use in Luminescent Solar Concentrators Meredith Hyldahl, Sheldon Bailey, Paul Fontecchio, Bruce Wittmershaus A Luminescent Solar Concentrator (LSC) is a translucent plate that uses embedded fluorescent materials to absorb sunlight. The fluorescence that is produced is then transferred to the edges of the plate via total internal reflection where it is absorbed by photovoltaic cells. We compare a LSC made of CdSe/ZnS core-shell quantum dots (QD) (Evident Technologies) embedded in a transparent epoxy to a LSC made with the fluorescent organic dye Lumogen Red (BASF) cast in a thin polymer film. Fluorescence and absorption spectra and edge light output measurements are reported in this study. The Lumogen Red LSC outperforms the QD LSC suggesting a lower fluorescence quantum yield for the QDs. QDs are also easily oxidized, whereas the Lumogen Red dye is relatively more stable in the presence of oxygen. The merits of QDs as a fluorescent material for a LSC are discussed in terms of light output, photostability, and cost. [Preview Abstract] |
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C1.00234: Effects of magnetic and electric fields on the excitonic properties of quantum rings Zdenka Barticevic, M\'{o}nica Pacheco, Jorge Simonin, Cesar Proetto We have studied the effects of an external electric field on the excitonic and optical spectra of a semiconductor quantum ring threaded by a magnetic flux. We have make a detailed analysis of the ground-state properties of radially polarized excitons and its dependence with magnetic fields applied perpendicular to the ring plane and electric fields parallel to the ring plane. In the absence of the electric field, the total angular momentum of the polarized exciton remains a good quantum number, even in the interacting regime, as a consequence of the Coulomb interaction only depends on the relative coordinate and the azimuthal rotational symmetry of the structured rings. The electric field breaks the azimuthal symmetry and mixes the eigenfunctions with differents angular momentum. For the extended regimen we have found that the electric field destroys the oscillations of the ground-state energy as a function of the magnetic field. The low-lying energy levels are almost independent of the magnetic field up to a region in energy where periodic Aharonov-Bohm-type oscillations appear. [Preview Abstract] |
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C1.00235: Strong Blue Photoemission from Au/ZnO Nanocomposite Material Akira Ueda, Esosa Ejomo, Roberto Aga, Warren Collins, Richard Mu Several layers of Au (5 nm) and ZnO (20 nm) were alternatively deposited on Si and SiO$_{2}$ substrates with an electron beam evaporator. With post-annealing of the samples in air, the samples were characterized with XRD, RBS, SEM, AFM, and PL. The samples annealed at higher temperatures (\underline {$>$}700$^{o}$C) exhibit the growth of ZnO nanocrystals in the system. Along with these observations, the samples annealed at higher temperatures emit strong blue photons due to an electric field. [Preview Abstract] |
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C1.00236: Faraday rotation in one-dimensional magnetic photonic crystals in electric field I.L. Lyubchanskii, N.N. Dadoenkova, M.I. Lyubchanskii, E.A. Shapovalov, A.E. Zabolotin, Y.P. Lee, Th. Rasing In the last few years, magnetic photonic crystals (MPCs) or magnetic photonic bandgap materials, are the objects of intensive investigations because of promising application in photonics [1]. A large enhancement of the Faraday rotation (FR) in one-dimensional (1D) MPC was reported [2,3]. In this report, the influence of external electric field on the FR in 1D MPC with magnetic and non-magnetic defect layers is theoretically studied. For the theoretical description of FR we introduce electrical polarization, which depends on magnetization and external electric field. Numerical calculations of the dependence of FR on the strength and the direction of electric field is done for the 1D MPC based on yttrium-iron garnet. [1] I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, and Th. Rasing, J. Phys. D: Appl. Phys. 36, R277 (2003). [2] M. Inoue and T. Fujii, J. Appl. Phys. 81, 5659 (1997). [3] M. Steel, M. Levy, and R. M. Osgood, J. Lightwave Technol. 18, 1298 (2000). [Preview Abstract] |
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C1.00237: Optical and magneto-optical properties of 1-D dielectric and magnetic photonic crystals. M.D. Huang, Y.H. Lu, P.J. Kim, S.Y. Park, Y.P. Lee The optical properties of one-dimensional (1-D) photonic crystals (PCs) and magnetic PCs (MPCs), composed of dielectric TiO$_{2}$ and Al$_{2}$O$_{3}$ as well as magnetic Bi:YIG layers deposited on a glass substrate, are investigated in this work. The structure of dielectric 1-D PCs was optimized and a narrow omni -- photonic bandgap (PBG) is found away from the designed wavelength. When a Bi:YIG layer with an optical thickness of quarter wavelength is inserted, no defect mode is found within the PBG despite the structural defect. However, when the thickness becomes half wavelength, a defect mode can be obtained at the designed wavelength, revealing the localization of light. More magnetic defect layers induce correspondingly more defect modes within the PBG. Large Faraday rotation angles, indicating strong magneto-optical (MO) effects, are obtained at the defect modes in the MPCs. A considerable amount of coupled light, whose polarization is perpendicular to that of incident light, confirms the enhanced MO effects at the defect modes. [Preview Abstract] |
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C1.00238: Band gap of a 3D dyed polystyrene photonic crystal from optical absorption. Na Young Ha, Jeong Weon Wu Three-dimensional (3D) photonic crystals (PCs), fabricated from colloidal spheres doped with organic dye and whose optical absorption overlaps with the photonic band gap (PBG), have been studied to determine the relation between the PBG widening and the increased contrast in refractive indices. In this work, we report on the identification of the role of the optical absorption of the dye in determining the PBG shape of a 3D dyed PC, which is fabricated from colloidal dyed-polystyrene spheres consisting of an inner core and an outer shell. In analyzing the optical reflection spectra of 3D dyed PCs, an analytical electromagnetic wave scattering theory was rigorously employed, with the dispersive and absorptive optical responses of the composite dyes fully taken into account. It was subsequently found that the characteristic PBG shape of the 3D dyed PC, when measured in the reflection spectra, results from two superimposed contributions with distinct origins, i.e., a Bragg reflection and a high reflection associated with the strong dye absorption. [Preview Abstract] |
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C1.00239: Faraday effect of 1-D magnetic photonic crystals for normal and parallel incidence to the periodic direction Y. H. Lu, M. D. Huang, S. Y. Park, P. J. Kim, Y. P. Lee, J. Y. Rhee We calculated the Faraday rotation of one-dimensional (1-D) magnetic photonic crystals (MPCs), which are based on the dielectric Ti$_{2}$O$_{3}$ and Al$_{2}$O$_{3}$, and the magnetic Bi:YIG, by employing 4 x 4 transfer-matrix method for the general case that the linearly polarized incident beam is parallel to their periodic direction, as mostly studied for the 1-D MPCs. Furthermore, even for a special case of normal incidence, the calculation of Faraday rotation was also carried out for such discontinuous thin films with a 1-D array structure and the existence of rotation was proved, which had been scarcely studied yet. The magneto-optical Faraday effects obtained for these two cases are compared and discussed in detail. [Preview Abstract] |
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C1.00240: Modeling and fabrication of photonic bandgap waveguiding structures M.Y. Tekeste, P.R. Rice, J.M. Yarrison-Rice Novel photonic devices based on the idea of photonic bandgap (PBG) crystals are poised to make contributions in modern optoelectronic and telecommunication applications. These nanophotonic devices have the ability to guide light with very low loss even around tight corners. Several PBG waveguide structures are modeled using using the finite difference time domain technique in EMlab software. The resulting electric field distributions allow us to study single line defect waveguiding and a wavelength demultiplexer structure for single mode propagation, the depth of light leakage into the lattice, and transmission coefficients. These models inform the experimental fabrication process where a 2D triangular lattice is etched into the silicon nitride on silicon dioxide planar wafer which has been patterned via e-beam lithography. SEM micrographs record the various fabrication steps. Optical characterization of the structures will include bulk transmission measurements, as well as near field scanning microscopy. [Preview Abstract] |
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C1.00241: Fano Resonance in Photonic Crystals and Quantum Mechanics Solomon Duki, Francesc Ferrer, H. Mathur We study the resonant transmission through a photonic crystal channel dope device. The frequency dependence of the resonant transmission is shown to have an asymmetric Fano line shape. In contrast to previous work[1] we find the symmetric Lorentzian line shape results only under special conditions of high device symmetry. We also study quantum systems in which the resonant scattering cross section has an asymmetric Fano line shape as a function of energy. Surprisingly the associated long-lived quasi-bound state under goes simple exponential decay, just as it would in the symmetric Lorentzian case. [Preview Abstract] |
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C1.00242: Raman Spectroscopy from Optical Trapped Nano Coated Microsphere Complexes Emanuela Ene, Chuck Blackledge, James Wicksted The Raman measurements from optically trapped gold nanowires and from nanoparticles coated on microspheres, under various visible laser excitation wavelengths, are being studied. Changes in the Raman spectra for the trapped coated microspheres when they were positioned at different distances from an immersed photonic crystal (PC) are being investigated. We are also developing a method which has the potential of detecting certain molecules present in biological environments. [Preview Abstract] |
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C1.00243: ABSTRACT WITHDRAWN |
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C1.00244: Inelastic cotunneling current and shot noise of an interacting quantum dot with ferromagnetic correlations Bing Dong, Norman J. M. Horing, V. Fessatidis We explore inelastic cotunneling through a strongly Coulomb-blockaded quantum dot attached to two ferromagnetic leads in the weak coupling limit using a Langevin equation approach.$^1$ We first develop a Bloch-type equation to describe the cotunneling-induced spin relaxation dynamics, and then derive explicit analytical expressions for the local magnetization, current, and its fluctuations. On this basis, we predict a novel zero-bias anomaly of the differential conductance in the absence of a magnetic field for the anti-parallel configuration, and asymmetric peak splitting in a magnetic field, which are ascribed to rapid spin-reversal due to underlying spin-flip cotunneling.$^2$\\ $^1$ B. Dong, N. J. M. Horing, and H. L. Cui, Phys. Rev. B {\bf 72}, 165326 (2005).\\ $^2$ B. Dong, X. L. Lei, and N. J. M. Horing, cond-mat/0509098. [Preview Abstract] |
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C1.00245: Electron transport properties in InAs ballistic devices Masatoshi Koyama, Masataka Inoue, Masashi Furukawa, Hiroshi Takahashi, Toshihiko Maemoto, Shigehiko Sasa A ballistic rectifier is one of the applications using ballistic electron transport properties, and has been fabricated by using high quality compound semiconductor heterostructures. We have observed a rectification for the first time in InAs triangular anti-dot structures at 77K and room temperature [1]. InAs/AlGaSb heterostructures provide relatively long mean free path for ballistic electron transport because of its high carrier density (1.0 * 10$^{12}$ cm$^{-2}$ at 77K) and high electron mobility (200,000 cm$^{2}$/Vs at 77K). In the present report, we will focus on nonlinear electron transport properties in InAs asymmetric anti-dot structures as well as ballistic rectification effects at higher temperatures. In addition, the observed magnetotransport properties in the InAs ballistic rectifiers will be also presented at the conference. [1] M. Koyama et al., presented at the 14$^{th}$ Int. Conf. on Nonequilibrium Carrier Dynamics in Semiconductors, 2005. [Preview Abstract] |
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C1.00246: Electrode fabrication and attachment of organometallic molecules for conductivity measurements S. Rajagopal, N. Smith, J.M. Yarrison-Rice, C. Urig, T. Scott, S. Zou, H. Zhou The primary goal of this research is to understand the bonding and electronic structure within this class of compounds and the influence of a gated electric field on their conductivity. We report an approach for connecting a single molecule containing di-metal units to electrodes with nanometer gaps. We have succesfully fabricated pairs of terminal electrodes with intial gaps of $\sim $75 nm which we then close using electrodepostion and re-open with electromigration to nanometer gaps. The results of the time resolved voltage curve during the electrodepostion process show that most of electrodes have a very short closing time. We have also fabricated lateral three terminal devices for studying the influence of a gated third electrode. The present results show that a gap to gate distance of less than 50nm is acheivable. Our next step is to deposit molecules on the thin gap, and to measure the electrical conductivity when a single molecule bridges the gap and conducts current. [Preview Abstract] |
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C1.00247: Correlating Internal Chemical and Physical Structure with Electrical Data for Nanoscale Molecular-Electronic Devices Jason J. Blackstock, William F. Stickle, Carrie L. Donley, Duncan R. Stewart, R. Stanley Williams The critical limitation for most nanoscale molecular-electronic devices is the lack of physical/chemical characterization accompanying electrical data. Present most device geometries and fabrication processes are incompatible with conventional photon and electron spectroscopies and scanning probe microscopies -- critical layers and interfaces are frequently inaccessibly buried inside the as-built device structures. We present the fabrication of a new stencil-based nanopore device geometry, along with techniques for studying the in-situ characterization of the as-build internal properties of these devices. These methods were developed in combination to allow the cleaving of completed device stacks at internal inorganic/organic interfaces in a UHV environment. This cleaving process exposes the uncontaminated and unaltered internal nanoscale chemical and physical structure in UHV for examination with a range of conventional tools. We specifically present on XPS, IR and STM data from several metal/organic-monolayer/metal device stacks of interest, and conclude by correlating temperature-dependant and IETS electrical data on nanoscale devices with the physical/chemical characterization. [Preview Abstract] |
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C1.00248: Thermoelectric Properties of a Nanocontact Keivan Esfarjani, Mona Zebarjadi Thermoelectric properties of a nanocontact made of two capped single wall carbon nanotubes (SWCNT) are calculated within the tight-binding approximation and by using Green's function method. It is found that doped semiconducting nanotubes can have high Seebeck coefficients. This in turn leads to very high figures of merit(ZT) for p-doped tubes which turn out to have also a large electrical to thermal conductivity ratio. Transport in the nanocontact device is dominated by quantum interference effects, and thus it can be tuned by doping (charge transfer and/or impurity potential) or application of a (nano-)gate voltage, or a magnetic field. Another reason for high ZT in this device is the absence of phonon transport as there is barely a contact between the two sides. [Preview Abstract] |
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C1.00249: Microscopic Investigations of Phonon Thermal Conductivity in SiGe Superlattices with Rough Interfaces Shang-Fen Ren, Wei Cheng, Gang Chen Phonon thermal conductivity in semiconductor superlattices (SLs) has attracted a great research attention in recent years due to the potential applications of SLs in thermoelectric devices and other applications [1]. By using a microscopic model developed to investigate phonon properties in semiconductor nanostructures [2], we have calculated thermal conductivities of SiGe SLs with rough interfaces in both the growth and in-plane directions. The results are compared with SLs with perfect smooth interfaces as well as bulk random alloys. Our results show that thermal conductivities of SLs with rough interfaces are much lower than SLs with the same thickness but smooth interfaces in both directions. In the in-plane direction, the thermal conductivities of SLs with rough interfaces are about the same as random alloy but lower than random alloy in the growth direction. Our results indicate that the interface roughness is a true mechanism of thermal conductivity reduction in SLs.\newline References: [1] Partially Coherent Phonon Heat Conduction in Superlattices, B. Yang and G. Chen, Phys. Rev. B 67, 195311 (2003). [2] A Microscopic Investigation of Phonon Modes in SiGe Alloy Nanocrystals, S. F. Ren, W. Cheng, and P. Y. Yu, Phys. Rev. B 69, 235327 (2004). [Preview Abstract] |
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C1.00250: Semiconductor Nanocomposites for Direct Energy Conversion Applications Jeff Urban, Dmitri Talapin, Elena Shevchenko, Chris Murray, Mercouri Kanatzidis Novel materials for thermoelectric and photovoltaic applications may be rationally designed by assembling quantum dots with distinct thermal, optical, and electronic characteristics into nanocomposite superlattices and glassy thin films. Here we present the synthesis and initial thermoelectric characterization of semiconductor nanocomposites composed of lead chalcogenide (PbX = PbS, PbSe, PbTe) nanocrystals. Monodisperse nanocrystals of all PbX materials varying in size from $\sim $4-10nm are synthesized, and their structural, optical, and electronic properties are presented. Well-ordered nanocomposites composed of two different types of PbX nanocrystals are synthesized and their basic thermoelectric characteristics are studied. The strategy of using nanocrystal composites for thermoelectric applications will, in principle, provide an opportunity to independently tune the desired electronic and phonon scattering characteristics of these materials. [Preview Abstract] |
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C1.00251: Crossover in Thermal Transport Mechanism in Nanocrystalline Silicon Arun Bodapati, Pawel Keblinski, Patrick Schelling, Simon Phillpot Using vibrational mode analysis of model structures we demonstrate that lattice vibrations in small grain ($<$ 3 nm) structurally inhomogeneous nanocrystalline silicon are almost identical to those of homogeneous amorphous structures. In particular, the majority of the vibrations are delocalized and unpolarized. As a consequence the principal thermal conductivity mechanism in such nanocrystalline materials is essentially the same as in the amorphous material. With increasing grain size the ability of vibrations to ``homogenize'' over the nanocrystalline structure is gradually lost and the phonon spectra and polarization become progressively more like that of a crystalline material; this is reflected in a crossover in the mechanism of thermal transport. Interestingly, a few of the vibrational modes are localized either on the grain boundary and the grain interiors. [Preview Abstract] |
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C1.00252: Switching Light through Arrays of Sub-wavelength Holes in Vanadium Dioxide E. U. Donev, J. Y. Suh, R. Lopez, R. F. Haglund, L. C. Feldman Transmission of near- and far-field light through periodic arrays of sub-wavelength holes is a subject of intense interest. We present the first studies on perforated vanadium dioxide (VO$_{2})$ thin films that can modulate the transmission of near-infrared light by virtue of their semiconductor-to-metal transition. Modulation arises because of the marked difference in dielectric contrast between the holes and the surrounding material in the two phases of VO$_{2}$. In perforated structures consisting of a silver (or gold) layer atop a VO$_{2}$ layer, the modulation effect constitutes a novel kind of dynamical control of the enhanced optical transmission through sub-wavelength holes in opaque metal films. Surprisingly, such double-layer structures exhibit a reversal in the optical switching of VO$_{2}$, as the near-infrared transmission during the metallic phase exceeds its semiconducting-phase counterpart---opposite of the transmission behavior of plain VO$_{2}$ films. We explain this by accounting for the loss of transmitted intensity due to leaky evanescent waves inside the holes and scattering at the entrance and exit apertures. [Preview Abstract] |
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C1.00253: Integrated Semiconductor-Ferroelectric Nanostructures S. S. Nonnenmann, R. S. Joseph, L. Cao, J. E. Spanier The integration of semiconductor and ferroelectric nanostructured materials provides new opportunities for investigating ferroelectric stability in nanostructures and for the design of multifunctional nanoscale devices. We present progress in the development of new synthetic strategies for the preparation of nanostructures consisting of semiconducting and ferroelectric components. We report on characterizations of the structural, electronic and functional properties of these hybrid nanostructures and devices via electron microscopy, Raman scattering spectroscopy, scanning probe microscopy, and electronic transport measurements. [Preview Abstract] |
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C1.00254: Magnetic resonance study of nanoparticles systems Natalia Noginova, Feng Chen, Tracee Harris, Emmanuel Giannelis, Athanasios Bourlinos, Vadim Atsarkin Magnetic nanoparticles of gamma-Fe$_{2}$O$_{3}$ coated by organic molecules and suspended in liquid and solid matrices, as well as non-diluted magnetic fluid have been studied by ESR in the dependence on temperature and relative concentration. The ESR spectrum demonstrates an interesting double feature shape, with narrow peak at g=2 growing in intensity with increase in temperature. Angular dependence of the ESR signal in field cooled samples unambigously points to the dominating uniaxial magnetic anisotropy of the nanoparticles, suggesting a strong surface effect. The interpretation based on the FMR equations with account made for thermal fluctuations of the magnetic moment is compared with ``paramagnetic'' model suggesting a discrete energy spectrum of the lowest high-spin multiplet. Consideration of the superparamagnetic nanoparticles as intermediate between paramagnetic and ferromagnetic entities allows us to explain most of the obtained experimental results and estimate parameters of the magnetization, particle interactions and magnetization dynamics. [Preview Abstract] |
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C1.00255: Interface effects in modulation-doped manganite superlattices Maria E. Gomez, G. Campillo, P. Prieto, A. Hoffmann, A. Berger, J. Guimpel, N. Haberkorn, A. Condo Epitaxial superlattices of antiferromagnetic La$_{1/3}$Ca$_{2/3}$MnO$_{3}$ and ferromagnetic La$_{2/3}$Ca$_{1/3}$MnO$_{3}$ were grown using a high-pressure sputtering technique. Structural analysis was performed by simulation of X-ray diffraction data using the SUPREX program and Transmission Electron Microscopy. Both techniques confirmed interfacial roughness in the range of one unit cell. Magnetization measurements showed that magnetization depth profile is incommensurate with the doping profile, such that the ferromagnetic order extends into the antiferromagnetically doped region beyond the chemical doping interface. Thermal demagnetization in the low temperature range obtained from the temperature dependence of the saturation magnetization shows an $\alpha $=5/2 power law dependence, independent of the ferromagnetic layer thickness. The $T^{5/2 }$term is associated with long-wave length spin waves, and corresponds to the anharmonic second-order expansion of the magnetization. This work was supported by COLCIENCIAS contract 043-2005, and U.S. DOE-BES under contract W-31-109-ENG-38. [Preview Abstract] |
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C1.00256: Isolated hollow nano-spheres of Co on the surface Toshifumi Terui, Takashi Nagase, Hiroyuki Hasegawa, Shinro Mashiko, Yasuharu Koduka, Ye Quan-Lin, Hirofumi Yoshikawa, Mototaka Onishi, Kunio Awaga In magnetic materials of sub-micron and the nano-meter size, peculiar magnetic structures and characteristics are expected. The hollow sphere of Co is an interesting material in such nano magnetic materials because of the unique structure. The diameter and the thickness of shell of the hollow sphere of Co can be accurately controlled between 100-500nm and 40nm respectively. It is necessary to examine the physical properties about isolated hollow sphere of Co to apply this material as nano-spin material. Therefore, we combined the top down and the bottom up technique to isolate the sample on the surface. For example, the nano-gap electrode and patterns were fabricated by EB lithography and FIB, and manipulation and the conduction measurement were performed by SEM with probe. [Preview Abstract] |
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C1.00257: INSTRUMENTATION AND MEASUREMENTS POSTER SESSION |
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C1.00258: Low-Cost Cavity Ring-Down System For Measurement Of High Reflectivity Semiconductor Mirrors Daniel Tremblay, Susan Lehman A cavity ring-down system consisting of a half-symmetric optical resonator with a swept cavity design has been constructed from off-the-shelf components in order to investigate ultra-high reflectivity distributed Bragg reflectors (DBRs). Cavity ring-down is a sensitive technique often used for spectroscopy that measures the buildup and decay of laser light within a high finesse optical cavity. Once light is resonant in the cavity, the resonance is interrupted so that the light within the cavity decays. From this measured decay time, the amount of light lost per pass to mirror losses or absorptive and scattering losses is determined. As a measurement of time rather than absolute intensity, cavity ring-down has the advantage of not requiring calibration since it is unaffected by drifts in laser intensity or detector sensitivity. This low-cost ring-down system was designed with one planar mirror and one concave mirror to allow simple conversion to DBR measurement. The concave mirror is mounted on a piezoelectric modulator to enable rapid sweeping of the cavity length, eliminating the need for an acousto-optic modulator to shutter the light off, but increasing the analysis complexity due to Doppler shifting of the light by the moving mirror. A cw-laser tunable over 30 nm is used to probe the cavity and DBR system. [Preview Abstract] |
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C1.00259: Potentiometric Sensing of the Organic Molecules Yantian Wang, Vijay Jain, Harriman Lee, Kalle Levon, Miriam Rafailovich, Jonathan Sokolov A prototype detector was constructed for the detection of complex biomolecules, such as viruses and complete chromosomes. The technology is based on ref. [1], where the technique was demonstrated for small molecules. A monolayer of 11-mercapto-1-undocanol (thiol) is co-absorbed with the organic molecules on a gold plated electrode. The thiolated molecules self assemble into a highly organized crystalline film chemically anchored to the surface. The bio-molecules which are not attached and can then be removed by washing in water, leaving behind templated regions, or cavities in the monolayer with specific size and shape. The electrochemical response between the modified electrode and the Ag/AgCl reference electrode was measured by the potentiometer. When the electrode was exposed to the solution containing the template molecules, in a concentration as low as $10^{-6}M$, a sharp potential response was observed, while very slight response was observed when exposed to other kind of molecules. This was attributed to the selective absorption of the molecules onto the electrode. Reference: [1]. Zhou Y., Yu B., Shiu E., Levon K., \textit{Anal. Chem.} 2004, 76, 2689. [Preview Abstract] |
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C1.00260: Magnetic Domain Wall Motion as a Basis for a New Type of Sensor. Seong-Jae Lee, Yevgen Melikhov, Choon-Mahn Park, Hans Hauser, David Jiles It has been found that the periodic motion of a magnetic domain wall under the action of a magnetic field can be used as a basis for linear and angular displacement sensor. The domain wall between two opposite domains is created by the field from two opposite permanent magnets and the periodic motion is excited by an external ac current. When the up-domain covers both the incident and reflected laser beam paths, the Faraday rotation reaches a positive maximum and when the down-domain covers both beams, the Faraday rotation reaches a negative maximum. If when the domain wall is between the incident and reflected laser beams, the Faraday rotation cancels and a reference or nominal ``zero'' rotation occurs. The sensor system consists of a laser, magneto-optic film, magnets, and a detector. By observation of the pattern of detected light intensity as a result of periodic movements of magnetic domain wall, we can extract information about linear or angular displacement a surface with resolution down to 3 $\mu $m or 0.01 deg, respectively. [Preview Abstract] |
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C1.00261: The challenge of characterizing an inefficient antenna field for health protection purposes Marjorie Lundquist Growing evidence that the electromagnetic field around electrical wires is harmful to human health prompted a 1990s National Academy of Sciences study of power-frequency (50-60 Hz) fields; results for power-frequency fields were negative but data suggested that fields from \it transients \rm may be hazardous.$^1$ Transients represent high frequencies that can reach into the radiofrequency (RF) range. What instrument can be used to measure an RF field around electric wires carrying RF current? Such an RF field is that of an \it inefficient antenna\rm , which lacks the pure far-field region characteristic of an \it efficient antenna field \rm for which standard RF measuring instruments are calibrated, making it impossible to obtain a properly calibrated measurement with such instruments. The \it magnetic induction current \rm d\bf B\rm/d$t$ is explored as an alternative way to characterize the \it inefficient antenna RF field \rm sheathing electric wires carrying RF due to \it poor power quality \rm (\it e.g.\rm , switching transients) or to utility use of \it power line carrier\rm $^2$ or of FCC-approved \it broadband on power lines\rm . $^1$National Research Council, \bf Possible Health Effects of Exposure to Residential Electric and Magnetic Fields\rm , Washington, DC: National Academy Press, 1997. $^2$M. Vignati \& L. Giuliani, Environ. Health Perspect. \bf 105\rm (Suppl 6):1565-1568(1997). [Preview Abstract] |
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C1.00262: Current Status of LANSCE Single Crystal Diffractometer - SCD Alice I. Acatrinei, Luke L. Daemen, Monika A. Hartl, Jacob Urquidi The Single Crystal Diffractometer (SCD) at LANSCE, Los Alamos National Laboratory, represents a powerful tool for many crystallographic and magnetic structure determinations. The instrument is located at the Lujan Neutron Scattering Center and utilizes the time-of-flight (TOF) Laue technique for neutron scattering data collection. This technique, combined with a 25 cm $\times $ 25 cm multi-wire 3He position-sensitive detector and the possibility of two axis of rotation for sample orientation yield to an 80{\%} sphere of coverage in reciprocal space. The redesign and status of the Single Crystal Diffractometer at LANSCE are reported. We give an overview of the instrument characteristics and of the of calibration and data evaluation activities (higher intensity, lower background, better profile shape, improved resolution). [Preview Abstract] |
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C1.00263: Effects of asphericity in charge distribution on electron scattering amplitude. Jin-Cheng Zheng, Lijun Wu, Yimei Zhu The sensitivity of atomic scattering factors to valence-charge distributions has been compared quantitatively for x-ray and electron diffraction. It is found that electron diffraction provides information about valence charge densities via the low-order structure factors, which are relatively insensitive to thermal vibrations, but sensitive to the charge distribution that characterizes the chemical bonding properties in materials. The effects of asphericity in charge distribution on electron scattering amplitude have been examined using both analytical and numerical methods. We show that the aspheric effects are dominated in low-order scattering region, where the electron scattering factor of Bragg reflections can be measured very precisely by quantitative electron diffraction, and therefore enables us to quantitatively determine the spherical and aspherical orbital ordering. The applications of quantitative electron diffraction in strongly correlated materials are discussed. [Preview Abstract] |
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C1.00264: Analytical form for the tip-sample interaction in liquid for Atomic Force Microscopy Fredy Zypman Knowledge of the functional form of force-separation curves in Atomic Force Microscopy (AFM) is necessary to develop reconstruction algorithms to predict the morphology and chemical activity of the sample under study. In vacuum, the tip and the sample can be modeled as a collection of atoms. The tip-sample force can thus be evaluated from the appropriate atom-atom forces. These elemental forces have been modeled via Morse, 6-12 pair potentials, and more detailed quantum approaches with non pair-wise forces. Nevertheless, a large section of the AFM community is interested in tip-sample interactions in the presence of fluids. The production of theoretical expressions for colloidal interactions relevant to AFM has been hampered by the fact that analytical solutions to the Poisson-Boltzmann equation (PBE) are restricted, thus far, to planar geometries. Numerical solutions for other geometries do exist, but they are computationally expensive. We present a simple theoretical expression for the interaction forces between the Atomic Force Microscope tip, and a sample immersed in an electrolytic solution. Our result is based on the Surface Element Integration of the Dejarguin-Landau-Verwey-Overbeek interaction between flat surfaces. We apply our results to the Van der Walls and to the electrostatic double layer cases. Finally, we use our expression to show how it simplifies the analysis of extant experimental data. Acknowledgment. Work supported by Research Corporation through grant CC5786. [Preview Abstract] |
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C1.00265: 3D ESR-MRI with A Sub-Micrometer Resolution Using Magnetic Resonance Force Microscopy Shigenori Tsuji, Yohsuke Yoshinari, Kosuke Inomata We will present our progress of ESR Magnetic Resonance Force Microscopy (MRFM). In order to improve our previously achieved resolution (2$\sim $3 micrometer), we used an electropolished magnetic tip made of a sintered Nd2Fe14B permanent magnet, which generated a larger magnetic field gradient (8000 T/m) in the very vicinity of the magnetic tip. To avoid a collision between a sample glued on a cantilever and the magnetic tip placed on a 3D stage, the tip-sample direction was set parallel to the cantilever long axis. Magnetic resonance force signals were induced by a cyclic saturation technique. In this setup, the observed signals had an anti-symmetrical phase with respect to a plane that contains a specimen and is perpendicular to the vibrational direction of the cantilever. MRFM image was then reconstructed from the force map through FT deconvolution. At present, our MRFM can produce 3D ESR-MRI with a sub-micrometer spatial resolution. [Preview Abstract] |
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C1.00266: Optical properties of the tips for apertureless near-field microscopy Disha Mehtani, N. Lee, R. D. Hartschuh, A. Kisliuk, M. D. Foster, A. P. Sokolov, I. Tsukerman Apertureless near-field optical microscopy is based on the enhanced optical signal in the vicinity of a metal or metal-coated tip via surface plasmon generation in the metal. Resonant excitation of the plasmons is crucial for maximizing enhancement under the tip. However, it remains a challenge to measure the optical properties of the nanoscale apex of a tip with a radius much smaller than the wavelength of light. We have developed a system to measure optical properties of tips based on the principle of total internal reflection microscopy. Optical resonance spectra of silver- and gold-coated tungsten and silicon nitride tips exhibit a dependence on the metal deposited. We also measured the wavelength dependence of tip-enhanced Raman signal. The enhancement of the Raman signal for silicon with gold-coated silicon nitride tips was found to be $\sim $ 3 times stronger for a wavelength of 647 nm than for 514.5 nm. The former is closer to the plasmon resonance observed for this tip at $\sim $680 nm. Additional examples correlating enhancement with resonance excitation will be presented. [Preview Abstract] |
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C1.00267: High contrast nano-Raman spectroscopy with optimized polarization Nam-Heui Lee, Ryan Hartschuh, Disha Mehtani, Alexander Kisliuk, Mark Foster, Alexei Sokolov, John Maguire For nanoscale characterization of chemical composition, structure, stresses and conformational states, tip-enhanced Raman spectroscopy (TERS) is an attractive tool. A TERS spectrometer based on side illumination geometry that shows reproducible enhancement of the order of 10$^{3}$-10$^{4}$, for a variety of molecular, polymeric and semi-conducting materials using silver- and gold-coated silicon nitride tips, will be presented. The radius of the spot from which the Raman signal comes is estimated to be 20nm for CdS thin films. For thick samples, such as a silicon wafer, polarization was optimized to achieve high contrast between the near- and far-field Raman signals. Additionally, systematic studies to estimate the localization volume of the detected near-field Raman signal with the optimized polarization are being performed. Raman imaging with sub-wavelength lateral resolution will be demonstrated on several nano-structures. [Preview Abstract] |
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C1.00268: UHV LT-STM system with Sample and Tip Exchange Michael Dreyer, Jonghee Lee, Hui Wang, Dan Sullivan, Barry Barker We developed and built a low temperature scanning tunneling microscope system with ultra high vacuum sample and tip preparation capabilities. The STM is mounted inside an UHV can which is submerged in a He bath cryostat. The cryostat is equipped with two superconducting magnets allowing a maximum in plane field of 2 T and a maximum out of plane field of 9 T. The two fields can be combined to a 1 T vector field. The vacuum can is connected to an UHV system at room temperature consisting of two chambers: One dedicated to transferring samples and tips to the STM, and the other chamber used for tip/sample preparation. It is equipped with two electron beam evaporators, an argon ion sputter gun as well as sample heaters. The whole system is supported by an optical table to decouple the STM from building vibrations. The system was successfully used to study standing electron waves on gold (111) as well as vortices on NbSe2. Details of the microscope, sample and tip handling system, as well as the UHV system will be presented. [Preview Abstract] |
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C1.00269: Modification of Tips for Use With Tip-Enhanced Raman Spectroscopy (TERS) Scott Hamilton, Nam-Heui Lee, Disha Mehtani, Ryan Hartschuh, Alexei Sokolov, Mark Foster In tip-enhanced Raman spectroscopy (TERS) the Raman signal is enhanced only in the vicinity of a probe tip that can be positioned near the surface of a sample. TERS tips were made by vapor-depositing gold onto AFM tips. These tips create plasmon resonances in the focal spot of the incident laser beam. Variation in the enhancement provided by the tips with the morphology of the metal surface was studied. Enhancement was found to be a function of film thickness and roughness. Deposition of metal nanoparticles on the tip surface was also studied as an alternative method of modification. Optical properties of various nanoparticles are being determined experimentally, allowing comparison with theoretical calculations. [Preview Abstract] |
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C1.00270: Digitally Controlled Quad Sine Wave Generator. Mohammed Z. Tahar Square, triangular, and sine and cosine waves of same frequency are generated with single digital command, using off the shelf components. This method does not synthesize the waves using the continuous digital control of the out put(s), as for arbitrary wave functions. The frequency ranges from below one to thousands of Hz, with the use of one capacitor. Also, the method lends itself to the use of embedded microcontrollers for frequency and independent amplitude control through the use of multiplying digital to analog converters. Because of the omnipresence of microcontrollers, the method is an inexpensive computer controlled frequency quad sine wave generation. With the addition of an analog-to-digital converter, one can use such a generator for systems studies in control and measurements. [Preview Abstract] |
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