Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Z39: Surfaces, Interfaces and Colloids |
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Sponsoring Units: DCP Chair: Phillip Geissler, University of California, Berkeley Room: A124/127 |
Friday, March 25, 2011 11:15AM - 11:27AM |
Z39.00001: Two-dimensional soft solids: a rheological study Gabriel Espinosa, Duyang Zang, Dominique Langevin, Bernard Binks Many soft solids, such as concentrated suspensions, emulsions, foams, behave in a similar way under an applied shear: they exhibit a Maxwell-type relaxation with a characteristic relaxation time that varies inversely with the applied shear rate. When the storage and loss moduli are measured at different frequencies and constant shear rate, the curves obtained can be rescaled [1]. We will show here that the behavior in two dimensions can be strikingly similar. We will present data on monolayers of nanoparticles and on mixed layers made with DNA and surfactant. The physical origin of the relaxation time will be discussed. The nonlinear behavior will be also discussed. Depending on the compaction degree, the layers can behave as brittle or plastic solids. This has been confirmed by images of the layers after a shear deformation made using Brewster angle microscopy. \\[4pt] [1] H. M. Wyss, K. Miyazaki, J. Mattsson, Z. Hu, D. R. Reichman, and D. A. Weitz, Phys. Rev. Lett. \textbf{98}, 238303 (2007). [Preview Abstract] |
Friday, March 25, 2011 11:27AM - 11:39AM |
Z39.00002: ABSTRACT WITHDRAWN |
Friday, March 25, 2011 11:39AM - 11:51AM |
Z39.00003: Direct measurement of short range colloidal interactions using digital holographic microscopy Rebecca W. Perry, Jerome Fung, David M. Kaz, Guangnan Meng, Vinothan N. Manoharan Using digital holographic microscopy, we record the 3D positions of micron-sized polystyrene particles as they approach and retreat from each other. Analysis of the holograms using an exact solution for the scattering from pairs of spheres allows us to separate vibrational, translational, and rotational motion. The vibrational mode supplies the information needed to characterize the inter-particle interactions down to separation distances on the order of 10 nm. In particular, we study an aqueous system of one micron diameter sulfate-coated polystyrene beads suspended in a solution of 95 nm hydrogel particles. The attractive depletion interaction we measure deviates from the Asakura-Oosawa model, likely because of electrostatic interactions at these short distances. [Preview Abstract] |
Friday, March 25, 2011 11:51AM - 12:03PM |
Z39.00004: Fabrication of Monolayer of Polymer/Colloids Hybrid at a Water-Air Interface Chi-Chih Ho, Ting-Hui Chen, Po-Yuan Chen, Keng-Hui Lin, Wen-Tau Juan, Wei-Li Lee Polymer-assisted assembly of polystyrene (PS) colloids with diameter ranging from 100 nm to 1 $\mu$m at water-air interface is demonstrated. Initially, PS colloids were slowly spread onto water surface and crystallized into triangular lattice with finite separation between colloids due to the coulomb repulsive force. By adding merely 1-3 ppm water-soluble polyethylene oxide (PEO) in water, the colloids gradually moved closer. Eventually, the separation between colloids was equal to or less than 60 nm determined from its diffraction pattern by a laser beam. In addition, the Brownian motion of colloids was suppressed by the PEO adsorption effect which was demonstrated from the analysis of colloids trajectory recorded by ultra high speed camera. We showed that the resulting monolayer of colloids /PEO hybrid can be deposited on various substrates, including a plastics sheet, curved surface and even across 10 $\mu$m-diameter hole. Our method may further extend the scope of nanosphere lithography technique for large area nanostructure fabrication. [Preview Abstract] |
Friday, March 25, 2011 12:03PM - 12:15PM |
Z39.00005: Heterogeneous crystallization of hard-sphere colloids near a wall Kyril Sandomirski, Elshad Allahyarov, Hartmut L{\"o}wen, Stefan Egelhaaf Confocal microscopy experiments and equilibrium Brownian Dynamics computer simulations were combined to investigate heterogeneous crystallization near a hard wall in a suspension of hard-sphere colloids. Particles near the wall initially rearrange, before an extended regime of steady-state crystal growth is observed. Finally, a depletion zone develops which slows down the progressing crystal-fluid interface. In good agreement between experiment and simulation, the steady-state growth velocity shows a maximum in its dependence on the bulk volume fraction. Beyond this, these techniques allow us to obtain local microscopic information on the level of individual particles, namely the temporal evolution of the density profiles in the fluid and crystal phase as well as the width of the interface. [Preview Abstract] |
Friday, March 25, 2011 12:15PM - 12:27PM |
Z39.00006: $^{19}$F NMR Study of Molecular Aggregation of Lithium Perfluorooctylsulfonate in Water at Temperatures from 30 to 250 \r{ }C Dobrin Bossev, Mutsuo Matsumoto, Masaru Nakahara $^{19}$F NMR chemical shifts have been measured to determine the critical micelle concentration (cmc) and aggregation number ($m)$ of lithium perfluorooctylsulfonate (LiFOS) in water at temperatures ranging from 30 to 250 \r{ }C under the saturation pressure. The cmc slightly increases in the temperature range from 30 to 100 \r{ }C, whereas above 125 \r{ }C the increase is much steeper; cmc is 6.5, 13.2, and 161 mmol kg$^{-1}$ at 30, 100, and 250 \r{ }C, respectively. The aggregation number, estimated on the basis of a mass action model exhibits a rapid decrease in the temperature range of 30 - 125 \r{ }C and becomes almost constant at higher temperatures; $m$ is 36, 6.8, and 2.4 at 30, 100, and 250 \r{ }C, respectively. Thermodynamic parameters indicate similar values for the free energy at all temperatures, and constant values for the enthalpy and entropy of aggregation at high temperatures. [Preview Abstract] |
Friday, March 25, 2011 12:27PM - 12:39PM |
Z39.00007: Dielectric dispersion of clustered living cells via the boundary integral equation method Sai Kit Yung, Kin Lok Chan, Kin Wah Yu We have developed a boundary integral equation (BIE) method for computing the dielectric response of clusters of biological particles like living cells. In the BIE, we formulate a surface integral equation for the scalar potential for an arbitrary number of particles of various shapes [1]. BIE method avoids matching the complicated boundary conditions on the surfaces of the particles. Numerical solutions of the eigenvalue equation yield a dielectric dispersion spectrum through the spectral representation [2]. While BIE method is valid for arbitrary surfaces, we confirm it for two approaching cylinders and a concentric cylinder. In many typical cases, the numerical results are in excellent agreement with the exact analytic results. Moreover, BIE method offers a convenient way to compute the alternating current responses, and hence the dielectric dispersion of clustered cell suspensions. \\[4pt] [1] Yu KW, Wan JTK, Computer Physics Communications 142, 368 (2001). \\[0pt] [2] Huang JP, Yu KW, Phys. Rep. 431, 87 (2006). [Preview Abstract] |
Friday, March 25, 2011 12:39PM - 12:51PM |
Z39.00008: Multi scale computer simulations of the self-assembly of block copolymeric beta-peptides Jagannath Mondal, Arun Yethiraj There is considerable interest in a class of molecules made from $\beta$-amino acids (which contain an additional backbone carbon atom when compared with natural amino acids). Block copolymers of $\beta$-peptides, where one block is hydrophobic and the other is hydrophilic, self-assemble into micelles. In this work we use computer simulations to provide insight into the self-assembly of these molecules. All-atom simulation results for the free energy of association of a pair of these block co polymeric $\beta$- peptides show that a {\it homochiral} hydrophobic block promotes self assembly compared to a {\it heterochiral} hydrophobic block, consistent with experiment. We have also developed a coarse-grained model for these block co-polymers and simulations using this model show that these molecules spontaneously forms micelles, and the morphology of these micelles is concentration dependent, with spherical micelles at low concentrations and worm-like micelles at high concentrations. [Preview Abstract] |
Friday, March 25, 2011 12:51PM - 1:03PM |
Z39.00009: Ab initio Study of Structure and Hydrogen Bonding of Cellulose Crystals and Surfaces James Davenport, Yan Li We have studied the equilibrium structure and hydrogen bonding of cellulose crystals and surfaces using semi-empirical dispersion corrections to density functional theory (DFT+D)[1], which has been shown to be an efficient alternative to more advanced methods for weakly bound aromatic assemblies[2]. The predicted crystal structures for both I$_\alpha$ and I$_\beta$ phases agree well with experiments. The cohesive energy was decomposed into interchain and intersheet interactions and analyzed in terms of hydrogen bonding and van der Waals dispersion forces. Both interactions were found to be responsible for holding cellulose sheets together. In particular, the dispersion corrections to DFT proved to be indispensable in reproducing the equilibrium intersheet distance and binding strength. Adsorption energy and configuration of water molecules on cellulose surfaces were found to depend sensitively on the surface orientation, adsorption site and contribution from vdW interactions.\\[4pt] [1] S. Grimme, J. Comput. Chem. 27, 1787 (2006).\\[0pt] [2] Y. Li, D. Lu, H-V. Nguyen and G. Galli, J. Phys. Chem. A 114, 1944 (2010). [Preview Abstract] |
Friday, March 25, 2011 1:03PM - 1:15PM |
Z39.00010: Interfacial free energy and stiffness of the solid-melt interface of NaCl Tatyana Zykova-Timan, Erio Tosatti, Daan Frenkel The importance of the interfacial free energy for the equilibrium morphology of crystals is well understood. In contrast, much less is known about to the so-called ``interfacial stiffness'' that governs fluctuations of, e.g., solid-liquid interfaces. We carried out molecular dynamics simulations of capillary wave fluctuations on various faces of NaCl crystals in contact with its melt, that provides new information on the behaviour of this interface at the atomistic level. The capillary fluctuations connect directly with the interfacial stiffness, and indirectly also to the interface free energy. In our simulations we studied the (100)-liquid interface and adjacent vicinals. From the angular dependence of the surface stiffness, we deduce an estimate of NaCl(100)-melt interfacial free energy and discuss limitations of the fluctuation approach. Finally we compare this estimate of the surface free energy with values obtained through other methods [1,2,3] and discuss the differences [4]. \\[4pt] [1] T. Zykova-Timan, D. Ceresoli, U. Tartaglino, and E. Tosatti, Phys. Rev. Lett. 94, 176105 (2005). [2] C.Valeriani, E. Sanz and D. Frenkel, J. Phys. Chem. ,122, 194501 (2005). [3] T. Zykova-Timan, C. Valeriani, E. Sanz, E. Tosatti and D. Frenkel, Phys. Rev. Lett., 100, 036103 (2008). [Preview Abstract] |
Friday, March 25, 2011 1:15PM - 1:27PM |
Z39.00011: Utilization of Metal Oxides and Chalcogenides Stabilized in Organic Solvents Lester Lampert, Robby Flaig, Jorge Camacho, James Hamilton Metal oxides and metal chalcogenides are important materials for a variety of applications including photocatalysis for decomposition of water, conductive and optical coatings, catalysts, photovoltaics, pryoelectrics, self-cleaning surfaces, pigments, and high efficiency Li-insertion materials in batteries among many other applications. Fundamental discoveries of surprising solubility of insoluble materials such as single and multi-walled carbon nanotubes and graphene has lead us to discover that certain metal oxides and metal chalcogenides such as TiO2 are soluble in certain solvents. Due to the industrial importance of TiO2, discovering stable pure solvent systems demonstrates a possibility to avoid surface modification of TiO2 nanoparticles by use materials such as of (3-methacryloxypropyl)-trimethoxysilane and various other methods of artificial stabilization. We have created thin films of TiO2, transparent ultraviolet (UV) --absorptive polymers, and Li-ion battery anodes with graphene-TiO2 hybrid materials. [Preview Abstract] |
Friday, March 25, 2011 1:27PM - 1:39PM |
Z39.00012: EPR, Endor and DFT Studies on X-Irradiated Single Crystals of L-Lysine HCl 2H$_{2}$O and L-Arginine HCl H$_{2}$O Yiying Zhou, William H. Nelson When proteins and DNA interact, arginine and lysine are the two amino acids most often in close contact with the DNA. In order to understand the radiation damage to DNA in vivo, which is always associated with protein, it is important to learn the radiation chemistry of arginine and lysine independently, and then complexed to DNA. This work studied X-irradiated single crystals of L-lysine$\cdot$HCl$\cdot$2H$_{2}$O and L-arginine$\cdot$HCl$\cdot$H$_{2}$O with EPR, ENDOR techniques and DFT calculations. In both crystal types irradiated at 66K, the carboxyl anion radical and the decarboxylation radical were identified. Specifically, the calculations performed on the cluster models for the carboxyl anion radicals reproduced the proton transfers to the carboxyl group from the neighboring molecules through the hydrogen bonds. Moreover, computations supported the identification of one radical type within irradiated arginine as the guanidyl radical anion with an electron trapped by the guanidyl group. Based on the radicals detected in the crystal irradiated at 66K and at 298K, and the annealing experiments from the irradiation at 66K, the mechanisms of the irradiation damage on lysine and arginine were proposed, and the possible effects of irradiated arginine and lysine to the DNA within chromatin were analyzed. [Preview Abstract] |
Friday, March 25, 2011 1:39PM - 1:51PM |
Z39.00013: Detection of Nitro aromatics via fluorescence quenching of pegylated and siloxanated 4, 8-dimethylcoumarins Abhishek Kumar, Mukesh Pandey, Jayant Kumar There is considerable interest in developing chemical sensors for detection of trace explosives. Optical sensors, which rely on the change in optical properties of the material, proved to be very effective. Therefore, there is a need to develop materials for optical sensors which can interact specifically with analytes and detect them sensitively. Here, we report the synthesis of co-polymers of 4, 8-dimethylcoumarins with poly (ethylene glycol) (PEG) and polydimethylsiloxane (PDMS) using \textit{Candida Antarctica lipase} as a catalyst under solvent-less condition. The low T$_{g}$ of PEG and PDMS may facilitate porous structure in solid films which allows quencher molecules to easily diffuse in and out of these films. In addition, the co-polymers prevent aggregation and lend themselves easily for thin film fabrication which otherwise is difficult because of low molecular weight of coumarin. Fluorescence quenching of these co-polymer in presence of nitro aromatics, 2,4-dinitrotoulne and 2,4,6-trinitrotoluene, in solution and in vapor phase will be reported. [Preview Abstract] |
Friday, March 25, 2011 1:51PM - 2:03PM |
Z39.00014: Correlated electrolyte solutions and ion-induced attractions between nanoparticles Jos Zwanikken, Monica Olvera de la Cruz Information about the degree of association can be obtained from a nonlinear Debye-Hueckel theory [1], in agreement with simulation and experimental results [2], in strong contrast with the widely applied (linear) Debye-Hueckel limiting law. The radial distribution functions calculated within this nonlinear theory are indistinguishable from molecular dynamics simulations of the restricted primitive model for divalent salts up to 0.1 molar concentrations. We apply the method to study the cohesive effects of strong couplings between ions on the effective interactions between nanoparticles, and the screening cloud around functionalized nanoparticles.\\[4pt] [1] J. W. Zwanikken, and M. Olvera de la Cruz, Phys. Rev. E 82, 050401(R) (2010).\\[0pt] [2] C. Valeriani, P. Camp, J. Zwanikken, R. van Roij, and M. Dijkstra, J. Phys.: Condens. Matter 22, 104122 (2010); Soft Matter 6, 2793 - 2800 (2010). [Preview Abstract] |
Friday, March 25, 2011 2:03PM - 2:15PM |
Z39.00015: ABSTRACT WITHDRAWN |
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