Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L43: Focus Session: Stable Glasses, Fluids Under Confinement and at Interfaces |
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Sponsoring Units: DPOLY GSOFT GSNP Chair: Zahra Fakhraai, University of Pennsylvania Room: 214C |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L43.00001: Observation of Charge Inversion and Divalent Ion Transport in Nanochannels Xin Li, Weihua Guan, Ben Weiner, Mark Reed Ion transport in nanochannels has attracted increasing attention in recent years, with potential applications ranging from ionic control and biosensing to energy storage and conversion. Exciting phenomena occur from the nanoscale confinement of fluids and new models are expected. While most of the previous work in the field has focused on simple monovalent electrolytes, we report a systematic study of divalent ion transport in a well-defined nanochannel fabricated via standard semiconductor methods. Inversion of net surface charge at the fluid/solid interface has been observed by a novel method of open potential measurement. Moreover, the relation of this charge inversion phenomena with the strong correlated liquid (SCL) theory has been deeply discussed. Intriguing observations from conductance measurement reveal ion-surface interactions and ion-ion correlations. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L43.00002: Electrostatic effects of dielectric interfaces on confined electrolyte Yufei Jing, Vikram Jadhao, Jos W. Zwanikken, Monica Olvera de la Cruz The behavior of ions in liquids confined between interfaces characterized by different dielectric permittivities is crucial to many nanoscale assembly processes in synthetic and biological materials. The presence of multiple interfaces and associated dielectric heterogeneities often complicates computing the desired ionic distributions via simulations or theory. Electrostatic correlation effects in a system with electrolyte confined by two planar dielectric interfaces are systematically studied by Car-Parrinello molecular dynamics simulations and liquid state theory. Results for ionic density profiles for various electrolyte concentrations, stoichiometric ratios and dielectric contrasts are presented. We also investigate the interactions between two planar surfaces and effects of the dielectric interfaces on the double layer structure near the interfaces which lies at the heart of soft matter physics. [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L43.00003: Squeezout of a model ionic liquid under confinement and charging Erio Tosatti, Rosario Capozza, Andrea Benassi, Andrea Vanossi Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film, including even-odd switching of the structural layering, and important changes of planar ordering within layers. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including the effect a neutral tail attached to one of the model ions. Using open, grand-canonical-like conditions which allow the flow of ions in and out of the interplate gap, we simulate the liquid squeezout and obtain the distance dependent forces between the plates during their adiabatic approach under load. Effective free energy curves obtained by integration of these forces versus interplate distance show the local minima that correspond to layering, and predict the switching between one and another under squeezing and charging. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L43.00004: Electrical charging effects on sliding lubrication properties of a model confined ionic liquid Rosario Capozza, Andrea Benassi, Andrea Vanossi, Erio Tosatti Ionic liquids lubricants, used under conditions of nanometric confinement between parallel plates or tip-surface gaps, explore the dependence of friction upon charging, suggestive of some electrical control of friction. Using a simple ionic liquid model, we first study by molecular dynamics the friction between parallel plates under conditions of successive layering reached by squeezout under an increasing inter-plate force. We then simulate the frictional changes brought about by different charging states of the plates, related to charging-induced switches corresponding to squeezout (or suck-in) transitions between different layering states as predicted by local minima in the charge-dependent enthalpy curves. Although the actual frictional behavior obtained does depend upon the assumed features and parameters of the model liquid and its interaction with the plates, the broader scenario obtained for charging effects, its relationship to the equilibrium layering and its enthalpy characterization appear of general value. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L43.00005: Crossover in the local diffusive dynamics of equilibrium and supercooled confined fluids Jonathan Bollinger, Thomas Truskett Confined fluids are ubiquitous in natural and technological contexts, and relating emergent structural motifs to dynamics is critical to facilitate the inverse design of nano- and micro-fluidic systems. Crucially, such thin film systems are frequently tuned between equilibrium and glassy states, as during, e.g., processing of polymer thin films. We use molecular dynamics simulations and a Fokker-Planck equation based method to examine the position-dependent diffusive dynamics of binary hard-sphere fluids confined to slit pores that are designed to mimic realizable thin films [Nugent et al. PRL 2007, 99]. At moderate densities, local single-particle mobilities normal to the direction of confinement are higher in regions of high local packing fraction. However, as the average packing fraction is increased into the supercooled regime, this local positive correlation between packing fraction and mobility is reversed. We discuss the outlook for a universal mechanistic framework that can unite these disparate local correlations between packing and mobility and also predict average diffusivities of the inhomogeneous fluids. Auxiliary measurements of the simulated films suggest that this behavioral dichotomy should also emerge in structurally similar experimental colloidal suspensions. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L43.00006: Geometrical frustration and correlated capillary instabilities among concentric polymer toroids Zheng Zhang, Gene Hilton, Yifu Ding We present the first study on the simultaneous capillary instability among concentric viscous toroids. An array of concentric polystyrene (PS) toroids were lithographically fabricated with a constant radial spacing between neighboring toroids. The toroids were confined in a poly (methyl methacrylate) (PMMA) matrix. PS and PMMA were used because of their immiscibility and well-characterized physical properties. The glass transition temperature ($T_{\mathrm g}$) of the pattern are well above room temperature. We found that the radial contraction mode of toroids (Pairam \& Fern{\' a}ndez-Nieves, PRL 2009) was inhibited due to substrate confinement. Upon further annealing, the toroids ruptured along the circumferential direction at a finite wavelength. Depending on the relative volume of PS, the rupture behavior of each toroid (with different aspect-ratios) can be non-correlated or correlated radially. In the correlated case, geometric frustration due to the toroidal curvature was observed, which led to an intriguing branching behavior in the correlated instability and closely resembles a Cayley tree with fractal coordination number of 3. [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:48AM |
L43.00007: Ultrastable Glasses and the Random First Order Transition Theory of Glasses Invited Speaker: Peter Wolynes I will discuss the implications of the RFOT theory for the dynamics of ultrastable glasses focusing on the achievable limits to stability and the heterogeneous and homogeneous mechanisms of their rejuvenation. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L43.00008: Probing the Dynamics of Thin TPD Glass Films via Dewetting Yue Zhang, Ethan Glor, Tianyi Liu, Chen Li, Zahra Fakhraai Enhanced mobility of surface layer has been observed in both polymer glasses and small molecule organic glasses. In polymers, the mobile surface layer is believed to have great effects on the properties of thin films. Similar studies in small molecule glasses are significantly more challenging due to dewetting Understanding the dynamics of this mobile layer, and its effect on thin film dynamics can be important in understanding heterogeneous dynamics in glassy systems. In this work, we investigate the properties of the mobile layer and its effect on the overall properties of thin glass films of small molecule organic glasses. We show that thin (thickness below 30nm) TPD (N,N$'$-Bis(3-methylphenyl)-N,N$'$-diphenylbenzidine) films prepared by physical vapor deposition (PVD), can be unstable and dewet in a hole growth manner due to enhanced mobility at temperatures as low as Tg-35K. By following the kinetics of dewetting, we investigate the mobility changes with temperature and film thickness. These studies can elucidate the relation between the enhanced mobility and the stability of thick films of the same materials prepared at similar deposition temperatures and thus the formation mechanisms and unique properties of physical vapor deposited glasses. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L43.00009: Dewetting of a Liquid-Liquid System Stefan Bommer, Nikolas Becker, Sebastian Jachalski, Dirk Peschka, Barbara Wagner, Ralf Seemann In recent years a thorough understanding of thin film dewetting from solid substrates was developed. However, the understanding of a thin liquid film dewetting from another liquid remained scarce. By \textit{in situ} AFM studies we explore the dewetting dynamics and the morphologies of liquid polystyrene (PS) dewetting from liquid polymethyl-methacrylate (PMMA). Using a selective solvent allows to remove the dewetted PS layer and to image the liquid/liquid interface at selected times. Combining the PS/air and the PS/PMMA interfaces we obtain the full three dimensional shape of the dewetting morphologies. The characteristic shapes of the rim profiles, the equilibrating droplets and their dewetting dynamics depend not only on the ratios of viscosity and surface tension of the two liquids but also on the relative film height of the underlying liquid. The latter originates from the flow field of the dewetting liquid which penetrates surprisingly deep into the lower liquid it is dewetting from [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L43.00010: Coupling the coffee-ring effect to phase separation in drying polymer-nanocrystal deposits Erik K. Hobbie, Joseph B. Miller, Austin C.P. Usselman, Rebecca J. Anthony, Uwe R. Kortshagen, Alexander J. Wagner, Alan R. Denton The coupling between the coffee-ring effect and liquid-liquid phase separation is examined for ternary mixtures of solvent, polymer and colloidal nanocrystal. Using real-space imaging and spectroscopic techniques, we resolve the kinetic morphology of the drying front for varied molecular weight of the polymer. Our results demonstrate that the size of the polymer chain has a significant impact on the nature of the coupling between the two instabilities, and we relate these observations to simulations, measured and predicted binodal curves, and the observed shape of the flow field in the confined region at the contact line. The results inform a blade coating process that we exploit to print homogeneous or periodically patterned microscopic wires of nanocomposite material. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 11:00AM |
L43.00011: Surface Diffusion of Molecular Glasses and Its Role in Crystal Growth and Glass Engineering Invited Speaker: Lian Yu Amorphous solids and glasses are important in many areas of science and technology. We report recent progress toward measuring surface diffusion on molecular glasses. A rough surface flattens to minimize its surface energy and this process occurs by surface diffusion at short length scales. Surface diffusion on molecular glasses is at least one million times faster than bulk diffusion,$^{\mathrm{1,2}}$ and remains fast after significant bulk aging.$^{\mathrm{3}}$ This high surface mobility enables fast surface crystal growth$^{\mathrm{4}}$ and the formation of stable glasses by vapor deposition.$^{\mathrm{5}}$ Relying on rapid surface equilibration, vapor deposition can build glasses layer-by-layer to achieve exceptionally low energy and high density. A remarkable feature of glass-forming molecular liquids is that the mechanism of surface evolution transitions from viscous flow to surface diffusion at modest viscosities. Under the same condition, this transition is not observed for silicate and polymer liquids, indicating a material dependence of surface diffusion. (1) Zhu, L.; Brian, C.; Swallen, S. F.; Straus, P. T.; Ediger, M. D.; Yu, L. Phys. Rev. Lett. 2011, 106, 256103. (2) Brian, C. W.; Yu, L. J. Phys. Chem. A. 2013, 117, 13303. (3) Brian, C. W.; Zhu, L.; Yu, L. J. Chem. Phys. 2014, 140, 054509. (4) Sun, Y.; Zhu, L.; Kearns, K. L.; Ediger, M. D.; Yu, L. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 5990. (5) Swallen, S.; Kearns, K.; Mapes, M.; McMahon, R.; Kim, S.; Ediger, M.; Yu, L.; Wu, T.; Satija, S. Science 2007, 315, 353. [Preview Abstract] |
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