Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F33: The Physics of Confined Structural Fluids IIFocus
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Sponsoring Units: DPOLY Chair: Erik Watkins, UC - Davis Room: 336 |
Tuesday, March 15, 2016 11:15AM - 11:51AM |
F33.00001: Coherent X-ray Scattering from Liquid-Air Interfaces Invited Speaker: Oleg Shpyrko Advances in synchrotron x-ray scattering techniques allow studies of structure and dynamics of liquid surfaces with unprecedented resolution. I will review x-ray scattering measurements of thermally excited capillary fluctuations in liquids, thin polymer liquid films and polymer surfaces in confined geometry. X-ray Diffuse scattering profile due to Debye-Waller like roughening of the surface allows to probe the distribution of capillary fluctuations over a wide range of length scales, while using X-ray Photon Correlation Spectroscopy (XPCS) one is able to directly couple to nanoscale dynamics of these surface fluctuations, over a wide range of temporal and spacial scales. I will also discuss recent XPCS measurements of lateral diffusion dynamics in Langmuir monolayers assembled at the liquid-air interface. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F33.00002: A particle-in-mesh method for Brownian Dynamics simulation of many-particle systems with hydrodynamics interactions in a confined geometry Xujun Zhao, Juan Hernandez-Ortiz, Dmitry Karpeyev, Juan de Pablo, Barry Smith In this work, we present an efficient parallel particle-in-mesh method for Brownian Dynamics simulations of many-particle systems confined in micro- and nano-fluidic devices. A general geometry Ewald-like method (GGEM) combined with finite element method is used to account for the hydrodynamic interaction. A fast parallel Krylov-type iterative solver with hybrid preconditioning techniques is developed for solving the large sparse systems of equations arising from finite element discretization of the Stokes equations. In addition, the current computer code is developed based on PETSc, a scalable library of numerical algorithms developed at Argonne, SLEPc - Scalable Library for Eigenvalue Problem Computations, and libMesh, a finite element library for numerical solution of PDEs built on top of PETSc, which allows for direct simulation of large scale systems with arbitrary confined geometries. This scheme is applied to Brownian dynamics simulations of flowing confined polymer solutions and colloidal dispersions in micro-fluid channels. The effects of hydrodynamics interactions and geometric confinement on the migration phenomena are illustrated. [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F33.00003: Structural and dynamical properties of water on chemically modified surfaces: The role of the instantaneous surface Selemon Bekele, Mesfin Tsige Surfaces of polymers such as atactic polystyrene (aPS) represent very good model systems for amorphous material surfaces. Such polymer surfaces are usually modified either chemically or physically for a wide range of applications that include friction, lubrication and adhesion. It is thus quite important to understand the structural and dynamical properties of liquids that come in contact with them to achieve the desired functional properties. Using molecular dynamics (MD) simulations, we investigate the structural and dynamical properties of water molecules in a slab of water in contact with atactic polystyrene surfaces of varying polarity. We find that the density of water molecules and the number distribution of hydrogen bonds as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering of water molecules near the water/PS interface. For the dynamics, we use time correlation functions of hydrogen bonds and the incoherent structure function for the water molecules. Our results indicate that the polarity of the surface dramatically affects the dynamics of the interfacial water molecules with the dynamics slowing down with increasing polarity. [Preview Abstract] |
Tuesday, March 15, 2016 12:15PM - 12:27PM |
F33.00004: Ion transport and dehydration in sub-nanoscale pores Subin Sahu, Massimiliano Di Ventra, Michael Zwolak Ions in solution develop tightly bound layers of water -- hydration layers -- which stabilize disassociation and enable ionic currents to flow. Sub-nanometer pores in a membrane enable ions to pass provided that they shed their hydration shell. This process has an associated large energy penalty that is predicted to give rise to "quantized" steps in the ionic conductance.\footnote{ Zwolak, M., Lagerqvist, J. \& Di~Ventra, M. Quantized ionic conductance in nanopores. \emph{Phys. Rev. Lett.} \textbf{103}, 128102 (2009). }\textsuperscript{,}\footnote{ Zwolak, M., Wilson, J. \& Di~Ventra, M. Dehydration and ionic conductance quantization in nanopores. \emph{J. Phys.: Condens. Matter} \textbf{22}, 454126 (2010).} Using all-atom molecular dynamics simulation, we demonstrate that the ionic current begins to show nonlinear behavior as the radius of the pore is reduced to the sub-nanometer scale. This nonlinear behavior is seen as a sharp rise in the pore resistance and excess noise in the current. Our work sheds light on basic mechanism of ion transport through sub-nanoscale pores. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 12:39PM |
F33.00005: Coordinated Water Under Confinement Eases Sliding Friction Adrian Defante, Nishad Dhopotkar, Ali Dhinojwala Water is essential to a number of interfacial phenomena such as the lubrication of knee joints, protein folding, mass transport, and adsorption processes. We have used a biaxial friction cell to quantify underwater friction between a hydrophobic elastomeric lens and a hydrophobic self-assembled monolayer in the presence of surfactant solutions. To gain an understanding of the role of water in these processes we have coupled this measurement with surface sensitive sum frequency generation to directly probe the molecular constitution of the confined contact interface. We observe that role of confined coordinated water between two hydrophobic substrates covered with surfactants is the key to obtaining a low coefficient of friction. [Preview Abstract] |
Tuesday, March 15, 2016 12:39PM - 1:15PM |
F33.00006: Understanding dynamic changes in live cell adhesion with neutron reflectometry Invited Speaker: Ann Junghans Understanding the structure and functionality of biological systems on a nanometer-resolution and short temporal scales is important for solving complex biological problems, developing innovative treatment, and advancing the design of highly functionalized biomimetic materials. For example, adhesion of cells to an underlying substrate plays a crucial role in physiology and disease development, and has been investigated with great interest for several decades. In the talk, we would like to highlight recent advances in utilizing neutron scattering to study bio-related structures in dynamic conditions ($e.g.$ under the shear flow) including \textit{in-situ} investigations of the interfacial properties of living cells. The strength of neutron reflectometry is its non-pertubative nature, the ability to probe buried interfaces with nanometer resolution and its sensitivity to light elements like hydrogen and carbon. That allows us to study details of cell - substrate interfaces that are not accessible with any other standard techniques. We studied the adhesion of human brain tumor cells (U251) to quartz substrates and their responses to the external mechanical forces. Such cells are isolated within the central nervous system which makes them difficult to reach with conventional therapies and therefore making them highly invasive. Our results reveal changes in the thickness and composition of the adhesion layer (a layer between the cell lipid membrane and the quartz substrate), largely composed of hyaluronic acid and associated proteoglycans, when the cells were subjected to shear stress. Further studies will allow us to determine more conditions triggering changes in the composition of the bio-material in the adhesion layer. This, in turn, can help to identify changes that correlate with tumor invasiveness, which can have significant medical impact for the development of targeted anti-invasive therapies. [Preview Abstract] |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F33.00007: Adsorption of CO2 in hydrated MCM-41 Studied by SANS Bo Wang, Garfield T. Warren, Matthew Bryan, Paul E. Sokol Adsorption of CO$_{\mathrm{2}}$ in hydrated MCM-41 was studied as a function of CO$_{\mathrm{2}}$ pressure by Small-Angle Neutron Scattering (SANS). Measurements were carried out on hydrophobic Si-MCM-41 and hydrophilic Al-MCM-41 with pore sizes of 4nm with no aqueous layer as well as monolayers and bilayers of water pre-adsorbed on the surface. SANS was measured as CO$_{\mathrm{2}}$ was introduced into the pores, which has the ability to probe the microscopic arrangement of water and CO2 confined within the pores. We will present the results of analysis indicating whether water or CO$_{\mathrm{2}}$ is more strongly attracted to the surface in these different samples. This study was prepared by Indiana University under award 70NANB10H255 from the National Institute of Standards and Technology, U.S. Department of Commerce. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F33.00008: Probing the Hydrodynamic Boundary Condition from Surface Perturbations in Thin Liquid Films Oliver Baeumchen, Paul Fowler, Thomas Salez, Michael Benzaquen, Mark Ilton, Joshua McGraw, Elie Raphael, Kari Dalnoki-Veress For flows on the micro- and nanoscale, the hydrodynamic boundary condition of a liquid at a solid surface plays an enormous role. In recent years much has been learned about this slip boundary condition from flows that are driven by capillary forces, e.g.\ dewetting thin liquid films featuring a three-phase contact line [1]. Recently, we have shown that the amplification of surface perturbations in thin liquid films allows for a quantification of slippage in the absence of a contact line [2]. We also show that the opposite approach, i.e.\ the capillary levelling of initially perturbed free surfaces [3], is sensitive to the slip boundary condition at the solid/liquid interface. Thin film models comprising slip enable a quantification of the slip length of viscous liquids of various molecular properties. [1] O. B\"aumchen et al., Phys.\ Rev.\ Lett.\ 113, 014501 (2014). [2] S. Haefner et al., Nature Comm. 6, 7409 (2015). [3] J.D. McGraw et al., Phys.\ Rev.\ Lett.\ 109, 128303 (2012). [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 1:51PM |
F33.00009: Dynamic arrest of colloids in quenched-disordered nanofiber networks Anh Phan, Kenneth Schweizer The effect of quenched-disordered high aspect ratio nanorod networks on the kinetic arrest of relatively dilute colloid or nanoparticle suspensions is theoretically studied using equilibrium replica integral equation and dynamical activated hopping theories. The adsorbing templates act as an external field which can destroy macrophase separation and induce variable colloidal microstructures. When the colloid-template attraction is weak, a large-mesh network only weakly perturbs dynamical arrest in pores driven by colloid aggregation. Reducing the mesh size increases constraints and enhances colloid localization. For strong interfacial attraction templates, colloids can be kinetically arrested in large-mesh networks even when they are purely repulsive hard spheres due to dynamic blocking effects. However, the localization length is significantly larger, more akin to a glass-like, not gel-like, form of arrest. Decreasing the template mesh results in colloid localization at smaller interfacial attraction strengths. An overall kinetic arrest map is constructed based on the interplay of inter-colloid attraction, colloid-template attraction, and template mesh size. The effect of colloid localization on the composite dynamic elastic shear modulus can be estimated. [Preview Abstract] |
Tuesday, March 15, 2016 1:51PM - 2:03PM |
F33.00010: Effect of confinement on ionic liquid molecules in porous polymeric network Prasad Raut, Shichen Yuan, Dr. Toshikazu Miyoshi, Dr. Sadhan Jana Ionic liquids (ILs) have attractive physicochemical properties but their room temperature liquid state necessitates pairing of IL with other solid, porous materials for fabrication of devices. Such materials are called ionogels. Loading of bulky IL molecules in the pores can dramatically affect the physical properties as function of the pore surface chemistry, pore size, and IL polarity. In this study porous syndiotactic polystyrene (sPS) network was made via thermos-reversible gelation. 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) is incorporated into the pores of sPS. DSC study and the temperature dependence of $^{\mathrm{13}}$C-CPMAS NMR show that on confinement; the melting point of PYR14TFSI contained in the ionogel increased in comparison to the bulk PYR14TFSI. At room temperature, WAXD study of the ionogels showed diffraction pattern for PYR14TFSI in nanopores, correspondingly $^{\mathrm{1}}$H NOESY experiments show strong non-bonded cation-cation correlation in ionogels. The results for the bulk IL does not show non-bonded correlation at room temperature, this increment of local order in ionogel might be the results of crystallization of IL molecules in confined geometry. [Preview Abstract] |
Tuesday, March 15, 2016 2:03PM - 2:15PM |
F33.00011: Spacetime of Fluid and Gas Dayong Cao The spacetime coordinates do not measure the spacetime. It measures a structure of the object. The structure is massenergy center and spacetime around. It is build up by massenergy and spacetime together. The density of massenergy of solid is bigger than the one of the fluid or gas; contrariwise, the density of spacetime of the fluid or gas is bigger than the one of the solid. Because the density of spacetime is inversely proportional to the density of massenergy. The Einstein's equation has the other formula for the structure of the center of spacetime. The spacetime is wave, and the spacetime effect of the fluid and gas are about buoyancy, pressure, resistance, and temperature will be taken into Einstein's equation. It should explain of the low density asteroid-1950 DA and a rock hull of 67P/Churyumov-Gerasimenko. http://meetings.aps.org/link/BAPS.2015.APR.T1.24 http://meetings.aps.org/link/BAPS.2015.APR.H14.8 [Preview Abstract] |
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