Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session X31: Nanoconfined and Interfacial WaterFocus
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Sponsoring Units: DCP GSOFT Chair: Nicolas Giovambattista, CUNY Room: 331 |
Friday, March 18, 2016 8:00AM - 8:36AM |
X31.00001: TBA Invited Speaker: Shekhar Garde |
Friday, March 18, 2016 8:36AM - 9:12AM |
X31.00002: Water in nanoconfined spaces: from superhydrophobicity to Janus interfaces to curved hydrophobes Invited Speaker: Alenka Luzar The talk will review our theoretical and molecular simulation works that predict and elucidate thermodynamic driving forces and kinetic factors pertinent to nanoconfined water. Retrieval of superhydrophobicity on nanostructured surfaces will be one example. We will discuss a new mechanism for water mediated (Laplace) attraction between solutes with contrasting polarities (Janus interfaces) that can play an important role by enabling adhesion between polar and nonpolar particles in both, biophysical systems and heterogeneous nanomaterials. Other examples will show how macroscopic thermodynamics remarkably works down to molecular lengthscales. We will elucidate why water-induced interaction between curved hydrocarbon surfaces can be repulsive. [Preview Abstract] |
Friday, March 18, 2016 9:12AM - 9:24AM |
X31.00003: Behavior of aqueous solutions in hydrophobic confinement studied using molecular simulations Sumit Sharma Biological processes, such as formation of cell membranes, vesicles and folding of protein molecules, entail formation of a predominantly hydrophobic interior devoid of water. These processes occur in crowded aqueous environments comprising of amino acids, carbohydrates, ionic species, protein molecules, etc. Kinetics of these processes involve drying of hydrophobic pockets. Previous studies reveal that the kinetics of evaporation of water in hydrophobic confinement significantly slow down as the confinement gap increases. Presumably, the constituents of aqueous environment in biological systems modulate the kinetics of evaporation of confined water. In this work, we employ forward flux sampling in molecular dynamics simulations to study the role of solutes at different concentrations in modulating the kinetics and mechanism of evaporation of water under hydrophobic confinement. The results of these simulations will be useful for understanding optimum conditions for protein folding and other biological self-assembly processes. [Preview Abstract] |
Friday, March 18, 2016 9:24AM - 9:36AM |
X31.00004: Quasi-Elastic Neutron Scattering Study of Characteristic Features of Water Dynamics in Confined Geometries Souleymane Diallo, Naresh Osti, Alexandra Cote, Eugene Mamontov, Anibal Ramirez-Cuesta, David Wesolowski Water trapped in restricted environments is ubiquitous in nature and known to influence many biochemical and geophysical processes. Understanding the structural and dynamical properties of nano-confined water (very different than those of the bulk phase) is thus of key fundamental interests. We present a survey of various quasi-elastic neutron (QENS) studies of nano-confined water, which we further analyzed in the context of a proposed universal scaling law. Using this predictive law, we specifically investigate how the diffusive behavior of water changes with changing hydration level, confinement size, or geometry. Finally, we present our recent QENS results of water in nanoporous media evaluated using this scaling law. [Preview Abstract] |
Friday, March 18, 2016 9:36AM - 9:48AM |
X31.00005: Salt Solutions in Carbon Nanotubes: The Role of Cation-$\pi$ Interactions Tuan Anh Pham, Golam Mortuza, Brandon Wood, Edmond Lau, Tadashi Ogitsu, Steven Buchsbaum, Zuzanna Siwy, Francesco Fornasiero, Eric Schwegler Understanding the structure of aqueous electrolytes at interfaces is essential for predicting and optimizing device performances for a wide variety of emerging energy and environmental technologies. In this work, we investigate the structure of two common salt solutions, NaCl and KCl, at a hydrophobic interface within narrow carbon nanotubes (CNTs). Using a combination of first-principles and classical molecular dynamics simulations, we find that the solvation structure of the cations in the CNTs can deviate substantially from the conventional weakly interacting hydrophobic picture. Instead, interactions between solvated ions and the $\pi$-orbitals of the CNTs are found to play a critically important role, with the ion solvation structure ultimately determined by a subtle interplay between cation-$\pi$ interactions and the intrinsic flexibility of the solvation shell. In the case of K$^{+}$, these effects result in an unusually strong propensity to partially desolvate and reside closer to the carbon wall than either Na$^{+}$ and Cl$^{-}$, in sharp contrast to the known ion ordering at the water-vapor interface. [Preview Abstract] |
Friday, March 18, 2016 9:48AM - 10:00AM |
X31.00006: Confined water between two graphene layers Francois Peeters, Mario Sobrino Fernandez, Mehdi Neek-Amal Water confined between two layers with a separation of a few Angstrom forms a layered two- dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that monolayer ice with a rhombic-square structure nucleates between graphene layers which is non-polar and non-ferroelectric. We provide different energetic considerations and H-bonding results that explain the inter-layer and intra-layer properties of two-dimensional ice. The controversional AA-stacking found experimentally [G. Algara-Siller et al. Nature 519, 443445 (2015)] is consistent with our minimum energy crystal structure of bilayer ice. Furthermore, we predict that odd-number of layers of ice has the same lattice structure as monolayer ice, while even number of ice layers exhibit the square ice AA-stacking of bilayer ice.We predict that an inplane electric field polarizes the water molecules resulting in distinct-ferroelectricity. Electrical hysteresis in the response of the total dipole moment of monolayer ice is found [Preview Abstract] |
(Author Not Attending)
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X31.00007: Structure, Spectroscopy and Thermodynamics at the Water -- Graphene Interface Tod Pascal, Craig Schwartz, Keith Lawler, David Prendergast The recent discovery of an ordered two-dimensional phase of water with a square lattice between graphene sheets has led to tremendous interest in the structure of confined water, particularly under pressure.[1] Despite being recently discovered, this finding is fiercely being debated, with other researchers suggesting that the observed structures is due to the presence of NaCl, while various theoretical models predict the formation of water ice between graphene only under enormous external pressures.[1-3] Herein, by examining the EELS data, combined with simulated spectroscopy calculations and molecular dynamic simulations, we examine the thermodynamic properties of nano-encapsulated water, and demonstrate how charge transfer and chemical defects alters the phase diagram. [4] \begin{enumerate} \item Algara-Siller, G. et al., Nature 519, 443--445 (2015). \item Mario, S. F., Neek-Amal, M. {\&} Peeters, F. M., arXiv:1509.08242 [cond-mat] (2015) \item Jiao, S. {\&} Xu, Z., arXiv:1509.07215 [cond-mat] (2015) \item Schwartz, C. et al., In preparation \end{enumerate} [Preview Abstract] |
Friday, March 18, 2016 10:12AM - 10:24AM |
X31.00008: ABSTRACT WITHDRAWN |
Friday, March 18, 2016 10:24AM - 10:36AM |
X31.00009: Probing the water on chemically heterogeneous surface: interfacial-structural analysis for surface charge distribution Sucheol Shin, Adam Willard We introduce the novel method for predicting the charge distribution of chemically heterogeneous surface, but reconstructed from the perspective of the interfacial water molecules. Our approach is to analyze the response of water to a disordered surface and infer from that response the heterogeneous distribution of surface charge. We accomplish this using a framework that is based on a probabilistic description of water’s interfacial molecular structure and maximum likelihood estimation. This framework allows to deduce the apparent charge that is most congruently represented by the set of water configurations over the particular region of a surface. We demonstrate that the estimated charge distribution is consistent to the actual distribution for a static model substrate and hence that our method can be applied to investigate a dynamic fluctuating substrate such as the surface of a hydrated protein. This novel technique provides the useful information that can reflect the influence of fluctuations in the structure of biomolecule. [Preview Abstract] |
Friday, March 18, 2016 10:36AM - 10:48AM |
X31.00010: Enhanced configurational entropy in high-density nanoconfined bilayer ice Fabiano Corsetti, Jon Zubeltzu, Emilio Artacho Understanding the structural tendencies of nanoconfined water is of great interest for nanoscience and biology, where nano/micro-sized objects may be separated by very few layers of water. We present a study of water confined to a 2D geometry by a featureless, chemically neutral potential, in order to characterize its intrinsic behaviour. We use molecular dynamics simulations with the TIP4P/2005 potential, combined with density-functional theory calculations with a non-local van der Waals density functional and an {\em ab initio} random structure search procedure. We propose a novel kind of crystal order in high-density nanoconfined bilayer ice. A first-order transition is observed between a low-temperature proton-ordered solid and a high-temperature proton-disordered solid. The latter is shown to possess crystalline order for the oxygen positions, arranged on a close-packed triangular lattice with AA stacking. Uniquely amongst the ice phases, the triangular bilayer is characterized by two levels of disorder (for the bonding network and for the protons) which results in a configurational entropy twice that of bulk ice. [Preview Abstract] |
Friday, March 18, 2016 10:48AM - 11:00AM |
X31.00011: Determination of interfacial properties using a PC-SAFT based classical density functional theory for fluid mixtures of industrial interest Jian Yang, Diego Cristancho, Rakesh Srivastava In this paper, a recent development of a PC-SAFT based classical density functional theory (DFT) is applied to the determination of interfacial properties of pure fluids and mixtures of industrial interest. Initially, the DFT formalism is described and the methodology for the property calculations explained. The consistency of this approach allows the determination of interfacial properties for fluids using the PC-SAFT equation of state parameters determined from bulk physical property data, such as vapor-liquid-equilibrium and densities. This methodology is an excellent alternative for the predictions of interfacial property of fluids and extrapolation to high pressure ranges where experimental measurements becomes challenging. [Preview Abstract] |
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