Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B43: Focus Session: Fluids Under Confinement, Water at Interfaces and in Confinement |
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Sponsoring Units: DPOLY Chair: Elisa Riedo, Georgia Institute of Technology Room: 214C |
Monday, March 2, 2015 11:15AM - 11:27AM |
B43.00001: Molecular Dynamics Simulations of Water Evaporation Chengyuan Wen, Gary Grest, Shengfeng Cheng The evaporation of water from the liquid/vapor interface is studied via large-scale molecular dynamics simulations for systems of more than a million atoms at 550K and 600K. The TIP4P-2005 water model whose liquid/vapor surface tension is in excellent agreement with experiments is used. Evaporative cooling at the interface is observed from temperature profiles determined from both translational and rotational kinetic energy. During evaporation, the density of water is slightly enhanced near the liquid-vapor interface. The velocity distribution of water molecules in the vapor phase during evaporation at various distances relative to the interface fit a Maxwell-Boltzmann distribution. While our results indicate an imbalance between evaporating and condensing water molecules, local thermal equilibrium is found to hold in addition to mechanical equilibrium. [Preview Abstract] |
Monday, March 2, 2015 11:27AM - 11:39AM |
B43.00002: Structure of the Ice-Clathrate Interface Andrew Nguyen, Matthew Koc, Tricia Shepherd, Valeria Molinero In the laboratory, clathrates are customarily synthesized from ice and gas guest. It is not clear how and whether ice assists in the nucleation of clathrate hydrates. The structure of the ice-clathrate interface can help assess the role of ice in clathrate nucleation. However, only few studies have addressed the structure of the ice-clathrate interface. Here, we use molecular dynamic simulations to study the structure of the ice-clathrate interface. There is no lattice matching between any plane of ice and clathrate hydrates, therefore an interfacial transition layer has to form to connect the two crystals. We investigate the structure of the ice-clathrate interface produced by alignment and equilibration of the crystals, competitive growth of the two crystals from a common solution, and nucleation of hydrate in the presence of a growing ice front. We find that the interfacial transition layer between ice and clathrate has a width of two to three water layers and it is disordered in all cases. Water in the interfacial transition layer has tetrahedral order lower than either ice or clathrate and higher than liquid water under the same thermodynamic conditions. [Preview Abstract] |
Monday, March 2, 2015 11:39AM - 11:51AM |
B43.00003: Experimental evidence for empty cage methane clathrate hydrates grown using surfactants. Jeffrey Botimer, Derek Dunn-Rankin, Peter Taborek Clathrate hydrates are non-stochiometric ice-like crystalline compounds consisting of host water molecules forming a cage-like structure around guest molecules. The guest molecule is necessary for the stability of the hydrate. Surfactants have been shown to greatly enhance the kinetics of hydrate growth, which is important for many applications. We have built custom cells that allow in situ Raman and optical imaging of the growth of methane clathrate hydrates from liquid water. In our studies, above 0C, we observe the formation of solid that precedes the absorption of methane gas required to form clathrate hydrates. Our research shows that sodium dodecyl sulfate (SDS) causes a fundamental change in the growth mechanism of methane hydrates, creating a temporary empty cage clathrate structure. The existence of this transitional state is confirmed by in situ Raman measurements, in situ NMR. We have simultaneously monitored the gas uptake and the NMR signal of the growing hydrate in a high pressure NMR cell. The empty cage solid structure appears to be unique to surfactant assisted hydrate growth, and begins to disappear for low SDS concentrations (\textit{\textless }25ppm). [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:03PM |
B43.00004: Formation of 1D adsorbed water structures on CaO(001) Xunhua Zhao, Saswata Bhattacharya, Luca M. Ghiringhelli, Sergey V. Levchenko, Matthias Scheffler Understanding the interaction of water with oxide surfaces is of fundamental importance for basic and engineering sciences. Recently, a spontaneous formation of one-dimensional (1D) adsorbed water structures have been observed on CaO(001) [1]. Interestingly, at other alkaline earth metal oxides, in particular MgO(001) and SrO(001), such structures have not been found experimentally. We calculate the relative stability of adsorbed water structures on the three oxides using density-functional theory combined with the {\em ab initio} atomistic thermodynamics. Low-energy structures at different coverages are obtained with a first-principles genetic algorithm. Finite-temperature vibrational spectra are calculated using {\em ab initio} molecular dynamics. We find a range of ($T$, $p$) conditions where 1D structures are thermodynamically stable on CaO(001). The orientation and vibrational spectra of the 1D structures are in agreement with the experiments [1]. The formation of the 1D structures is found to be actuated by a symmetry breaking in the adsorbed water tetramer, as well as by a balance between water-water and water-substrate interactions, determined by the lattice constant of the oxide.---[1] X. Shao, Y. Fujimori, M. Sterrer, H.-J. Freund, and N. Nilius, to be published. [Preview Abstract] |
Monday, March 2, 2015 12:03PM - 12:15PM |
B43.00005: Characterization of the Mobility and Reactivity of Water Molecules on TiO2 Nanoparticles by 1H Solid-State Nuclear Magnetic Resonance Xiaoliang Wang, Lili Zhu, Pingchuan Sun, Dongshan Zhou, Gi Xue Understanding interfacial water behavior is essential to improving our understanding of the surface chemistry and interfacial properties of nanomaterials. Here using 1H solid-state nuclear magnetic resonance (1H SSNMR), we successfully monitored ligand exchange reaction between oleylamine (OLA) and adsorbed water on titanium dioxide nanoparticles (TiO2 NPs). Three different types of interfacial waters with different reactivities were distinguished. The mobility of the adsorbed water molecules was characterized by dipolar filtered 1H SSNMR. Our experimental results demonstrate that the adsorbed water can be categorized into three different layers: rigid water species with restricted mobility closest to the surface of TiO2 NPs; less mobile water species weakly confined on TiO2 NPs; and water molecules with high mobility. Water in the third layer could be replaced by OLA, while water in the first and second layers remained intact. The finding that the interfacial water with the highest mobility has the strongest reactivity has guiding significance for tailoring the hydrophilic and hydrophobic properties of TiO2 NPs. [Preview Abstract] |
Monday, March 2, 2015 12:15PM - 12:27PM |
B43.00006: Diffusive Dynamics of Water inside Hydrophobic Carbon Micropores Studied by Neutron Spectroscopy and MD Simulation Souleymane Diallo, Lukas Vlcek, Eugene Mamontov, Jong Keum, Jihua Chen, Joseph Hayes, David Wesolowski, Ariel Chialvo Using neutron scattering, we have investigated the ambient pressure diffusive dynamics of water in microporous Kynol$^{TM}$ ACF-10 (with average micropore size of $\sim$11.6 {\AA}) from temperature $T=$ 280 K in its stable liquid state down to $T=$ 230 K into the metastable supercooled phase. The observed characteristic relaxation times and diffusion coefficients are found to be respectively higher and lower than those in bulk water, indicating a slowing down of the water mobility with decreasing temperature. Comparison between the experimental observations and complementary molecular dynamics simulations of a model system, in which we studied the diffusion of water within the 12 {\AA} gap of two parallel graphene sheets will be presented. [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 12:39PM |
B43.00007: Quantum tunneling and vibrational dynamics of ultra-confined water Alexander I. Kolesnikov, Lawrence M. Anovitz, Georg Ehlers, Eugene Mamontov, Andrey Podlesnyak, Timothy R. Prisk, Andrew Seel, George F. Reiter Vibrational dynamics of ultra-confined water in single crystals beryl, the structure of which contains $\sim$ 5 {\AA} diameter channels along the c-axis was studied with inelastic (INS), quasi-elastic (QENS) and deep inelastic (DINS) neutron scattering. The results reveal significantly anisotropic dynamical behavior of confined water, and show that effective potential experienced by water perpendicular to the channels is significantly softer than along them. The observed 7 peaks in the INS spectra (at energies 0.25 to 15 meV), based on their temperature and momentum transfer dependences, are explained by transitions between the split ground states of water in beryl due to water quantum tunneling between the 6-fold equivalent positions across the channels. DINS study of beryl at T=4.3 K shows narrow, anisotropic water proton momentum distribution with corresponding kinetic energy, E$_{K}$=95 meV, which is much less than was previously observed in bulk water ($\sim$150 meV). We believe that the exceptionally small E$_{K}$ in beryl is a result of water quantum tunneling $\backslash$ delocalization in the nanometer size confinement and weak water-cage interaction. [Preview Abstract] |
Monday, March 2, 2015 12:39PM - 12:51PM |
B43.00008: Nanomechanical measurements of ionic effect on nanoconfined water Edward Kramkowski, Shah Khan, Peter Hoffmann The behavior of liquid molecules confined to nanometer-scale spaces is a topic of particular interest to a variety of fields. From lab-on-a-chip medical device manufacturers to petroleum engineers involved in oil recovery, a wide range of researchers could benefit from a better understanding of the mechanics of nanoconfined liquids. Previous research has shown that above a critical strain rate, a confined liquid exhibits a solid-like response that oscillates with a period roughly equal to the molecular diameter of the liquid being observed. This indicates that when a liquid is compressed at a rate faster than the molecules can diffuse in bulk out from between the confining surfaces, it dynamically solidifies into an anisotropic layered liquid. In order to better understand the influence that the confining surfaces have on this behavior, we have been observing how the addition of different classes of ions at varying concentrations to a pure water sample either enhance or suppress the natural tendency of the water to order. The work indicates that an ion's effect on the liquid's structure is commensurate with its classification according to the Hofmeister series, with the amount of deviation from the pure behavior governed by the ionic concentration. [Preview Abstract] |
Monday, March 2, 2015 12:51PM - 1:03PM |
B43.00009: Supressed Water Crystallization in Nano-Structured Physical Hydrogel Clinton Wiener, Bryan Vogt, Robert Weiss Suppressed water crystallization occurs in some organisms, such as the common wood frog, which allows it to hibernate in a frozen state without damage to its cells. Knowledge of the behavior of supercooled water and alternate ice forms may have many implications to many fields of science. Supercooling of water by several degrees below the normal freezing point is often observed in hydrogels that have attractive interactions with water, e.g., hydrogen bonding. Repulsive confinement, such as in hydrophobic porous carbon, can have even more significant effects on the supercooling of the entrapped water. This talk describes the freezing behavior in nano-structured, hydrophobically modified poly(dimethyl acrylamide) hydrogels that possess attractive and repulsive interactions with water and are physically crosslinked by hydrophobic nanodomains. Three distinct water freezing regimes were observed in the hydrogel swollen to about 50{\%} water by weight. Differential scanning calorimetry detected three crystallization exotherms at 254K, 244K, and 227K. Quasi-elastic neutron scattering experiments have shown that although the water mobility was suppressed at room temperature, the water remained significantly mobile below the normal freezing point of water. The talk will discuss how tuning the concentration of the hydrophobic composition of the hydrogel affects the porous length scales in the hydrogel, which may alter the state of water and the crystal form produced by supercooling. [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:15PM |
B43.00010: ABSTRACT WITHDRAWN |
Monday, March 2, 2015 1:15PM - 1:27PM |
B43.00011: Ice-like Behavior of Ultra-Confined Water Timothy Prisk, Alexander Kolesnikov, Eugene Mamontov, Lawrence Anovitz Water confined within microporous minerals presents an extreme example of fluid confinement, where the water molecule is trapped within cages or pore channels which are not much larger than the water molecule itself. Hemimorphite Zn$_4$Si$_2$O$_7$(OH)$_2$$\cdot$H$_2$O is a microporous silicate mineral containing confined molecular water which interacts with the crystal structure by means of hydrogen bonding. The water molecule forms a set of coplanar hydrogen bonds with the hydroxyl groups, forming a system of two-dimensional ice within the pore channel. In this presentation, we report quasi-elastic and inelastic neutron scattering studies of water and hydroxyl proton dynamics within hemimorphite. The scattering data reveal strong anisotropy in the vibrational behavior of the water molecule, with the scissors and stretching normal mode motions occurring only on a single crystallographic plane. The effective density of states of the protons extracted from the scattering data reproduces the water contribution to the mineral's heat capacity. [Preview Abstract] |
Monday, March 2, 2015 1:27PM - 1:39PM |
B43.00012: The consequences of water in adhesion, friction and wetting Ali Dhinojwala, Adrian Defante, Tarak Burai, Matthew Becker The interactions of hydrophobic surfaces are relevant to numerous processes in physical and biological sciences.~~ We have used contact mechanics, contact angle measurements, and a biaxial friction cell to quantify adhesion, wetting and friction behavior in wet environments between two low energy surfaces.~ To gain an understanding of the role of water in these processes we have coupled these measurements with surface sensitive sum frequency generation to directly measure the contacting interface. These results provide a direct molecular probe to understand macroscopic phenomena. [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 1:51PM |
B43.00013: How different is water crystallization from polymer crystallization under confinement? George Floudas, Yasuhito Suzuki, Hatice Duran, Martin Steinhart, Hans-Juergen Butt The freezing mechanism of water under confinement can be fundamentally different from the bulk. Despite fundamental importance, the lack of well-defined confining media precluded a systematic investigation. Herein we employ self-ordered nanoporous aluminum oxide (AAO) which contains arrays of discrete, parallel and cylindrical nanopores with uniform pore length and diameter to study the effect of confinement on water crystallization. By varying different parameters such as pore size, temperature and cooling rate, the respective conditions under which the hexagonal form (I$_{\mathrm{h}})$ and the less common form of cubic ice (I$_{\mathrm{c}})$ could be studied. We found a transition from heterogeneous nucleation of I$_{\mathrm{h}}$ to homogeneous nucleation of predominantly I$_{\mathrm{c}}$ with decreasing pore diameter. Furthermore, the monotropic I$_{\mathrm{c}}$ $\to $ I$_{\mathrm{h}}$ transition commonly observed upon heating is suppressed inside pores having diameters $\le $ 35 nm. These findings lead to the phase diagram of water under confinement. It contains a predominant cubic form, a form known to exist only in the upper atmosphere\textbf{. }There are many similarities between the freezing of water and the crystallization of polymers under confinement. [Preview Abstract] |
Monday, March 2, 2015 1:51PM - 2:03PM |
B43.00014: Frictional energy barrier and blocking temperature in water molecules and carbon nanotubes system Jianwei Zhang, Jiaxi Li, Wenfeng Li Water transport through hydrophobic channels of single-walled carbon nanotubes has attracted a lot interests, especially, various potential applications of SWCNTs have been proposed for designing novel nanofluidic devices. By adopting Molecular dynamics method, we investigated mechanics and statistics properties of water molecules escaping from a confined single-walled carbon nanotube. From our numerical MD simulations and statistical model, we determined the friction energy barrier of water molecules in (10.10) SWCNT is 9.88 kcal/mol, and which is the minimal energy for flowing a water molecules in CNT. By only using friction energy barrier and relaxation time parameter, our model can fit all different situations MD simulation results. In order to describing the frictional lock behavior of water molecules, we introduced a new blocking temperature, below this temperature (391K for our system), water is locked in CNT due to friction energy barrier. We found that the blocking temperature is closely related to system response time, and it also shows a linear behavior to frictional energy barrier. Furthermore, we found several other interesting statistics results when a water molecules leaving SWCNTs. [Preview Abstract] |
Monday, March 2, 2015 2:03PM - 2:15PM |
B43.00015: The Role of Water and Carbon Dioxide Intercalation on Na-Montmorillonite Swelling Behavior at Geological Carbon Sequestration Conditions Meysam Makaremi, Kenneth Jordan, George Guthrie, Evgeniy Myshakin Swelling of Na-montmorillonite in the environment relevant to geological CO$_{2}$ sequestration in deep underground formations is investigated by conducting classical Monte Carlo and molecular dynamics simulations. Both the binary (clay-water or clay- CO$_{2})$ and the ternary (clay-water- CO$_{2})$ systems containing the clay, water and carbon dioxide phases are simulated, and the free energy for clay swelling is calculated as a function of the interlayer distance. The calculations indicate that while water intercalates into the clay layer and forms stable monolayer and bilayer hydration states, in the absence of interlayer water adsorption of dry carbon dioxide is thermodynamically unfavorable. In the ternary system, two hydration states are observed with interlayer spacings corresponding closely to those of the pure water binary system. In addition, the simulations of the ternary system show that the incomplete first hydration state is more effective at adsorbing CO$_{2}$ molecules than is the incomplete second hydration state. [Preview Abstract] |
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