Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F04: Water Dynamics in Different Environments: Experiment and Theory III. Nanoconfined WaterFocus
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Sponsoring Units: DCP DCOMP DBIO DSOFT Chair: Angelos Michaelides, Univ Coll London Room: 109 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F04.00001: Investigating graphene oxide-aqueous interfaces Invited Speaker: Revati Kumar Graphene oxides (GO) are nanosheets of graphene with oxygen bearing defects. The GO sheet is highly heterogeneous with the sp3carbons, connected to oxygen bearing functional groups, interspersed between the usual sp2carbons of graphene resulting in competition between aromatic regions and highly hydrophilic domains (from the oxygen containing functional groups, typically -OH and epoxy groups) at the GO-aqueous interface. GO materials are increasingly gaining traction for ion and molecule separations. The interfacial region between the GO material and aqueous solutions plays a key role in these applications. Our efforts are focused on gaining molecular level insight into the interfacial ordering using molecular simulations. Classical and Born-Oppenheimer molecular dynamics were performed to study the interfacial water structure, including hydrogen bonding environments, using different order parameters. The simulations were used to gain insight into the results from recent vibrational sum frequency generation experiments. The reactivity of the graphene oxide-neat water interface as well as in the presence of an acidic excess proton were also investigated. The results of this study will be presented and discussed. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F04.00002: Viscoelasticity and dynamics of nanoconfined water by atomic force microscopy Peter Hoffmann, Edward Kramkowski, Shah H Khan Our group has conducted extensive measurements of the viscoelastic properties of nanoconfined water in hydrophilic environments using a specialized high-resolution dynamic atomic force microscopy technique. Here we will present an overview of our findings, including the observation of dynamic solidification, the effect of ions on ordering and dynamics, and the recent observation of the compression rate dependence of the effective viscosity. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F04.00003: Hydrogen bonding structure of confined water templated by a metal-organic framework with open metal sites Kelly Hunter, Adam J. Rieth, Mircea Dinca, Francesco Paesani While the properties of bulk water are difficult to understand, water in confinement is even more poorly understood. Metal-organic frameworks (MOFs) are unique a class of materials that display high adsorption properties. Recently, the MOF Co2Cl2BTDD has been shown to adsorb water at low relative humidity, attracting interest for applications in harvesting water from air. Here, we investigate structural and dynamical properties of water adsorbed in Co2Cl2BTDD as a function of relative humidity using many-body molecular dynamics simulations with the MB-pol model. Comparisons of the experimental and theoretical infrared spectra allow us to elucidate the mechanism of pore filling, with water initially binding to the open metal sites and forming one-dimensional chains along the interior of the framework. These chains nucleate pore filling, establishing a three-dimensional hydrogen-bond network. As the pore fills, the spectroscopic features and orientational dynamics indicate a gradual transition from “ice-like” to “liquid-like” properties modulated by the heterogenous confinement, with individual water molecules exhibiting distinct behavior depending on their specific location inside the pores. Nat. Commun. 2019, 10, 1-7. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F04.00004: Vibrational dynamics and quantum tunneling of water molecules in bassanite Alexander Kolesnikov, Lawrence {Larry} M. Anovitz, Stephan Irle Using inelastic neutron scattering (INS) we studied dynamics of bassanite (CaSO4*0.5H2O), a structure of which has channels formed by CaO8 and CaO9 polyhedra with water molecules residing in the channels and occupying two different positions. The INS spectra showed that at low temperature (T=5 K) intramolecular O-H stretching modes of water are at high energy, around 445 meV (compared to 410 meV in ice-Ih), and the intermolecular librational band is at low energies, 35-90 meV (65-125 meV in ice-Ih), indicating weak hydrogen bonds acting on water molecules. At lower energies we observed a peak at about 1 meV, which shows the behaviour of tunneling mode: its intensity decreases with temperature increase and shows nonmagnetic momentum transfer dependence. In the talk we will discuss the observed INS results and attempt to explain the tunneling of water molecule, which was not observed before in other INS experiments involved confined water molecules in the presence of hydrogen bonds. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F04.00005: Structure and Dynamics of Aqueous Solutions in Carbon Nanotubes: Insights from First-Principles Simulations Fikret Aydin, Cheng Zhan, Eric R Schwegler, Tuan Anh Pham Carbon nanopores underpin a large array of materials systems and technological applications, including supercapacitors and water desalination. In these devices, understanding of the ion solvation and dynamics is essential for predicting and optimizing the performance; however, many mechanistic details remain enigmatic. Here, we employ first-principles simulations to unravel key features of the solvation structure of several common ions confined within graphene slit pores and carbon nanotubes (CNTs). We find that polarizable ions exhibit a stronger adsorption at the interfaces and these effects are found to be significantly enhanced under confinement. In addition, we find that confinement significantly influences ion selectivity and transport, i.e., ions with a small radius are found to yield a notably larger energy barrier to reach the pore entrance. Our study points to the complex interplay between confinement and specific ion effects, which has broad implications in optimizing nanopores for ion selectivity and energy storage. |
Tuesday, March 3, 2020 9:24AM - 10:00AM |
F04.00006: One atom thick angstrom-scale capillaries: Water flow Invited Speaker: Radha Boya It has been an ultimate but seemingly distant goal of nanofluidics to controllably fabricate capillaries with dimensions approaching the size of small ions and water molecules. But surface roughness makes it challenging to produce capillaries with precisely controlled dimensions. We have developed a method for fabrication of narrow and smooth angstrom (Å) scale capillaries through van der Waals assembly of 2D-materials, with atomically flat sheets at the top and bottom separated by spacers made of 2D-crystals with a precisely controlled number of layers. These capillaries can be envisaged as if individual atomic planes are removed from a bulk layered crystal leaving behind flat voids of a chosen height. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F04.00007: Nano-confined water and ions in cement pores Abhay Goyal, Ivan Palaia, Katerina Ioannidou, Emmanuel Trizac, Roland JM Pellenq, Emanuela Del Gado We use numerical simulations to study the behavior of water confined by planar surfaces in the presence of divalent ions. The dynamics and mobility of the water are found to be strongly dependent on confinement. At large surface separations, most of the water behaves like in bulk conditions, but in high confinement the dynamics slow down and become coupled to the ions. This in turn increases the ion ordering and thus the overall attraction between two charged surfaces when the confinement is high. From these observations, we develop an analytical prediction of the attractive strength based on the formation of correlated ion-water structures. These results reveal a new mechanism for strong electrostatic cohesion of charged particles due to the restructuring of confined water. This effect is very relevant for the case of cement, where it explains the incredible strength of the material and could be the basis for intelligent design of cements. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F04.00008: Microscopic study of proton kinetic energy anomaly for confined water Mohammad Moid, Yacov Finkelstein, Raymond Moreh, Prabal K Maiti Several anomalies, related to structural and dynamical transition, have been reported for water at different thermodynamic conditions and environments. Of particular interest, the reported anomalies of the proton mean kinetic energy, Ke(H), in nanoconfined water, as measured by deep inelastic neutron scattering (DINS), are a longstanding problem related to proton dynamics in hydrogen-bonded systems. We used classical MD method to deduce Ke(H) by calculating the proton vibrational density of states, H-VDOS, for the case of water inside single wall carbon nanotubes (SWCNT) of varying diameters. The mean vibrational density of states (VDOS) of protons in water nanoconfined inside single wall carbon nanotubes (SWCNTs) is calculated as a function of temperature and SWCNT diameter, DCNT. The calculated VDOS are utilized for deducing the mean kinetic energy of the water protons, Ke(H), by treating each phonon state as a quantum harmonic oscillator. The calculation depicts a strong confinement effect as reflected in the drop of the value of Ke(H) at 5K for DCNT < ~12Å, while absent for larger diameters. The results also reveal a very significant blue and red shifts of the stretching and bending modes respectively compared to those in bulk ice, in agreement with experiment. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F04.00009: Water dynamics in Evaporating Nanodroplets Luis Ruiz Pestana, Teresa Head-Gordon The evaporation of droplets on heated substrates has been intensively studied in the last several decades. As such, well validdated continuum theories have been developed that describe the modes of evaporation, evaporating profiles, and also predict the internal convective flows compatible with the evaporating modes. The evaporation of small nanoscale droplets plays a key role in a myriad of scientific and technological applications from atmospheric chemistry to the cooling of nanoelectronics to catalysis, where evaporating nanodroplets produced by electro spray ionization are increasingly being used to accelerate chemical reactions. At the nanoscale, however, where large surface to volume ratios govern the behavior, and fluctuations play a major role, it remains unclear whether the continuum theories can be applied to predict the the response. Here, we put that to the test and use classical molecular dynamics simulations of water nanodroplets of two different sizes both suspended under isothermal evaporation conditions and on heated substrates with different levels of hydrophobicity. We focus on mapping the convective flows that develop within water nanodroplets and the resulting evaporating profiles, with the aim of assessing the predictive power of the continuum theories. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F04.00010: A molecular view of glycerol-water hydrogen bonding patterns Cameron Mackie, Bo Xu, Oleg Kostko, nikhil chari, emily zhang, Martin P Head-Gordon, Musahid Ahmed Photoionization dynamics of micro-hydrated molecules in the gas phase when combined with theory can reveal information on the solution phase. Synchrotron based molecular beam mass spectrometry of water-glycerol clusters in the gas phase and terahertz time domain spectroscopy in solution coupled to calculations reveal the nature of hydrogen bonding in glycerol water solutions and provides a general picture of the interaction of polyols with water. A novel hydrogen bonding pattern is theoretically observed at specific glycerol to water concentrations. A significant shortening (and strengthening) of hydrogen bond lengths (~1.6 Å) are observed between H2O molecules where one of the H2O molecules is held in a “tweezed” fashion by the two hydroxyl groups of glycerol. This hydrogen bond shortening is also observed to reach beyond the first hydration shell. Experimental results show a clear preference for certain clusters to retain two water molecules due to the enhanced hydrogen bonding strengths. This shortening of hydrogen bonds is also proposed to explain the experimentally observed decrease of excess molar volumes with concentrations for various polyols. |
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