Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L25: Physics of Liquids IIIFocus
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Sponsoring Units: GSNP DSOFT DCP Chair: Fausto Martelli, IBM TJ Watson Research Center Room: 402 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L25.00001: Energy landscapes: from molecules and nanodevices to glasses and machine learning Invited Speaker: David Wales The potential energy landscape provides a conceptual and computational framework for |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L25.00002: Nanoscale dynamics of liquids: S(Q,ω) with 0.8 meV resolution using x-rays Alfred Q. R. Baron, Daisuke Ishikawa We describe a new instrument for measuring the dynamic structure factor of liquids, S(Q,ω) , at the RIKEN SPring-8 Center in Japan using inelastic x-ray scattering (IXS) (see https://arxiv.org/abs/1504.01098). A long, 15m, insertion device provides unprecedented x-ray intensity, making practical experiments possible with sub-meV resolution at sub nm-1 momentum transfers. This allows new insight into the mesoscale crossover regions between hydrodynamic and atomistic behavior of liquids. The performance will be illustrated with examples, including new results from liquid water [Ishikawa & Baron, submitted] and liquid iron [Baron, Inui, Ishikawa, et al, work in progress], demonstrating the range of the instrument and its applicability to even rather difficult experiments. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L25.00003: The formation of nanoripples by ultra-low energy ion irradiation reveals the liquidus nature of metallic glass surface Peng Luo, Camilo Jaramillo Correa, Jessica Crystal Spear, Jean Paul Allain, Yang Zhang We report an experimental investigation of ion irradiation on metallic glasses (MGs), with extremely low ion energy of 50~225 eV, orders of magnitude lower than that often used in previous studies. Highly periodic ripples with a wavelength of 20 nm and an amplitude of 0.5 nm were developed on MG surfaces under irradiation. With increasing irradiation time, we can identify three regimes: appearance of initial random islands, coarsening of the pattern through annihilation reactions of mobile defects, and finally saturation of the ripples. No change is observed for the devitrified counterparts with the same treatment. These findings reveal the liquidus nature of glass surface even far below the glass transition temperature and provide new clues for surface modification of amorphous materials. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L25.00004: Study of Mesoscale Structure and Dynamics of Associated Liquid 2-propanol by Neutron Scattering and Molecular Dynamics Simulations Yanqin Zhai, Antonio Faraone, Yang Zhang Monohydroxy alcohols are good model systems for studying the impact of hydrogen bonding on the structure and dynamics of liquids and on the macroscopic transport properties such as viscosity. We investigated 2-propanol by static and quasielastic neutron scattering experiments on a series of partially and fully deuterated samples at temperatures ranging from the liquid, the deeply supercooled, to the glassy state. Corresponding Molecular Dynamics (MD) simulations are performed to further understanding the collective dynamics of the system. We focus on the mesoscale structures associated to the structure factor pre-peak at wavevector Q ~ 0.8 Å-1. The dynamics of these molecular associates is at least one order of magnitude slower than the dynamics at the structure factor peak, at Q ~ 1.4 Å-1. MD simulations show that 2-propanol molecules prefer to form chain-like structures with approximately 10% of the rings although the hydroxyl group is located in a non-terminal position. The emergence of multiple relaxation processes as the system is cooled towards the melting temperature and below is observed, which could be related to the non-Arrhenius increase of the viscosity. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L25.00005: Self-Diffusion of Liquid Normal Hydrogen: A Quasi-Elastic Neutron Scattering Study Timothy Prisk, Scott Hanna, Richard Azuah Quantum zero-point motion plays an important role in determining the properties and behavior of liquid hydrogen. For example, by comparing the predictions of classical molecular dynamics with centroid molecular dynamics, several theoretical studies have suggested that the self-diffusion constant of liquid para-hydrogen is dominated by zero-point motion. In this presentation, we report quasi-elastic neutron scattering measurements of liquid normal hydrogen under saturated vapor pressure. Our empirical estimates of the self-diffusion constant and Arrhenius activation energy are in good agreement with accepted values obtained by nuclear magnetic resonance. As previous theoretical work has generally focused upon temperatures near the triple point, we will argue that further development in this area would be useful. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L25.00006: A Microscopic Description of Dielectric Relaxation in Water using Quasi-Elastic Neutron Scattering Yadu Krishnan Sarathchandran, Yuya Shinohara, Eugene Mamontov, Wojciech Dmowski, Takeshi Egami Water exhibits an anomalously high dielectric constant, ε=78, at ambient temperature. This is caused by a Debye peak in the dielectric spectrum with a maximum at ~20 GHz. It is reported that this Debye peak reflects some hydrogen bond mediated, collective dipolar dynamics in water. However, a clear microscopic description of this phenomenon is lacking. We report our study on the microscopic picture of water’s dielectric relaxation using the time-dependent pair-distribution function, the Van Hove function. The dynamic structure factor of water, S(Q, E), is measured using quasi-elastic neutron scattering over a wide momentum transfer range by making use of recent advances in analyzer crystal options at BASIS, SNS. S(Q, E) is double Fourier transformed to obtain the Van Hove function, g(r, t), to investigate the temporal evolution of molecular correlations in real-space up to 10 picoseconds. Our findings align with previous studies on the time-scale of the Debye process and the higher frequency excess Debye process, although significantly differ in the microscopic description. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L25.00007: Atomic dynamics of liquid Hg studied by high-resolution inelastic x-ray scattering Daisuke Ishikawa, Alfred Q. R. Baron High-resolution Inelastic X-ray Scattering (IXS) is a powerful tool for measuring the dynamic structure factor, S(Q,ω), in liquids. Very recently, we began to operate a new instrument that allows practical measurements on liquids of the most interesting low Q region at BL43LXU of the RIKEN SPring-8 Center in Japan. Liquid dynamics in this region is important since this region corresponds to transition from hydrodynamic to solid-like elastic regimes. Liquid metals are particularly interesting since they behave quite differently from molecular liquids due to strong atomic interactions. We use the new setup to investigate liquid Hg with energy resolution >0.8 meV at temperature near the melting point Tm = 234.3 K. We will discuss details of transition of the speed of sound in liquid Hg, the quasi-elastic line-width, and a new approach to fitting dynamical spectra. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L25.00008: Isotope effect in liquid water explored by X-ray absorption spectroscopy Chunyi Zhang, Linfeng Zhang, Jianhang Xu, Fujie Tang, Xifan Wu The X-ray absorption spectra (XAS) of both liquid H2O and D2O are computed using our recently developed approximate computational approach in solving Bethe-Salpeter equation. In the above, the molecular structures are obtained from the well-equilibrated trajectories generated by path-integral deep potential molecular dynamics (DPMD). In particular, the DPMD force field is constructed from ab initio path-integral molecular dynamics based on the strongly constrained and appropriately normed (SCAN) density functional. Our preliminary results indicate that the experimentally observed isotope effects in the XAS spectra are qualitatively reproduced by our theoretical prediction. The H-bond network in heavy water is slightly more structured than that in light water, which is consistent with the less prominent pre-edge and main-edge of theoretical XAS spectrum of D2O than that of H2O. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L25.00009: The Long-range Ordering of Ions in Aqueous Salt Solutions Evgenii Fetisov, John L Fulton, Shawn Michael Kathmann, Christopher J Mundy, Gregory K Schenter The importance of understanding the long-range structure in aqueous salt solutions has recently come to the forefront when it was suggested that the ordering of water in the presence of ions possibly reaches length scales up to 10 nm. A much more important question regards the long-range ordering of the ions themselves since their arrangement critically affects processes such as nucleation/crystallization and the solution energetics related to activity coefficients and osmotic pressure. We use a combination of molecular dynamics and X-ray diffraction to correlate experimentally measured long-range structure to the precise spatial distribution of species in aqueous solutions of alkali and alkali earth halides. For the first time, we quantitatively differentiate and explain a separate region in the fluid structure factor containing diffraction-like features at low Q values (“pre-peaks”) that lead to the oscillatory behavior in the ion-ion and ion-water pair distribution functions. These features are shown to be due to a combination of correlated (e.g., cation-cation and cation-water) and anti-correlated (cation-anion and anion-water) atomic positions. In addition, we also explore the influence of salt concentration on the position and magnitude of the pre-peaks. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L25.00010: Influence of ionic species on water broadband electrodynamics Vasily G. Artemov, Henni Ouerdane Proton exchange plays a central role in modern electrochemical systems. While it is well described for times larger than milliseconds [1], it is an important process not fully understood on nanoscale distances and subpicosecond timescales. Here, we discuss the dynamical structure of water from femtoseconds to seconds time intervals using a combination of broadband dielectric spectroscopy and infrared spectroscopy methods. Accounting for dielectric properties [2], isotopic effects [3] and confinement effects [4], we present a model of water based on the time-dependence of the ionic species concentration, over the whole time interval between the intermolecular direct current (below microseconds) and intramolecular infrared vibrations (sub-picoseconds), which so far was hardly achievable. Our approach provides a new vision on the hydrogen bonding in water taking into account the role of ionic species on the intermolecular interactions; and we discuss how this paves the way to innovative design of electrochemical energy storage devices. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L25.00011: Supramolecular Interactions and Non-Equilibrium Properties of Non-Aqueous Electrolytic Solutions for Next Generation Flow Batteries Hossam Farag, Ilya A Shkrob, Lu Zhang, Lei Cheng, Yang Zhang Non-aqueous electrolytes enable batteries to operate at higher cell potentials compared to its aqueous counterpart due to the wider electrochemical stability window of the former. Super-concentrated electrolytic solutions are emerging as a new class of liquid electrolytes with various unusual functionalities beneficial for advanced Li battery applications. However, a desired high ionic conductivity is missing in the high-concentrated regime due to a reduction in ionic mobility. Reduced ionic motility is ascribed to an increase in solution viscosity whose mechanism is still not fully understood. We hypothesize that we could tune the solution viscosity via modulating the supramolecular interactions enabling a groundbreaking solution for fast recharging rate of these batteries. We carried out MD simulations to investigate the mechanism by which the ionic conductivity decreases. We first observed a reduction in the number free-ion carriers via formation of contact ion pair in this high concentration regime. Further investigation of the mechanism by which viscosity increases is still undergoing. Herein, we present the simulation results and relative analysis. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L25.00012: Local Dynamics in Metallic Liquids Studied by Inelastic Neutron Scattering Zengquan Wang, Hui Wang, Wojciech Dmowski, Kenneth F Kelton, Takeshi Egami Local dynamics in liquid metals has been poorly understood when compared to their crystalline counterparts. For instance, the atomistic origin of the viscous behavior is not well elucidated, even though viscosity is one of the most basic properties for liquids. In this research, inelastic neutron scattering (INS) experiments were carried out on various metallic liquid droplets (including single, binary, and complex BMG forming liquids), using an electro-static levitator, at different temperatures at SNS. The dynamic structure function S(Q, E) and the Van Hove correlation function G(r,t) were then obtained. Compared with Molecular Dynamics (MD) simulation results, the local configuration change was analyzed based on distinct G(r,t) and proved as the elementary excitation in high temperature metallic liquids, thus controlling their shear viscosity. Also, self diffusion behaviors were analyzed based on self G(r,t). A comprehensive understanding of the local dynamics was made in various metallic liquids. |
Wednesday, March 4, 2020 10:48AM - 11:00AM |
L25.00013: High-resolution neutron imaging study of kinetics of H2O water vapor uptake from air into sessile heavy water droplets Jae Kwan Im, Leekyo Jung, Jan Crha, Pavel Trtik, Joonwoo Jeong At the surface of a liquid, the liquid molecules escape and enter the encompassing air as a gas, and the gas molecules join the liquid concurrently. Here we report the neutron imaging of a sessile heavy water (D2O) droplet that absorbs light water (H2O) vapor from the ambient air. A quantitative image analysis utilizing the Beer-Lambert law enables us to measure the attenuation coefficient of the specimen and estimate H2O content within the droplet. We double-check this result with a quantitative Fourier-transform infrared spectroscopy and conclude that small D2O droplets with a large surface-to-volume ratio can be very hygroscopic, e.g., the 15 percent of a D2O droplet of 10 microliters can be replaced with H2O in 10 minutes. |
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