Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V17: Physics of Liquids IIFocus Session Live
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Sponsoring Units: GSNP DCP DFD DSOFT Chair: Yang Zhang, University of Illinois at Urbana-Champaign |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V17.00001: Dynamic diversity of soft medium-range homo-radical self-assembly and rigid metal-organic network in non-aqueous redox flow batteries Hossam Farag, Aman Preet Kaur, Lily A Robertson, Ilya A Shkrob, Lu Zhang, susan odom, Yang Zhang Understanding the physical and electrochemical rate processes which occur in the bulk of nonaqueous electrolytic solution is a major step towards control and design of electrochemical systems, e.g., nonaqueous redox flow batteries. Here, a combination of experimental SAXS ,conductance measurements, and computational molecular dynamics, is used to probe the dynamics of nonaqueous electrolytes as a varying function of the battery state of charge (SOC), and electrolyte concentration. Two solutions were compared: one contained metal cation electrolyte prone to form rigid hetero-charge network, and one contained phenothiazine organic catholyte preferring softer homo-radical stacking. For the latter, conductivity data show that a faster charge transport is present at high electrolyte concentration. This discrepancy in behavior becomes less pronounced as we go to lower concentration and is absent in the dilute limit. Our findings indicate enhanced dynamics in terms of bulk ionic conductivity driven by a softer medium-range emergent homo-radical stacking structure. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V17.00002: Chemical Phenomena at the Critical Point of Solution James Baird, Pauline Norris, Xingjian Wang, Joshua Lang The principle of critical point universality is known to govern critical effects in physical phenomena such as superconductivity, superfluidity, and the liquid – vapor transition. Using a binary liquid mixture with a critical point of solution, we have shown that critical effects can also be observed in chemical phenomena as diverse as solubility, adsorption, and ion exchange. At fixed temperature and pressure, chemical critical effects occur when no more than one composition variable is held fixed. The assertion that only three variables are fixed, namely temperature, pressure, and one composition variable, is affirmed by application of the phase rule. In the case of three fixed variables, critical effects have been observed in more than 20 different experiments involving a wide variety of solids and solvent pairs.1 Recently, we have added to this tally by observing a critical effect in the solubility of the optically active R-enantiomer of zinc tartrate dissolving in a critical mixture of isobutyric acid + water. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V17.00003: Atomic Trajectories in Liquid Films Driven over a Substrate Metehan Cam, Christopher G Goedde, Seth H Lichter The dynamics of Lennard-Jones liquid films forced over a solid substrate is presented. At low forces the majority of atoms remain stationary in their equilibrium positions, while a small percentage of atoms propagate as nonlinear waves over the substrate. Atoms do not follow the direction of the external driving force. In a solution, different species of atoms follow different directions from one another, resulting in the solute atoms partitioning from one another and from the solvent. We aim to apply new knowledge of the physics of the liquid-solid interfaces for developing molecular-level separation mechanisms mediated by solid substrates. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V17.00004: Charge oscillations in ionic liquids: A microscopic cluster model Yael Avni, Ram Adar, David Andelman In spite of their enormous applications as alternative energy storage devices and lubricants, room-temperature ionic liquids (ILs) still pose many challenges from a pure scientific viewpoint. We develop an IL microscopic theory in terms of ionic clusters, which describes the IL behavior close to charged interfaces. The full structure factor of finite-size clusters is considered and allows us to retain fine and essential details of the system as a whole. Beside the reduction in the screening, it is shown that ionic clusters cause the charge density to oscillate near charged boundaries, with alternating ion-size thick layers, in agreement with experiments. We distinguish between short-range oscillations that persist for a few ionic layers close to the boundary, as opposed to long-range damped oscillations that hold throughout the bulk. The former can be captured by finite-size ion pairs, while the latter is associated with larger clusters with a pronounced quadrupole (or higher) moment. The long-wavelength limit of our theory recovers the well-known Bazant-Storey-Kornyshev (BSK) equation in the linear regime, and elucidates the microscopic origin of the BSK phenomenological parameters. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V17.00005: Dynamic view on ionic liquids acting in confinement for wood pretreatment Henrich Frielinghaus, Noemi Szekely, Gaetano Mangiapia, Claas Hövelmann, Caroline Marks, Joern Viell It is known that ionic liquids enhance the exploit of resources from pretreated wood. More cellulose and lignin is made available as valuable chemicals for biodegradable products. We monitored the pretreatment process of beech wood by an ionic liqiud in operando using small angle neutron scattering. In this dynamic process we could identify three stages: (1) the impregnation, i.e. the flooding of the wood by the liquid, (2) the formation of small voids on the nanoscale, and (3) the formation of restructured nanocellulose fibrils on larger scales. In the first two stages confinement plays an important role that finally leads to swelling and the fracture of the cell walls. All of this is set in context with findings from other authors, and with the next step of enzymatic hydrolysis. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V17.00006: Conductance of Li-Ionic-Liquid Mixtures in Nanoporous MOFs as Separators for Li-Ion-Batteries Micaela Vazquez, Modan Liu, Zejun Zhang, Abhinav Chandresh, Anemar Bruno Kanj, Wolfgang Wenzel, Lars Heinke Metal-organic framework (MOF) based separators in Li-ion-batteries help stabilize the solid electrolyte interphase and strongly affect the battery performance. The mobility and conduction of lithium and organic ionic liquids (ILs) in these materials is crucial and depends on the MOF structures and the IL loading. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V17.00007: Phase diagram of the two-dimensional symmetric associating lattice gas Ingrid Ibagon, Alexandre P. Furlan, Ronald Dickman We use extensive Monte Carlo simulations to investigate the phase diagram of the symmetric associating lattice gas (ALG) model. The ALG is defined on a triangular lattice in which each site can be either empty or occupied by a single molecule. Molecules have four bonding and two non-bonding arms. The model exhibits three phases: gas/disordered, low-density liquid (LDL), and high-density liquid (HDL) [1]; as well as water-like anomalous behavior. Recently, new results for the ALG [2] raised some questions about the structure of the phase diagram. Our results show a new continuous HDL-gas line which starts at finite chemical potential μ and extends to infinite μ [2]. For the LDL-gas transition, the scenario is controversial. Previous simulation results revealed a continuous transition [3], while Husimi Lattice calculations resulted in a discontinuous one [4]. Our simulations show that this transition is discontinuous. |
Thursday, March 18, 2021 4:24PM - 5:00PM Live |
V17.00008: The Shape of Data in Chemistry – Insights Gleaned from Complex Solutions and Their Interfaces Invited Speaker: Aurora Clark
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Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V17.00009: No underscreening in dense electrolytes Johannes Zeman, Svyatoslav Kondrat, Christian Holm Recent experiments have reported anomalously large screening lengths of interactions between charged surfaces confining concentrated electrolytes and ionic liquids. Termed underscreening, this effect was ascribed to bulk properties of dense ionic systems. Herein, we study bulk ionic screening with extremely large-scale molecular dynamics simulations, allowing us to assess the range of distances relevant to the experiments. Our results yield two screening lengths satisfying distinct scaling relations. However, with an accuracy of 10−5 kBT in interionic potentials of mean force, we find no signs of underscreening, suggesting that other than bulk effects might be at play in the experiments. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V17.00010: Expansion and shrinkage of the electrical double layer in charge-asymmetric electrolytes Guillermo Guerrero-Garcia, Enrique Gonzalez-Tovar The spatial extension of the electrical double layer determines many thermodynamic and electrokinetic properties of charged colloids in solution. In the classical Debye-Hückel formalism of point-ions, the thickness of the electrical double layer surrounding a charged colloid can be characterized by the bulk Debye length of the supporting ionic fluid. As a result, that approach neglects the influence of the colloidal charge on the spatial extension of the ionic cloud. In this work, we study the thickness of the electrical double layer as a function of the colloidal charge in the presence of several binary charge-asymmetric 1:z electrolytes with monovalent counterions and multivalent coions. The thickness of the ionic cloud is quantified here via the capacitive compactness, which represents essentially the separation distance between two electrodes associated to the corresponding effective electrical double layer capacitor. Our theoretical calculations show that the electrical double layer may expand or shrink as a function of the surface charge density, in the presence of multivalent coions, which is confirmed by primitive model Monte Carlo simulations. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V17.00011: Effect of Electric Fields on the Director Field and Shape of Nematic Tactoids Mohammadamin Safdari, Roya Zandi, Paul Van der Schoot Tactoids are spindle-shaped droplets of a uniaxial nematic phase suspended in the co-existing isotropic phase. Recent experiments on tactoids of chitin nanocrystals in water show that electrical fields can very strongly elongate tactoids even though the difference between the dielectric properties of the isotropic and nematic phases differ only very subtly. We explain this by extending the Ocean-Frank elastic model of Kaznacheev et al. for bipolar tactoids to partially bipolar tactoids, where the degree of bipolarness of the director field is free to adjust itself to optimize the sum of the elastic, surface, and Coulomb free energies of the drops. By means of a combination of a scaling analysis and a numerical study, we study the elongation and director field of the tactoids as a function of their size and the strength of the electric field, and how these depend on the surface tension and anchoring strength, the various elastic constants, and the electric susceptibility anisotropy. We find that if the director field is bipolar, tactoids cannot elongate more strongly tactoids with a uniform director field unless the director field is somehow fixed in the field-free configuration. Presuming this to be the case, we find reasonable agreement with experimental data. |
Thursday, March 18, 2021 5:36PM - 5:48PM Live |
V17.00012: Symmetries and Hard Disk Configuration Spaces Ozan Ericok, Jeremy Mason Hard disks systems are often considered as prototypes for simple fluids. Critical points (mechanically-balanced configurations) in the hard disk configuration space are involved in estimating the configurational entropy, and could contain valuable information about the origins of phase transitions. Since configuration spaces generally contain multiple configurations related by physical symmetries, they are usually quotiented by the action of these symmetries. A metric respecting the desired physical symmetries is proposed, and quotient maps that transform the configuration space into the quotient space are examined. The original and quotiented configuration spaces are explicitly triangulated, and the topological and geometric properties are studied for small number of disks on a square and hexagonal torus. It is found that the number of the critical points depends in unexpected ways on the application of physical symmetries, with implications for the apparent configurational entropy and mixing time of these systems. |
Thursday, March 18, 2021 5:48PM - 6:00PM Live |
V17.00013: Structural and electronic transition in liquid rubidium Daniela Kartoon, Guy Makov Rubidium, like the other alkali metals, exhibits multiple structural transformations in its solid phase upon application of pressure. Recent experiments [Gorelli 2018] and calculations [Bryk 2013] suggest it also goes through a phase transformation in its liquid state, along the 573K isotherm, slightly above its melting curve. We employ \textit{ab-initio} molecular dynamic simulations to study the structural and electronic characteristics of this liquid-liquid transition. Applying the quasi-crystalline model (QCM) we find that the short-range order of liquid Rb changes abruptly from bcc-like to b-tin-like at pressures between 14-20 GPa. The electronic structure of liquid Rb is investigated in order to reveal the underlying mechanism of this transition, which we claim is not related to the Peierls transition but rather to the electronic band structure. |
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