Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J25: Physics of Liquids IIFocus
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Sponsoring Units: GSNP DSOFT DCP Chair: Yang Zhang, University of Illinois at Urbana-Champaign Room: 402 |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J25.00001: Using Algebraic and Geometric Topology to Characterize Hierarchical Organization in Complex Solutions and Their Interfaces Invited Speaker: Aurora Clark Complex, multicomponent, solutions are often characterized by multiple length and timescale correlations that challenge chemical intuition. Recently developed tools are leveraging graph-theoretical interpretations of the intermolecular networks of interactions in such systems, supporting topological data analysis as a means to characterize organizational patterns, from the identification of molecular species and solvation environments, to new interpretations of fluid phase transformation. One may interpret these topological descriptors as high-dimensional order parameters that can also be used to enhance sampling of the energy landscape. Complementary geometric topological methods of liquid surfaces have also emerged as a powerful tool for the identification of interfacial structures responsible for transport. Ongoing work is combining both the algebraic and geometric topology formalism to create a holistic approach that relates hierarchical organizational patterns to structure and even function within complex solutions and their interfaces. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J25.00002: Hanging droplets from liquid surfaces Ganhua Xie, Joe Forth, Shipei Zhu, brett helms, paul ashby, Ho Chueng Shum, Thomas Russell Nature uses surface tension to support dense objects on liquid surfaces, from water striders to insect larvae for mating and survival, which has inspired fabrication of man-made robotic systems for transport across water. These systems present hydrophobic surface to prevent sinking. Here, we show that a droplet of a denser aqueous solution, containing a polyelectrolyte can hang on the surface of a less dense aqueous solution containing an oppositely charged polyelectrolyte. The magnitude of the interfacial forces acting on the droplet and the shapes of the hanging droplets can be controlled by releasing heights of the droplet and the polyelectrolyte concentrations. Coacervate sacs with homogeneous and heterogeneous surfaces can be produced that hang from the surface and, by capillary forces, form well-ordered arrays. Controlled locomotion and rotation can be achieved by functionalizing the hanging droplets with magnetic microparticles. The suspended droplets are in direct contact with air enabling in situ manipulation of the droplets and using the encapsulated aqueous phases for compartmentalized cascading chemical reactions with selective transport. These hanging droplets have potential applications in functional micro-reactors, micro-motors and biomimetic micro-robots. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J25.00003: Dipolar dimer liquid Junyi Zhang A lattice liquid model, dipolar dimer liquid (DDL), is proposed motivated by the water. The DDL on the bipartite lattice may be exactly mapped to the annealed Ising model on random graphs. We showed that there exists a phase transition of the DDL when the density is not too small. In the low temperature phase, which we called glacia phase, the polar charges are ordered while the dimers are still free to move and rotate. On two-dimensional square lattice and honeycomb lattice, we may bound the critical temperature $T_c^G$ by comparing the Ising model on random graphs to the exactly-solved Ising models. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J25.00004: Extended equation of state for non-ideal mixtures near the consolute critical point. Yevgenii Rudnikov, MYKOLA POTOMKIN The problem of constructing the equations of state and calculating the thermodynamic parameters of mixtures near the liquid-liquid critical point using the parameters of their components remains an urgent task of the condensed matter physics.To solve it, the new method of choosing the countdown start for calorific values is founded, in which the corresponding states law for liquids is satisfied. An analysis of thermodynamic consistency conditions in the dissolution of solution components allow concluding that a consistent calculations of the mixture parameters for variable values are approximate due to excessive non-additive contributions to them; similar calculations are exact for values which remain constant for components. Using the proposed approach for liquid components of obtained and literature data for mixtures C4H8O2 - H2O, CH4O – C6H14, C6H7N – D2O, the constant combinations of thermodynamic parameters have been found. It allowed using the consistent rules for calculating the calorific parameters of mixture and obtaining the parameters of the theory of critical mixtures. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J25.00005: Numerical Modeling of Room Temperature Ionic Liquids Katherine Klymko, John Bell, Alejandro Garcia, Sean Carney, Andy Nonaka We present a mesoscale numerical model for room temperature ionic liquids. The model uses a fluctuating low Mach number formulation based on a thermodynamically consistent formulation. Repulsion effects between the different ions are represented by an excess free energy. We first investigate the structure of the fluid to quantify the interplay between electrostatic forces and repulsion of the different ions. We then investigate the structure of the electric double layer that forms at a solid surface at fixed potential as a function of the applied voltage. Finally, we investigate the effect of composition dependence of the electric permittivity in the presence of an external field. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J25.00006: Evaporation of Lennard-Jones Monomer-Dimer Mixtures Binghan Liu, Shengfeng Cheng Evaporation and condensation are important physicochemical processes for the conversion between liquids and gases. We use Lennard-Jones (LJ) liquids as model systems to study the nonequilibrium physics of evaporation. The evaporation of pure LJ fluids has been studied extensively. However, the studies on evaporating liquid mixtures are limited and the relevant physics is poorly understood. Here we employ molecular dynamics simulations to study the evaporation behavior of LJ monomer-dimer mixtures. During fast evaporation, the concentration of LJ dimers, which are less volatile, increases significantly from the bulk of the mixture to the evaporating liquid-vapor interface. Correspondingly, the concentration of LJ monomers exhibits a negative gradient in the same region. In other words, the LJ monomers and dimers stratify in the region below the evaporating interface. Furthermore, the degree of stratification is stronger at higher evaporation rates. The effect of evaporative cooling on stratification is also clarified on the basis of thermophoresis. This stratification phenomena may be utilized to separate suspended particles interacting differently with the components of an evaporating liquid mixture. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J25.00007: Decomposing thermal fluctuations in fluids with hydrodynamic modes Xiaohui Deng Presenter: |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J25.00008: Correlation between local viscosity and the atomic-level stresses in liquids. Takuya Iwashita Liquids are ubiquitous, but the atomic origin of the viscosity remains unknown because of structural disorder. To study the relationship between viscosity and local structures we performed molecular dynamics simulations on various metallic liquids. Here the local structures of the liquids are characterized by the atomic-level stresses which describe the local mechanical states. We showed strong correlation between local viscosity and atomic-level stress in the liquids; for example, the atomic sites under compression are more unstable against shear than those under tension. The results indicate a universal structure-dynamics relationship in liquids. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J25.00009: Importance of nuclear quantum effects on the hydration of chloride ion Jianhang Xu, Zhaoru Sun, Fujie Tang, Deyu Lu, Xifan Wu The solvation structure of Cl- ion in aqueous solution is determined by the H-bonding between the solvated ion and surrounding water molecules, which is in competition with the water-water H-bonds in the solvent. We performed ab initio path-integral molecular dynamics simulations based on the SCAN functional. We find that quantum nuclei tilt the above balance compared to conventional classical simulations. Nuclear quantum effects (NQE) weaken the ion-water H-bonding strengths as shown by the increased first-peak position in the ion-oxygen pair distribution function. In turn, the H-bond interactions among water molecules in the solvent become effectively strengthened. As a result, the population of interstitial water molecules increases in the first coordination shell, which are non-bonded to Cl- ion, however, are H-bonded to other water molecules in a tetrahedral network. By including NQEs, our local dielectric response function calculations suggest that the surrounding water molecules electronically screen the charge of Cl- more effectively than the classical counterpart. Our resulting solvation structures are in excellent agreement with the recent neutron scattering experiments by Soper et al. |
Tuesday, March 3, 2020 4:42PM - 4:54PM |
J25.00010: Connectedness of the configuration space of hard disk systems Ozan Ericok, Jeremy Kyle Mason Hard disk systems are often regarded as prototypes for simple fluids, and can offer valuable insight into the origins of phase transitions and glass transitions in general. A phase transition is usually believed to occur when averages of thermodynamic quantities over the accessible part of the configuration space change discontinuously. A phase transition could then be driven by a discontinuous change in the accessible region, and this depends on the connectedness of the configuration space as a function of disk radius. A regularized potential energy function is defined on the configuration space, the critical points of which correspond to configurations where the topology of the configuration space changes, and are extensively sampled for small numbers of disks. Knowledge of the critical points allows the configuration space to be decomposed into regions that are homeomorphic to spheres of known dimensions, but does not indicate how these regions are attached to one other. Preliminary attaching maps are then found using the zero-temperature string method, resulting in a complete characterization of the topology of the configuration space of hard disk systems for small numbers of disks. |
Tuesday, March 3, 2020 4:54PM - 5:06PM |
J25.00011: The stability-limit conjecture revisited Pheerawich Chitnelawong, Francesco Sciortino, Peter Poole The stability-limit conjecture (SLC) proposes that the liquid spinodal of water returns to positive pressure in the supercooled region, and that the apparent divergence of water’s thermodynamic response functions as temperature decreases are explained by the approach to this reentrant spinodal. Subsequently, it has been argued that the predictions of the SLC are inconsistent with general thermodynamic principles. Here we reconsider the thermodynamic viability of the SLC by examining a model equation of state for water first studied to clarify the relationship of the SLC to the proposed liquid-liquid phase transition in supercooled water. By demonstrating that a binodal may terminate on a spinodal at a point that is not a critical point, we show that the SLC is thermodynamically permissible in a system that has both a liquid-gas and a liquid-liquid phase transition. We also describe and clarify other unusual thermodynamic behavior that may arise in such a system, particularly that associated with the so-called “critical-point-free” scenario for a liquid-liquid phase transition, which may apply to the case of liquid Si. |
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