Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S17: Physics of Liquids IFocus Live

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Sponsoring Units: GSNP DCP DFD DSOFT Chair: Yang Zhang, University of Illinois at UrbanaChampaign 
Thursday, March 18, 2021 11:30AM  12:06PM Live 
S17.00001: Toward a microscopic understanding of the dynamics of simple glassforming liquids Invited Speaker: Patrick Charbonneau The dynamical arrest predicted by modecoupling theory and the entropy crisis at the random firstorder transition are both exact descriptions of simple glassforming liquids, albeit only in the abstract limit of infinitedimensional systems. What survives of these features and what other processes contribute to the dynamics of threedimensional glass formers are questions that remain largely unanswered. In this talk, I present our recent advances toward a microscopic understanding of the finitedimensional echo of these infinitedimensional features, and of some of the activated processes that affect the dynamical slowdown of simple yet realistic glass formers. 
Thursday, March 18, 2021 12:06PM  12:18PM Live 
S17.00002: Potential Energy Landscape Formalism for Quantum Liquids Nicolas Giovambattista, Gustavo E Lopez The potential energy landscape (PEL) formalism is a theoretical approach within statistical mechanics used extensively in the past to study classical liquids and glasses. Here, we extend the PEL formalism to the case of quantum liquids. As an example, we apply the PEL approach to study a family of quantum monatomic liquids using pathintegral Monte Carlo simulations. We focus on the energy (E_{IS}), pressure (P_{IS}) of the local minima of the PEL (inherent structures, IS) explored by the liquids. We find that, similar to the classical case, the quantum liquids exhibit a PELindependent regime at high temperatures and a PELinfluenced regime at low temperatures, where the topography of the PEL plays a major role. Remarkably, the ringpolymers representing the atoms of the quantum liquids are collapsed at the IS. Accordingly, an IS of the quantum liquid, in its own PEL, is also an IS of the classical liquid in the classical liquid PEL (CLPEL). A pictorial interpretation of the behavior of quantum liquids using the CLPEL (as opposite of the quantum liquid PEL) is provided. In this approach, the quantum liquid is represented by a pancakelike patch that expands over multiple IS of the CLPEL, changing shape with time while describing a fuzzy trajectory on the CLPEL 
Thursday, March 18, 2021 12:18PM  12:30PM Live 
S17.00003: Role of hydrogen bonded associates on the nanoscale dynamics of liquid and supercooled 2propanol Yanqin Zhai, Peng Luo, 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 2propanol by static and quasielastic neutron scattering experiments supported by molecular dynamics simulations on a series of partially and fully deuterated samples at temperatures ranging from the liquid, the deeply supercooled, to the glassy state. The results indicate that the macroscopic shear viscosity has the same temperature dependence as the dynamics at the prepeak correlated with the Hbonded associates, which highlights the fundamental role played by these structures in defining the macroscopic rheological properties of the system. Importantly, the characteristic relaxation time at the prepeak follows an Arrhenius temperature dependence whereas at the structure peak exhibits a nonArrhenius behavior on approaching the supercooled state. The origin of this differing behavior is attributed to an increased structuring of the hydrophobic domains of 2propanol accommodating a more and more encompassing Hbond network, and a consequent set in of dynamic cooperativity. 
Thursday, March 18, 2021 12:30PM  12:42PM Live 
S17.00004: Local selfmotion of water through the Van Hove function Yuya Shinohara, Wojciech Dmowski, Takuya Iwashita, Daisuke Ishikawa, Alfred Q R Baron, Takeshi Egami We report that the selfpart of the Van Hove functions of water can be determined through inelastic Xray scattering (IXS) experiments at highQ. Usually, a limited Q range prevents one from obtaining the realspace information from the Van Hove Functions without the termination errors that are associated with Fourier transformation. This difficulty can be mitigated if we focus on the time range in which the intermediate scattering function decays to zero within the accessible Q range. The selfpart of the Van Hove functions is extracted from the shortrange correlations. We found that the diffusivity estimated from the shortrange dynamics of water is different from the longrange diffusivity measured by other methods, possibly due to developing intermolecular dynamic correlation. This information will bridge the gap between the hydrodynamic behavior and the phononic behavior at very short times. 
Thursday, March 18, 2021 12:42PM  12:54PM Live 
S17.00005: Bulk and interfacial thermodynamics and dynamics of ionic liquidsoil mixtures: A molecular dynamics simulation study Daria Lazarenko, Fardin Khabaz Ionic liquids (ILs) are molten salts that are known for their low vapor pressure, thermal stability, low toxicity, and promising rheological behavior that make ILs great candidates for highperformance, sustainable lubricants. In this work, allatom MD simulations will be used to predict morphology, rheology, and interfacial thermodynamics of imidazoliumbased ILs in oil. In the first step, we will present the effect of IL content and the molecular structure of ILs in hexadecane on the density, structure, and dynamics of the mixture at different temperatures in bulk. The impact of IL content, molecular structure, and temperature on the nanostructure of the mixture will be determined by performing clustering analysis of ions that directly affect the dynamics and rheology of these mixtures. The influence of the formation of ionic structures in oil on the dynamics, shear, and extensional rheology of ILoil in bulk will be investigated. In the next step, the interfacial and microstructure of ILoil mixtures comprised of different IL contents and molecular structures near solid surfaces will be considered, and the free energy of adsorption will be determined. The results presented in this work will guide the experimental design of IL additive for tribological applications. 
Thursday, March 18, 2021 12:54PM  1:06PM Live 
S17.00006: Realspace Dynamics in Liquid Gallium using Inelastic Neutron Scattering Yadu Krishnan Sarathchandran, Yuya Shinohara, Wojciech Dmowski, Douglas L Abernathy, Takeshi Egami Liquid gallium is of strong theoretical interest due to the asymmetry of its prominent peak in the static structure function close to the melting point, which indicates the unusual nature of its atomic bonding. It also possesses higher density in the liquid state than in the solid state, and lower coordination number, similar to the strongly covalent systems such as water and silicon. These behaviors are different from other simple metallic systems, such as Fe and CuZr. In this work, we demonstrate the anomalous nature of the correlated atomic dynamics of liquid gallium in realspace and time using the Van Hove function, G(r,t). The Van Hove function was determined by double Fourier transforming the dynamic structure factor, S(Q, E), which was measured by inelastic neutron scattering measurements. 
Thursday, March 18, 2021 1:06PM  1:18PM Live 
S17.00007: Experimental evidence of predicted dynamicsstructurethermodynamic correlation in glassforming liquids Baicheng Mei, Yuxing Zhou, Kenneth Schweizer The microscopic Elastically Collective Nonlinear Langevin Equation (ECNLE) theory of glassy dynamics in conjunction with an a priori mapping of thermal liquids to an effective hard sphere fluid captures the structural alpha relaxation time of nonpolar molecular liquids over 14 decades. We have revisited this theory for monodisperse hard sphere metastable fluids using the modifiedVerlet closure integral equation theory as structural input. Simulation comparisons show the equationofstate, correlation lengths, radial distribution function, and structure factor are remarkably well captured. Numerical ECNLE theory calculations then predict the logarithm of the alpha time scales as an inverse power law of the dimensionless compressibility, a thermodynamic property that quantifies the amplitude of long wavelength density fluctuations. The scaling is linear (cubic) in the low (high) barrier regime, establishing an operational link between glassy relaxation and thermodynamics via pair structure (J.Phys.Chem.B,124, 6121 (2020)). The predicted connection is directly tested using solely experimental data, and is well verified for molecular liquids. By introducing one adjustable parameter to capture the low to high barrier crossover, experimental data over 14 decades can be linearized. 
Thursday, March 18, 2021 1:18PM  1:30PM Live 
S17.00008: Towards a new paradigm for liquids dynamics (and thermodynamics) matteo baggioli, Alessio Zaccone An analytical derivation of the vibrational density of states (DOS) of liquids, and in particular of its characteristic linear in frequency lowenergy regime, has always been elusive because of the presence of an infinite set of purely imaginary modes  the instantaneous normal modes (INMs)  which are absent in crystalline solids. By combining an analytic continuation of the Plemelj identity to the complex plane with the purely overdamped dispersion relation of the INMs, we amend this situation and we derive a closedform analytic expression for the lowfrequency DOS of liquids. The obtained result explains from first principles the widely observed linear in frequency term of the DOS in liquids, whose slope appears to increase with the average lifetime of the INMs. The analytic results are robustly confirmed by fitting simulations data for LennardJones liquids, and they also recover the Arrhenius law for the average relaxation time of the INMs, as expected. Finally, using the same framework, one could derive formally the specific heat of liquids which appears to be in good agreement with the experimental data. 
Thursday, March 18, 2021 1:30PM  1:42PM Live 
S17.00009: Ascent dynamics: an efficient algorithm probing long timescale dynamics Zhixia Li, Yang Zhang MD simulations is a powerful tool of studying the atomistic behavior of disordered and amorphous materials, but the covered timescales are 78 orders of magnitude shorter than dynamics scale when system approaches to glass state. Here, we present a new accelerated simulation method, ascent dynamics, which allows the system to escape deep energy minima through crossing saddle points with given index explicitly at finite temperatures. Master equation approach is then used to analyze the trajectory data to compute viscosity and relaxation time. Using this new algorithm, relaxation time and viscosity are not only in well agreement with traditional molecular dynamics simulation at high temperature, but they can be probed reliably at the low temperature regime. Our results show that we achieve over 10 orders of magnitude gain in the equilibration time scale compared to conventional methods, thus paving the road to computational studies of long timescale phenomenon. 
Thursday, March 18, 2021 1:42PM  1:54PM Live 
S17.00010: Two Liquids in One: LiquidLiquid Transition in Ionic Liquids Matthew Harris, Thomas P Kinsey, Durgesh Wagle, Gary A. Baker, Joshua Sangoro A liquidliquid transition is a transformation from one liquid structure to another through a firstorder phase transition. This type of phase transition has been reported in various systems, including water, silicon, phosphorous, and triphenyl phosphite. Recently, a liquidliquid transition has been identified in ionic liquids bearing the trihexyltetradecylphosphonium cation. Understanding this transition is vital to our understanding of the liquid state in general. In this study, a homologous series of ionic liquids with various anions has been investigated using Xray scattering techniques, broadband dielectric spectroscopy, Raman spectroscopy, and differential scanning calorimetry to characterize the nature of the liquidliquid transition and identify molecular parameters that influence the phase behavior in these materials. The results suggests a spinodal decomposition mechanism of the liquidliquid transition and the type of anion plays a key role in determining the phase behavior of the material. 
Thursday, March 18, 2021 1:54PM  2:06PM Live 
S17.00011: Isothermal Crystallization Monitoring and TimeTemperatureTransformation of Amorphous GDC0276 and nifedipine: Differential Scanning Calorimetric and Rheological measurements Sixue Cheng, Paroma Chakravarty, Karthik Nagapudi, Gregory B McKenna Cold crystallization is an important topic in understanding the stability of amorphous pharmaceutical ingredients (API). In the present work, the isothermal crystallization of amorphous pharmaceutical compounds GDC0276 and nifedipine are monitored by two different screening techniques: differential scanning calorimetric and rheometric measurements. For both techniques, the classic Avrami equation was applied to describe the isothermal crystallization kinetics from the induction to the completion period, and the timetemperaturetransformation diagrams were constructed for induction and completion time points of crystallization. The temperature dependence of viscosity was obtained from the rheological measurement and used to estimate the kinetic term in a modified classic nucleation and crystal growth model, which is further fitted to the temperature dependence of the crystal induction and completion times. The modification assumed is that the kinetics follow the viscosity to the 0.75 power as suggested by recent work. From the crystallization kinetics modeling, the solidliquid interfacial energy was determined and compared with that obtained from melting point depression measurements. The differences between the values from the two methods are discussed. 
Thursday, March 18, 2021 2:06PM  2:18PM Live 
S17.00012: Probing medium viscoelasticity using signal transmission through coupled harmonic oscillators Avijit Kundu Longitudinal waves can propagate quickly through incompressible Newtonian Fluids (like water). For closely spaced transmitterreceivers, a signal emitted by a transmitter can backpropagate through the medium to the receiver and cause motional resonance of the system. This paper explores a similar problem in Jeffery viscoelastic fluid constituted of multiple polymeric timeconstants. We optically trap two particles in harmonic potentials, externally modulate one particle (transmitter) with different frequencies and waveforms and see its effects on the hydrodynamically coupled motion of the other particle (receiver). The resulting resonance characteristics of this coupled system is related to the polymeric timeconstants; the quality factor falls off with increasing polymeric time constants. We demonstrate this experimentally by tracking the fluctuationresponse of each particle through the Optical Tweezers setup and the correlation between their trajectories. Also, the transmission and attenuation of the signal through the polymeric mesh over the deltacorrelated viscous noise gives a rich physical insight into the microrheological property of the viscoelastic fluid. 
Thursday, March 18, 2021 2:18PM  2:30PM Live 
S17.00013: Improvements of Simulation Methods in Microphase Formers Mingyuan Zheng, Patrick Charbonneau Microphases are thermodynamically stable mesoscale structures that typically result from competing shortrange attractive and longrange repulsive (SALR) interactions. If repulsion sufficiently strongly frustrates attraction, simple gasliquid coexistence is indeed replaced by a rich set of ordered and disordered structures. Even though the latter are less aesthetic materials targets, they have found a number of applications in drug delivery, nanoscale patterning and lithography. They are also largely overlooked by theoretical treatments. Numerical studies have thus been necessary to reveal their rich interplay between structure and dynamics. This richness, however, makes efficient configurational sampling challenging. In this work, we evaluate the sampling efficiency of several enhanced Monte Carlo sampling techniques for disordered microphases, and devise optimized algorithms for specific regimes including cluster and percolated fluids. With these improved algorithms, the disordered phase can be thoroughly studied, revealing an even richer than anticipated set of morphologies. 
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