Collective Dynamics of Liquids in Space and Time

ABSTRACT

Liquids are condensed matter, in which the positions of constituent particles appear randomly distributed and are subject to constant change due to thermal fluctuations. The coordinated rearrangement of particle positions under quiescent and non-equilibriums conditions gives rise to complicated properties of liquids, such as viscoelasticity and non-Newtonian flow. Therefore, how a liquid relaxes is a fundamental question of both technological and scientific significance. Scattering techniques and molecular dynamics have been the major tools in advancing our understanding of liquids. Owing to the dominance of scattering experiments in characterizing the structure and dynamics of liquids, the relevant theoretical developments have been commonly carried out in reciprocal space (inverse length) based on wavevector q. However, the interpretation on q is not straightforward except at two extremes, where q approaches 0 or infinity. In contrast, in this talk, I will demonstrate the collective dynamics of model liquids seen from real-space and time using so-called van Hove correlation function. I will present my recent finding on how the seemingly disordered structure of liquids relaxes in a statistical manner, which calls for a new theoretical framework to describe the dynamics of liquids. The computer simulation results on van Hove function will be shown first followed by experimentally determined results from inelastic X-ray scattering measurements on water.

BIOGRAPHY

Dr. Bin Wu graduated from Department of Engineering Physics at Tsinghua University with bachelor’s and master’s degrees in 2006 and 2009 respectively. During master’s training, he devised an explosive detection technique by upgrading the conventional X-ray cargo inspection system and this technique has been registered as a patent. In 2013, Bin received a doctoral degree in Nuclear Engineering and Sciences from Rensselaer Polytechnic Institute for his study on structural and dynamical characteristics of PAMAM dendrimer by combining neutron scattering experiments and molecular dynamics simulations. After graduation, Dr. Wu was employed as a postdoc researcher at the University of Tennessee, where he investigated the dynamics and stress correlations of supercooled liquids primarily using computer simulations and theories. In 2017, he was hired as a neutron scattering scientist at the Oak Ridge National Laboratory, where he served on the beamline of General-Purpose Small Angle Neutron Scattering Spectrometer. In 2018, he moved to the University of Michigan as a postdoc research fellow and started studying the fundamental interaction mechanism between dislocation and precipitate in Al-Cu alloys. As of March 2019, Dr. Wu has published 24 peer-reviewed scientific papers, among which he first- and corresponding-authored 8 articles.