Spatiotemporal Mapping of Mesoscopic Polymer Dynamics

The study of liquid dynamics at mesoscopic scales is still strewn with difficulty due to limitations in theory and experiment. Historically, significant attention has been given to the analysis of space-time correlation functions and their frequency-Fourier-transforms at a few discrete wavenumbers. The massive computing power afforded by modern HPC clusters and the advent of wide-angle neutron spin-echo spectrometer, however, have unlocked a more intuitive and powerful approach to this problem. Using molecular dynamics simulations, here we demonstrate the benefits of spatiotemporally mapping intermediate scattering functions on a dense grid of correlation times and wavenumbers. We show that this approach is particularly useful for elucidating the mesoscopic dynamics in polymeric liquids. Compared to the traditional method, direct visualization of density space-time correlation functions on two-dimensional colormaps permits appraisals of complicated dynamical behavior at mesoscales in an "impressionistic" manner. The new perspective offered by the spatiotemporal mapping method should prove useful for the study of liquid dynamics in general.