CPM Seminar

Slow, non-diffusive dynamics in glassy soft matter

Robert Leheny

Department of Physics
Johns Hopkins University

For many disordered soft solids such as gels and concentrated emulsions, the solid phase is separated from a fluid state by an ergodic-nonergodic transition that leaves the system in an out-of-equilibrium configuration. Often these out-of-equilibrium materials display a protracted evolution of their dynamical properties that bears resemblance to behavior seen in molecular and polymer glasses. In order to understand these dynamics at a microscopic scale we have investigated such disordered soft solids through x-ray photon correlation spectroscopy (XPCS), a technique uniquely suited for elucidating the nanoscale motions in glassy materials. After a brief introduction to XPCS, the talk will describe our findings from studies on a set of materials that includes clay suspensions, sheared depletion gels, and concentrated nanoemulsions. In short, the dynamics we observe are distinct from the cooperative diffusion in liquids near the glass transition. Rather, they are a type of exceedingly slow, non-diffusive motion that can be modeled as strain in response to heterogeneous local stress and that are apparently universal to a range of disordered materials.