Spatially Heterogeneous Dynamics in Supercooled Liquids

TLDR

Dynamics in supercooled liquids are spatially heterogeneous, with regions differing by orders of magnitude in speed, and recent evidence has confirmed this view. This review surveys experimental studies that quantify the size, lifetime, magnitude, and origin of dynamical heterogeneities in supercooled liquids. The authors review experimental techniques used to characterize spatially heterogeneous dynamics. Understanding these heterogeneities informs the design and use of glass‑forming materials such as polymers, metallic glasses, and pharmaceuticals.

Abstract

Although it has long been recognized that dynamics in supercooled liquids might be spatially heterogeneous, only in the past few years has clear evidence emerged to support this view. As a liquid is cooled far below its melting point, dynamics in some regions of the sample can be orders of magnitude faster than dynamics in other regions only a few nanometers away. In this review, the experimental work that characterizes this heterogeneity is described. In particular, the following questions are addressed: How large are the heterogeneities? How long do they last? How much do dynamics vary between the fastest and slowest regions? Why do these heterogeneities arise? The answers to these questions influence practical applications of glass-forming materials, including polymers, metallic glasses, and pharmaceuticals.