Direct experimental evidence of a growing length scale accompanying the glass transition

TL;DR

This paper provides direct experimental evidence that the glass transition involves a growing dynamic correlation length scale, supporting the idea that larger regions must move collectively as the material approaches vitrification.

Contribution

It introduces new multipoint dynamical susceptibilities to quantitatively measure the size of dynamically correlated regions during glass formation.

Findings

Growing dynamic correlation length scales observed near the glass transition

Experimental validation of the collective motion hypothesis in glass formation

Applicability to both molecular liquids and colloidal suspensions

Abstract

Understanding glass formation is a challenge because the existence of a true glass state, distinct from liquid and solid, remains elusive: Glasses are liquids that have become too viscous to flow. An old idea, as yet unproven experimentally, is that the dynamics becomes sluggish as the glass transition approaches because increasingly larger regions of the material have to move simultaneously to allow flow. We introduce new multipoint dynamical susceptibilities to estimate quantitatively the size of these regions and provide direct experimental evidence that the glass formation of molecular liquids and colloidal suspensions is accompanied by growing dynamic correlation length scales.