Direct Measurement of the Structural Change Associated with Amorphous Solidification using Static Scattering of Coherent Radiation

TL;DR

This study demonstrates that speckle scattering at individual wavevectors reveals significant temperature-dependent structural changes during glass formation, providing a direct measure of heterogeneity and structural order.

Contribution

It shows that the weak temperature dependence of structure factor is due to averaging effects and introduces speckle scattering as a method to directly measure structural heterogeneity.

Findings

Speckle scattering reveals a Debye-Waller factor with strong temperature dependence.

A new quantity proportional to local restraint variance is extracted.

The method distinguishes liquid from glass based on structural order.

Abstract

In this paper we demonstrate that the weak temperature dependence of structure factor of supercooled liquids, a defining feature of the glass transition, is a consequence of the averaging of the scattering intensity either due to the use of an incoherent radiation source or explicit angular averaging. We show that the speckle scattering at individual wavevectors, calculated from a simulated glass former, exhibits a Debye-Waller factor with a sufficiently large temperature dependence to represent a structural order parameter capable of distinguishing liquid from glass. We also extract from the speckle intensities a quantity proportional to the variance of the local restraint, i.e. a direct experimental measure of the amplitude of structural heterogeneity.