Direct measurements of growing amorphous order and non-monotonic dynamic correlations in a colloidal glass-former

TL;DR

This study provides direct experimental evidence of growing amorphous order and non-monotonic dynamic correlations in a colloidal glass, supporting the thermodynamic nature of the glass transition as predicted by RFOT.

Contribution

The paper introduces a novel experimental approach using holographic optical tweezers to measure amorphous order and dynamic correlations in a colloidal glass-former, validating key RFOT predictions.

Findings

Observation of a static point-to-set length indicating amorphous order growth

Discovery of non-monotonic dynamic correlations with area fraction

Change in morphology of cooperatively rearranging regions

Abstract

While the transformation of flowing liquids into rigid glasses is omnipresent, a complete understanding of vitrification remains elusive. Of the numerous approaches aimed at solving the glass transition problem, the Random First-Order Theory (RFOT) is the most prominent. However, the existence of the underlying thermodynamic phase transition envisioned by RFOT remains debatable, since its key microscopic predictions concerning the growth of amorphous order and the nature of dynamic correlations lack experimental verification. Here, by using holographic optical tweezers, we freeze a wall of particles in an equilibrium configuration of a 2D colloidal glass-forming liquid and provide direct evidence for growing amorphous order in the form of a static point-to-set length. Most remarkably, we uncover the non-monotonic dependence of dynamic correlations on area fraction and show that this non-monotonicity follows directly from the change in morphology of cooperatively rearranging regions, as predicted by RFOT. Our findings suggest that the glass transition has a thermodynamic origin.