Growing Dynamical Facilitation on Approaching the Random Pinning Colloidal Glass Transition

TL;DR

This study provides experimental evidence that dynamical facilitation, a purely dynamic theory, plays a significant role in the colloidal glass transition, especially when particles are randomly pinned, challenging thermodynamic explanations.

Contribution

The paper demonstrates experimentally that dynamical facilitation grows with density and pinning fraction, supporting its role in the glass transition and linking it to heterogeneous cooperative motion.

Findings

Dynamical facilitation increases with density and pinning fraction.

Heterogeneous string-like cooperative motion emerges naturally within facilitation.

Purely dynamic origin of the glass transition cannot be ruled out.

Abstract

Despite decades of research, it remains to be established whether the transformation of a liquid into a glass is fundamentally thermodynamic or dynamic in origin. While observations of growing length scales are consistent with thermodynamic perspectives like the Random First-Order Transition theory (RFOT), the purely dynamic approach of the Dynamical Facilitation (DF) theory lacks experimental validation. Further, for glass transitions induced by randomly freezing a subset of particles in the liquid phase, simulations support the predictions of RFOT, whereas the DF theory remains unexplored. Here, using video microscopy and holographic optical tweezers, we show that dynamical facilitation in a colloidal glass-forming liquid unambiguously grows with density as well as the fraction of pinned particles. In addition, we show that heterogeneous dynamics in the form of string-like cooperative motion, which is believed to be consistent with RFOT, emerges naturally within the framework of facilitation. Most importantly, our findings demonstrate that a purely dynamic origin of the glass transition cannot be ruled out.