Growing Surface Tension of Amorphous-Amorphous Interfaces on Approaching the Colloidal Glass Transition

TL;DR

This study measures the surface tension of amorphous interfaces in colloidal liquids approaching the glass transition, revealing a rapid increase that influences the dynamics and morphology of relaxing regions, with implications for glass formation theories.

Contribution

It introduces a novel method to identify amorphous interfaces in bulk colloidal liquids and quantifies their surface tension growth near the glass transition.

Findings

Surface tension increases rapidly across the mode-coupling area fraction.

Non-monotonic dynamical correlations observed in bulk supercooled liquids.

Surface tension growth also seen with pinned amorphous walls.

Abstract

There is mounting evidence indicating that relaxation dynamics in liquids approaching their glass transition not only becomes increasingly cooperative (1,2) but the relaxing regions also become more compact in shape(3-7). While the surface tension of the interface separating neighboring relaxing regions is thought to play a crucial role in deciding both their size and morphology(8-10), owing to the amorphous nature of these regions, even identifying these interfaces has not been possible in bulk liquids. Here, by devising a scheme to identify self-induced disorder sites in bulk colloidal liquids, we directly quantified the dynamics of interfaces delineating regions of high and low configurational overlap. This procedure also helped unveil a non-monotonicity in dynamical correlations that has never been observed in bulk supercooled liquids. Using the capillary fluctuation method (11,12), we measured the surface tension of amorphous-amorphous interfaces with supercooling and find that it increases rapidly across the mode-coupling area fraction. Remarkably, a similar growth in the surface tension is also seen in the presence of a pinned amorphous wall. Our observations help prune theories of glass formation and opens up new research avenues aimed at tuning the properties of amorphous-amorphous interfaces, and hence the glass itself, in a manner analogous to grain boundary engineering in polycrystals (13).