Formation of a transient amorphous solid in low density aqueous charged sphere suspensions

TL;DR

This study reports the experimental formation of a transient amorphous solid from low-density charged colloidal spheres, revealing short-range order and shear rigidity, which eventually transforms into a crystalline structure over days.

Contribution

First experimental observation of a low-density charged sphere glass, providing insights into transient amorphous states in colloidal suspensions.

Findings

Transient amorphous solid exhibits short-range order and shear rigidity.

The amorphous state transforms into a crystalline structure over hours to days.

Dynamic light scattering indicates possible dynamic heterogeneity.

Abstract

Colloidal glasses form from hard spheres, nearly hard spheres, ellipsoids and platelets or their attractive variants have been studied in detail. Complementing and checking theoretical approaches and simulations, the many different types of model systems have significantly advanced our understanding of the glass transition in general. Despite their early prediction, however, no experimental charged sphere glasses have been found at low density, where the competing process of crystallization prevails. We here report the formation of a transient amorphous solid formed from charged polymer spheres suspended in thoroughly deionized water at volume fractions of 0.0002-0.01. From optical experiments, we observe the presence of short-range order and an enhanced shear rigidity as compared to the stable polycrystalline solid of body centred cubic structure. On a density dependent time scale of hours to days, the amorphous solid transforms into this stable structure. We further present preliminary dynamic light scattering data showing the evolution of a second slow relaxation process possibly pointing to a dynamic heterogeneity known from other colloidal glasses and gels.We compare our findings to the predicted phase behaviour of charged sphere suspensions and discuss possible mechanisms for the formation of this peculiar type of colloidal glass.