Metastable and Unstable Cellular Solidification of Colloidal Suspensions

TL;DR

This paper investigates the complex solidification behavior of colloidal suspensions, revealing instability and metastability domains through high-resolution imaging, and explaining interface instabilities via particle diffusion and constitutional supercooling.

Contribution

It introduces the first direct observation and explanation of instability and metastability domains in colloidal suspension solidification.

Findings

Identification of instability and metastability domains.

Link between particle diffusion and interface instabilities.

Impact of unstable conditions on crystal morphology.

Abstract

Colloidal particles are often seen as big atoms that can be directly observed in real space. They are therefore playing an increasingly important role as model systems to study processes of interest in condensed matter physics such as melting, freezing and glass transitions. The solidification of colloidal suspensions has long been a puzzling phenomenon with many unexplained features. Here we demonstrate and rationalize the existence of instability and metastability domains in cellular solidification of colloidal suspensions, by direct in situ high-resolution X-ray radiography and tomography observations. We explain such interface instabilities by a partial Brownian diffusion of the particles leading to constitutional supercooling situations. Processing under unstable conditions leads to localized and global kinetic instabilities of the solid/liquid interface, affecting the crystals morphology and particle redistribution behaviour.