Non-equilibrium melting of colloidal crystals in confinement

TL;DR

This study explores the non-equilibrium melting behavior of charged colloidal crystals under confinement, revealing complex morphologies and dynamics driven by salt concentration gradients and pressure, supported by experimental and theoretical analysis.

Contribution

It introduces a novel experimental setup and a theoretical model to analyze non-equilibrium melting in colloidal crystals, highlighting the effects of gradients and shear on morphology.

Findings

Melting velocity depends on salt concentration and pressure.

Interface position and morphology are influenced by gradient strength.

Shear induces a transition from polycrystalline to single crystalline structures.

Abstract

We report on a novel and flexible experiment to investigate the non-equilibrium melting behaviour of model crystals made from charged colloidal spheres. In a slit geometry polycrystalline material formed in a low salt region is driven by hydrostatic pressure up an evolving gradient in salt concentration and melts at large salt concentration. Depending on particle and initial salt concentration, driving velocity and the local salt concentration complex morphologic evolution is observed. Crystal-melt interface positions and the melting velocity are obtained quantitatively from time resolved Bragg- and polarization microscopic measurements. A simple theoretical model predicts the interface to first advance, then for balanced drift and melting velocities to become stationary at a salt concentration larger than the equilibrium melting concentration. It also describes the relaxation of the interface to its equilibrium position in a stationary gradient after stopping the drive in different manners. We further discuss the influence of the gradient strength on the resulting interface morphology and a shear induced morphologic transition from polycrystalline to oriented single crystalline material before melting.