Surface melting and crystallisation driven by sedimentation: a particle resolved study

TL;DR

This study explores how reversing gravity affects sedimented colloidal suspensions, revealing structural transformations during melting and crystallisation, supported by experiments, simulations, and a coarse-grained model.

Contribution

It provides new insights into the microscopic mechanisms and kinetic pathways of crystallisation and melting in sedimented colloids under gravity reversal.

Findings

Reversal of gravity induces melting and reorganisation of colloidal crystals.

Identification of key structural mechanisms involving five-fold and cubic symmetries.

A coarse-grained model reproduces the reaction network of crystallisation processes.

Abstract

We investigate the effects of the reversal of the gravitational field onto a sedimented and partially crystallised suspension of nearly-hard sphere colloids. We analyse the structural changes that take place during the melting of the crystalline regions and the reorganisation and assembly of the sedimenting particles. Through a comparison with numerical simulation, we access the single-particle kinetics and identify the key structural mechanism in the competition between five-fold symmetric and cubic crystalline structures. With the use of a coarse-grained, discrete model, we reproduce the kinetic network of reactions underpinning crystallisation and highlight the main microscopic transitions.