Polydispersity induced solid-solid transitions in model colloids

TL;DR

This study uses advanced simulation and theoretical methods to investigate how polydispersity influences phase transitions and demixing in model colloids, revealing multiple fractionated solid phases and near-continuous transitions.

Contribution

It introduces a combined Monte Carlo and free energy approach to exactly treat fractionation in polydisperse colloids, uncovering new phase behavior.

Findings

Polydispersity induces multiple solid-solid demixing transitions.

Demixed phases are strongly fractionated with narrower size distributions.

Some transitions are nearly continuous with large-scale size fluctuations.

Abstract

Specialized Monte Carlo simulation techniques and moment free energy method calculations, capable of treating fractionation exactly, are deployed to study the crystalline phase behaviour of an assembly of spherical particles described by a top-hat "parent" distribution of particle sizes. An increase in either the overall density or the degree of polydispersity is shown to generate a succession of phase transitions in which the system demixes into an ever greater number of face-centred cubic "daughter" phases. Each of these phases is strongly fractionated: it contains a much narrower distribution of particle sizes than is present in the system overall. Certain of the demixing transitions are found to be nearly continuous, accompanied by fluctuations in local particle size correlated over many lattice spacings. We explore possible factors controlling the stability of the phases and the character of the demixing transitions.