Phase transitions on non-uniformly curved surfaces: Coupling between phase and location

TL;DR

This study investigates how non-uniform surface curvature influences phase behavior and particle localization in confined colloids, revealing that stable states are characterized by both phase and position, with transitions involving collective migration.

Contribution

It introduces a comprehensive analysis of phase transitions on non-uniformly curved surfaces, highlighting the coupling between phase state and particle location, which was not previously understood.

Findings

Stable colloid states depend on phase and location.

Transitions involve cooperative migration of colloids.

Behavior explained by cluster perimeter, stress, and packing considerations.

Abstract

For particles confined to two dimensions, any curvature of the surface affects the structural, kinetic and thermodynamic properties of the system. If the curvature is non-uniform, an even richer range of behaviours can emerge. Using a combination of bespoke Monte Carlo, molecular dynamics and basin-hopping methods, we show that the stable states of attractive colloids confined to non-uniformly curved surfaces are distinguished not only by the phase of matter but also by their location on the surface. Consequently, the transitions between these states involve cooperative migration of the entire colloidal assembly. We demonstrate these phenomena on toroidal and sinusoidal surfaces for model colloids with different ranges of interactions as described by the Morse potential. In all cases, the behaviour can be rationalised in terms of three universal considerations: cluster perimeter, stress, and the packing of next-nearest neighbours.