Ground-State Shapes and Structures of Colloidal Domains

TL;DR

This paper develops a phase diagram for colloidal domains considering the balance of attraction and repulsion, explaining pattern formation and phase separation in charged colloidal suspensions.

Contribution

It introduces a continuum model and symmetry analysis to predict stable colloidal structures and phase behavior based on control parameters.

Findings

Microphase separation occurs at zero surface tension ratio.

Above a critical ratio, phase separation dominates over microphase formation.

The model explains the absence of pattern formation in simple liquids.

Abstract

In charged colloidal suspensions, the competition between square-well attraction and long-range Yukawa repulsion leads to various stable domains and Wigner supercrystals. Using a continuum model and symmetry arguments, a phase diagram of spheres, cylinders, and lamellae is obtained as a function of two control parameters, the volume fraction and the ratio between the surface tension and repulsion. Above a critical value of the ratio, the microphase cannot be supported by the Yukawa repulsion and macroscopic phase separation occurs. This finding quantitatively explains the lack of pattern formation in simple liquids because of the small hard sphere diameter in comparison with the size of macromolecules. The phase diagram also predicts microphase separation at zero value of the ratio, suggesting the possibility of self-assembly in repulsive systems.