A theory of void formation in charge-stabilised colloidal suspensions at low ionic strength

TL;DR

This paper develops a theoretical framework based on Debye-Huckel theory to explain void formation and phase instability in charge-stabilized colloidal suspensions at low ionic strength, linking microscopic interactions to observed macroscopic anomalies.

Contribution

It introduces a novel theoretical explanation for voids and phase separation in colloids at low ionic strength, incorporating many-body attractions and phase coexistence analysis.

Findings

Identification of a phase instability region at high charges and low ionic strength.

Explanation of void structures and anomalies in colloidal suspensions.

Insights into possible charge density wave phases near critical points.

Abstract

Using a carefully justified development of Debye-Huckel theory for highly asymmetric electrolytes, one finds that a region of expanded phase instability, or miscibility gap, can appear for charge-stabilised colloidal suspensions at high charges and low ionic strengths. It is argued that this is offers a straightforward explanation for the observations of void structures and other anomalies in such suspensions in this region. The nature of the interface between coexisting phases, and general arguments that many-body attractions form a key part of the underlying physical picture, are also examined. The present analysis may also generate new insights into old problems such as coacervation in oppositely charged colloid or protein / polyelectrolyte mixtures, and suggests interesting new possibilities such as the appearance of charge density wave phases in colloidal systems in the vicinity of the critical solution points.