Phase Separation of Charge-Stabilized Colloids: A Gibbs Ensemble Monte Carlo Simulation Study

TL;DR

This study uses an advanced Gibbs ensemble Monte Carlo simulation to analyze phase separation in charge-stabilized colloids, showing good agreement with theoretical predictions and enabling efficient exploration of phase behavior.

Contribution

It introduces a new variant of the Gibbs ensemble Monte Carlo method for coarse-grained colloidal models with implicit microions, improving computational efficiency and accuracy.

Findings

Charge-stabilized colloids undergo phase separation below a critical salt concentration.

Simulation results match well with variational free energy theory predictions.

The method accurately reproduces pressures and pair distribution functions at moderate couplings.

Abstract

Fluid phase behavior of charge-stabilized colloidal suspensions is explored by applying a new variant of the Gibbs ensemble Monte Carlo simulation method to a coarse-grained one-component model with implicit microions and solvent. The simulations take as input linear-response approximations for effective electrostatic interactions -- hard-sphere-Yukawa pair potential and one-body volume energy. The conventional Gibbs ensemble trial moves are supplemented by exchange of (implicit) salt between coexisting phases, with acceptance probabilities influenced by the state dependence of the effective interactions. Compared with large-scale simulations of the primitive model, with explicit microions, our computationally practical simulations of the one-component model closely match the pressures and pair distribution functions at moderate electrostatic couplings. For macroion valences and couplings within the linear-response regime, deionized aqueous suspensions with monovalent microions exhibit separation into macroion-rich and macroion-poor fluid phases below a critical salt concentration. The resulting pressures and phase diagrams are in excellent agreement with predictions of a variational free energy theory based on the same model.