Structural correlations and phase separation in binary mixtures of charged and uncharged colloids

TL;DR

This study uses computer simulations to analyze structural correlations and phase separation in binary colloid mixtures, revealing limitations of DLVO theory at lower dielectric contrasts and predicting phase separation phenomena.

Contribution

It demonstrates the effectiveness of the primitive model in capturing colloid interactions and identifies conditions where DLVO theory fails, highlighting phase separation in charged-uncharged mixtures.

Findings

DLVO theory accurately predicts correlations at high dielectric constants.

Deviations occur at lower dielectric contrasts due to Coulomb coupling.

Fluid-fluid phase separation occurs, not captured by DLVO theory.

Abstract

Structural correlations between colloids in a binary mixture of charged and uncharged spheres are calculated using computer simulations of the primitive model with explicit microions. For aqueous suspensions in a solvent of large dielectric constant, the traditional Derjaguin-Landau-Vervey-Overbeek (DLVO) theory of linear screening, supplemented with hard core interactions, reproduces the structural correlations obtained in the full primitive model quantitatively. However for lower dielectric contrast, the increasing Coulomb coupling between the micro- and macroions results in strong deviations. We find a fluid-fluid phase separation into two regions either rich in charged or rich in uncharged particles which is not reproduced by DLVO theory. Our results are verifiable in scattering or real-space experiments on charged-uncharged mixtures of colloids or nanoparticles.