Phase separation in binary colloids with charge asymmetry

TL;DR

This study reveals that binary colloids with charge asymmetry can undergo phase separation driven by colloid-ion interactions, despite stable Yukawa pair interactions, especially under low salt conditions.

Contribution

It uncovers a new mechanism of phase separation in binary colloids caused by colloid-ion interactions, not predicted by traditional Yukawa models.

Findings

Phase separation occurs in charge-asymmetric colloids at low salt.

Crystallization of one species triggers phase separation.

Colloid-ion interactions drive the phase separation process.

Abstract

We report that binary dispersions of like-charged colloidal particles with large charge asymmetry but similar size exhibit phase separation into crystal and fluid phases under very low salt conditions. This is unexpected because the effective colloid-colloid pair interactions are accurately described by a Yukawa model which is stable to demixing. We show that colloid-ion interactions provide an energetic driving force for phase separation, which is initiated by crystallization of one species.