Effective potentials induced by mixtures of patchy and hard co-solutes

TL;DR

This study explores how mixtures of patchy particles and hard spheres as co-solutes influence colloidal interactions, revealing additive effects and conditions where additivity breaks down, aiding the design of colloidal structures.

Contribution

It demonstrates that effective potentials from binary co-solute mixtures are additive and identifies conditions where this additivity fails, advancing understanding of colloidal interactions in complex environments.

Findings

Effective potentials are additive in binary mixtures of patchy and hard sphere co-solutes.

Additivity breaks down near the demixing transition of the mixture.

The effective potential can be tuned by changing co-solute composition.

Abstract

The addition of co-solutes to colloidal suspensions is often employed to induce tunable depletion interactions. In this work we investigate effective colloidal interactions arising from binary co-solute mixtures of hard spheres and patchy particles. By changing the relative concentration of the two species, we show that the resulting effective potential $V_\text{eff}$ continuously changes from the one obtained for a single-component hard sphere co-solute to that mediated by the single-component patchy particle co-solute. Interestingly, we find that, independently of the relative concentration of the two components, the resulting $V_\text{eff}$ is additive, i.e., it is well-described by the linear combination of the effective interactions mediated by respective pure co-solutes. However, a breakdown of the additivity occurs when the co-solute mixture is close to the onset of a demixing transition. These results represent a step forward in understanding and predicting colloidal behaviour in complex and crowded environments and for exploiting this knowledge to design targeted colloidal superstructures.