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

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.

submitted to the JCP special issue on depletion interactions

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