Phase diagrams of binary mixtures of patchy colloids with distinct numbers and types of patches: The empty fluid regime

TL;DR

This study explores how different bonding energies influence phase behavior in binary patchy colloid mixtures, revealing complex phenomena like demixing, azeotropes, and conditions for 'empty' fluid regimes.

Contribution

It provides a detailed analysis of phase diagrams considering distinct patch types and energies, highlighting conditions for 'empty' fluid behavior and novel azeotropic features.

Findings

Rich phase behavior with miscibility gaps and demixing.

'Empty' fluid regime depends on relative bond strengths.

Discovery of negative azeotropes in specific energy configurations.

Abstract

We investigate the effect of distinct bonding energies on the onset of criticality of low functionality fluid mixtures. We focus on mixtures of particles with two and three patches as this includes the mixture where 'empty' fluids were originally reported. In addition to the number of patches, the species differ in the type of patches or bonding sites. For simplicity, we consider that the patches on each species are identical: one species has 3 patches of type $A$ and the other 2 patches of type $B$. We have found a rich phase behaviour with closed miscibility gaps, liquid-liquid demixing and negative azeotropes. Liquid-liquid demixing was found to preempt the 'empty' fluid regime, of these mixtures, when the $AB$ bonds are weaker than the $AA$ or $BB$ bonds. By contrast, mixtures in this class exhibit 'empty' fluid behaviour when the $AB$ bonds are stronger than at least one of the other two. Mixtures with bonding energies $\epsilon_{BB}=\epsilon_{AB}$ and $\epsilon_{AA}<\epsilon_{BB}$, were found to exhibit an unusual negative azeotrope.