Phase diagrams of binary mixtures of patchy colloids with distinct   numbers and types of patches: The empty fluid regime
  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. 
Daniel de las Heras, Jos\'e Maria Tavares and Margarida M. Telo da   Gama
cond-mat.soft cond-mat.mtrl-sci