Demixing can occur in binary hard-sphere mixtures with negative non-additivity

Abstract

A binary fluid mixture of non-additive hard spheres characterized by a size ratio $γ=σ_2/σ_1<1$ and a non-additivity parameter $Δ=2σ_{12}/(σ_1+σ_2)-1$ is considered in infinitely many dimensions. From the equation of state in the second virial approximation (which is exact in the limit $d\to\infty$) a demixing transition with a critical consolute point at a packing fraction scaling as $η\sim d 2^{-d}$ is found, even for slightly negative non-additivity, if $Δ>-{1/8}(\lnγ)^2$. Arguments concerning the stability of the demixing with respect to freezing are provided.