Polymer-Enforced Crystallization of a Eutectic Binary Hard Sphere Mixture

TL;DR

This study demonstrates how adding a non-adsorbing polymer to a binary mixture of polystyrene microgel spheres induces crystallization and phase separation, revealing new insights into binary hard sphere phase behavior.

Contribution

We introduce a polymer-enforced method to induce crystallization and phase separation in binary hard sphere mixtures, enabling exploration of previously inaccessible phase diagram regions.

Findings

Minor crystallization observed in binary mixture

Polymer addition induces inter-species fractionation

Reveals new phase behavior in attractive hard spheres

Abstract

We prepared a buoyancy matched binary mixture of polydisperse polystyrene microgel spheres of size ratio 0.785 and at a volume fraction of 0.567 just below the kinetic glass transition. In line with theoretical expectations, a eutectic phase behavior was observed, but only a minor fraction of the samples crystallized at all. By adding a short non-adsorbing polymer we enforce inter-species fractionation into coexisting pure component crystals, which in turn also shows signs of intra-species fractionation. We show that in formerly inaccessible regions of the phase diagram binary hard sphere physics is made observable using attractive hard spheres. Ancillary files: Correction to Soft Matter 2012, 8, 627