Microphase Separation and Stability of Chiral Rafts in Colloidal Membranes

Colloidal membranes are an experimental system composed of rod-like chiral particles that are driven by depletion interactions to self-assemble into one-rod-length thick monolayers. Their large size enables the study of behaviors that cannot be visualized in lipid bilayers, as they are described by the same continuum theory. Membranes formed from a mixture of short right-handed rods and long left-handed rods exhibit microphase separation, wherein one rod species forms finite-sized rafts floating in a background membrane of the other rod species. This system exhibits complex membrane-mediated interactions between rafts, which depend on the depletant concentration and the chirality of the rods. In this talk I will present a Ginzburg-Landau theory that explains the existence and interactions of rafts. Consistent with recent experiments, we find that decreasing the background chirality allows rafts to form with either right-handed (in the direction preferred by chirality) or left-handed (counter to the preferred direction) twist. Further, pairs of like-twisted rafts have repulsive interactions, while pairs of oppositely-twisted rafts have attractive interactions. The theory allows for a mechanistic understanding of these behaviors.