Phase Behavior of Contact Lens-Like Particles: Entropy-Driven Competition between Isotropic−Nematic Phase Separation and Clustering

Abstract

The novel phase behavior of hard partial spherical surfaces is reported, focusing on particles close to the platelet limit, similar to contact lenses. Spherical caps of sufficiently large radius of curvature exhibit a transition from the isotropic to the nematic discotic phase. By reducing the radius further, however, the latter phase is no longer stable, and the isotropic phase evolves into a different phase characterized by the simultaneous aggregation of the centers of the parent spheres and the organization of the concave particles on the corresponding and interpenetrating spherical surfaces. Contact lens-like particles thus exhibit a competition between a fluid−fluid phase transition and a clustering phenomenon, similar to what is observed in colloidal suspensions forming cluster phases or molecular systems forming micelles. For contact lens-like particles, however, this competition does not involve any energetic contribution and is purely entropy driven.