Self-assembly of cyclic polygon shaped fluid colloidal membranes through pinning

An isotropic mixture of rod-like viruses self-assembles into 2D fluid monolayer membranes in presence of non-adsorbing polymer through depletion attraction. These membranes are circular in shape due to surface tension. Surprisingly, cyclic polygon shaped colloidal membranes form when isotropic mixtures of two kinds of geometrically different rods are mixed with depleting polymer. Long rods form faceted core of the cyclic polygon whereas short rods phase separate into lobes that are connected through pinning points. We demonstrate that the origin of this stable out of equilibrium anisotropic shape of the membranes lies in the phenomenon of how one fluid membrane spreads over another in presence of disorder/pinning sites. We show that the pinning sites are not topological defects rather accumulation point of rods that are significantly different. Our results show a unique counter-intuitive scenario where disorder leads to self-assembly of ordered structure.