(64b) Assembly of Two Dimensional Colloids in an Elastic Two Dimensional Fluid

Bilayer phospholipid lamella are frequently employed as models to elucidate the behavior of living cells, but these same ultrathin sheets possess unique materials properties in their ability to assume complex contoured shapes and direct reversible colloidal assembly. Here we explore how the elasticity of thin fluid sheets can control the reversible assembly of Brownian plate-shaped membrane colloid, for instance into arrays and chains, and the nature of the transitions surrounding the assembly. Three classes of domain configurations are controlled by the availability of membrane bending, which is manipulated osmotically. When vesicles are deflated from a spherical shape by as much as 25% volume colloidal plates form a vesicle-encompassing pseudo-hexagonal lattice that maximizes the plate-plate distances. When the vesicles are inflated to within about 2% of their spherical volume, the colloidal plates associate closely but do not touch, assembling into chains. These two classes of assemblies are relatively persistent with long lived structures that suppress Brownian motion. A sharp boundary, near 2% deflation, distinguishes the two classes of assemblies with the domain distances switching sharply at these conditions suggesting cooperative behavior such as phase transition. In the final state, when vesicles are deflated by as much as 5% from a perfect sphere, domains are disordered and dynamic, with the positions changing on the timescale of minutes. This behavior was demonstrated for vesicles whose colloids occupied ~17% of the surface area and were in a size range of 10-40 um and with 4-100 colloids per vesicles, establishing the broad character of this behavior and the extreme utility of bending interactions.