Conformational switching in chiral self assembly

In the presence of a non-adsorbing polymer, monodisperse rod-like particles assemble into colloidal membranes, which are one rod-length thick liquid-like monolayers of aligned rods. We investigated liquid-liquid phase separation in a highly simplified system of colloidal membranes. The bulk phase separation of dissimilar rods is inherently unstable giving way to assembly of finite-sized highly monodisperse colloidal rafts. In membranes composed of rods of opposite chirality the rafts interact by universal long-ranged repulsive interactions. We studied the behaviour of colloidal rafts dissolved in a background membrane composed of achiral rods and find significantly more complex behaviours. In particular, in this limit we observed that rafts can acquire both long-ranged repulsive interactions as well as short-ranged attractions. The change in these effective membrane-mediated interactions is accompanied by the conformational change of the raft structure, wherein they switch their chiral twist. We quantified raft-raft repulsive interactions and correlated them to raft-induced membrane distortions. At high densities colloidal rafts with conformational degrees of freedom can assemble into a number of higher-order structures of increasing complexity. Amongst others these include highly regular trimers, tetramers as well an exotic square crystals comprised of two interdigitated lattices of colloidal rafts of opposite chirality.