Frank elasticity driven gelation and aging of self-assembled nanoparticle capsules

Controlling the assembly of colloidal particles in liquid crystal (LC) has recently been of both theoretical and experimental interest. The aggregation behavior of colloidal particles in LC can lead to the formation of new aggregate morphologies and fractal structures. Here we report the one pot synthesis of colloidal aggregates in nematic liquid crystal brought about by the isotropic to nematic phase transition. These aggregates are highly anisotropic on short length scales, with web-like morphologies composed of capsules organized into chains. Using fluorescence microscopy to observe capsules constructed of quantum dots, we perform temperature quenches and the capsules are formed within one second. Shortly after formation, the capsules spontaneously assemble into chains, which subsequently organize into clusters. As the number density of capsules increases with quench depth, these clusters form a gel-like morphology consisting of densely packed chains of capsules. Over time, the gels undergo aging and become more compact, which we quantify using a pair correlation function, g(r). Velocity analysis reveals that ageing effects are combination of Frank elasticity relaxation, and defect line breakage/shrinkage.