Active hierarchical self-assembly of liquid crystalline filamentous networks

Liquid-liquid phase separation plays a key role in a range of industrial purification processes, material synthesis pathways, and biological compartmentalization of cellular processes. While the phase separation of isotropic fluids in the binodal region is well-understood to proceed by the nucleation and growth of spherical droplets, it remains poorly understood how this phase separation proceeds for anisotropic fluids with orientational ordering or liquid-crystalline alignment—as is the case for many important synthetic materials and biological condensates. Here, we study the phase separation of a mesogenic liquid crystal from an isotropic fluid as a model system for liquid-liquid crystal phase separation. Instead of nucleating spherical droplets, subcooling below the binodal leads to the condensation of rapidly growing filaments, driven by elastic stresses associated with smectic alignment. The growing filaments produce active flows in the surrounding viscous fluid, and the resulting hydrodynamic confinement drives filament buckling and eventually collapse into discotic droplets. The topology of the tangling filaments during this densification and collapse produce a ramified, branchy network of discotic clusters tethered by filaments under elastic tension. We demonstrate that varying the thermal quench rate tuning the elastic stresses and active flows by varying the thermal quench rate provides control over the hierarchical assembly of the final microporous network architecture. By understanding and controlling these dynamics, we hope to provide general principles for the engineering of novel synthetic microstructures using active self-assembly driven by liquid crystal phase separation.