A Unified Model Reveals the Interfacial Structure and Dynamics of Lyotropic and Multiphase, Thermotropic Liquid Crystals

In recent years, lyotropic Liquid Crystals (LCs) have attracted considerable interest due to their biological relevance and emerging applications. However, their material behaviors are not fully understood. Here, we propose a unified model to understand lyotropic and other multiphase LCs. The model is based on the coupling of a phase field framework and a Landau-de Gennes free energy. It couples composition, nematic order, and hydrodynamics. We first validate it by successfully reproducing the spindle shape of nematic tactoids and the asymmetric shape of topological defects in the nematic-isotropic (NI) coexistence phase. We argue that the irregular defect shape is due to planar anchoring at NI interface. Our model can also be applied to elucidate the dynamics of multiphase, thermotropic LCs. Specifically, we study the coalescence of two nematic droplets. We find that the associated hydrodynamic flows always accelerate the coalescence process. We analyze in detail the fusion process of two radial droplets containing +1 defects. We predict that the system crosses a free energy barrier by generating a -1 defect at the contact point. Moving forward, we anticipate that the proposed model will provide a framework within which lyotropic and multiphase LCs can be understood.