Generation and regularization of zigzag focal conic domains guided by thermodynamic-driven topological defect evolution

Abstract

Liquid crystals, as typical anisotropic building blocks, tend to self-assemble into various ordered architectures during distinct thermodynamic processes. Research on the underlying mechanisms and rules may drastically promote our understanding of complicated structures. Here, zigzag focal conic domains (ZFCDs) are generated in rapid cooling process under an antagonistic boundary condition. After several thermal cycles beneath the nematic-smectic (N-S) phase transition point, the ZFCDs are well regularized. We found that the dislocations associated with the rapid cooling play vital roles in the formation of ZFCDs. A strong interphase correlation between the zigzag ± 1/2 disclination pairs and ZFCDs is observed above the N-S phase transition point. The orientational order inheritance and topological invariance across the phase transition indicate that similar disclination pairs exist in ZFCDs. These disclination pairs facilitate the opposite tilt direction and a half-pitch lateral shift between neighboring focal conic domains (FCDs), thus forming ZFCDs. During thermal cycles, the thermal motion of molecules induces the regularization and elimination of defect cores, further resulting in the ordered ZFCDs. Via properly controlling the cooling rate, large-area ordered ZFCDs are achieved in a wide film thickness range after thermal cycles. This study enriches the knowledge on the topological defect guided architecture of liquid crystals and may pave the way for the generation and regularization of ordered self-assembled systems.