Asymmetry-driven irregular topological defects and hydrodynamic cavitation of tadpole particles in nematic liquid crystals

Abstract

Topological defects (TDs) arise from the disruption of orientations that span multiple length scales, from nanometers in biological systems to miles in cosmic systems, often resulting from energy minimization leading to symmetric morphologies. Symmetry breaking is a challenge in creating new types of topological defects to understand self-assembly mechanisms when driving the system away from the equilibrium state. Nematic liquid crystals (LCs) provide an ideal system to create, annulate, and directly visualize TDs. We use asymmetric particles, named tadpole-shaped particles, which have sphere-shaped heads and long tails, to explore new symmetry-breaking defect morphologies when dispersing these tadpole particles into nematic liquid crystals. Experimental observations and numerical simulations demonstrated that the micrometer-sized SiO₂ tails exhibit exceptional flexibility, distorting the surrounding LC field into butterfly-shaped defects. As these particles moved through the LC medium under capillary forces, dynamic interfacial fluctuations between the air and LC phases facilitated the formation of metastable cavities. This novel system enabled cavity generation and revealed a unique formation mechanism driven by hydrodynamic cavitation, where a balance between capillary, elastic, and viscous forces led to cavity contraction and equilibrium restoration. Beyond advancing fundamental understanding, these findings open new avenues for designing microactuators, soft robotics, and adaptive materials, transforming the role of active particles in LC systems.