Dynamic Simulation of Capillary Breakup of Nematic Fibers: Molecular Orientation and Interfacial Rupture

We simulate the breakup of cylindrical fibers of a nematic liquid crystal surrounded by a quiescent Newtonian fluid. The nematic is described by the Leslie-Ericksen theory, and the interfacial motion is captured by a phase-field method from the initial linear instability to final breakup. The focus is on the coupling between liquid crystal molecular orientation and the evolution of the interface. In particular, we examine how molecular anchoring on the interface and orientational distortion in the bulk affect the growth of capillary waves. Results show that the nematic order tends to hinder capillary wave development, in qualitative agreement with prior linear instability analysis. For typical materials, however, the effect becomes prominent only for nano-scale fibers. In addition, anisotropic viscosity plays a significant role in the growth rate of the capillary wave. In the nonlinear stage of the instability, neighboring waveforms grow at different speeds and lead to daughter drops of nonuniform sizes, which typically display the bipolar configuration with two boojum defects. Despite quantitative differences, the breakup of nematic fibers proceeds in mostly the same way as Newtonian ones. The numerical simulations are in general agreement with previous experimental observations.