Active Control of Periodic, Three-Dimensional Disclination Networks in Nematic Liquid Crystals*

Disclinations are of fundamental interests to soft matter physics, particles physics, and mathematics. Topological defects are also of practical importance in sensing, photonics, and directed self-assembly of colloids and molecules. Disclinations in active nematic liquid crystals (LCs) are especially interesting due to their autonomous dynamics. However, these structures in three-dimensional (3D) active nematics are difficult to control, limiting their further applications. Here, we demonstrate a full control over the transformation of 3D disclinations that mimics their dynamics in active nematics. Specifically, using photo-patterned surfaces and continuum simulations, we show that during a mechanical or photo-induced transformation of the surface anchoring, periodic 3D disclinations can nucleate, deform, merge, and split in a nematic cell in a programmable manner. Continuum simulations based on Landau-de Gennes free energy functional demonstrate an excellent agreement with the experiment and reveal the change in their topologies during the transformation. These highly controlled defect transformations allow us to examine the topology and elastic properties of disclinations of varying morphologies, and to facilitate applications including novel LC-based photonic devices.