Annihilation dynamics of umbilical defects in nematic liquid crystals under applied electric fields.

Umbilical defects were induced in a nematic liquid crystal with negative dielectric anisotropy, confined to Hele-Shaw cells with homeotropic boundary conditions, and their annihilation dynamics were investigated experimentally. Dynamic scaling laws, previously proposed for Schlieren defects, were verified also for electric field induced umbilical defects while varying external parameters, such as electric field amplitude, frequency, Hele-Shaw cell gap, and temperature. In all cases, scaling relations of rho(t) proportional to t(-1) for the defect density and D proportional to (t(0) - t)(1/2) for the defect pair separation were obtained, independent of external field parameters. The experimental results give evidence of the universality of scaling relations for the annihilation of topological defects in liquid crystals, extended to umbilical defects and their annihilation dynamics under applied external fields.