Magnetic field induced transient periodic dissipative structures in nematics.

Abstract

The linearized version of nonstochastic continuum theory is used with the rigid anchoring hypothesis to study the occurrence of transient periodic dissipative structures (DS) induced in a nematic sample by a magnetic field H of supercritical strength applied in a Freedericksz geometry (H normal to n 0, the uniform initial director orientation with $\chi_{\rm a}$ the diamagnetic susceptibility anisotropy being positive). The time constant and domain wavevector of DS are found to depend on the field strength H, the initial tilt of n 0 relative to the sample planes and the oblique inclination of H in a plane normal to n 0. In general, DS occurs at high H while the occurrence of a nonperiodic mode is more favourable at low H. However, a nonperiodic mode endowed with certain properties might reappear at higher fields in a reentrant way when ${\bf n}_0$ is tilted and H oblique. The cases of negative $\chi_{\rm a}$ and finite director anchoring energy are treated briefly. Based on the known experimental and theoretical results for the static stripe phase it is suggested that the formation of DS may be hampered by utilizing non-Freedericksz geometries (with H not normal to n 0). By comparing energy dissipations of DS and the nonperiodic mode it is possible to arrive at the critical point separating the two in a simple geometry for short time regimes (immediately after the application of H).