Structure and dynamics of defects at thе electroconvection in twisted nematics
The influence of inhomogeneous director configurations on the specific features of the formation and evolution of structural defects in 90-twisted nematic liquid crystals is investigated in the regime of electrohydrodynamic instability. It is established that, unlike to nematics with a planar orientation, in which defects with topological indices of ±1 are formed, the domain structure of twisted nematic liquid crystals contains both the above defects and defects with a topological index of zero. It is shown that last defects are stable and their existence is associated with the axial velocity <i>v</i><sub><i></i>a</sub> of nematic liquid crystal flow in the domains. A regime of periodic oscillations of these structural defects of zero index was found where two edge dislocations with topological index +1 и -1 periodically generate and annihilate. On the basis of nonlinear motion equation for domain displacement the quantitative estimates for critical oscillation frequency of defect with S=0 was obtained.