Electrohydrodynamic Instability in Nematics with Oblique Director Orientation at the Boundaries

3 Electrohydrodynamic Instability in Nematics with Oblique Director Orientation at the Boundaries 

A new type of electrohydrodynamic instability in liquid crystals with tilted directors at the boundaries was revealed by Pikin et al. [63]. This instability is characterized by a domain pattern parallel to the projection of the initial director orientation. It is supposed that the director angle with respect to the substrate remains unchanged (x 2 -plane) while the periodic two-dimensional vortex motion appears in the yz-plane, where the 2 -axis is perpendicular to the substrates (Fig. 5.9). These domain structures seem to be observed in [64, 65] with the oblique director orientation achieved by means of oblique SiO evaporation. When the voltage exceeds its critical value the second domain pattern appears along the y-axis. 

The threshold voltage C/th of the domains appeared from the oblique orientation and their period Wth was calculated [63] 

The two-dimensional model [66] of this domain structure shows that its threshold considerably depends on the value of the Leslie viscosity coefficient as and the dielectric anisotropy Ae. Unlike the Kapustin-Williams domains, this instability could also be observed for negative conductivity anisotropy. There remains only one specific point where the instability ceases to exist, namely, the conductivity isotropy point. Act = 0. 

Electrohydrodynamic instabilities in liquid crystals are very sensitive to the frequency of the applied field. Low-frequency modes, described above, are observed at 

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