Dislocations and metastable chevrons in the electroconvective inplane normal roll state of a bent core nematic liquid crystal.

We report experimental results on the formation, dynamics, and annihilation of edge dislocations of opposite topological charge in the electroconvective inplane vortex state of a bent core nematic liquid crystal. The approach of paired, oppositely charged defects toward each other is a two-step process. Near constant velocity at large separation and accelerated motion close to annihilation are found, as in the case of nematic rolls belonging to standard electroconvection.

Competing instability modes in an electrically driven bent-core nematic liquid crystal.

Bent-core nematic electroconvection is a relatively less explored area, particularly in the low frequency regime. We focus here mainly on the instabilities occurring below 100 Hz in an initially planar monodomain of a bent-core nematic liquid crystal, which is negative in both conductivity and dielectric anisotropies. An unprecedented observation is the occurrence of three distinct bifurcation modes in a narrow region (10-17 Hz) that manifest, in the order of increasing threshold, as longitudinal, oblique and normal rolls.

Multiple electroconvection scenarios in a bent-core nematic liquid crystal.

We report on the anisotropic electrohydrodynamic states formed over a wide temperature range (∼45 °C) in a planarly aligned bent-core nematic liquid crystal driven by fields of frequency in the range 0.1 Hz-1 MHz. Three different primary bifurcation scenarios are generated in the voltage-frequency (V-f) plane, depending on the temperature T.

Permittivity, conductivity, elasticity, and viscosity measurements in the nematic phase of a bent-core liquid crystal.

We report on measurements of dielectric permittivity epsilon, electrical conductivity sigma, elastic moduli k(ii), and rotational viscosity gamma for a bent-core nematic liquid crystal. The static permittivity anisotropy epsilon(a) = epsilon(parallel)-epsilon(perpendicular) is negative; at a given temperature in the interval 107-123 degrees C, epsilon(parallel) shows two relaxations falling in the frequency bands 20-200 kHz and 0.9-2 MHz; epsilon(perpendicular) also shows a relaxation between 0.

Patterned electroconvective states in a bent-core nematic liquid crystal.

We report the results of investigations on the anisotropic electrohydrodynamic states arising in a highly conducting, planarly aligned, bent-core nematic liquid crystal driven by ac fields of frequency f in the range from 10 Hz to 1 MHz. Pattern morphologywise, two f regimes are distinguished. The low-f regime, wherein the primary bifurcation is to a state of periodic longitudinal stripes (LS), extends to an unprecedentedly large f, in the range 150-550 kHz, depending on the temperature T.

Shear deformation and division of cylindrical walls in free-standing nematic films under high electric fields.

We report on the behavior of cylindrical walls formed in a substrate-free nematic film of PCH5 under the action of an in-plane ac field. In the film, with vertical molecular alignment at all the limiting surfaces, annular Brochard-Leger walls are induced well above the bend-Freedericksz threshold. They exhibit, at high field strengths, a new type of instability not encountered in sandwich, or any other, cell configuration.