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. Whereas the second of these is the flexoelectrically enabled Carr-Helfrich mode, the other two are nonstandard electroconvection modes. Significantly, the first two instabilities remain unquenched even after bifurcation into the normal roll state below their respective codimension-2 points. The hybrid roll states display complex flows and morphologies. The study includes measurement of electrical parameters relevant to the discussion of results.