Electroconvection (EC) or electrohydrodynamic instability is an electric field induced nonlinear, dissipative pattern forming phenomenon in nematic liquid crystals.
EC may result in a rich variety of pattern morphologies depending on the control parameters (rms value and frequency of the applied voltage, temperature), the sample orientation (planar or homeotropic) and on material parameters (primarily on the signs of the dielectric (ea) and conductivity (sa) anisotropies).
The patterns can be observed by a polarizing microscope typically as dark and bright stripes (convection rolls), indicating a periodic spatial modulation of the director which is accompanied by a vortex flow of the substance.
Examples for EC patterns:
Standard EC patterns: a) conductive oblique rolls, b) conductive normal rolls, c) dielectric rolls in a
planar nematic with ea < 0 and sa > 0.
Nonstandard EC patterns: d) parallel rolls in a nematic with ea < 0 and sa < 0, e) normal rolls in a
planar nematic with ea > 0 and sa > 0.
Our group has been investigating both standard and nonstandard
EC patterns experimentally, in close co-operation with theoreticians at the