Electroconvection
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