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Flexoelectricity and competition of time scales in electroconvection
Tibor Toth-Katona
,Nandor Eber
,Agnes Buka
,Alexei Krekhov
Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences
Physikalisches Institut, Universitat Bayreuth
Novel behavior in electroconvection (EC) has been detected in
nematic liquid crystals (NLCs) under the condition of comparable
timescales of the director relaxation and the period of the
driving ac voltage. The studied NLCs exhibit standard EC (s-EC) at
the onset of the instability, except one compound in which
nonstandard EC (ns-EC) has been detected. In the relevant
frequency region, the threshold voltage for conductive s-EC bends
down considerably, while for dielectric s-EC it bends up strongly
with the decrease of the driving frequency. We show that inclusion
of the flexoelectric effect into the theoretical description of
conductive s-EC leads to quantitative agreement, while for
dielectric s-EC a qualitative agreement is achieved. The frequency
dependence of the threshold voltage for ns-EC strongly resembles
that of the dielectric s-EC.
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