Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Oct;82(4):046215. doi: 10.1103/PhysRevE.82.046215. Epub 2010 Oct 19.

Nematic electroconvection under time-reversed excitation.

Physical review. E, Statistical, nonlinear, and soft matter physics

Dirk Pietschmann, Thomas John, Ralf Stannarius

PMID: 21230373 DOI: 10.1103/PhysRevE.82.046215

Abstract

We study nematic electrohydrodynamic convection (EHC) under excitation with superimposed harmonic wave forms. Within the standard model for EHC, a time reversal of the excitation does not affect threshold voltages and pattern wavelengths obtained in a linear stability analysis. This was confirmed in experiments with superimposed square waves [Heuer, Phys. Rev. E 78, 036218 (2008)]. We show here that this symmetry with respect to time reversal of the excitation breaks down close to the transition from the conduction regime to the dielectric regime. The EHC standard model without flexoelectric terms fails to predict quantitatively correct threshold curves and wavelengths in a certain parameter range below the transition. This is an indication that a more elaborate description of the EHC mechanism is necessary in this range. We suggest that the weak electrolyte model has to be employed for a correct description. This is in accordance with observations of traveling rolls and of localized structures at onset of the convection in earlier experiments described in literature.

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• Journal Article