Equation nemato-electrohydrodynamic

This section deals with the influence of flexoelectricity on electroconvection with planar geometry and the most studied material parameter combination a < 0 and Oa > 0. The analysis makes use of the common nemato-electrohydrodynamic equations, 4s jjj addition the flexopolarization... 

Besides cell thickness d of the nematic layer, which has almost no effect in the case ei = es = 0, reveals a strong influence on EC for finite flexocoefficients. This is demonstrated in the lower panel of Fig. 4.5, where for d = 10 /Ltm the conductive branch is totally absent. Then, as with the conductive regime, one can find a transition from oblique to normal dielectric rolls above a Lifshitz frequency In a recent experiment the oblique dielectric rolls at small w have indeed been observed. The threshold characteristics Uc and qc and the obliqueness angle a. could be well reproduced by a theoretical analysis of the nemato-electrohydrodynamic equations including flexopolarization. ... 

Finally we would like to point out that the magnitude ao of the electrical conductivity in nematics plays an important role. For Fig. 4.5 we chose electrical conductivities in nematics commonly used in experiments. A closer look at the linear nemato-electrohydrodynamic equations (see the Appendix in Krekhov et shows that the thickness d as well as ao appear only through the dimensionless parameter Q oc Td/rq oc aocP. Thus decreasing ao by a factor of 16 is equivalent to a reduction of d by a factor of 4 (compare Fig. 4.5a and Fig. 4.5b). 

Hz, there are normal dielectric rolls and for f < /l oblique ones. The transition to flexodomains is observed at ft 0.1 Hz. A recent theoretical analysis has demonstrated that such a scenario is possible within the nemato-electrohydrodynamic equations including flexopolarization. 

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