Electrohydrodynamic Instabilities in Polymer Nematics

Let us now briefly describe electrohydrodynamic instabilities in polymer nematics. The first observation of the Kapustin-Williams domains in nematic polymers were reported in [117, 118]. The qualitative picture of the phenomenon is, in fact, the same as that for the conventional nematics (domains perpendicular to the initial director orientation in a planar cell, typical divergence of the threshold voltage at a certain, critical frequency, etc.). The only principal difference is a very slow dynamics of the process of the domain formation (hours for high-molecular mass compounds [117]). The same authors have observed longitudinal domains in very thin samples which may be referred to as the flexoelectric domains [5-14] discussed in Section 5.1.1. 

The electrohydrodynamic instabilities were extensively studied on the main chain aromatic polyester [119] 

Appeared when velocity gradient wq/Lb of flow motion exceeds the critical value t o Vc where Vc is maximum radical velocity of the vortex (Fig. 5.21) 

EHI resembles a grid pattern which oscillates (Fig. 5.17) at voltages slightably above the threshold. 

EHI looks like fingerprint textures at low frequencies and like Maltese crosses at high frequencies (Fig. 5.21). 

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