Dynamic Scattering in SmA Liquid Crystal Phases

The occurrence of this scattering texture has been the subject of much research and speculation. The scattering, caused by ion flow, usually begins at the edge of electrodes or at point discontinuities formed by some topographical feature on the substrate. The importance of the substrate surface is clearly shown by reference to a study [58, 65] of 

The conductivity of the smectic phase is important rather than rely on impurities in the liquid crystal or degradation products of the dynamic scattering, it is desirable specifically to add ionic dopants. In the early work, the homeotropic aligning dopant [hexadecyltrimethyl ammonium bromide (HMAB)] conveniently also acted as the 

The conductivity of the SmA phase is also dependent on the texture or molecular arrangement of the smectic phase. The scattering state (asc) has a different conductivity to the homeotropic state (Ctr) it was found that when cTsc is larger than oVr, then dynamic scattering will occur [57] and that, as the ratio cTsc/cTtr increases, the threshold voltage decreases. 

The threshold voltage (or field) for dynamic scattering in SmA liquid crystals was predicted in 1972 [Eq. (2)] by Geurst and Goosens [67] who extended the Carr-Helf-rich model [64] for dynamic scattering in nematics. 

However, these expressions consider only the torques acting on the molecules and not the ability of the dopant to disrupt the smectic layers there are also some anomalies in the experimental work defining what is meant by the threshold voltage . Hence, it is not surprising that there are some problems in fitting experimental data to these predictions. For example, Eq. (1) predicts that V,h oc while experimentally a 

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