Static Dielectric Anisotropy of Nematics and Smectics

In experiment on nematic liquid crystals, both positive and negative anisotropy , is observed, the sign depending on chemical structure. The magnitude of e is often proportional to orientational order parameter S. In the isotropic phase the anisotropy disappears. Typical temperature dependencies of n and , are shown in Fig. 7.5. These observations can be accounted for by the Maier-Meier theory [5]. The latter is based on the following seven assumptions  

the molecules are spherical with radius a, but their polarizability is tensorial, 

the point molecular dipole p makes an angle p with the axis of maximum molecular polarizability 

a nematic liquid crystal has a center of symmetry and characterized by orientational quadrupolar order parameter S 

the analysis is performed within the framework of Onsager s theory of polar liquids, and the mean dielectric susceptibility was taken for the calculation of the Onsager factors h and F, introduced above 

---