Cyanobiphenyls elastic properties

This section contains an outline of the theory and results of experimental studies of the elastic properties of nematics. First, a short introduction of the standard theories is given and the characteristic quantities, used to describe nematic phase elasticity are introduced. After an overview of the standard methods of measuring elastic constants, a summary of the experimental results is given. In particular, we list a collection of papers dealing with the extensively explored cyanobiphenyls and the standard substance 4-methyloxy-4 -butylbenzylidene-aniline (MBBA). The next part is devoted to the less-common surface-like elastic constants, and this is followed by a sketch of the theoretical approaches to the microscopic interpretation of elastic constants and the Landau-de Gennes expansion. The section is concluded by a brief discussion of elastic theory for biaxial nematic phases. 

P. Karat and N. Madhusudana, Elastic and optical properties of some 4 -n-alkyl-4-cyanobiphenyls, part 11, Moi. Cryst Liq. Cryst, 40, 2 39 (197 73. 

Dielectric anisotropy is an additive molar property. Thus, a small amount of PEBAB [Ae 10] (about 10-15 mol %) dissolved in MBBA [Ac —0.2] will provide a material suitable for twisted nematic devices. The threshold will, of course, be higher for this mixture than for a pure positive one such as 4-pentyl-4 -cyanobiphenyl, where the dielectric anisotropy is much higher. There are other influences on the threshold voltage for liquid crystal cells, principally the materials elastic constants and, in the case of dynamic scattering, material viscosity. The response times also are dependent upon elastic constants, viscosity, and dielectric anisotropy. These factors are discussed at length in a review by Goodman." ... 

---