Surface Coupling between Nematic Liquid Crystals and Rubbed Polyimide Substrates for Pure Twist Deformation: Dependence on Rubbing Strength

Publisher Website
Google Scholar
Abstract
The optical detection of the surface coupling of nematic liquid crystals (NLCs) with rubbed polyimide substrates subjected to pure twist is described. Transmitted light beams through a cell comprised of homogeneously aligned NLC of a cyanobiphenyl, 5CB, inserted between crossed polarizers are observed as functions of applied magnetic field where the phase retardation occurring in the LC medium is measured and adjusted in advance by controlling the temperature. Torsional coupling strength has been investigated as a function of the rubbing strength which is expressed by the induced phase retardation occurring in the thin film of polyimide due to the rubbing. The torsional coupling constants AΦ, thus determined are 1.4 × 10−5 J/m2 for strong rubbing and 5.1 × 10−6 J/m2 for weak rubbing, respectively, at room temperature, whereas the polar coupling constants Aθ are independent of the rubbing strength and are shown to be Aθ > 1 × 10−3 J/m2.