Liquid Crystal Alignment Properties of Poly-(3-thiopheneacetate)/Dialkyldimethylammonium Complexes

Liquid crystal alignment properties were investigated in liquid crystal (LC) cells fabricated with poly (3-thiopheneacetate)/dialkyldimethyl ammonium (PTA-Cn) complexes, where n is the number of carbon atoms in the alkyl groups in dialkyldimethylammonium bromide. Homeotropic LC alignment was observed in PTA-Cn LC cells containing long alkyl groups (n = 14, 16, 18) with high pretilt angles close to 90 degrees. Homeotropic LC alignment was observed from prepared LC cell made from PTA-C12 film, while the homeotropic LC alignment was gradually changed to random alignment within 10 min. LC cells fabricated from PTA-C10 always showed random alignment behavior. The surface orientational order parameters of the alkyl groups of PTA-Cn films were estimated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy, producing values of 0.040, 0.111, 0.153, 0.151, and 0.170 for PTA-C10, PTA-12, PTA-14, PTA-16, and PTA-18, respectively. Therefore, homeotropic LC alignment behavior correlated well with the order of alkyl groups on the complex surface.