A study of high pretilt angle generation in nematic liquid crystal (5CB) on rubbed polythiophene surfaces with alkyl chain lengths

High pretilt angles in nematic liquid crystals (NLC) have been generated on rubbed polythiophene (PTP) surfaces with different alkyl chain lengths. The pretilt angle of the NLC, 4-n-pentyl-4′-cyanobiphenyl (5CB), was observed on unidirectionally rubbed PTP surfaces with alkyl chains with more than 9 carbon atoms. We obtained pretilt angle of 15-40° on rubbed PTP surfaces with 10 carbon atoms in the alkyl chain. Also, the pretilt angles of 65-80° of 5CB were obtained on rubbed PTP surfaces with 11 and 12 carbon atoms in the alkyl chain. We suggest that this high pretilt angle generation in 5CB is due to the surface-excluded volume effect by the alkyl chain lengths between the LCs and the PTP surfaces. Finally, we conclude the odd-even effect on rubbed PTP surfaces is clearly contributed to the pretilt angle generation.