Liquid crystal alignment film with mixture of polyimide and side chain LC by Langmuir-Blodgett technique

Abstract

The mixed films of poly(amic acidi and a side-chain liquid crystal, 11-[(4-cyano-4'-biphenyl)oxy] undecanyl vinyl ether(CN-11-M) were investigated as a LC alignment film to control the pretilt angle of a nematic LC. The mixed films were fabricated by the Langmuir-Blodgett technique. A stable monolayer of poly (amic acid) alkylamine salt (PAAS) and CN-11-M was formed at the air-water interface. A Y-type film on ITO glass was established at 25 mN/m and room temperature and was confirmed by FTIR spectroscopy. The number of layer was 4, and the ratio of PAAS and CN-11-M was varied. Surface tensions of these films were observed by measuring the contact angle of test liquid. Antiparallel cells were made to measure the pretilt angle of LC by crystal rotation method. Polar force in the mixed film increased with the amount of CN-11-M, but showed a maximum. The pretilt angles of nematic liquid crystal also showed the maximum ata fixed ratio of PAA and CN-11-M.