Monolayer behavior and in situ interfacial polymerization of polymerizable liquid crystal at the air-water interface and application to alignment layers for liquid crystal display

Abstract

The monolayers and interfacial polymerization of liquid crystalline n-[(4- cyano-4``-biphenyl)oxy] alkyl vinyl ether series were studied. All of the materials were synthesized from the reaction of 4-cyano-4``-(n-hydroxyalkane -1-yloxy) biphenyl and n-heptyl vinyl ether. At the air-water interface 3-[(4-cyano-4``-biphenyl) oxy] undecanyl vinyl ether] formed an unstable monolayer, but 11-[(4-cyano-4``-biphenyl) oxy] undecanyl vinyl ether] could form a stable monolayer. The limiting areas of homologues series of 8,10,11 -[(4-cyano-4``-biphenyl) oxy] undecanyl vinyl ether] were about 12, 15, and 18$Å^2$/molecule, respectively, and smaller than the flat area of hydrophilic cyanobiphenyl group. The monolayer of 11-[(4-cyano-4``-biphenyl) oxy] undecanyl vinyl ether] was transferred only as the Z-type on a hydrophilic substrate in the first few layers. The deposition of 11-[(4-cyano -4``-biphenyl) oxy] undecanyl vinyl ether] onto various substrates using a mixture with poly (amic acid) alkylamine salt were investigated to apply to liquid crystal display for alignment. Mixed films of the poly (amic acid) alkylamine salt and 11-[(4-cyano-4``-biphenyl) oxy]undecanyl vinyl ether] were completely miscible in dimethylacetamide and formed a stable monolayer at the air-water interface. Y-type LB film on ITO glass was confirmed by FTIR spectroscopy and UV-vis spectroscopy. The layer thickness of the Y-type deposition onto a Si wafer was determined to be 19.5Å by ellipsometry. The contact angles of all transferred films showed a sharp increases after first layer. The monolayer of the mixture was polymerized by UV-irradiation at 25 mN/m, and the extent of the reaction was investigated by UV-vis spectroscopy. A liquid crystal cell with a mixture LB alignment was fabricated and the polarized microscope textures of liquid crystals confirmed the alignment of liquid crystal display even without a rubbing process.