Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.339, 1-10, 2000
Liquid crystal alignment capability on polyimide Langmuir-Blodgett surfaces with alkyl chain lengths
The liquid crystal (LC) alignment capability in 4-n-pentyl-4'-cyanobiphenyl (5CB) on polyimide (PI) Langmuir-Blodgett (LB) surface with alkyl chain lengths was investigated. The pretilt angle of 5CB increased by unidirectional rubbing treatment on PI-LB surface. The induced optical retardation on PI-LB surface increased by the rubbing. The extrapolation length d(e) of 5CB for rubbed PI-LB surfaces with even-number is small, compared with odd-number near the clearing temperature T-c. The extrapolation length d(e) of 5CB with odd-number increases gradually as the temperature increases but it tends to diverge near the T-c. Therefore the polar anchoring strength with even-number is strong because of relatively high surface ordering caused by more crystalline surfaces. The anchoring energy of 5CB with alkyl chain length of 7 carbons is approximately 1 x 10(-3) (J/m(2)); it indicates the strong anchoring strength. In consequence, we suggest that the LC aligng capability in NLC on PI-LB surface is strongly related to the characteristics of the polymer.