INVESTIGATION OF ANCHORING TRANSITION OF LIQUID-CRYSTALS ON CROWN-ETHER MONOLAYERS BY ATOMIC-FORCE MICROSCOPY

The homeotropic and homogeneous alignment of a liquid crystal material, 4'-n-pentyl-4-cyanobiphenyl (5CB), were achieved by Langmuir monolayers of a double-armed crown ether liquid crystal, N,N-bis[4-(4-heptoxybenzoyloxy)benzo-yl]-1,10-diaza-4,7,13,16-tetracyclooxaotadecane (CELC) . We found that when the monolayer was deposited before the phase transition during monolayer compression, it induced liquid crystal alignment homogeneously; when the monolayer was transferred after the transition, homeotropic liquid crystal alignment was produced. Atomic force microscopy was used to examine the morphology and microstructure of the alignment agent. The results show a conformational change of the alignment agent before and after the transition. The anchoring transition is interpreted as the result of orientational change of the CELC monolayer. We present strong evidence that the orientational change of dipoles in the alignment agent can induce an anchoring transition.