EFFECTS OF CONFINEMENT AND SHEAR ON THE PROPERTIES OF THIN-FILMS OF THERMOTROPIC LIQUID-CRYSTAL

The surface forces apparatus technique was used to measure the normal forces, thin film viscosity, and lateral (frictional) forces between t wo surfaces interacting across 4'-n-octyl-4-cyanobiphenyl (8CB), to de termine the effects of confinement (film thickness) and shear (sliding velocity) on the ordering of the smectic-A and the nematic phases. Th e surface roughness and hydrophobicity were altered by different adsor bed surfactant monolayers to study the effects on the orientation and anchoring of 8CB. The positional order increases as the surface separa tion decreases, and the orientational ordering increases with increasi ng shear rate. The friction force in the planarly oriented nematic pha se resembles results for alkanes, while the better ordered smectic-A p hase exhibits lower friction forces. The liquid crystal orients perpen dicularly to surfactant-coated surfaces. On a loose-packed surfactant layer, it becomes strongly anchored, which increases the resistance to sliding, while on a close-packed monolayer the friction force is low, but the liquid crystal is easily removed by the applied load or press ure.