X-Ray Studies of Tilted Hexatic Phases in Thin Liquid-Crystal Films

X-ray-diffraction studies of the structures and phase transitions of the tilted hexatic phases (smectic F and smectic I in thin liquid-crystal films of 4-n-heptyloxybenzylidene-4-n-n-heptylaniline (70.7) are reported. The measured correlation lengths were strongly anisotropic in both phases. The smectic-I to smectic-F transition is first order as expected from the symmetry change. The smectic-F to smectic-G transition is first order with strong pretransition effects and becomes nearly second order as the film thickness is decreased. © 1985 The American Physical Society.