Correlation between surface and bulk orientations of liquid crystals on rubbed polymer surfaces : odd-even effects of polymer spacer units

TLDR: Using surface optical second-harmonic generation, this paper determined the molecular tilt angle and the in-plane orientational order of the liquid-crystal molecules 4'-n-octyl-4-cyanobiphenyl (8CB) on a series of polyimide surfaces.

Abstract: Using surface optical second-harmonic generation, we have determined the molecular tilt angle and the in-plane orientational order of the liquid-crystal molecules 4'-n-octyl-4-cyanobiphenyl (8CB) on a series of polyimide surfaces. The polyimides differ in the length of the flexible spacers in between neighboring aromatic cores. Using birefringence measurements, we obtained the bulk tilt angle of liquid-crystal cells having the same series of surfaces. The surface molecular tilt angle, the in-plane orientational ordering near the surface, and the bulk tilt angle all exhibit an odd-even effect related to the odd or even number of spacer units in the polyimides