Alignment of nematic liquid crystals on ruled grating surfaces

Ruled gratings of 0.33–3.33-μm wavelength fabricated with SiO, SiO2, and In2O3-SnO2 are used to study the topographical effects of the surface on the twisted nematic (TN) alignments of liquid crystals (LC’s). The types of LC’s are Schiff base, azoxy, biphenyl, biphenyl ester, and phenyl cyclohexane. All of the LC’s, except the azoxy, used in this study take good homogeneous and TN alignments on all grating films of wavelength less than 0.8 μm. The azoxy takes homeotropic alignment on the SiO and SiO2 grating surfaces. The agreement between experimental results and Frank elasticity theory is fairly good. Topographical effects can take precedence over chemical effects between the LC and surface when chemical anchoring is weak. Making use of the calculated elastic deformation energy of LC’s on grating and rubbed surfaces, we estimate the anchoring energies of homogeneous and homeotropic alignments. The application of grating cells to optical display is limited by the occurence of tilt domains.