Effect of substrate surfaces on the formation of nematic phase at the isotropic→nematic transition

The effect of substrate surfaces on the formation of the nematic phase at the isotropic→nematic transition of a mixture of 4‐cyano‐4′‐n‐pentylbiphenyl and hexamethyl‐benzene was studied by observing the textures with a polarizing microscope and measuring the birefringence induced by the substrate in the isotropic phase for two typical homogeneous aligning surface treatments: (1) polyvinylalcohol coating followed by rubbing and (2) SiO oblique evaporation. The two treatments resulted in completely different textures at the transition depending on the magnitude of the ordering, or equivalently the birefringence, induced by the substrate in the isotropic phase.