Vertical alignment of liquid crystals on plant-based vanillin derivative-substituted polystyrene films.

To investigate the alignment behavior of liquid crystal (LC) molecules, we synthesized a series of vanillin derivative-substituted polystyrene films (PVAN#, # = 20, 40, 60, 80, and 100), where # is the substitution ratio (%) of the vanillyl butyl ether (VAN) moiety as one of the bio-renewable vanillin derivatives. In general, a vertical LC alignment was observed in the LC cell fabricated using the polymer film having a higher molar content of VAN. Moreover, the surface energies of these polymer films were strongly related to the vertical LC alignment behavior. For example, a uniform vertical alignment was observed when the polar surface energy of the polymer was lower than approximately 2.05 mJ m, induced by the nonpolar and long carbon groups in the plant-based vanillin moiety. The LC cell fabricated using PVAN100 had good electrooptical characteristics such as voltage holding ratio and residual direct-current voltage and stable alignment under extreme external conditions.