Highly Photosensitive Surface Relief Gratings Formation in a Liquid Crystalline Azobenzene Polymer: New Implications for the Migration Process

Abstract

We have recently demonstrated a markedly photosensitive surface relief gratings (SRG) formation in thin films of liquid crystalline azobenzene-containing polymers, which proceeds from a cis-rich state of the azobenzene [Zettsu et al. Adv. Mater. 2001, 13, 1693; Macromolecules 2004, 37, 8692]. Such polymers exhibited unexpected enhancements in the sensitivity to light for the completion of SRG formation, the required energy dose being ∼103-fold lower than that for other azobenzene polymers systems widely employed. Here we report detailed results on the systematic explorations for understanding the migration mechanism. The cis-isomer content at the initial state and irradiation intensity crucially influenced the migration efficiency and the resulting relief structure in nonlinear manners. The Zisman plot showed that the light irradiation leads to a large change in the critical surface tension. Such results strongly suggest that the photochemically induced phase transition and the resulting spatial modulatio...