Periodic microstructure induced by 532 nm polarized laser illumination on poly(urethane-imide) film: orientation of the azobenzene chromophore

Relatively low-energy laser illumination, specifically the second harmonic (λ=532 nm) of a Nd:yttrium–aluminum–garnet (YAG) laser, was used to prepare laser-induced periodic surface structures (LIPSS) on surfaces of polymers doped and grafted with Dispersed Red 19. This dye strongly absorbs the laser light, and the use of 532 nm radiation avoids the photolysis reactions on polymers that often accompany the use of UV lasers. We find that LIPSS can be obtained on the grafted poly(urethane-imide) (PUI) film. Effects of scanning speed, laser fluence, and the angle of incidence on the formation of LIPSS were examined. Non-polarized and polarized transmission FT-IR spectroscopy were applied to characterize the orientation of azobenzene side groups, which were found to tend to align in the plane perpendicular to the direction of LIPSS.