Effects of solvent, film thickness, and hydrogen bonding on surface-relief gratings

This work focuses on the development of a new type of surface-relief grating (SRG) using more effective materials than a typical epoxy-based azopolymer for the recording layer of optical data storage. Thus, aniline-based azopolymers were synthesized by reaction of N,N-diglycidylaniline with aniline (An) followed by diazocoupling with 4-aminobenzonitrile or 4-nitroaniline. Such azopolymers when spin-cast from THF/dioxane showed better diffraction efficiency than those cast from THF alone due to residual dioxane creating a large free volume in the solid state. A second diazocoupling reaction of the diazopolymers initially obtained produced polymers with bis(diazobenzene) substituents which exhibited a higher saturation level of the diffraction efficiency for a thicker than for a thinner film. Azopolymers in which the diazo substituents incorporated hydroxyl groups ortho to the diazo unit were obtained via the reaction of the diglycidyl ether of bisphenol-A with aniline or 3-hydroxyaniline followed by coupling with diazotised hydroxynitroaminobenzene. These hydroxy groups, presumably as a result of their H-bonding to the diazo-N, effectively prevented the photoisomerization of the chromophores, so that the polymers showed no SRG at a normal laser intensity of 100 mW/cm 2 . Polyurethane-based azopolymers, synthesized with toluene-2,4-diisocyanate and disperse orange 17 containing no hydroxyl groups in the main chains, showed better diffraction efficiency than the other azopolymers with nitro group substituents.