Optimization of azopolymer films for optical memory applications by using ethylene glycol as a free-volumegenerator

Abstract

Azopolymers are well known for their photo-induced properties, in particular, the photoinduced birefringence. Improving their performance has been of great interest in recent years for the development of applications as,for example, polarization holography, lithography and optical storage. In this work, we present the optimization of the azopolymerfor optical memory applications by using ethylene glycol as a free-volume generator. Thin films were fabricated with Poly[1-[4-(3-carboxy-4-hydroxyphenyl-azo) benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) and ethylene glycol atdifferent % w/w concentrations.Samples were characterized by measuring the birefringence during recording, relaxation and erase cycles. The measured glass transition temperature (T_g) showed a minimum for the concentration 40 %w/w, at which the degree of decay, D = 1 - Δn_REM/Δn_MAX, reaches a maximum. Birefringence was also simulated using a stochastic model that includes the key factors involved in the recording process. We show that the material can be optimized for optical memories storage applications by balancing the free volume with the azobenzene concentration. This causes a decrease in the amount of azobenzenes while maintaining the efficiency of the samples.