On stress – strain responses and photoinduced properties of some azo polymers

Abstract

Mechanical properties of two amorphous azo polymers were characterized in tensile measurements and correlated with photoinduced behaviour of the materials observed upon irradiation with blue light of moderate intensity. Side-chain azobenzene poly(amide imide)s capable of forming high-quality free-standing layers of a large area and thickness of a few micrometers were chosen for the investigations. High Young's modulus of ca. 2 GPa and yield stress of the order of 30 MPa were found for the materials. Photoinduced birefringence measurements evidenced efficient chromophore orientation in both polymers, while polymer mass transport upon illumination with interference pattern was hardly observed. Nevertheless, subtle periodic changes in the surface topography of the films after irradiation with right- and left-handed circularly polarized beams suggested that opto-mechanical stress reached the value of a few tens of MPa, i.e., the minimum value needed for inducing plastic deformations in the studied azo polymers.