A Closer Look at the Light Induced Changes in the Visco-elastic Properties of Azobenze-Containing Polymers by Statistical Nanoindentation

The mechanical properties of azobenzene-containing polymer films are statistically measured by instrumented nanoindentation experiment in the dark and under illumination in the absorption band of the azobenzene molecules, with special emphasis on the creep behavior and recoverability. We use Dispersed Red 1 azobenzene derivatives, which remain in the stable trans isomer state in the dark and form a dynamical photo-stationary state between cis and trans isomer under illumination. Light induces a higher change in the film hardness than in the elastic stiffness, revealing the occurrence of a visco-plastic behavior of the film under illumination. Creep experiments performed at a constant load show a striking dissipative effect linked to the mass flowing under polarized illumination.