  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.
