Mass transport in low Tg azo-polymers: Effect on the surface relief grating induction and stability of additional side chain groups able to generate physical interactions

The nanostructuration ability of low glass transition temperature (Tg) azo-polysiloxanes films is investigated at working temperatures close or higher than the film Tg. The behavior of materials incorporating additional side chain nitrobenzene or naphthalene groups and as a result presenting different Tg is compared in terms of the surface modulation dynamics and stability of the induced topographic modifications. This comparison is carried out under light exposure and in dark environment. We demonstrate the ability to optically generate surface modulations on these materials even at operating temperatures corresponding to the film Tg. Along with a modification of the opto-mechanic properties correlated with the materials chemical structure, a collapse of the surface structures occurring with different dynamics in materials of similar Tg is highlighted. These observations suggest the existence of an additional mechanism rather than a purely thermal redistribution of the polymer chains in the films.