Thermodynamic theory of light-induced material transport in amorphous azobenzene polymer films

A novel thermodynamic approach is proposed that explains a number of experimental findings including the light-induced deformation of free-standing films and the formation of surface relief gratings for main inscription geometries. The magnitude of the elastic stress, estimated by taking the derivative of the free energy over the sample deformation, is shown to be sufficient to induce plastic deformation of the polymer film.