Theory of light-induced deformations in azobenzene polymers: structure-property relationship

Abstract

We propose a microscopic theory of light-induced deformation of side-chain azobenzene polymers using a statistical model which takes the chemical architecture of azobenzene macromolecules explicitly into account. The theory provides the values of the light-induced stress larger than the yield stress. This result explains a possibility for the inscription of surface relief gratings in glassy side-chain azobenzene polymers. We show that the photo-elastic behavior of azobenzene polymers is very sensitive to their chemical structure. Depending on the chemical structure, a sample can be either stretched or uniaxially compressed along the polarization direction of the linearly polarized light. For some chemical structures, elongation of a sample demonstrates non-monotonic behavior with the light intensity and can even change its sign (a stretched sample starts to be uniaxially compressed). These results are in agreement with experiments and recent computer simulations.