Theory of Light-Induced Deformation of Azobenzene Elastomers

Summary: A microscopic theory is proposed to describe light-induced deformation of photo-sensitive elastomers bearing azobenzene chromophores in their strands. We use an orientation approach in which it is assumed that the light-induced deformation is caused by reorientation of azobenzene chromophores with respect to the electric vector of the linearly polarized light, E , due to the trans-cis-trans photoisomerizaion process whose efficiency depends on the orientation of the chromophores with respect to the vector E . In the framework of the Gaussian approximation for elasticity of network strands it is shown that the value of the light-induced deformation depends on the chemical structure of network strands, namely, on the orientation distribution of chromophores around the main chains which is related to the length and elasticity of spacers. Depending on the chemical structure, azobenzene elastomers can demonstrate expansion or uniaxial contraction along the vector E , as well as non-monotonic deformation with increasing light intensity (expansion at small light intensities and contraction at high ones).