Photoinduced ordering and deformation of azobenzene-containing polymers under illumination with circularly polarized light

Abstract

One of actual tasks in materials science is the development of stimuli-sensitive materials which are able to change their properties under external influences. Azobenzene-containing polymers change their properties when exposed to light. These polymers contain in their structure azobenzene chromophores which are transformed from the ground trans-state to an excited cis-state under illumination with the light. The probability of the trans-cis transition depends on the orientation of the chromophores relative to the polarization direction of the light, leading to orientational ordering and deformation of these polymers. The present work is devoted to theoretical study of the kinetics of photoinduced ordering and deformation in azobenzene-containing polymers. In previous theoretical works, the deformation of azobenzene-containing polymers under illumination with the light in a steady state, as well as the kinetics of deformation under the influence of linearly polarized light, were investigated. In the present work, the theory of the kinetics of deformation and ordering in these polymers under the influence of circularly polarized light is proposed. It is shown that relative elongation of the polymer along the direction of light propagation under illumination with the circularly polarized light can reach values 2 times higher than under illumination with linearly polarized light of the same intensity. The higher is the light intensity, the greater is the magnitude of photoinduced deformation. Depending on the polymer structure and on the orientation of azobenzene chromophores in polymer chains, either stretching or compression of the material along the direction of light propagation can be observed. The results of theoretical calculations are in qualitative agreement with experimental data available in the literature. Thus, the proposed theory demonstrateы the possibility to control the magnitude and direction of photoinduced deformation by varying the intensity and polarization of light, as well as by changing the structure of the polymer material. Results of the work may be of interest for practical applications that require control of deformation of materials using light irradiation (artificial muscles, robotics, mechanical engineering, etc.).