Poling and relaxation dynamics of side-chain and crosslinkable polymers

The growth of the macroscopic second order nonlinear optical properties of side-chain and crosslinkable copolymer species is theoretically modelled. The model describes the rotational diffusion of nonlinear diazo-dye dipoles, in the presence of crosslinking sites randomly distributed in the copolymer matrix, under application of a periodic electric poling field. The time dependence of the orientational probability distribution for the crosslinked dipoles has been calculated. Such distribution have been used in order to evaluate the temporal growth of the second order nonlinear optical properties and their asymptotic value when saturation of the crosslinking process is attained. The results of the theoretical model are compared to the experimental ones, obtained for a crosslinkable copolymer, Red Acid Magly. In the experiments the r33 component of the electro-optic coefficient is measured by means of a modified electro-optic ellipsometry setup. The comparison shows a good agreement between experimental and numerical results. The model can be used in order to find the best values of the copolymer parameters, necessary in order to maximize the final second order nonlinear optical properties.