Effects of viscoelastic properties on the dielectric and electrooptic responses of low-T_g guest-host polymers

The dynamics of the electrooptic and dielectric properties in low-T_g photorefractive guest-host polymers are directly related to the orientational dynamics of doping nonlinear optical chromophores. We report on experimental results on the orientational mechanisms of chromophores above T_g, investigated by ellipsometry and dielectric spectroscopy. These measurements have been performed on plasticized poly(N-vinylcarbazole) and polysiloxane functionalized with a carbazole pendant, doped with nonlinear optical chromophores. The data are compared to the mechanically measured complex shear compliance of the materials. The results of this comparison demonstrate that the orientational dynamics of chromophores are entirely ruled by the viscoelastic properties of the polymer matrix. In addition, the influence of the chromophore size is investigated and interpreted by using free volume and rheological laws. Finally, the evidence of an anelastic memory, induced by the orientation of the chromophores below T_g, is pointed out.