Role of the polymer viscoelasticity on the orientational processes of chromophores and on the photorefractive performances in low T_g doped polymers

The dynamics of the photorefractive properties in low glass transition temperature (T_g) doped polymers essentially depend on the photoconductivity of the host and on the orientational dynamics of nonlinear optical chromophores imbedded in the matrix. A high rotational mobility of push-pull chromophores is required to observe the so-called orientational enhancement. The influence of T_g on the photorefractive performances of guest-host polymers has been previously pointed out. However, the effects of the viscoelastic properties of polymers on the orientational processes of chromophores are neglected in most of the studies devoted to the optimization of photorefractive dynamics. In the present work, the orientational dynamics of chromophores are investigated by dielectric spectroscopy and ellipsometric dynamical measurements in various low T_g doped polymers. The experimental results show the role of different physical parameters (temperature, applied electric field magnitude, amount of plasticizer, average molecular weight of polymer) on the rotational mobility of chromophores. These data underline the necessity to take into account the viscoelastic behavior to improve the dynamics of photorefractive polymers.