Memory effects above T_g in poled guest/host polymers

We present systematic experiments of electric field poling and relaxation of 4-(dimethyl-amino)-4′-nitrostilbene doped at 1 wt % in poly(isobutyl methacrylate) in a sandwich configuration of ITO electrodes using the second harmonic generation technique. A novel ultraslow relaxation mode at temperatures far above the glass transition temperature T_g has been identified qualitatively with a special repoling technique. Isothermal alignment and relaxation of the chromophore orientations show significant differences in their mean rates and in their sensitivity to variations of the field strength and the presence of small amounts of plasticizer molecules. A tentative qualitative model is proposed in which the necessity for considering nonlinear responses is postulated.