Study of the orientational relaxation dynamics in a nonlinear optical copolymer by means of a pole and probe technique

We report measurements on the isothermal relaxation dynamics of the electro-optic coefficient of electric field poled polymeric films. The studied copolymer is a side-chain Disperse Red 1/poly–methyl–metacrylate combination. The isothermal relaxation is shown to follow a Kohlrausch–Williams–Watts stretched exponential dependence, whose parameters are strongly dependent on temperature. The average decay constant is shown to follow an Arrhenius temperature dependence below the glass transition Tg, while it is described by a Vogel–Fulcher–Tamann–Hesse above Tg. The values of the decay constant confirm a much better stability of the polymer orientation with respect to guest-host systems. The relaxation is shown to be due to a broad distribution of relaxation rates, the width of which can be qualitatively described by an empirical relation, which has already been used for guest-host systems. The measurement technique permits monitoring relaxation in a standard dielectric relaxation configuration and performing unconventional poling of the samples.