Nonlinear dielectric response of poled amorphous polymer dipole glasses

Abstract

Temperature-dependent spectra of the linear, second- and third-order nonlinear dielectric permittivities are reported for an amorphous polymethylmethacrylate/Disperse Red 1 guest–host polymer and a poly(styrene maleic anhydride)-Disperse Red 1 side-chain polymer glass. Both polymer systems contain Disperse Red 1 chromophores, a very strong molecular dipole. In guest–host polymers with low dye loading, the dipole density and dipole moment of the chromophores can be determined from the linear and third-order nonlinear dielectric relaxation strength, associated with the micro-Brownian motion of the chromophore dipoles. The second-order nonlinear dielectric permittivity is non-vanishing in the glassy state only in poled polymers. Contributions to the second-order dielectric permittivity arise from piezoelectricity and from the elasto-optical and electronic electro-optical Pockels effect. In poled polymer dipole glasses with nonlinear optically active chromophores, the electronic electro-optical response is the dominant source for the second-order nonlinear dielectric permittivity. Therefore, electrical current versus voltage measurements enable a measurement of the electro-optical Pockels effect in poled polymer chromophore dipole glasses.