The growth and decay processes of the optically induced birefringence in an azobenzene-functionalized polymer, DR19FPOZ (full name given in the text), and in another azobenzene guest/host polymer system have been studied. The temperature dependence of the birefringence signal is studied, and possible mechanisms associated with the growth and decay segments of the signal are analyzed. Rate constants deduced from the optically induced birefringence signal are also investigated as a function of the laser excitation power and film thickness. The rate constants associated with the growth and decay processes and activation energies are obtained for the polymer system below the glass transition temperature.

The behavior of surface and trapped charge that originate during contact electric-field poling of a model guest–host nonlinearly active polymer has been investigated. Charge effects in thin films of para-nitroaniline doped polymethylmethacrylate were studied during and after the poling process by simultaneous measurement of the current through the poling circuit and the second harmonic generation (SHG) signal from the polymer system. The poling current present in a fresh sample was found to differ in both magnitude and temporal dependence to that observed in the sample during subsequent polings. The magnitude of the steady-state current eventually reached during the poling process was found to depend on temperature and is related to the mobility of charge. A sharp drop-off in SHG signal intensity that occurred when the poling electrodes were grounded is shown to result from the removal of surface charge that orients chromophore dipoles near the surface of the film; the decay in the macroscopic polarization that then occurs is prolonged by charges trapped in the polymer matrix. The build-up of trapped charge explains a memory effect in which the SHG signal relaxation time gradually increased as the film was subjected to multiple polings until a steady-state value was reached. Finally, it is demonstrated that the charges trapped in the polymer matrix are released only after the polymer is heated to high above its temperature of glass transition and the SHG signal has completely decayed away.

The solvent effect on the molecular first hyperpolarizability, β, of p-nitroaniline (pNA) has been investigated. Using the hyper-Rayleigh scattering technique, we have also determined β of pNA in DMSO using 1064 nm laser radiation. This β value has not been previously reported. With the help of Onsager's theory, we have arrived at a correction factor to account for the solvent dependence of the values of the intrinsic hyperpolarizability β0. The Onsager model significantly removes the strong solvent dependence of β (or β0) on the dielectric constant.

A detailed quasieslatic light (QEL) scattering study of the polystyrene-poly(methyl methacrylate) (PS-PMMA)/benzene ternary solution with both polymers in the semidilute concentration regime was carried out. Two types of the PS-PMMA/benzene solution have been studied: one at fixed composition but different total polymer concentrations, and the other at fixed total polymer concentration but different compositions. Two diffusion modes in the intensity-intensity time correlation function of the scattered light were observed in these solutions. These two modes correspond to the eigenmodes of the diffusivity matrix that governs the time evolution of the concentration fluctuations of the polymers in the ternary solution. The concentration and composition dependencies of the relaxation rates and the amplitudes of these modes were investigated. From the relaxation rates and amplitude factors, the elements of the diffusivity matrix were determined as a function of polymer concentration and composition. By using the diffusivity data, the self-diffusion coefficients of PS and PMMA and the Flory-Huggins interaction parameter F, between PS and PMMA were deduced. The concentration and composition dependencies of these quantities were studied. At fixed composition, the self-diffusion coefficients of PS and PMMA were found to decrease with increasing total polymer concentration, whereas at fixed concentration they decreased with decreasing fraction of its own kind. The value of the Flory-Huggins interaction parameter, F, between PS and PMMA was found to range from 0.008 to 0.026, depending on concentration and composition. The F values obtained by our method are in good agreement with those obtained by other techniques, indicating the reliability of our method.

First hyperpolarizabilities (β) of two tricyanovinylthiophene nonlinear optical chromophores were determined using second harmonic, hyper-Rayleigh, scattering. The use of an external standard in the determinations is compared with the previous use of an internal standard. The first hyperpolarizability of the well-known chromophore 4 dimethylamino 4′ nitrostilbene (DANS) was also determined using the external standard method and its value is compared to those in the literature. A new method of analyzing the hyper-Rayleigh scattering signal by recording a histogram of the scattered energy is reported. This method is shown to give more reliable results in a shorter period of time than the usual static gate method. The histogram function provides additional information in the form of the histogram width which is shown to be an indication of the mean-square concentration fluctuations of the chromophores in solution. The effects of molecular interactions on the concentration dependence of the hyper-Rayleigh scattering signal is discussed. It is shown that depending on the concentration range, the β value of para-nitroaniline, used as the external standard, can agree with two different values reported in the literature. Results on the depolarization ratio of the hyper-Rayleigh scattered light from one of the tricyanovinylthiophene chromophores are presented. At low concentration the depolarization ratio agrees with the theoretically predicted value based on C2v symmetry. However, at higher concentration the measured depolarization ratio increases indicating molecular interactions.