DOPANT ORIENTATION DYNAMICS IN DOPED 2ND-ORDER NONLINEAR OPTICAL AMORPHOUS POLYMERS .2. EFFECTS OF PHYSICAL AGING ON POLED FILMS

Polymer relaxation and physical aging phenomena at temperatures well below the glass transition have been examined in corona- and contact-poled, doped poly (methyl methacrylate) (PMMA), polystyrene, and bisphenol A polycarbonate films using in situ second harmonic generation (SHG). The local polymer microenvironment has been studied by examining dopant orientation and disorientation in samples physically aged before or during poling as a function of aging time and temperature. The dopant orientation, related to the observed SHG intensity, is sensitive to the surrounding local mobility and free volume. Films aged before corona poling showed decreased SHG intensities upon application of the electric field, due to decreased mobility and local free volume reducing rotational mobility of the dopant in the matrix. No SHG intensity could be observed in doped PMMA films aged for 100 h at 25 °C before poling, indicating that the regions of local free volume and mobility sufficiently large to allow mobility of the dopant are removed. Samples aged during corona and contact poling showed improved temporal stability of the SHG intensity after the electric field was removed, indicating changes in free volume and chain mobility surrounding the dopant. The effect of the corona poling used to orient the dopants on the measured intensity is discussed in terms of a field-induced surface/space charge region within the polymer film. © 1990, American Chemical Society. All rights reserved.