Characterization of Glassy State Relaxations in Styrene and Methacrylate Based Nonlinear Optical Materials

ABSTRACTSub-Ts relaxations in polymethylmethacrylate (PMMA) and in narrow molecular weight polystyrene (PS) thin films with and without second order nonlinear optical dyes have been examined using time domain dielectric spectrometry. Dyes used include 4-[N, N-dimethylamino]-4’-nitrostilbene (DANS) and 4-[N-ethyl, N-hydroxyethylaminoJ-4’-nitroazobenzene (DR1) at a level of 0.19 mole percent. In dye/PS blends, dye relaxations are seen to occur at frequencies similar to the frequencies of the β-relaxation of pure PS below the glass transition temperature. Analysis of the glassy phase dispersion leads us to conclude that, at near room temperature, appreciable dye reorientation occurs on a time scale of a few seconds. This dye reorientation is coupled to the dynamic motions of the localized polystyrene subunits. Experiments using dye in PMMA did not conclusively reveal dye motions because of the intrinsically large dispersion of PMMA itself. The β-relaxation frequency range is higher in the PMMA dye/polymer blend than in dye-containing PS implying dye reorientation would likewise occur more rapidly than in PS. Our results indicate that the randomization of dye orientation observed in a dye/polymer system depends on the rapid, local chain motions which continue at temperatures well below the glass transition temperature, as well as on the long range, slow relaxations associated with the glass-to-rubber transition.

Dichroic behavior of the absorbance signals from dyes NK2367 and WW375 in skeletal muscle fibers.

Absorbance signals were recorded from voltage-clamped single muscle fibers stained with the nonpenetrating potentiometric dyes NK2367 and WW375 and illuminated with quasimonochromatic light from 560 to 800 nm, linearly polarized either parallel (0 degree) or perpendicular (90 degrees) to the fiber long axis. The signals from both dyes depend strongly on the incident polarization. At any wavelength and/or polarization condition, the total absorbance signal is a superposition of the same two signal components previously identified with unpolarized light (Heiny, J. A., and J. Vergara, 1982, J. Gen. Physiol., 80:203)--namely, a fast step signal from the voltage-clamped surface membrane and a signal reflecting the slower T-system potential changes. The 0 degree and 90 degrees spectra of both membranes have similar positive and negative absorbance peaks (720 and 670 nm, respectively, for dye NK2367; 740 and 700 nm for dye WW375); in addition, they have the same dichroic maxima (670 for NK2367; 700 for WW375). However, for the surface membrane, the 0 degrees spectra are everywhere more positive than the 90 degrees spectra, whereas the reverse is true for the T-system, which results in a dichroism of opposite sign for the two membranes. These spectral characteristics were analyzed using a general model for the potential-dependent response of an absorbing dye (Tasaki, I., and A. Warashina, 1976, Photochem. Photobiol., 24:191), which takes into account both the dye response and the membrane geometries. They are consistent with the proposal that the dye responds via a common mechanism in both membranes that consists of a dye reorientation and a change in the absorption maxima.