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Physical-Chemical Studies on Rodlike Polymer Compositions

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Final rept.

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Third harmonic generation THG is used to study the third-order nonlinear optical properties of nematic and isotropic solutions of polyphenylene benzobisthiazole, PBZT, and related small molecule model compounds. Maker fringe patterns MFP for isotropic preparations are analyzed in terms of postulated surface layers comprising regions in which the rodlike chains tend to have their axes parallel to the plane of the surface, creating a negatively birefringent uniaxial nematic layer. The THG with the nematic solution exhibits intensity with polarization components unexpected for uniaxial nematic symmetry, along with other unexpected features in the MFP. This behavior is attributed to the effects of surface layers, postulated to exhibit biaxial nematic symmetry, in which the uniaxial nematic symmetry is broken in regions on the scale of a wavelength. Features of the texture of the nematic phase of PBZT solutions are discussed. The nature of twist-loop defects in the texture is described, along with certain defects in the form of an ellipsoid of revolution, postulated to result from a molecular weight fractionation in the heterodisperse polymer. Light scattering studies on dilute solutions of a polyn-dodecyl thiophene are given to elucidate supramolecular structure that leads to a thermochromic effect. The supramolecular structure may play a role in the molecular organization in the solid state, with influence on electronic and nonlinear optical behavior.

Subject Categories:

  • Organic Chemistry
  • Physical Chemistry
  • Polymer Chemistry
  • Optics

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