Dynamic Light Scattering Investigations of Segmental Motion and Viscoelasticity in Polymers

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This study of the dynamics of local segmental motion in polymers will include polymer solutions in semi-dilute and concentrated regions and in miscible polymer blends. The techniques to be used are various types of dynamic light scattering, including photon correlation spectroscopy, Brillouin scattering and holographic grating relaxation. Properties such as dynamic longitudinal and shear compliances, dynamic longitudinal and shear moduli, hyper- sonic velocity and attenuation coefficient, mutual and tracer diffusion coefficients of labeled chains in the semi-dilute or/and concentrated polymer solutions will be investigated. The spectrum will be measured as a function of polymer molecular weight, concentration, scattering wavevector, and solvent qualities. Efforts will be made to relate the dynamic light scattering to the mechanical relaxation spectrum of the polymer solution. Experi- mental verification of theoretical predictions is part of this research. The kinetics and thermodynamics interaction in miscible polymer blends will also be investigated by the static and dynamic light scattering intensity measurements. By combining the results of mutual and self-diffusion coefficients of the polymer blend, the role of cross velocity correlations between segments of the same chain and between neighboring chains will be clarified. The mutual diffusion coefficient will be measured by using photon correlation spectroscopy, the self diffusion coefficient by pulsed field gradient NM or by the holographic grating relaxation tech- nique whenever appropriate. Understanding of the thermodynamic interactions and the dynamics of local segmental motion is vital to various application of polymers in diverse areas, such as coatings, electronics, optics, and structural materials.