Dynamic light scattering study of internal motions of polymer coils in dilute solution

Abstract

Internal motions of a high molecular weight (Afw = 8.12 X 106) polystyrene with a narrow distribution of Mz/Mw < 1.04 in benzene has been studied by dynamic light scattering. By means of a prism-cell light-scattering spectrometer, the translational diffusion of the center of mass of the polymer coil has been precisely determined at KRS « 1 corresponding to using the self-beating technique at a scattering angle < 3°. With the experimentally measured translational diffusion coefficient, a solid base for internal motion studies could be formulated. The first cumulant obtained from the cumulante analysis of the measured intensity time correlation function approached K3 dependence at KRg > 1, indicating that the polymer chain dynamics could be described in terms of the non-free-draining model. Extraction of information on the internal motions was made by comparing the contin output line-width distributions from the experimental data with those from the simulated data based on a theoretical model for polymer coils in the non-freedraining limit. By selecting appropriate KRe ranges, the first two internal relaxation times could be obtained. At regimes of 1 < x < 3 and 3 < x < 6, where x = (KRt)2, the first internal relaxation time n (the longest one) and the second internal relaxation time r2 were determined, respectively. To our knowledge, for a flexible polymer coil in solution, t2 was determined experimentally for the first time. The experimental observations agreed very well with the theoretical predictions based on polymer chain dynamics with hydrodynamic interactions.

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