DYNAMIC LIGHT-SCATTERING STUDY OF INTERNAL MOTIONS OF POLYMER COILS IN DILUTE-SOLUTION

Internal motions of a high molecular weight (M(w) = 8.12 x 10(6)) polystyrene with a narrow distribution of M(z)/M(w) less-than-or-equal-to 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 KR(g) << 1 corresponding to using the self-beating technique at a scattering angle-theta less-than-or-equal-to 3-degrees. With the experimentally measured translational diffusion coefficient, a solid base for internal motion studies could be formulated. The first cumulant-OMEGA obtained from the cumulants analysis of the measured intensity time correlation function approached K3 dependence at KR(g) > 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-free-draining limit. By selecting appropriate KR(g) ranges, the first two internal relaxation times could be obtained. At regimes of 1 less-than-or-equal-to x less-than-or-equal-to 3 and 3 less-than-or-equal-to x less-than-or-equal-to 6, where x = (KR(g))2, the first internal relaxation time tau-1 (the longest one) and the second internal relaxation time tau-2 were determined, respectively. To our knowledge, for a flexible polymer coil in solution, tau-2 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.