Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
We examine several methods for analyzing the spectrum of light scattered from polydisperse polymer solutions. General expressions are reviewed for the inelastic scattering spectra and integrated intensities due to the pure translational normal mode of motion, using both heterodyne and homodyne detection, in terms of the molecular weights, concentrations, scattering form factors, and diffusion coefficients of the individual polymeric species, These results are used to obtain general expressions for the limiting slopes and intercepts of various rearranged versions of the equation I(v) = (A/π)2/(v2 + γ2) that permit linear plotting: I(v) is the intensity of light scattered at frequency v, A is the integrated intensity, and γ is the spectral halfwidth, K2D/2π, where K is the scattering vector and D the diffusion coefficient. These results are applied to the special case of a Schulz-Zimm distribution, neglecting form factors, to obtain explicit expressions relating the average diffusion coefficients determined by these procedures to other measurable quantities: the mean polymer radius; the diffusion coefficient of the weight-average species; and, together with the weight-average sedimentation coefficient, the weight-average molecular weight. Numerical calculations for two particular cases indicate the relative merits of the various data analysis procedures. Homodyne detection gives average values that are closer to weight averages than does heterodyne detection.
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