Spectral Distribution of Light Scattered from Flexible-Coil Macromolecules

Abstract

The spectral distribution of light scattered from monodisperse, infinitely dilute solutions of optically isotropic, flexible‐coil macromolecules in the free‐draining approximation of the pearl‐necklace model is related to the macromolecular translational diffusion coefficient D and the set of intramolecular relaxation times, τ k . The spectral distribution for scattering parameter x < 1 (small scattering angle and/or small molecules) is shown to consist essentially of a single Lorentzian line with half‐width proportional to D . For x > 3 (large scattering angle and molecules with end‐to‐end distance ≳1000 Å), additional Lorentzian terms each with half‐width dependent on D and some of the τ k become important in the equations for the scatteredspectral density. At x = 3 , these terms are 15% of the total integrated scattered intensity. They rise to 50% at x = 7 . Although the resultant line shape is complex, it is shown that the dominant contribution to this “intramolecular” spectral density comes from terms containing the longest relaxation time τ 1 .