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, τk. 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 τk become important in the equations for the scattered spectral 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 τ1.