QUASI-ELASTIC LIGHT-SCATTERING FROM SOLUTION OF SPHEROIDAL MACROMOLECULES

The form factors in quasi-elastic light scattering are calculated for spheroidal particles undergoing translational and rotational diffusion. Using spheroidal coordinates and spheroidal wavefunctions, form factors for orientational fluctuations are obtained. Calculations are performed for prolate spheroidal particles with various axial ratios. The sum of the form factors of the pure translational term and the other translation-rotation terms gives the total scattering intensity. The translation-rotation terms approach zero at small scattering angles and only the pure translational term contributes to the small angle scattering. The contribution of the translation-rotation terms is comparable to the pure translational term for larger axial ratio at large scattering angles. The result approaches that for a sphere in the limiting case where the axial ratio approaches 1 and that for a rod at high axial ratio. The rotational effect contributes to the line broadening of the spectrum or the change of the single exponential decay of the autocorrelation function of the scattered light. The effects of the rotational motion and the polydispersity of the system are discussed. © 1978.