EFFECT OF POLYDISPERSITY AND 2ND VIRIAL-COEFFICIENT ON LIGHT-SCATTERING BY RANDOMLY CUT RANDOM COILS

The light scattering by an initially monodisperse population of Gaussian random coils in a theta solvent is described by the well known Debye function: P(theta) = D [u(theta)] = (2/u2)(e-u-1 + u), where u = u0 = <S2>q2. S is the radius of gyration, and q = (4-pi-approximately-n/-lambda)sin(theta-/2) is the magnitude of the scattering vector, lambda-being the vacuum wavelength of the incident light, approximately-n the index of refraction, and theta-the scattering observation angle. If the molecules undergo random scission, P(theta) = D(u0 + r), where r is the average number of scissions per original molecule. In a good solvent, one should include the effect of the second virial coefficient A2 on the light scattering. In the single contact approximation this can be done by using Kc/R = 1/MP(theta) + 2A2c for an originally monodisperse solution. K is a constant, R the absolute Rayleigh scattering ratio, and c the concentration. The above equation is generalized to originally polydisperse solutions and branched random coils without loops. We discuss its mathematical limits and range of validity, and how to apply it to experimental situations. It is speculated that it may work fairly well when the penetration function psi-is less than about 0.1. We also discuss possible methods of extending its range of validity.