Size and Size Distribution Characterization

The use of classical, or time-averaged, light scattering methods to characterize the size and size distribution of macromolecules in dilute solutions or particles in dilute dispersions is discussed. The necessary scattering relations are presented systematically, starting with three cases at infinite dilution: the scattering extrapolated to zero angle, the scattering at small angle, and the scattering for arbitrary angle, including the inversion of the scattering data to estimate the size distribution. The relations needed to effect an extrapolation to infinite dilution from data on dilute solutions are also discussed. These sections are followed by remarks on light scattering methods, and concluding sections giving examples for several applications. The Rayleigh-Gans-Debye approximation is usually appropriate in the scattering from dilute polymer solutions, and is also adequate for the scattering from dilute dispersions of small particles. It is assumed when appropriate, but more complete theories are introduced where necessary, as in the use of the Mie-Lorentz theory for large spherical particles.