Light Scattering Techniques

Abstract

The aim of light scattering experiments with solutions of macromolecules is to determine their size and shape. However, as a matter of fact, interactions among the macromolecules also affect light scattering, and the retrieval of information on size and shape may be complicated. This comes as follows. To analyze light scattering data, one has to solve a theoretical problem first: given a set of particles of known size, shape and optical properties, and distributed in the solvent in a defined way, find the field at all space points when they are illuminated by a monochromatic wave of arbitrary polarization. This problem entails the solution of Maxwell’s equations with given boundary conditions. In the so-called Rayleigh-Debye-Gans approximation, which holds when the refractive index difference between particles and solvent is small compared to the solvent index and when the phase difference between a wave propagating inside the particle and one propagating outside is small in terms of the wavelength of the light, the problem reduces to the evaluation of interferences between scattering amplitudes emanating from all the volume elements in space. For spherical particles the result is easy to write down.