ON THE DEFINITION AND USE OF DEVIATION FUNCTIONS FOR TREATMENT OF QUASI-ELASTIC LIGHT-SCATTERING DATA

A theory for deviation functions defined as the deviation from strict gaussian behaviour of electric field correlation functions obtained fr om Quasi-Elastic Light Scattering experiments is presented. Its applic ation to systems with different types of particle size distributions i s treated both theoretically and by numerical examples. Expressions ar e given for distributions where the correlation function can be expres sed as a Laplace transform in closed form. The theory is also compared with experiments on solutions of polymers with a variety of molecular mass distributions. It is concluded that even if the procedure based on deviation functions cannot compete with other numerical inversion m ethods in the direct determination of molecular size distributions it may substantially help to visualize the magnitude of the effect of pol ydispersity and serve as a prerequisite for a decision concerning how far it is meaningful to pursue more precise calculations. This is esse ntially equivalent to a judgement of the noise level of the experiment and of the ''information content'' to be expected.