Collect. Czech. Chem. Commun. 1993, 58, 2535-2551

On the Definition and Use of Deviation Functions for Treatment of Quasi-Elastic Light Scattering Data

Lars-Olof Sundelöfa and Bedřich Porschb

a Physical Pharmaceutical Chemistry, Uppsala University, BMC, Box 574, S-751 23 Uppsala Sweeden
b Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic


A theory for deviation functions defined as the deviation from strict gaussian behaviour of electric field correlation functions obtained from Quasi-Elastic Light Scattering experiments is presented. Its application to systems with different types of particle size distributions is treated both theoretically and by numerical examples. Expressions are given for distributions where the correlation function can be expressed as 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 methods in the direct determination of molecular size distributions it may substantially help to visualize the magnitude of the effect of polydispersity and serve as a prerequisite for a decision concerning how far it is meaningful to purse more precise calculations. This is essentially equivalent to a judgment of the noise level of the experiment and of the "information content" to be expected.