Comparison between the classical and QELSS determination of diffusion coefficients. Sharp polymer fractions

Abstract

Simple modification of the method of cumulants for an evaluation of QELSS data within the error limit of 2% in the case of narrow polymers is suggested. Model calculations of the deviations from the exponential decay due to polydispersity are presented, criteria of applicability of the 1st and 2nd cumulant fit at a given accuracy are derived and verified experimentally. The required agreement between the classical and QELSS diffusion constant is achieved if the QELSS measurements are made at concentrations where the effect of concentration dependence of the diffusion constant may be neglected.