Effect of molecular association on diffusion in binary liquid mixtures



A predictive equation for the mutual diffusion coefficient is developed for binary solutions which contain a self-associating component. The solution is modeled as a nonideal multicomponent mixture consisting of the solvent molecules and various association complexes. The model provides for a unique mobility for each of the species present and accounts for both physical and chemical contributions to the solution thermodynamics and their effects on the diffusive fluxes. The predictions of the theory were evaluated for n-alcohols in nonpolar solvents using data for six systems at temperatures ranging from 293 to 363 K. In each case, the predictions of this theory are found to be superior to other currently available methods.