PREFERENTIAL SOLVATION IN BINARY-MIXTURES - COMPARISON BETWEEN THE QUASI-LATTICE QUASI-CHEMICAL MODEL AND THE STEPWISE SOLVENT EXCHANGE MODEL

The quasi-lattice quasi-chemical (QLQC) model and the stepwise solvent exchange (SSE) model are both used in solvation chemistry to describe preferential solvation of solutes in binary mixtures. A critical asse ssment of the SSE model reveals a basic flaw. The usual assumption in the SSE model, that the activity coefficients of the solvent molecules in the solvation shell equal that of the bulk liquid, can be regarded as being a correction for this flaw. Comparison of the QLQC model wit h the SSE model explains the cause and meaning of the adjustable, extr a parameters, which have been added to the SSE model in order to accou nt for experimental data.