Thermochimica Acta, Vol.525, No.1-2, 103-113, 2011
Application of the Kirkwood-Buff formalism to CH3(CH2)(n-1) OH + polyether mixtures for n=1, 2, 3
1-Alkanol + polyether mixtures have been investigated using the Kirkwood-Buff formalism. The alcohols considered are methanol, ethanol or 1-propanol. The ethers are 3,6-dioxaoctane, 2,5,8-trioxanonane, 2,5,8,11,14-pentaoxapentadecane, polyethylene glycol 250 dimethyl ether (PEG-250), 1,3-dioxolane, 1,4-dioxane and 1.3,5-trioxane. Data for the Kirkwood-Buff integrals, coefficients of linear solvation and local mole fractions are reported. From these data, we show that the replacement of a linear monoether by a linear polyether in mixtures with a given 1-alkanol leads to a weakening of the effects related to the self-association of the alcohol, which is also supported by the temperature dependence of the Kirkwood-Buff integrals. Interactions between like molecules are enhanced in systems with cyclic diethers compared to those involving cyclic monoethers. Dipolar interactions increase with the chain length of the 1-alkanol in solutions with a given polyether. Evaluation of size effects suggest that, in mixtures with components which differ largely in size, heterocoordination is due to such effects and not to specific interactions between unlike molecules. These trends are consistent with the available data in the literature on excess enthalpies or entropies. The small absolute values of the linear coefficients of preferential solvation of the considered mixtures suggest that the distribution of the molecules is nearly random. Preliminary calculations in the framework of the Flory model confirm this conclusion. (C) 2011 Elsevier B.V. All rights reserved.