Studies of compressibility properties of solutions of BU₄NBr in DMF and DMF-water mixtures

Abstract

The apparent molar volumes (f_v) and compressibilities (f_k) have been evaluated for Bu₄NBr from the experimental measurements of density and sound velocity properties at 25°C of its solutions in DMF and in DMF-water mixtures. From the infinite dilution properties (viz, (φ_v ^oand φ_k ^o of Bu₄NBr) the transfer volumes and transfer compressibilities have been calculated for different mole-fractions of DMF in mixed solvent system. It is observed that φ_v^o of Bu₄NBr goes through a minimum and a maximum of concentrations of ~10 mol %and -~50 mol % of DMF in water respectively, while f_k^o goes through a maximum of a concentration of -35 mol % of DMF. These results are interpreted in terms of the effects of hydrophobic hydration in low concentration region and effects of hydrophobic interaction at moderate concentrations of DMF in water. It appears that the presence of cosolvent affects the structural interactions in water and the cation-cation interaction of Bu₄NBr in a specific way to indicate microheterogeneity.