Volume changes on mixing perfluoroalkanes with alkanes or ethers at 298.15 K

Excess molar volumes VE at 298.15 K have been determined by means of a vibrating-tube densimeter for binary mixtures of n-hexane with a perfluoroalkane, C5–C8, and of perfluorohexane with a n-alkane, C5–C8, or an ether (diethyl, dipropyl, dibutyl, butyl methyl, and butyl ethyl ether). The systems perfluoropentane+hexane, perfluorohexane+pentane or hexane or diethyl ether have been investigated in the entire mole fraction range, while the other mixtures only in the miscibility regions. The observed VE values are positive (up to 5.5 cm3 mol−1) and among the largest known for non-electrolyte systems. Limiting partial molar volumes, V̄°, have been evaluated for each component of the examined mixtures. The behaviour of V̄° has been discussed in terms of the scaled particle theory (SPT) and of a simple group additivity scheme based on surface interactions. An estimate has been made of the average separation distance of solvent from solute molecules.