Solubility of water in perfluoroalkylalkanes surfactants: Evidence of specific interaction between water and the surfactant molecule

Abstract

The solubility of water in five liquid perfluoroalkylalkanes was measured as a function of temperature (283 K–313 K) and the thermodynamic functions of solution and solvation were calculated. The studied perfluoroalkylalkanes cover a range of relative lengths of the hydrogenated and perfluorinated segments.This is the first time the solubility of water in these substances has been measured, which is surprising given their pharmaceutical and medical relevance. The new data thus fills an important gap in the literature.The liquid organization of the water-in-PFAAs solutions was further investigated using atomistic molecular dynamics simulations, providing structural and energetic evidence about the solvation shell of water within the different solvents.The results indicate the existence of a specific interaction between the water molecule and the dipole located at the centre of the surfactant molecules, which explains the increased solubility of water in these solvents, relatively to alkanes and perfluoroalkanes. These findings also help to interpret the formation of nano-patterned molecular films of PFAA at the surface of water and of wet silicon wafers.