Perfluoroalkanes and perfluoroalkylalkane surfactants in solution: Partial molar volumes in n-octane and hetero-SAFT-VR modelling

Partial molar volumes at infinite dilution have been obtained for 3 perfluoroalkylalkanes (PFAA) in n-octane at 298.15 K from experimental apparent molal volumes. The results were interpreted estimating the contributions of the hydrogenated and perfluorinated segments to the partial molar volume. For this reason, partial molar volumes at infinite dilution for 3 perfluoroalkanes (PFA) in n-octane at 298.15 K have also been obtained. The results were further interpreted using the hetero-SAFT-VR equation of state, which models the perfluoroalkylalkanes as heterosegmented di-block chains. The cross interactions, both intra and intermolecular, were characterised using parameters developed in earlier studies for (alkane + perfluoroalkane) mixtures: the calculations are thus fully predictive. The theory is able to accurately predict the volumetric behaviour of the solutions of perfluoroalkylalkanes, without fitting to any experimental data.

► Partial molar volumes at infinite dilution of perfluoroalkylakanes in octane were measured at 298.15 K.
► The contribution to the partial molar volume of the CH2 and CF2 segments were evaluated.
► The contribution to the partial molar volume of the CH2–CF2 junction was evaluated and found to decrease with increasing length of the fluorinated segment.
► Hetero-SAFT-VR theory is able to accurately predict the results without any fitting.