Systems Involving Hydrogenated and Fluorinated Chains: Volumetric Properties of Perfluoroalkanes and Perfluoroalkylalkane Surfactants

Abstract

As part of a combined experimental and theoretical study of the thermodynamic properties of perfluoroalkylalkanes (PFAAs), the liquid density of perfluorobutylpentane (F4H5), perfluorobutylhexane (F4H6), and perfluorobutyloctane (F4H8) was measured as a function of temperature from 278.15 to 353.15 K and from atmospheric pressure to 70 MPa. The liquid densities of n-perfluoropentane, n-perfluorohexane, n-perfluorooctane, and n-perfluorononane were also measured at room pressure over the same temperature range. The PVT behavior of the PFAAs was also studied using the SAFT-VR equation of state. The PFAA molecules were modeled as heterosegmented diblock chains, using different parameters for the alkyl and perfluoroalkyl segments, that were developed in earlier work. Through this simple approach, we are able to predict the thermodynamic behavior of the perfluoroalkylalkanes, without fitting to any experimental data for the systems being studied. Molecular dynamics simulations have also been performed and used to calculate the densities of the perfluoroalkylalkanes studied.

SAFT-γ force field for the simulation of molecular fluids: 8. Hetero-segmented coarse-grained models of perfluoroalkylalkanes assessed with new vapour–liquid interfacial tension data

“…For each data point at a single temperature, at least 50 independent images of at least 10 different drops are collected, and the average value and standard deviation recorded. The liquid densities of the PFAAs, required for the calculation of the surface tension from the drop profiles, are determined in our current study or taken from previous work [73,74].…”

“…The connecting groups (FH and FHE), which bridge the alkyl and the perfluoroalkyl chains, are introduced to account for the presence of the dipole moment between the two chemical moieties in an effective manner; the FH and FHE groups are characterized by dispersion energies which differ markedly from the values for the alkyl (CE, CM, C4) or perfluoroalkyl (FE, FM) groups. The like and unlike interactions of the FH and FHE groups with the FE, FM, CE, CM, and C4 groups are estimated with the SAFT-γ Mie EoS [37] from the experimental liquid densities and vapour pressures of the F 4 H 2 , F 4 H 5 , F 4 H 6 , F 4 H 8 , F 6 H 2 , F 6 H 6 , and F 6 H 8 pure components [73][74][75]. The final SAFT-γ Mie parameter set for the CG groups characterizing the PFAA molecules is summarized in Table 3.…”

“…For instance, the fluid-phase behaviour of the binary alkane -perfluoroalkane mixtures has been investigated extensively with the SAFT-HS [66,67], SAFT-VR [68,69], soft-SAFT [70], PC-SAFT [71], and hetero-SAFT VR [72] EoSs. The properties of the PFAA molecules including the volumetric properties [73,74], vapour pressures [75], and solution behaviour of mixtures with n-alkanes and perfluoro-n-alkanes [72,76,77] have also been examined with the hetero-SAFT VR EoS [78]. These EoSs cannot, however, be used on their own to describe the interfacial tension of the systems unless they are incorporated within other approaches such as density functional [79][80][81] or square gradient [52,82,83] theories.…”

“…The results are interpreted by comparison with the corresponding properties for nalkanes, perfluoro-n-alkanes, and their mixtures, though the analysis is hampered by the lack and inconsistency of existing data. The densities of perfluorobutylethane (F 4 H 2 ) and perfluorohexylethane (F 6 H 2 ) are measured at atmospheric pressure with an Anton Paar DMA5000 vibrating tube densimeter, according to the procedure described in previous work [74].…”

Viscosity of liquid systems involving hydrogenated and fluorinated substances: Liquid mixtures of (hexane+perfluorohexane)

“…The optimized potentials for liquid simulations all-atom (OPLS-AA) force field, originally developed for alkanes [8] and extended to perfluoroalkanes [9], was used to model the molecules studied. The OPLS-AA force field was developed to accurately reproduce experimental properties of liquids, and recent studies [2,10] demonstrate excellent agreement with experiment for pressure vs. density isotherms of PFAA alkanes. Simulations were performed using the LAMMPS simulation engine [11], carried out in the NVT ensemble (constant number of atoms, temperature, and volume) at a temperature of 298 K to match experiment.…”