title: Microscopic and thermodynamic properties of the HFA134a-water interface: atomistic computer simulations and tensiometry under pressure.
abstract: A combined computational and experimental approach is used to determine the interfacial thermodynamic and structural properties of the liquid 1,1,1,2-tetrafluoroethane (HFA134a)-vapor and liquid HFA134a-water (HFA134a|W) interfaces at 298 K and saturation pressure. Molecular dynamics (MD) computer simulations reveal a stable interface between HFA134a and water. The "10-90" interfacial thickness is comparable with those typically reported for organic-water systems. The interfacial tension of the HFA134a|W interface obtained from the pressure tensor analysis of the MD trajectory is in good agreement with the experimental value determined using in situ high-pressure tensiometry. These results indicate that the potential models utilized are capable of describing the intermolecular interactions between these two fluids. The tension of the HFA134a|W interface is significantly lower than those typically observed for conventional oil-water interfaces and similar to that of the compressed CO(2)-water interface, observed at moderate CO(2) pressures. The MD and tensiometric results are also compared and contrasted with the HFA134a|W and chlorofluorocarbon-water tension values estimated from a parametric relationship. This represents the first report of the interfacial and microscopic properties of the (propellant) hydrofluoroalkanes (HFA)|W interface. The results presented here are of relevance in the design of surfactants capable of forming and stabilizing water-in-HFA microemulsions. Reverse aqueous microemulsions in HFA-based pressurized metered-dose inhalers are candidate formulations for the systemic delivery of biomolecules to and through the lungs.
authors.affiliation: Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan 48202, USA.
authors.forename: Robson P S
authors.initials: RP
authors.lastname: Peguin
authors.forename: Parthiban
authors.initials: P
authors.lastname: Selvam
authors.forename: Sandro R P
authors.initials: SR
authors.lastname: da Rocha
mesh_terms: D003198:Computer Simulation; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D008853:Microscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D011312:Pressure; D013499:Surface Properties; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D004980:Ethane / Q000031:analogs & derivatives; D005466:Fluorocarbons
chemical_list: D006845:Hydrocarbons, Fluorinated; D014867:Water; C063006:norflurane; D004980:Ethane; D005466:Fluorocarbons