Microscopic and Thermodynamic Properties of the HFA134a-Water Interface:Atomistic Computer Simulations and Tensiometry under Pressure

摘要

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.