Interfacial Thermodynamics of Surfactants at Elevated Pressure

While surfactant use under elevated pressures is not a novel field, experimental measurements of surfactants in extreme environments is lacking in the literature. Thermodynamically, pressure impacts the concentration of surfactants at a pressurized interface, thus affecting the interfacial tension. The relationship between the concentration, pressure, and interfacial tension for a given surfactant has not been measured sufficiently for nearly any surfactant. In this work we use a novel high pressure microtensiometer to probe surfactant transport and equilibrium thermodynamics at the water-CO₂ vapor interface. We show that surfactant isotherms are highly dependent on pressure illustrating that key thermodynamic and kinetic parameters are strong functions of pressure. Furthermore, we show that surfactant performance is significantly decreased at elevated pressures. We outline the importance of experimental measurements of surfactant behavior on predicting high pressure performance of a variety of surfactant chemistries.