Adsorption of amphiphiles at an oil‐water vs. an oil‐metal interface

Studies were conducted to investigate whether adsorption of amphiphiles from oil onto a degreased metal can be predicted from knowledge about adsorption of the amphiphiles at the oil‐water interface. The surface of a degreased metal comprises oxides, hydroxides, and adsorbed water vapor, which form from the reaction of the metal with air and moisture. If the behaviors of amphiphiles at water‐oil and metal‐oil interfaces are similar, this information can be useful in the development of cheaper and quicker methods of estimating amphiphile adsorption properties on degreased metals. The amphiphiles used were safflower oil (SA) and jojoba oil (JO), both of which are plant‐based oils, and methyl palmitate (MP). SA is a triester whereas JO and MP are monoesters. The interfacial tension of water‐hexadecane was measured as a function of amphiphile concentration in hexadecane and used to estimate an interfacial‐based free energy of adsorption, ΔGads. The resulting interfacial‐based ΔGads values for SA were identical to those reported from friction‐based adsorption isotherms. The corresponding values for the monoesters were within the range reported from friction‐based adsorption isotherms.