Effect of unsaturation of C18 fatty acids at liquid paraffin-water interfaces

Unsaturated C-18 fatty acids are the largest constituents of the vegetable oils that are used in the pharmaceutical and cosmetic industries. To investigate effects of various vegetable oils on the stability of multiple emulsions, configuration of oleic, linoleic and linolenic acids at the liquid paraffin-water interface was studied by measuring the interfacial tensions and calculating the interfacial excess and molecular cross-sectional areas of the acids at 0.1 to 10% w/w concentrations as well as of the pure acids. Linolenic acid produced the lowest interfacial tension followed by oleic and linoleic acids. The results have been explained in terms of preferential interfacial adsorption and hydrophobic hydration. Linolenic acid has the highest interfacial excess value of 2.24 x 10(-10) moles/cm(2), followed by oleic acid, 1.49 x 10(-10) moles/cm(2), and linoleic acid,1.33 x 10(-10) moles/cm(2). The findings suggest that hydrophobic hydration of the fatty acids depends strongly on the number of the double bonds present. The study contributes to explaining stability problems involved in the vegetable oil based multiple emulsion systems.