Properties of the non-polar oil/water interface. Part 1.—Procedures for the accurate measurement of the interfacial pressure of an insoluble monolayer
The technique of Brooks and Pethica for measuring the surface pressure of an insoluble monolayer at a non-polar oil/water interface using a hydrophobic Wilhelmy plate and an all-glass interfacial trough is extended to give greater accuracy and ease of measurement. The original Brooks frame is still included but the classical torsion wire assembly is now replaced by an electronic microbalance. The stringent precautions necessary to obtain accurate interfacial pressures at the heptane/water interface are described and the good reproducibility of results from the prescribed technique is shown for some cationic, anionic and zwitterionic monolayers. These data are used to illustrate the many complex issues in spreading at this interface.