The influence of electrolytes on gaseous monolayers I. Neutral films

An equimolar mixture of a long-chain cationic and anionic detergent when spread on dilute substrates at the oil/water interface has been shown to obey the theoretical relationship $\Pi $(A-A$_{0}$ = kT. However, on concentrated substrates this relationship is no longer obeyed and the increased surface pressure observed has been attributed to a nonspecific penetration of the interface by the substrate ions. Good agreement has been obtained between the number of penetrating ions calculated from the increased surface pressure found on concentrated substrates and the number calculated directly using a modified Stern treatment.