Novel effects of counterions on langmuir films of 22-tricosenoic acid

It has long been known that metallic counterions at very low concentrations have a significant effect on the isotherm, lateral cohesion and viscosity of a fatty-acid Langmuir monolayer on a water surface. The evidence for four new effects is presented. Counterions are shown to impair crystallinity, inhibit epitaxial deposition, reduce initial drainage speed, and cause a variation of drainage speed with time, all phenomena of great importance in the deposition of Langmuir-Blodgett films. On the basis of the time elapsed between monolayer spreading and the onset of the phenomenon, the counterion effects are seen to be divided into two categories. Gel and phase-change models are discussed, while the growth of water-surface crystallites is shown to be a secondary effect.