Behavior of dinonylnaphthalene sulfonate monolayers at the air–water interface

The interfacial behavior of the sodium salt of dinonylnaphthalene sulfonic acid, a highly surface-active metal extractant, has been studied using Langmuir trough techniques. Monolayer desorption experiments were conducted at various surface pressures and substrate compositions. The rates of film contraction were found to be consistent with diffusion-controlled dissolution. Pressure–area isotherms indicated the presence of a single surface phase with a two-dimensional compressibility characteristic of a liquid-condensed film. Monolayer collapse occurred at a limiting molecular area of 67 Å2. Comparison of the monolayer dissolution rates with metal extraction rates indicates the dominance of an interfacial extraction mechanism over an aqueous phase extraction mechanism.