The rate of spreading of monolayers on liquids

Abstract

The rate of spreading of a monolayer over a liquid film is quantitatively related to the surface tension gradient that causes the spreading, the viscosity of the substrate liquid, the pressure gradient, and the thickness of the substrate. The relation is verified through a simple experimental setup. The monolayer was first spread on water contained in a glass trough, which was then inclined by lifting it on one edge so that the bulk of water flowed to the other side along with the surface film, leaving behind a thin surfactant-free layer of water sticking to the surface of the glass. The resulting surface tension gradient gave rise to respreading of the monolayer to the clean surface. The rate of this respreading was noted and shown to be in good agreement with the theoretical expression.