Some Physical Properties of Monolayers and Their Relation to Evaporation Retardation

Abstract

This chapter describes a few physical properties of monolayers and their relation to evaporation retardation. The monolayer of cetyl alcohol fulfills two somewhat antagonistic conditions required to prevent evaporation: (1) it gives a compact monolayer with quite strong cohesion forces between the paraffinic residual chains and (2) at the same time, its spreading rate and resealing ability are fairly good. The fulfillment of the first condition assures an effective barrier against evaporation, while the second property is necessary to maintain the monolayer on the surface despite external disturbances from wind, waves, and so on. In an experiment described in the chapter, the pressure-area isotherms of films containing cetyl and octadecyl alcohol in different proportions were determined using petroleum ether as the spreading solvent. Polyvinyl cetyl pyridonium and dimethyldioctadecyl ammonium salts gave surface films of entirely different properties. The chapter discusses the effect of added nonvolatile paraffin oil on the surface properties of the fatty alcohols. Spreading and pressure evolution rates of hexadecanol, octadecanol, and their mixtures were measured. Addition of small quantities of liquid nonvolatile paraffin oil improved the spreading properties. The chapter highlights the dependence of the efficacy of evaporation retardation by fatty alcohol monolayers on addition of minute amounts of paraffin oil.