Diagnosis of the nature of polymer—solute reactions in monolayers on aqueous solutions from pressure/area curve slope changes

Abstract

The change in slope of the pressure/area (PA) curve for a polymer monolayer film on water, when a solute is introduced into the aqueous subphase is discussed. Three general effects on the slope are identified and interpreted as follows: Type A, slope decreased, weak complex formed between monolayer and a surface-active solute, or a more compressible conformation of the polymer caused by reaction with the solute. Type B, slope unchanged, and curve may or may not be displaced to the right, solute aligned beneath and parallel to the monolayer polymer chains, or forming weak acid—base type cross-links with the polymer at the water surface; Type C, slope increased, the curve sometimes vertical in the upper portion, rigid film, with extremely high viscosity, formed by strong polymer—solute bonds, often with cross-linking of the poylmer chains by multiple bonds with the solute. In some special cases the effect can be produced by solutes that appear to become entangled with protein monolayers by hydrophobic forces.