Dynamic surface properties of nonionic surfactant solutions

Equilibrium and dynamic surface properties for solutions of some pure nonionic surfactants have been measured and analysed quantitatively. Surface dilational modulus against frequency curves show a behaviour which below the critical micellar concentration (c.m.c.) can be fully interpreted on the basis of diffusional exchange between surface and bulk with a diffusion coefficient which is, within measuring error, independent of concentration. No evidence for an adsorption or desorption barrier was found. The modulus extrapolated to infinitely high frequency can be used to obtain information about the surface equation of state for the monolayers. To a good approximation the monolayer behaviour can be described over a wide range of surface pressures by a Temkin isotherm, pointing to a strong repulsive interaction between the adsorbed nonionic molecules.Above the c.m.c. evidence was found for an additional relaxation mechanism which causes the dilational modulus to decrease quickly with increasing concentration.The relationship between oscillatory and extensional dynamic surface properties is discussed as well as some aspects of the relation between such properties and foam and emulsion behaviour.