VISCOELASTIC PROPERTIES OF DODECYLAMMONIUM CHLORIDE MONOLAYERS

Monolayers of dodecylammonium chloride formed at the solution-air inte rface at different electrolyte concentrations have been investigated b y dynamic surface light scattering. Pronounced maxima in the damping o f capillary waves were observed at surfactant concentrations around 0. 1 X CMC. These maxima occur at concentrations just above the break poi nts in the surface tension vs concentration curves caused by first-ord er phase transitions from a gaseous to a liquid-expanded state. The ex perimental results were analyzed by comparisons with theoretical calcu lations based on the standard theory of light scattering due to capill ary waves on liquid surfaces, and the molecular theory of the surface tension of ionic surfactant solutions presented earlier by Eriksson an d Ljunggren. In this way it was possible to account satisfactorily for the observed concentration and salt dependencies of the central frequ ency and width of the spectral peak. (C) 1995 Academic Press, Inc.