DYNAMICS OF THE SURFACE-TENSION AND 2-DIMENSIONAL PHASE-TRANSITIONS IN MONOLAYERS OF SOLUBLE SURFACTANTS AT THE AIR-WATER-INTERFACE

The dynamics of the surface tension of aqueous solutions of hexadecylt rimetnylammonium bromide (HTAB) and sodium dodecylsulfate (SDS) at 220 -degrees- and surfactant concentrations less than 0.1 CMC was studied by the drop-weight method. The dependence of the surface tension on th e formation time of the interface is nonmonotonic; corresponding curve s are characterized by an inflection at certain values of the surface tension independent of the surfactant concentrations. The inflections on the curves describing the dynamics of the surface tension and the a dsorption of the surfactants may be associated with the two-dimensiona l phase transition in the adsorbed layers of the surfactants from the liquid-expanded to the liquid-condensed state.