A state equation for an ionized monolayer and its corresponding adsorption isotherm for one-one valent long-chain electrolytes taking account of the interaction between amphiphilic ions are proposed. The validity of the equations is demonstrated using adsorbed layers of cetyl trimethyl ammonium bromide (CTAB) on the basis of high precision (+ 0,02 mJ. m -2) tensiometric measurements at the water-air and water-octane interfaces at 303-343 K. Analysis of the values measured for interracial tension and ionisation potential has shown for both interfaces the existence of three regions characterized by different extents to which the interactions between adsorbed amphiphilic ions are manifested. The region of low surface occupancy, fl _-> ~ 0,1 (ideal behaviour of monolayer), the region -0,1< 0 <-0,7 where interactions are weak (attraction constant a 0 = const = -1) and the region 0 > ~ 0,7 where the layer approaches the condensed state (a~ increases monotonously) were examined. An important role is shown to be played by the hydrophobic interactions between the segments of hydrocarbon chains of adsorbed cetyl trimethyl ammonium (CTA +) ions immersed into water.

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