Abstract: This paper covers the method of direct measurement of the disjoining pressure isotherm for sing, isolated foam films stabilized with TTABabove cmc by microinterferometric technique. It has been studied that the relation of disjoining pressure and film thickness, and the difference between the surface tension of solution and that of the common black film under different liquid film thickness conditions. The experimental results show that common black film thickness depends on the disjoining pressure and electrolytic concentration. At a low disjoining pressure, the film thickness decreases with the increase of the disjoining pressure. At a high disjoining pressure, the film thickness decreases slightly with the increase of the disjoining pressure. This signifies that the transition between black films is jumping. The electrolyte can reduce the interaction forces between two charged monolayers of film and thin the film, so the equilibrium thickness of film decreases with increasing electrolyte concentration of the solution from which they are formed. The surface tension of common black film calculated from the disjoining pressure isotherm is slightly different from the surface tension of solution.

Key words: Disjoining pressure isotherm, Common black film, Newton black film, Surface tension of film, Black film thickness