Studies on the relation of black film thickness and film tension

This paper covers the method of direct measurement of the disjoining pressu re isotherm for sing, isolated foam films stabilized with TTAB above cmc by microinterferometric technique. It has been studied that the relation of d isjoining pressure and film thickness, and the difference between the surfa ce tension of solution and that of the common black film under different li quid film thickness conditions. The experimental results show that common b lack film thickness depends on the disjoining pressure and electrolytic con centration. At a low disjoining pressure, the film thickness decreases with the increase of the disjoining pressure. At a high disjoining pressure, th e film thickness decreases slightly with the increase of the disjoining pre ssure. This signifies that the transition between black films is jumping. T he electrolyte can reduce the interaction forces between two charged monola yers of film and thin the film, so the equilibrium thickness of film decrea ses with increasing electrolyte concentration of the solution from which th ey are formed. The surface tension of common black film calculated from the disjoining pressure isotherm is slightly different from the surface tensio n of solution.