The elasticity of open and closed thin foam films is analyzed. The elasticity modulus of a closed film is shown to be additive with respect to contributions from Gibbs elasticity and disjoining pressure. A detailed expression for the film elasticity modulus explains the pronounced maxima of foaminess and foam stability near the critical micelle concentration observed earlier in many experiments. A theory of transversal elasticity of thin foam films is formulated under conditions excluding the action of Gibbs elasticity. Near the critical micelle concentration, the theory predicts maxima of the transversal elasticity modulus and of the films thickness as functions of concentration at a given disjoining pressure. The prediction has been verified experimentally by measuring the film thickness in equilibrium foam as a function of height.

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It is reported the discovery of optical activity of micellar solutions of sodium dodecyl sulfate, cetyltrimethylammonium bromide, and poly(oxyethilene)(4)dodecyl ether as typical representatives of anionic, cationic, and nonionic surfactants. The surfactants exhibit dextrorotation. Since the optical activity of the ionic surfactants appears only above the Krafft point, it should be ascribed to micellar aggregates. Optical rotation as a function of the surfactant concentration displays a pronounced maximum near the critical micelle concentration (the subsequent decrease of optical activity corresponds to formation of spherical micelles that cannot possess optical activity by symmetry). For sodium dodecyl sulfate, the maximum correlates well with extremes of other properties of surfactant solutions (foaminess, foam stability, Gibbs' and transversal elasticity of thin foam films), which was described earlier. Naturally, films and foams of sodium dodecyl sulfate solutions also demonstrate optical activity.

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