Behaviour of cetyltrimethylammonium bromide, Triton X-100 and Triton X-114 in mixed monolayer at the (water–air) interface

• Joos equation modified by us is useful for the ternary mixtures of surfactant.
• Composition of the CTAB + TX-100 + TX-114 monolayer is not proportional to the bulk phase.
• Synergetic effect of the TX-100, TX-114 and CTAB mixtures is confirmed by the adsorption efficiency.
• Adsorption efficiency of ternary mixtures is not related to their effectiveness.

The measured values of the surface tension of aqueous solution of binary and ternary mixtures including CTAB, TX-100 and TX-114 were compared to those calculated from the Joos equation modified by us. It appeared that it is possible to predict, at the first approximation, the changes of the surface tension of aqueous solutions studied as a function of concentration of all possible binary and ternary mixtures in the range from 0 to the minimal value of their surface tension. However, the deviations of the calculated values of surface tension from those measured depend on the synergetic effect in the reduction of water surface tension. This effect was established by the values of the molecular interaction parameter calculated from the Rosen and Hua equations. From these equations the relative mole fraction of three surfactants in the mixed monolayer at the (water–air) interface was also determined and compared to that obtained by using surface excess concentrations of particular surfactants in this monolayer. As follows from this comparison the Rosen and Hua equations give the proper relation between the mole fraction of TX-100, TX-114 and CTAB in the monolayer but on the condition it is determined at the same concentration of each surfactant in the mixture. The synergetic effect of ternary mixture in the reduction of the water surface tension is also reflected in the changes of the values of the Gibbs standard free energy of adsorption which was determined by using the Langmuir and Gu and Zhu equations. It appeared that the Gu and Zhu isotherm of adsorption proposed for the solid-solution interface is also useful for determination of the Gibbs standard free energy of adsorption at the (water–air) one.

Synergetic effect of the binary and ternary mixtures of surfactants at their concentration equal to 1 · 10−5 M in the reduction of the water surface tension.Figure optionsDownload as PowerPoint slide