Synergistic adsorption of Triton X-100 and CTAB surfactants at the toluene + water interface

Equilibrium interfacial tension measurements at 25.0 °C of the toluene + water system with two widely used surfactants, octylphenol decaethylene glycol ether (Triton X-100) and cetyl trimethyl ammonium bromide (CTAB) having concentrations much lower than their CMC were performed. According to the obtained parameters from the Szyszkowski equation, Triton has higher adsorption tendency than of CTAB. The results obtained for surfactants mixtures are analyzed by the theory of non-ideal interactions in binary mixtures (NIBMs) and the interfacial composition and the interaction parameter in the mixed adsorbed monolayer are determined. The attractive interaction shows a maximum value at nearly equal surfactants bulk mole fraction. The synergism is achieved for Triton bulk mole fractions of 0.30 and higher, and the highest degree of synergism (40.6%) is found for the bulk mole fraction of 0.52 with the lowest investigated constant interfacial tension of 28.0 mN m−1. A correlation was developed for variation of the interaction parameter with bulk mole fraction.

► Significant synergism in interfacial tension reduction is achieved with αTriton > 0.3.
► The highest degree of synergism (40.6%) is appropriate to the lowest used interfacial tension.
► The attractive interaction parameter finds its maximum absolute value at α ≈ 0.5.
► An alternative variation for interaction between surfactants is revealed at the interface.
► A correlation is introduced for the interaction parameter in the sense of ease of applications.