Dynamic interfacial tensions of binary nonionic–anionic and nonionic surfactant mixtures at water–alkane interfaces

Abstract

The influences of nonionic surfactant on interfacial properties of anionic–nonionic surfactant against alkanes are studied by measuring the dynamic interfacial tension (IFT). The surfactants chosen are fatty alcohol polyoxyethylene carboxylate (C12EO3C) and fatty alcohol polyoxyethylene (C12E3) with various counterions, Na+, Mg2+, and Ca2+. On the basis of our experimental results, one can find that the addition of nonionic surfactants C12E3 could achieve an ultralow IFT value at some specific alkane carbon numbers under NaCl condition and the obvious synergistic effect on reducing IFT can be observed during all experimental alkane carbon numbers. However, for MgCl2 systems, the ultralow IFT values can be achieved by pure C12EO3C solutions and one can observe synergistic effect and antagonistic effect on IFTs at higher and lower alkane carbon numbers respectively by adding nonionic surfactant. On the other hand, for CaCl2 systems, the addition of 0.05% C12E3 shows the same influence on the IFTs as that of NaCl systems, while the similar effect as that of MgCl2 systems will be observed when adding 0.1% C12E3. An interfacial model combined two mechanisms, controlling hydrophilic–lipophilic balance and forming mixed adsorption film, responsible for varying IFT has been provided based on the difference of ion radius. By adding nonionic surfactant, the mechanisms of forming mixed adsorption film and controlling hydrophilic–lipophilic balance play crucial roles in effecting IFTs for NaCl systems and MgCl2 systems, respectively. Moreover, for CaCl2 systems, the responsible mechanism of forming mixed adsorption film will change into controlling hydrophilic–lipophilic balance with the increase of nonionic surfactant concentration.