Interfacial Activity of 2-Ethylhexan-1-ol-Based Surfactants in Quasi-ternary Systems

The surface properties of quasi-ternary systems comprising two surfactants in water were studied in the light of previously published hypotheses of specific two-dimensional arrangements of associated surfactant molecules and compatibility of their hydrophobic chains. In contrast to the studies of model ternary systems of pure components reported previously in the literature, the title quasi-ternary systems were prepared as water solutions of two polydisperse mixtures of surfactants: an anionic one (quasi-component 1) and nonionic one (quasi-component 2). The complex quasi-components used were polydisperse in terms of both ethylene oxide substituent numbers and the carbon chain length, obtained as received under industrial conditions from commercial raw materials. The novel surfactants which are the subject of the present study were synthesized by elongation of the hydrophobic chain of 2-ethylhexan-1-ol molecules by catalytic polyaddition of methyloxirane (propylene oxide), followed by introduction into the resulting transformed structure of a hydrophilic group (in the form of a polyether chain and/or a sulfosuccinate group). All synthesized surfactants were therefore polydispersed mixtures of methyloxirane and oxirane (ethylene oxide) homologues. It was shown that, in the case of the quasi-ternary aqueous systems studied, the extrema of the investigated functions describing the surface properties occur in the neighborhood of some specific stoichiometric ratios of the surfactant concentrations, namely 1:3/3:1. On the other hand, synergistic effects associated with the compatibility of the hydrophobic chains studied were not confirmed.