Surface activity of mixtures of oxyethylated methyl dodecanoate and sodiumdodecylbenzenesulfonate

Surface and interfacial tension and detergency of mixtures containing oxyet hylated methyl dodecanoate and sodium dodecylbenzenesulfonate were determin ed. Synergism in the surface tension reduction was not observed. The compet ition for adsorption at the air/water interface between oxyethylated methyl dodecanoate and sodium dodecylbenzenesulfonate depended on the considered surface tension, the weight ratio of surfactants in the aqueous phase, and the hydrophile-lipophile balance of the nonionic surfactant. Generally, cov erage of the interface with oxyethylated methyl dodecanoate increased when surface tension decreased. Non-ionics were the dominant species at the inte rface in the important region of surface activity, i.e., for surface tensio ns below 40 mN m(-1). The mole fraction of the hydrophobic nonionic at the interface was higher than the contribution of hydrophilic oxyethylates. An increase of the surfactant ratio in the bulk phase affects the interfacial ratio of surfactants in the same way. The lowest interfacial tension (1.5 m N m(-1)) at the hexadecane/water interface was observed for oxyethylated me thyl dodecanoate having an average degree of oxyethylation equal to 8 and 1 0. Nearly 5 min was needed to achieve equilibrium value. Mixtures with sodi um dodecylbenzenesulfonate decreased the interfacial tension somewhat less efficiently but the equilibrium was rapidly established. The standard washi ng powders containing oxyethylated methyl dodecanoates exhibited washing ab ility similar to that obtained for the powder with traditional alcohol oxye thylate.