Surface Activity of Mixtures of Oxyethylated Methyl Dodecanoate and Sodium Dodecylbenzenesulfonate

摘要

Surface and interfacial tension and detergency of mixtures containing oxyethylated methyl dodecanoate and sodium dodecylbenzenesulfonate were determined. Syner- gism in the surface tension reduction was not observed. The competition for adsorption at the air/water interface between oxyethylated methyl dodecanoate and sodium dodecylben- zenesulfonate depended on the considered surface tension, the weight ratio of surfactants in the aqueous phase, and the hydrophile-lipophile balance of the non ionic surfactant. Gen- erally, coverage of the interface with oxyethylated methyl do- decanoate increased when surface tension decreased. Non- ionics were the dominant species at the interface in the im- portant region of surface activity, i.e., for surface tensions below 40 mN m-1. The mole fraction of the hydrophobic non- ionic at the interface was higher than the contribution of hy- drophilic 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 mN m-1) at the hexadecane/water interface was observed for oxyethylated methyl dodecanoate having an average degree of oxyethyla- tion equal to 8 and 10. Nearly 5 min was needed to achieve equilibrium value. Mixtures with sodium dodecylbenzenesul- fonate decreased the interfacial tension somewhat less effi- ciently but the equilibrium was rapidly established. The stan- dard washing powders containing oxyethylated methyl dodec- anoates exhibited washing ability similar to that obtained for the powder with traditional alcohol oxyethylate.