Interfacial tension of alkylglucosides in different APG/oil/water systems

The interfacial performance of pure alkylglucosides (C₈G₁, C₁₀G₁ and C₁₂G₁) and of technical grade alkylpolyglucoside (APG) surfactants was investigated in three different water/oil systems (decane, isopropylmyristate and 2-octyldodecanol). From the dependence of the interfacial tension on the surfactant concentration below the CMC the cross-sectional area of the molecules at the decane/water interface was estimated. The plateau values of the interfacial tension at the CMC_c are independent of temperature and almost independent of added electrolyte in the decane/water system. The ability of the surfactants to lower the oil/water interfacial tension is most pronounced for the nonpolar oil. The partition coefficient of the surfactant between oil and water phase (k_c) was estimated from the CMC and the observed break point of the interfacial tension after equilibration of the two phases. In decane/water,k_c is nearly zero for all surfactants studied. For the polar oils,k_c increases with the chain length of the surfactant up tok_c10 for C₁₂G₁ in octyldodecanol/water. The values of_c in the different oil/water systems appear to be correlated withk_c and exhibit a minimum neark_c=1.