Dieter Nickel

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 CMCσc 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 (kc) was estimated from the CMC and the observed break point of the interfacial tension after equilibration of the two phases. In decane/water,kc is nearly zero for all surfactants studied. For the polar oils,kc increases with the chain length of the surfactant up tokc≈10 for C12G1 in octyldodecanol/water. The values ofσc in the different oil/water systems appear to be correlated withkc and exhibit a minimum nearkc=1.

Phase behaviour of alkyl polyglucosides in combination with fatty alcohols and alkyl sulphates

Abstract Dilute C 12 14 alkyl polyglucoside (Glucopon600CS®) solutions containing small amounts of fatty alcohols (hydrocarbon chain length greater than 4) show three different lamellar phases (Lαl, Lα−h, Lαh) which are characterized by increasing fatty alcohol: surfactant ratios. The middle lamellar phase appears, in some aspects, like a mixture of the lower and upper lamellar phases. The lower and middle lamellar phases are optically biaxial and are therefore probably in tilted crystalline states. The upper lamellar phase is in the liquid state and is uniaxial. On the addition of alkyl sulphates together with the appropriate amount of the fatty alcohols, to a 5% alkyl polyglucoside solution the middle lamellar phase predominates. Pentanol and hexanol favour the upper lamellar phase while longer-chain fatty alcohols favour the lower lamellar phase. A cholesteric phase with characteristic fingerprint texture appears in highly concentrated surfactant solutions containing decanol or higher fatty alcohols. The characteristic fingerprint texture of this phase is due to myelinic figures which occur in the two-phase region between the lower lamellar phase and an isotropic phase. The fingerprints can be oriented in strong magnetic fields. The cholesteric phase interacts strongly with polarized light which is travelling in the direction of the helical axis.