Alkyl polyglycosides phase behavior

The phase behavior of a technical Cg/io alkyl polyglycoside is illustrated in Fig. 11 [52]. At temperatures above 20°C, the Cg/io alkyl polyglycoside is present up to very high concentrations in an isotropic phase of which the... 

Similarly to anionic surfactants, alkyl polyglycosides react to the addition of cosolvents that increase the solubility of the surfactant in the oil phase. In the decane-water-alkyl polyglycoside system, the addition of the cosolvent i-butanol results in a drastic reduction in the interfacial tension between oil and aqueous phase and, hence, in the formation of a third phase, the microemulsion [70]. As expected, the range in which this three-phase microemulsion exists is only slightly dependent on temperature and, in contrast to anionic surfactants, is also hardly affected by electrolytes [70]. Systematic investigations of the phase behavior confirm these initial results for a number of simple hydrocarbons from hexane to hexadecane and aromatics [71,72]. 

The nonionic class of alkyl polyglycosides differs from fatty-alcohol ethoxy-lates by its characteristic structure which considerably affects the association of molecules in solution, the phase behavior, and the interfacial activity. The hydrophilic head of the glucose ring, associated with the surrounding water molecules by hydrogen bonds, is rather voluminous as compared to the alkyl chain. However, the hydration is low compared to fatty alcohol ethoxylates. Therefore, basic phenomena like cloud point, thermal phase inversion, or gel formation in medium concentrations of pure solutions cannot be observed in case of the alkyl polyglycosides. 

The solubilization of comparably small amounts of oil components in rinse and shampoo formulations demonstrates the basic emulsification properties which alkyl polyglycosides should be expected to show as nonionic surfactants. However, a proper understanding of phase behavior in multicomponent systems is necessary in order to evaluate alkyl polyglycosides as powerful emulsifiers in combination with suitable hydrophobic coemulsifiers [42]. 

In fact, the phase behavior and interfacial tension of snch alkyl polyglycoside emulsifier systems closely resemble those of conventional fatty alcohol ethoxylate systems if temperatnre as a key phase behavior parameter is replaced by the mixing ratio of the hydrophilic/lipophilic emnlsihers in the non-ethoxy-lated system [46],... 

Figure 12.7 Phase behavior (left) and interfacial tension (right) of water/dodecane/alkyl polyglycoside/sorbitan laurate mixtures with an oil/water ratio of 1 1 at 25 °C (Reproduced by permission of Verlag fiir Chemische Industrie from ref. 44)...

In this study, the phase behavior of microemulsions consisting of alkyl polyglycosides and ethoxylates as hydrophilic emulsifiers, a lipophilic coemulsifier, an oily component, and water is evaluated in terms of micro-emulsion formation and stability. Parameters such as temperature, oil polarity, and composition of the surfactant mixture are discussed. It was shown that both the concentration range and the temperature stability could be extended by using suitable mixtures of emulsifiers and coemulsifiers. 

The phase behavior of alkyl polyglycoside (APG)/water mixtures differs in certain aspects from other nonionic surfactants, especially with regard to the influence of the temperature. Whereas the hydrate shell of the ethoxylate head group depends largely on temperature, the interaction of the sugar unit... 

The similarity between alkyl polyglycosides and fatty alcohol ethoxylates is not confined to phase behavior but also applies to the interfacial tension of the emulsifier mixture. With an APG/SML ratio of 4 6, the hydrophilic/ lipophilic properties of the emulsifier mixture are balanced and the interfa-... 

The phase behavior of the emulsifier system with fixed oil and water contents is shown in Fig. 10. A microemulsion is formed at a GMO concentration between 15 and 25% of the total emulsifier system with C12/14 alkyl polyglycoside/Cg/ro alkyl polyglycoside in a suitable mixing ratio. The necessary amount of GMO differs only slightly from the optimal alkyl poly-glycoside/GMO ratio that was found in the simple model emulsion as discussed earlier. 

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