CLOUD POINT PHENOMENA IN THE PHASE-BEHAVIOR OF ALKYL POLYGLUCOSIDES IN WATER

A characteristic feature of nonionic surfactants such as, in particular, ethoxylates in aqueous solution is a lower consolute temperature. Alkyl polyglucosides are also nonionic surfactants which, because of their ecological and technical properties, are becoming more and more important. So far, no lower consolute temperatures have been observed in aqueous solutions of them, although in some cases at low concentrations there are wide regions of coacervation. These phenomena are particularly pronounced in the presence of electrolytes. Detailed investigations have now shown that, for very narrow ranges of structure, alkyl polyglucosides actually do also have lower consolute temperatures. Compared with ethoxylates, the effects of electrolytes are very unusual. Thus, all inorganic salts, with only small differences, result in a distinct reduction in the cloud point, whereas alkalis have a strong hydrotropic effect. The electrolyte sensitivity is very much higher than for the ethoxylates. The effects of the alkyl polyglucosides can be explained on the assumption that there is a negative electric charge on the surface of the micelles while the ethoxylates are more or less uncharged. This was demonstrated by the effect of ionic surfactants on the cloud point, and by direct measurements of the zeta potential both in emulsions and in micelles.