Physico-chemical basics of microemulsions with alkyl polyglycosides

Abstract

Alkyl polyglycosides are a nonionic surfactant class based on sugar and fatty alcohol; they are being used to an ever-increasing extent in cleaning and personal care products because of their excellent environmental and skin compatibility. Although they are nonionic like the fatty alcohol ethoxylates, on account of the different interaction of the sugar residue with water, the phase behavior of the alkyl polyglycosides clearly differs from that of the fatty alcohol ethoxylates. This also affects the formation of microemulsions in oil-water-surfactant systems. Microemulsions form when the hydrophilic-lipophilic properties of the surfactant film at the oil water interface are balanced. Depending on the surfactant type, this hydrophilic-lipophilic balance can be adjusted by means of different formulation parameters: In the case of fatty alcohol ethoxylates this is possible via the temperature as a parameter which is easily changed; in the case of the alkyl polyglycosides it can only be achieved by mixing with hydrophobic cosurfactants. In this respect alkyl polyglycosides are similar to anionic surfactants. This leads to interesting applications since — in contrast to fatty alcohol ethoxylates — temperature-stable microemulsions on the basis of APG can be produced. Through addition of anionic surfactants and variation of the oil/water ratio, microemulsions with “tailor-made” application properties such as viscosity or interfacial tension can be obtained. Small-angle x-ray scattering experiments and conductivity tests provide an insight into the structure of these microemulsions.