Langmuir 1993,
9, 2921-2925
Microemulsions Formed by Alkyl Polyglucosides and Alkyl Glycerol Ether
2921
an
K. Fukuda,* O. Sóderman,*’1 B. Lindman,1 and K. Shinoda1 1
1, Chemical Centre, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden, and Tokyo Research Labs, Kao Corporation, Bunka 2-1-3,
Physical Chemistry
Sumida-ku, Tokyo 131, Japan
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Received May 11, 1993. In Final Form: August 16, 19939
A surfactant is described which has the capability of mixing large amounts of hydrocarbon and water into a homogeneous solution. The surfactant system is a mixture of dodecyl polyglucosides with an average number of glucose units of 1.8 and a branched alkyl glycerol monoether which acts as a cosurfactant. A one-phase, liquid solution containing 4 wt % of this mixture, water, and a hydrocarbon (cyclohexane) can be prepared at any ratio of water to hydrocarbon (i.e., from neat water to neat hydrocarbon). This is achieved by varying the surfactant to cosurfactant molar ratio. Investigations by the NMR self-diffusion technique of the microemulsion microstructure give evidence for dramatic changes in the ratio of waterto-oil self-diffusion (by approximately 5 orders of magnitude). The microemulsion is of the oil droplets in water type at high surfactant to cosurfactant molar ratios and of the water droplets in oil type at lower ratios. At intermediate surfactant to cosurfactant ratios, the HLB of the surfactant mixture is balanced and a bicontinuous microemulsion with a low mean curvature surfactant layer is formed. At intermediate oil to water ratios, the microemulsion microstructure changes dramatically with small changes of the surfactant to cosurfactant ratio.
Introduction
dertaken an investigation of microemulsions formed by alkyl polyglucosides. Surfactant systems which form microemulsions containing equal amounts of oil and water are termed balanced. Of particular interest are such surfactant systems that achieve this with low amounts of surfactants. Several such systems have been designed. The microstructure of these systems is typically bicontinuous and consists of a monolayer of surfactant of zero spontaneous curvature separating oil domains from water domains.14 The more detailed microstructure of these systems as well as the theoretical description of them is presently a topic of considerable interest.16 The effectiveness of a surfactant in forming these microemulsions can be related to the spontaneous or preferred curvature (Ho) of the amphiphilic film that it forms. This follows from the fact that the actual areaaveraged curvature (H) of the surfactant film will tend to be as close to Ho as possiible.1617 The value of
