Abstract
Experimental evidence of corresponding states in water, n-alkane(), and n-alkyl polyethylene glycol ether systems is presented. Striking similarities in both the phase behaviour and the interfacial tensions for a variety of systems are highlighted. For some selected systems the trajectories of the middle phases in the three-phase regime are precisely determined. Projections of the middle-phase trajectories onto the - plane of the phase prism shape nearly perfect parabolae, whereas the projections onto the T - plane exhibit a sigmoidal shape. Here is the surfactant volume fraction, and is the oil-in-water-plus-oil volume fraction. It is found that the trajectories collapse into single curves, if the surfactant concentration scale is reduced by the maximum of the parabolae, , which is the surfactant volume fraction of the symmetric microemulsion, and if the temperature axis is reduced by the difference of the upper and lower critical endpoint temperature, . It is found that the maximum length scale set by the surfactant volume fraction can be used to reduce the interfacial tension scale, that is plotting versus the reduced temperature scale. These reductions yield a remarkable superposition of the interfacial tension data of 17 different systems, the carbon number of the oil k ranging from 8 to 14, the hydrophilic surfactant head j from 3 to 6 and the surfactant tail length i from 8 to 12.
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