Wetting transition in a three-phase surfactant/oil/water microemulsion system

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Abstract
Experimental results have been found for a wetting transition involving a three‐component (amphiphile/oil/water) microemulsion system that forms top, middle, and bottom liquid phases. For all temperatures between the wetting transition temperature (Tw) and the upper critical endpoint temperature (Tuc) the middle phase microemulsion of the C6H13(OC2H4)2OH/n‐C16H34/H2O system appeared to wet the interface between the top and bottom phases, whereas below Tw it did not. Compositions of the phases below and above Tw are reported, also. Within the experimental uncertainties, Tw equaled the optimal temperature (at which the top–bottom tension passes through a minimum), as determined from the compositions of the middle phase. The wetting transition temperature, Tw=45.14±0.02 °C, was more than 15 °C below the upper critical endpoint temperature, Tuc=60.94±0.03 °C. This appears to be the first example of a temperature‐induced wetting transition that involves a middle‐phase microemulsion system.