The interfacial tension of the binary two-phase mixture of water and ethylene glycol isobutyl ether (EIB) was measured as a function of temperature in the vicinity of the lower critical solution temperature Tc under atmospheric pressure. The interfacial tension decreased with decreasing temperature and approached zero at Tc. The thermodynamic quantities of interface formation were evaluated by applying equations developed previously to the interfacial tension vs temperature curves. The results were compared with those of the water and diethylene glycol diethyl ether system examined previously, and the effect of the molecular structure of the ether molecule on its interfacial behavior was discussed. It was suggested that the hydration of the ethylene oxide groups of ether molecules was an important factor in the interface formation as well as in the mixing of component molecules of the systems investigated here.
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