Wetting observed by evanescent-wave-generated fluorescence spectroscopy II. Selective excitation: methylcyclohexane + perfluoromethyl cyclohexane at the upper critical endpoint

Wetting at the solid (SF4 glass)-liquid interface of the binary liquid mixture methylcyclohexane + perfluoromethylcyclohexane is studied using evanescent-wave-generated fluorescence spectroscopy (EWGFS). The fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene (DPH) is used to discriminate between the two coexisting liquid phases by means of selective excitation of DPH in the methylcyclo-hexane-rich phase using a laser operating at 371 nm. A wetting transition is observed beginning at 32°C with a wetting layer apparently attaining maximum thickness at 38°C in relation to an upper critical solution temperature TUCS 46°C, but more specific information regarding the order and position of the transition cannot be established until a number of experimental design changes are implemented.