Wetting observed by evanescent-wave-generated fluorescence spectroscopy .2. Selective excitation: Methylcyclohexane plus 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 approximate to 32 degrees C with a wetting layer apparently attaining maximum thickness at approximate to 38 degrees C in relation to an upper critical solution temperature T-UCS approximate to 46 degrees 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.