Wetting observed by evanescent-wave-generated fluorescence spectroscopy I. Differential solubility: 2,6-Lutidine + water at the lower critical endpoint

Wetting at the solid-liquid interface of the binary liquid mixture 2,6-lutidine + water near its lower critical endpoint at TLCS = 34°C is studied using evanescent-wave-generated fluorescence spectroscopy (EWGFS), otherwise known as total internal reflection fluorescence (TIRF). The validity of the technique is assessed. In particular, the underlying assumptions are critically reviewed with a view to extending the technique both to other less experimentally accessible mixtures and to the study of as-yet-not-entirely resolved wetting phenomena such as prewetting. Although a wetting transition is observed for the named mixture, more specific information regarding the order and position of the transition cannot be established until a number of experimental design changes are implemented, in particular, better stirring of the mixture to achieve diffusional equilibrium without hysteresis.