WETTING OBSERVED BY EVANESCENT-WAVE-GENERATED FLUORESCENCE SPECTROSCOPY .1. DIFFERENTIAL SOLUBILITY - 2,6-LUTIDINE PLUS WATER AT THE LOWER CRITICAL END-POINT

Wetting at the solid-liquid interface of the binary liquid mixture 2,6 -lutidine + water near its lower critical endpoint at T-LCS = 34 degre es C is studied using evanescent-wave-generated fluorescence spectrosc opy (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 extendi ng the technique both to other less experimentally accessible mixtures and to the study of as-yet-not-entirely resolved wetting phenomena su ch as prewetting. Although a wetting transition is observed for the na med mixture, more specific information regarding the order and positio n of the transition cannot be established until a number of experiment al design changes are implemented, in particular, better stirring of t he mixture to achieve diffusional equilibrium without hysteresis.