MONOLAYERS, CRITICAL LAYERS AND WETTING FILMS IN A LIQUID-LIQUID-SOLID SYSTEM UNDERGOING A WETTING TRANSITION - EXPERIMENTAL-STUDY

Experimental adsorption isotherms have been drawn for the water-2,5 lutidine liquid system against silica, at several temperatures, on both sides of the liquid-liquid coexistence curve and for the coexisting phases. In the two-phase liquid system, perfect wetting, probably due to long range interactions is made by the water rich phase, whereas lutidine, probably due to chemical forces is preferentially adsorbed. In water rich monophases, at very low lutidine concentrations, lutidine forms monolayers on silica. Close to the phase separation, lutidine adsorption strongly increases and diverges for T-->T(c), the critical temperature of the liquid system: a critical behaviour. In lutidine rich phases, adsorption behaviour is quite different, and T(W), the wetting transition temperature is the important parameter for the behaviour of the adsorption at coexistence. The set of experimental results is very similar to the results of the theoretical literature, and both can be used as a guide for further experimental exploration of the so-called ''prewetting'' transition.