No abstract

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-Tc, the critical temperature of the liquid system: a critical behaviour.In lutidine rich phases, adsorption behaviour is quite different, and T,, the wetting transition temperature ir 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.

The adsorption of 2, 5 DMP (2, 5-dimethylpyridine) at the free surface of water (1)-2, 5 DMP (2) liquid mixtures was determined from surface tension and activity measurements. Two divergences were found: the former was observed at Tc for the critical isochore and the 2, 5 DMP-rich γ-phase which, at coexistence, completely wets the surface at Tc, whereas the latter was noticed at Tw for the water-rich β-phase. These results were compared with those found under similar conditions for the same liquid system with silica as the wall; this comparison is quite fruitful because, with silica, the preferentially wetting phase is the β-phase.

Surface state changes described as phase transitions or simple molecular rearrangements have become a key issue in modern science. Indeed, they have an impact on the development of numerous (nano)technologies; they are also involved in biochemical and chemical mechanisms at the molecular level and also in environmental phenomena. At last, they have been at the origin of flourishing statistical descriptions that have illuminated new and very interesting aspects of surface behaviors. Here, to obtain still lacking coherent sets of experimental data on systems in which molecular interactions and thermodynamic properties are different, the adsorption behaviors of three aqueous mixtures in contact with a dense and homogeneous silica were studied versus concentrations and temperatures. Of course, these mixtures displayed very different bulk phase properties. Their stairlike isotherms are interpreted through surface phase diagrams; each of them is very similar to the corresponding bulk phase diagram. Their comparison gives new insights into the different surface states, the role of solvent in the surface, and the probable molecular mobility.