Wetting transitions and other wetting properties of water–2,5 lutidine system

The wetting behavior of the water–2,5 lutidine system has been studied around the lower consolute point (Tc=13.1 °C). We have measured contact angles and surface tensions by varying the concentration and temperature. In the diphasic region, a wetting transition has been observed at 46–47 °C on a silica wall by direct observation of the solid–liquid–liquid contact angle. The perfect wetting occurs close to Tc, the wetting phase is water rich. At the liquid–vapor interface, the analysis of the values of the surface tensions shows that, close to Tc, they obey critical laws and that a lutidine rich phase perfectly wets the vapor and the water rich phase. These behaviors have been analyzed on the basis of the contact angles of the monophasic on a silica wall on both sides of the coexistence curve, and the general variation of the surface tensions. A second wetting transition has been shown on a differently washed glass surface. Reference is made to the theoretical and experimental works following the early work of Cahn.