Wetting and Random Field Transition of Binary Liquids in a Porous Medium.

Mixtures of lutidine and water imbibed in porous Vycor have been studied using Raman, elastic and quasielastic light scattering. At low temperatures adsorption of lutidine on the internal glass surface gives rise to local composition gradients. At higher temperatures a transition from complete to partial wetting occurs. Composition fluctuations extend over several pores and the local chemical and geometrical randomness sets the stage for a random field transition. The critical exponent beta associated with this latter transition is small in agreement with theoretical predictions.