Wetting transition of a binary liquid mixture at a solid boundary
Sektion Physik der LMU München - Geschwister-Scholl-Platz 1
80539 München, Germany
Accepted: 10 December 1999
We present the observation of a first-order wetting transition of the binary liquid mixture 2-propanol and perfluoromethylcyclohexane at a liquid-solid interface, where one component (2-propanol) of the gravity-separated mixture is selectively adsorbed on the surface of a silicon substrate. The system undergoes a wetting transition from a thin adsorbed film to a macroscopic wetting layer at with pronounced premonitory growth of the adsorbed film. The microscopic density profile of the prewetting film is derived from fits to temperature-dependent X-ray reflectivity measurements. Our experimental data clearly indicate a film structure dominated by strong density gradients, which is in contrast to the frequently used “homogeneous slab” models, but confirms density functional calculations. Time-resolved measurements during equilibration reveal new details of the adsorption film growth process, in particular the existence of separate density and thickness growth regimes.
PACS: 61.10.Kw – X-ray reflectometry (surfaces, interfaces, films) / 64.75.+g – Solubility, segregation, and mixing; phase separation / 68.45.Gd – Wetting
© EDP Sciences, 2000