Discrete solvation layering in confined binary liquids.

Area of Science:

• Colloid and Surface Science
• Materials Science
• Physical Chemistry

Background:

• Understanding liquid behavior at interfaces is crucial for lubrication and nanotechnology.
• Confined liquids exhibit unique properties compared to bulk liquids.
• Binary liquid mixtures present complex interfacial phenomena.

Purpose of the Study:

• To measure solvation force profiles of binary liquid mixtures confined between solid surfaces.
• To investigate the layering and binding of different liquid components.
• To compare experimental results with theoretical predictions and other experimental techniques.

Main Methods:

• Atomic force microscopy (AFM) was employed to probe solvation forces.
• Measurements were performed on squalane/octamethylcyclotetrasiloxane (OMCTS) mixtures confined between Si3N4 tips and highly oriented pyrolytic graphite (HOPG).
• Hexadecane/OMCTS mixtures were studied between alkanethiol-functionalized tips and freshly cleaved mica.

Main Results:

• Oscillatory solvation force profiles were observed for both systems, indicating discrete solvation layers.
• Squalane layers on HOPG exhibited strong repulsive forces, suggesting significant binding.
• OMCTS layers on mica showed less ordering and slightly larger periodicities within the attractive force regime.

Conclusions:

• The study demonstrates the ability of AFM to resolve distinct solvation layers in binary liquid mixtures.
• Substrate properties significantly influence the ordering and binding of confined liquid layers.
• Experimental findings align with molecular simulations but diverge from surface force apparatus results.