Solvation forces in branched molecular liquids.

The solvation force of squalane confined between a silicon tip and a graphite surface has been measured by atomic force microscopy. This highly branched molecule shows oscillatory force profiles similar to those of spherical and linear chain molecules. Squalane molecules closest to the substrate are tightly bound and finer details imply that interdigitation occurs. This agrees with computer simulations for branched molecules but differs qualitatively from force balance experiments. These differences arise from the smaller confinement area and the different chemical nature of the surfaces.