Discrete solvation layering in confined binary liquids.
The solvation force profiles of squalane/octamethylcyclotetrasiloxane (OMCTS) mixtures confined between Si3N4 tips and highly oriented pyrolytic graphite (HOPG) and hexadecane/OMCTS confined between alkanethiol-functionalized tips and freshly cleaved mica have been measured by atomic force microscopy. Measurements on HOPG reveal oscillatory behavior where discrete solvation layers of both squalane and OMCTS are observed in a single force curve. The large repulsive force of the first solvation layer (squalane) on HOPG indicates that it is strongly bound. Oscillatory behavior is also observed for hexadecane/OMCTS on mica excepting that the oscillations are found in the attractive regime. The OMCTS layers in this case are less ordered with slightly larger (approximately 1 A) periodicities. These results are in agreement with computer simulations for binary liquid mixtures but differ qualitatively from surface force apparatus experiments.
Lim
R Y H
RY
Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602.
O'Shea
S J
SJ