ADHESION AND SOLVATION FORCES BETWEEN SURFACES IN LIQUIDS STUDIED BY VAPOR-PHASE EXPERIMENTS

We show how solvation forces in liquids can be measured hy studying the interaction of surfaces in vapor. This is a convenient method of obtaining information on the inner part of the solvation force, where the surfaces are separated by only a few molecular layers. In particular, the pull-off force between mica surfaces in contact in liquids may be determined easily and accurately this way. Results presented for octamethylcyclotetrasiloxane (OMCTS), cyclohexane, and n-pentane are largely in agreement with published data obtained by measurements in the liquid phase. Contrary to earlier results, the pull-off force (contact adhesion) is much larger than expected from extrapolation down to contact of the minima of the solvation force. The large values (up to 100 mJ m-2) of the adhesion in nonpolar liquids illustrate how misleading it can be to use the Lifshitz theory to predict the contact adhesion of a polar solid.