Partial Air Wetting on Solvophobic Surfaces in Polar Liquids

The properties of solvophobic surfaces in polar liquids are studied by sedimentation experiments as well as by force measurements using a scanning force microscope (SFM). Depending on whether the polar liquid contacts the solvophobic surface under normal air pressure or under vacuum the experimental results are different. Sedimentation velocities of vacuum-contacted solvophobic surfaces are similar to those of solvophilic vacuum- or air-contacted ones. However, for the air-contacted solvophobic surfaces there is a slip boundary condition of the hydrodynamic flow causing a change of the sedimentation velocity of about 20%, and a long-range attraction varying with the polarity of the liquid molecule is observed between them. These effects can be explained by an incomplete air dewetting of the solvophobic surface when brought into contact with the polar liquid at normal air pressure. Copyright 1999 Academic Press.