Molecular conformation and disjoining pressure of polymeric liquid films

Abstract

Atomic force microscopy, angle resolved x-ray photoelectron spectroscopy, and ellipsometry are applied to study the conformation of fluorocarbon polymers in molecularly thin liquid films, 5–130 Å thick, on solid surfaces. The combination of these techniques shows that the physisorbed polymers at the solid surface have an extended, flat conformation. In addition, the disjoining pressure of these liquid films is determined from atomic force microscopy measurements of the distance needed to break the liquid meniscus that forms between solid surface and force microscope tip. For a monolayer thickness of ∼7 Å, the disjoining pressure is ∼5 MPa, indicating strong attractive interaction between the polymer molecules and the solid surface. The disjoining pressure decreases with increasing film thickness in a manner consistent with a strong attractive van der Waals interaction between the liquid molecules and the solid surface.