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.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Burnham and Colton analyzed the elastic properties of HOPG and gold [237]. Mate et al [238] use the same set-up to study the thickness of liquid polymeric films [239,240]. Moiseev et al [241] measure forces with an STM-detection AFM between an Al 2 O 3 tip and an Al 2 O 3 surface.…”

Roughness of thin perfluoropolyether lubricant films: influence on disk drive technology

“…While this intercept has several contributors, our results indicate that several nanometers come from the roughness of the lubricant-air interfaces. Second, force-vs.-distance curves measured by atomic force microscopy show that, when a sharp tip is brought into contact with lubricant, the tip experiences a meniscus force at a distance 3 to 5 nm larger than expected from the film thickness [5], due to lubricant transfer to the tip and lubricant-air interface roughness.…”

“…If this interaction comes mainly from van der Waals forces, then (3) where is the Hamaker constant [4]. For a 2 nm thick lubricant film, typical for today's disk drives, nm, using J [5] and mN/m. So, capillary waves on the surface of lubricant films in disk drives have very short wavelengths, ranging from 1 to 31 nm.…”

Forces and pressures in adsorbing partially directed walks

“…This loss of entropy induces a net force on the obstacle [24], and if the polymer can move freely, then it will tend to move away from the obstacle. The induced force is repulsive, and the polymer exerts an average net pressure on the wall.…”