Measurement of adhesion force due to condensed water vapor in a crossed-fiber system.

Abstract

Little agreement exists in the scientific literature concerning the adhesion force between "small" particles, ranging in size from molecular clusters to 100 microns in diameter. Measured adhesion forces are affected by the very process by which particles come into contact, the environmental history of their time in contact, and the method of their removal. We built two instruments to perform repeated identical adhesion measurements between crossed quartz fiber pairs in a controlled environment. We find that multiple discrete values of adhesion force can occur for identical pull-off conditions and that the force as a function of relative humidity can be double-valued depending on whether relative humidity is increasing or decreasing. Our work shows that atmospheric water vapor greatly influences the adhesion force, both by condensing to form a liquid meniscus in the contact region between the particles, and by being adsorbed onto the quartz surfaces. Our adhesion force measurements are compared to predictions of adhesion force based on surface deformation theory and exact meniscus theory. In addition, our measured thickness of an adsorbed layer of water on a 0.6520 micron radius quartz fiber, using light-scattering techniques, differs from the adsorbed water layer thickness on a planar surface.