Measurement of interaction forces between micrometer-sized particles and flat surfaces using an atomic force microscope
Abstract
The Atomic Force Microscope is used to directly measure the interaction forces between micrometer-sized spheres and atomicaily flat substrates. In particular, the interaction between micrometer-sized polystyrene spheres and highly oriented pyrolytic graphite is measured. The study provides important information about the relative contributions to the net interaction due to both van der Waals and electrostatic forces. The two techniques used are unique to scanning force microscopy. One method, referred to as the static mode of operation, is used to directly measure the interaction force as a function of surface to surface separation. The second method, referred to as the dynamic mode of operation, provides information about the force gradient. The information provided by these two methods is found to be consistent. The variation of the interaction force with the surface-to-surface separation between the sphere and plane is determined using both a static and a dynamic atomic force technique. The measured interactions is dominated at long-range by an electrostatic force arising from localized charges triboelectrically produced on the sphere when it makes contact with the substrate. For small sphere-substrate separations, evidence for a van der Waals contribution to the interaction is observed. The data provide consistent estimates for both the Hamaker coefficient and the triboelectrically produced charge which can be measured to an accuracy of $\pm$10 electron charges.
Degree
Ph.D.
Advisors
Reifenberger, Purdue University.
Subject Area
Condensation
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