Session M24 - Tribology: Scanning Probes and Particle Adhesion.
MIXED session, Thursday morning, March 21
Room 120, America's Center

[M24.09] Electrostatic and van der Waals Interaction Forces Between Micron-size Spheres and Flat Substrates

B. Gady, R. Reifenberger (Purdue University), D.S. Rimai, L.P. Demejo (Eastman Kodak Co.)

The interaction force gradient between a micron-size polystyrene sphere and an atomically flat highly oriented pyrolytic graphite substrate has been analyzed as a function of surface-to-surface separation distance z_o using both an oscillating cantilever technique and a direct cantilever deflection technique. The interaction force was found to have two contributions. For z_o \geq 30 nm, an electrostatic force from charges triboelectrically produced and trapped on the polystyrene sphere dominates. For z_o \leq 30 nm, a van der Waals interaction, characteristic of a sphere near a flat plane, dominates. Fits to the data are in good agreement with theoretical expectations and allow quantitative estimates of the surface charge density triboelectrically produced on the sphere's surface.