Effects of Electrostatic and van der Waals Interactions on the Adhesion of Spherical 7 µm Particles

ABSTRACT

The force needed to detach spherical particles having a number average diameter of 7.1 μm from a polymeric, photoconducting substrate was determined by ultracentrifugation. In the absence of any release agents applied to the substrate, it was found that only a small fraction of the particles could be removed from the substrate even at the highest centripetal accelerations (354,000 g). However, when the substrate was coated with a thin layer of a release aid (zinc stearate), the force needed to separate the particles from the substrate was greatly reduced, thereby allowing the detachment force to be determined. Under these conditions, it was found that the release force varied with the square of the particle charge-to-mass ratio. Moreover, it was also found by extrapolation that the detachment force at zero charge, corresponding to the residual van der Waals interactions, was finite. These results suggest that both van der Waals and electrostatic interactions affect the adhesion of particles and, for micrometer-sized particles, electrostatic forces can become dominant under some circumstances. Conversely, the large increase in the adhesion of the particles to the substrate, in the absence of a good release agent, suggests that van der Waals forces would often dominate adhesive interactions of particles in this size range.