The force needed to remove the particles from a bare substrate was found to exceed 800 nN. Using JKR theory, the detachment force was estimated to be approximately 1100 nN for this case. In contrast, upon application of a thin layer of zinc stearate onto the substrate, the van der Waals forces were reduced to approximately 100 nN. The detachment force was then found to vary as the square of the particle charge. For an isolated particle of this size with a charge-to-mass ratio of about 36 μC/g, the electrostatic contribution was estimated to be approximately 80 nN. The calculated value, however, is estimated to approximately double if one includes the image charges associated with two adjacent particles found in the observed pearl-chain-like structures of the randomly-deposited particles. Unless the van der Waals forces are deliberately and significantly reduced through the use of release agents such as zinc stearate, they appear to be the dominant interactions controlling the adhesion of this size particle, with electrostatic contributions being at least an order of magnitude smaller. However, by using suitable release agents, the van der Waals forces can be reduced to the point where they account for less than half of the particle adhesion, depending upon the charge of the particles.
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