Elliott A. Eklund

Small particle adhesion: measurement and control

Abstract A number of technologies, including electrophotographic printing, require an understanding of particle–surface adhesion forces. At Xerox, we have developed and applied new techniques in order to understand the dependence of particle adhesion on physical properties, such as particle charge, shape and surface roughness. Atomic force microscopy and computer modeling were used to investigate the effects of surface roughness, external additives and applied electric fields on the adhesion of single particles. Centrifugal detachment was used to measure the adhesion force distribution of several hundred particles simultaneously and to determine its sensitivity to particle charge and size. Electric field detachment has enabled rapid characterizations of the adhesion of particle layers, providing insight into the roles of particle–surface contact area and nonuniform particle charging on the adhesion of ensembles of particles. The addition of digital photography to the detachment techniques has allowed in-situ visualization of particle detachment, enabling us to probe interparticle effects on adhesion.

Electric field detachment of a nonuniformly charged dielectric sphere on a dielectric coated electrode

Abstract In the electrophotographic process, charged toner particles are transferred from one surface to another with an electric field. To enable electric field transfer of toner, the externally applied field strength must be greater than a threshold value so that the Coulomb force can overcome the toner adhesion force at the residing surface. Toner particles in electrophotography are often charged by the phenomenon of triboelectricity. Triboelectrically charged particles tend to have nonuniform surface charge distributions which may significantly influence the electrostatic adhesion force and threshold field strength for detachment. In this work, the threshold detachment field strength and the electrostatic adhesion force associated with a nonuniformly charged dielectric sphere are determined efficiently by using the Galerkin finite element method to simultaneously solve the Laplace equation for the field distribution and an overall constraint equation for the force balance. Problems with various complicated geometric configurations can be treated within this computational framework. For illustrative purposes, however, we consider the axisymmetric problem of electric field detachment of a charged sphere on a dielectric coated donor electrode. Our analysis is particularly focused on the effects of a nonuniform charge distribution expressed in terms of Legendre functions on the spherical particle surface. The electrostatic adhesion force appears to vary linearly with the coefficient for each Legendre function. Depending on the orientation of the particle relative to the residing surface, the nonuniformity in the particle surface charge distribution may either enhance or reduce the electrostatic adhesion force.