Deformation and Non-uniform Charging of Toner Particles: Coupling of Electrostatic and Dispersive Adhesion Forces

Abstract

Both electrostatic and dispersive (van der Waals) forces contribute to particle adhesion, which has a significant effect on toner transfer in the electrophotographic process. Several approaches to adhesion measurements have yielded a large range of results for a variety of particle and environmental conditions. We present adhesion measurements taken in different environments using the metered air pulse method. They yield significantly different removal forces as a function of temperature for the same average particle charge. Particle deformation due to a combination of changes in particle stiffness with temperature and compressive electrostatic forces can predict the resulting adhesion increase. The morphology change is one of several factors which can contribute to the measured adhesion, which is significantly higher than values obtained by considering only the charged particle monopole and its image. Additionally, non-uniform charging in controlled adhesion experiments provides further muddling between the electrostatic and dispersive forces. This result is due to the electrostatic force having a component which is independent of the nominal charge under certain conditions. We find that the adhesion forces can be fully cubic with respect to the average particle charge, and that the components of the adhesion force may be much more difficult to decouple than previously thought.