(153b) Measurement of Force Curve Due to Electrostatic Charge on a Particle with Atomic Force Microscope

At present there are still a lot of uncertain points on the generation of the electrostatic charge on powder particles. Because the powder is a group of the particle, the analysis of electrification phenomenon should consider various factors. Then a single particle was paid to attention in this research to simplify the analysis. However, because the measurement of the charge on a single particle is not easy with conventional direct electrical method (Faraday cage) in this study, it was tried to measure force curves working on a particle due to electrostatic charge with atomic force microscopy (AFM). We used JSPM-4210 as an AFM and measured a force curve working on a single particle fixed on the tip of the cantilever by epoxy adhesive. Well-finished plates of 8 kinds of metal were used as a contacting target. Obtained force curve was evaluated by disk-to-disk charge interaction model. In this model it was assumed that the charge generated on the surface of a particle is localized only in the small contact area. The electrostatic interaction force was approximately calculated by considering the contact area to be a disk. As results, the fitted curves showed good agreements with the data. As for this, it was confirmed that the measured force curves were due to electrostatic interaction. In the measurement using 8 kinds of metal as contacting targets, the data of the estimated charge density scattered. However, all the estimated charge density were in the order of 10^-2-10^-1C/m², which is considerably bigger than that of 10^-4C/m² obtained in the impact charging experiments in our previous works. Additionally, a strong relationship between contact area and charge density was found. Now we are measuring the force curves under vacuum to obtain more findings of the cause of the current result.