The Determination of the Location of Contact Electrification-Induced Discharge Events
Contact electrification - the transfer of charges from one object to another when brought into contact and separated - is ubiquitous and has been known for a very long time. Yet, there are still fundamental questions that are not fully understood, such as the role of friction in the transfer of charges. Contact electrification is associated with friction, and yet it is not known if friction is the mechanism for contact electrification or merely incidental to the pressures required to bring the two surfaces together. The authors reported a system of a steel sphere rolling in a circular path on a disc made of organic insulator. A rotating bar magnet drives the rolling of the steel sphere. As the steel sphere rolls around the organic insulator, it will pick up positive charges (ions) from the organic insulator and when the electric field due to the excess charges exceed the dielectric field breakdown, there will be a discharge of positive ions back to the insulator. By placing electrodes beneath the organic insulator, the authors were able to track and pinpoint the location of these discharge events. The authors were then able to study more closely the conditions for discharge events. The schematics of the set-up in shown below.
The electrodes are able to measure the amount of charge on the steel ball by measuring the amount of charge induced on the electrode which can then be measured using an electrometer. To be more accurate, the electrode actually measures the amount of charges on the sphere, Qs