Contact Electrification
Dynamics of contact electrification
Contact electrification and triboelectricity are ubiquitous phenomena which are well known in daily life, e.g. encountering an electric shock when touching a door handle. However, the detailed processes are still not yet fully understood.
In our group we have developed a new experimental technique which enables us to study in great detail the charge transfer occurring when two objects come into contact. It relies on new electronic charge amplifiers that measure very small charges on a time scale of microseconds. To study the contact electrification a ball with a diameter of 1 millimeter is dropped onto a plate from a height of a few centimeters, so that it bounced several times. By measuring the charge induced in the plate it can be analyzed how the charge changes each time that it comes into contact with the surface.
The photo shows the inner part of the experimental setup. The wheel at the left side is used to transport the sphere to the upper level. A ball track which is not visible guides the spheres to the entrance hole of the upper plate of the parallel plate capacitor. The lower plate is connected to a charge sensitive amplifier measuring the induced charge.
The video displays in slow motion how the charge (red line) measured at the lower plate evolves in time. The blue line shows the corresponding height which can be deduced from the data. Between successive contacts the ratio between the two signals is given by the charge on the sphere (and a constant factor given by the geometry).
Article published in Sciences Advances in May 2021: Dynamics of contact electrification Mirco Kaponig, Andre Mölleken, Hermann Nienhaus und Rolf Möller
Talk presented at the annual meeting of the Electrostatics Society of America June 14-16, 2021:
Article in physicsworld in June 2021: Contact electrification explained at last