Polarity reversal in streaming electrification measurements

In the paper measurements of streaming electrification current in the range of low velocities are presented. The measurements were conducted in spinning disk system that uses wireless rotating electrometer. Using this system it is possible to measure electrification current in the range of several picoamperes. In proposed configuration the electrometer is installed in measurement object on the disk axle. The digital output is transferred using Bluetooth radio-frequency transceiver. This solution minimizes external disturbances and allows for measurement with standard uncertainty at the level of 30 fA depending on averaging time. The uncertainty slightly depends on spinning velocity. Several dependencies of averaged electrification current on rotational speed were shown. A fresh and C₆₀ fullerene doped transformer oil were used as an electrification source. It was observed that the electrification current can change its sign for different C₆₀ concentrations. Doping mineral oil leads to charge reversal in the electric double layer. The system presented in paper extends the range of possible research in the field of electrification on low velocities and can be useful in development of streaming electrification phenomena.