MEASURING CONTACT CHARGE-TRANSFER AT INTERFACES - A NEW EXPERIMENTAL-TECHNIQUE

A new experimental technique has been developed for measuring the amount of electric charge transferred when two dissimilar surfaces are brought into contact and separated without lateral motion in a controlled environment. The primary surfaces studied, silica and mica, are prepared with very low surface roughness (average roughness less than 0.5 nm); the macroscopic contact area, which can be measured directly, is therefore a better measure of microscopic contact area than is typically the case in contact electrification experiments, and the surface charge density can be more accurately determined. Observations reported include (1) the transfer of charge densities as high as 1 X 10(2) C/m2 after only a few contacts of a mica and silica surface in dry air or N2 gas at room temperature and (2) a reduction in transferred charge density in the silica-mica system as the relative humidity of the air in the environmental chamber is increased from 0% to 98%. The technique also permits the study of the rate at which the surface charge decays under various environmental conditions.