Studies in the Static Electrification of Filaments

Abstract

An apparatus has been constructed to rub filaments together under controlled mechanical and ambient conditions and to measure the charge remaining after separa tion. The apparatus is similar to that of Hersh and Montgomery, with refinements to ohtain better control of mechanical variables and to allow variation of ambient pressure. A photomultiplier has been added near the filaments to detect the incidence of electrical breakdown of the atmosphere. Many of Hersh's findings for 45°-45° rubs have been confirmed, specifically those on reproducibility and triboelectric series. On the other hand, some findings have not been substantiated when the range of vari ahles is extended. For nylon rubbed on polyethylene. the charge q shows a square-root dependence on the normal force F, in place of the linear dependence found by Hersh; the charge shows an inverse proportionality with diameter d, in contrast with the inde pendence noted by Hersh. For tantalum rubbed on nylon. the charge is found to depend on a combination of velocity v. conductivity σ, and presumably dielectric con stant . together with a characteristic distance l to be determined empirically. If the charge dependence on length of rub L is taken to he the proportionality found by Hersh. the combined relation is suggested, where the sign and the magnitude of c are in principle determined by the details of the band structure, but in practice are fixed experimentally. No detailed theoretical picture has been obtained to justify the rest of the expression, and it must be considered at present as an empirical relation whose generality and basis remain to be established.