Contact electrification between mercury and polyethylene: Effect of surface oxidation

The contact electrification between mercury and polyethylene films has been measured under a variety of conditions. For freshly prepared films, the mercury contact charging of polyethylene is low, ≈1 nC/cm2. For films exposed to the laboratory air for a few hours, the contact charging increases to ≈20 nC/cm2. A brief exposure of the polyethylene to air near a corona, or ozone from a generator, also increases the contact charging. The infrared spectra of unsaturated polyethylene crystals display the formation of ozonides when the crystals are exposed to ozone or the laboratory air. Since there is a strong correlation between the appearance of ozonides and an increase in contact charging, we believe that a definite charge exchange site on polymers has been identified for the first time. To substantiate our observation, we find that ozonization of saturated polyethylene does not significantly increase the contact charge exchange. Analogous results have been obtained for lower molecular weight hydrocarbons. The experimental results are discussed in terms of a model involving polymer surface states.