THE CONTACT CHARGING OF PTFE BY MERCURY - THE EFFECT OF A THIOPHENE MONOLAYER ON CHARGE-EXCHANGE

Contact charge exchange measurements have been made on polytetrafluoroethylene (PTFE) films charged by repeated contacts to mercury. The authors have shown previously that charge accumulates with repeated contacts until the surface reaches saturation, and that the saturation potential is strongly affected by impurities in the mercury. In this study they show that molecularly thin adsorbate layers on the mercury surface play a dominant role in the charge exchange. They have demonstrated this effect by chemisorbing 3-methylthiophene onto the metal surface. Thiophenes are known to form stable, strongly adsorbed monolayers on the surface of mercury, and they find that these monolayers diminish the electron transfer from pure mercury to PTFE; in contrast, a 3-methylthiophene monolayer increases electron transfer from a sodium-doped mercury contact, suggesting that the monolayer displaces the tarnish layer from the impure metal surface. © 1990 IOP Publishing Ltd.