Contact potential-difference studies of adsorption of polar vapors on metal and polymer surfaces

Abstract

Contact potential difference changes have been measured, at various water and ethanol vapor pressures, between the following electrode pairs: (a) gold vs. nickel; (b) gold vs. Teflon-coated nickel; (c) Teflon-coated gold vs. nickel; (d) Teflon-coated gold vs. Teflon-coated nickel. The results indicate that the contact potential difference changes from pairs (b) and (c) can be identified with the surface potential changes of the gold and nickel electrodes respectively, and that Teflon-coated electrodes are satisfactory reference electrodes in the study of surface potential changes caused by the adsorption of these gases. For nickel, the surface potential changes are not completely reversible with respect to gas pressure, the hysteresis being of the type associated with irreversible chemical combination between the adsorbed molecules and the metal surface. The gold surface potential changes also exhibit hysteresis but of a type better described in terms of two interconvertible surface states. The two states are postulated as a monolayer and multilayer of adsorbed molecules. The adsorption of water and ethanol on both gold and nickel increases the surface potential (decreases the work function) of both metals.