Thermodynamic Studies of PEG (Mw 20,000) Adsorption onto a Polycrystalline Gold Electrode

Abstract

Cyclic voltammetry, differential capacity, and chronocoulometry were employed in a quantitative study of polyethylene glycol (Mw 20000) (PEG20000) adsorption onto a polycrystalline Au substrate. The surface tension, film pressure, relative Gibbs surface excess, and the Gibbs energy of adsorption were determined as a function of the electrode potential. The results indicated that, in the potential interval studied (−0.9 to 0.35 V vs saturated calomel electrode), PEG20000 adsorbed onto the polycrystalline Au surface via its oxygen atoms as a flat submonolayer of rodlike molecules. The adsorbed mass increased considerably with the increasing PEG20000 concentration and more positive potential. In addition, the surface tension decreased as the quantity of PEG20000 adsorbed on the surface rose with the increasing PEG20000 concentration, an effect characteristic of surface active agents. The maximum surface concentration was found to be 4.59 × 10−10 moloxygen cm−2 for the highest PEG20000 concentration studied (100 μM). The Gibbs energy of adsorption (ΔGads) was determined using the Henry adsorption isotherm. On the basis of the ΔGads values obtained, it was concluded that the PEG20000 molecules were weakly chemisorbed on the polycrystalline Au surface.