Plasma polymerized films of carbocyclic compounds such as C6H12, C6H6, C6H5CH3, C6H5NH2, C3H5Cl, and C6H5OH were deposited on expanded graphite sheets and film durability was investigated by measuring cathodic polarization curves in aerated NaCl solution. The polymer film-coated sheets were employed as the working electrode. The films of hydrocarbons having a highly crosslinked structure (C6H12, C6H6, and C6H5CH3) inhibited cathodic reactions, and in these cases the main reaction is thought be oxygen reduction: H2O+1/2O2+2e-=2OH-. But in the other compounds studied, little inhibition occurred. In the hydrocarbons, cathodic activity was related to the O1s/C1s ratio obtained by X-ray photoelectron spectroscopy (XPS) and to the surface potential (SP) measured by a conventional vibrating electrode method. The cathodic reaction activity of the films decreased as the oxygen content decreased and as the surface potential decreased. It is suggested that the chemical and electrical nature of the hydrocarbon films plays an important role in cathodic reaction activity. Anodic polarization was also carried out for the C6H12 and C5H5OH films. The trend in the inhibiting effect was similar to that for cathodic polarization.
