Stability of atmospheric-pressure plasma induced changes on polycarbonate surfaces

Polycarbonate films are subjected to plasma treatment in a number of applications such as improving adhesion between polycarbonate and silicon alloy in protective and optical coatings. The surfaces that undergo changes in surface properties due to plasma treatment have a tendency to revert back to their original states. Thus, the stability of the plasma induced changes on polymer surfaces over a desired time period is an important issue. The objective of this study was to examine the effect of ageing on atmospheric-pressure helium-plasma treated polycarbonate (PC) sample as a function of treatment time. The ageing effects were studied over a period of 10 days. The samples were plasma treated for 0.5, 2, 5 and 10 min. Contact angle made by water droplet on polymer surfaces were measured to study surface energy changes. Modification of surface chemical structure was examined using X-ray photoelectron spectroscopy (XPS). Contact angle decreased from 93° for untreated samples to 30° for samples treated with plasma for 10 min. After 10 days the contact angle for the 10 min plasma treated sample increased to 67°, but it never reverted back to that of the untreated surface. Similarly, the oxygen-carbon (O:C) ratio increased from 0.136 for untreated samples to 0.321 for 10 min plasma-treated samples, indicating an increase in surface energy.