Plasma and chromic acid treatments of polycarbonate surface to improve coating–substrate adhesion

The influence of Ar/O₂ plasma activation and chromic acid etching of polycarbonate (PC) surface on the adhesion of coating to substrate was systematically studied by cross‐cut and tape peel methods through temperature‐shock aging tests. The differences between the wettabilities and elemental compositions of plasma‐treated and chromic acid‐treated PC surfaces prior to coating deposition were evaluated by contact angle measurements and X‐ray photoelectron spectroscopy. To elucidate the adhesion failure of the coatings, nanoindentation technique was employed for the quantitative assessment of the nanomechanical changes of coating depositions on PCs after temperature‐shock aging tests. The two surface treatments can significantly improve the hydrophilicity and polarity of the PC surface, resulting in excellent adhesion of the coating on the PC substrate. Temperature‐shock aging tests reveal that the adhesion of coating on plasma‐modified substrates is superior to that of chromic acid‐etched substrates. We propose that the improved adhesion of the coating on the plasma‐modified PC can be attributed to the higher wettability and more cross‐linking of C–O–Si bonds at the coating–substrate interface. Copyright © 2013 John Wiley & Sons, Ltd.