A comparative study of the effect of different surface treatments on polymeric substrates

In this work, we investigated the effect of three surface treatments on the properties of polymethyl methacrylate (PMMA) and polycarbonate (PC). The treatments consisted of ultraviolet-ozone, sputter etching and oxygen plasma. Their effect on the adhesion between a vacuum deposited TiO2 coating and the substrate were also assessed by cross-cut test. Detailed characterization of the optical properties, surface wettability, morphology and the chemical composition of the surface after the treatments was performed for the test samples. Reference samples without any surface treatment were also used for comparison purposes. Optical transmittance of the samples was not significantly altered by the surface treatments. Only the presence of the coating led to an increase of the system refractive index and to a small decrease of the light transmittance. All surface treatments lead to an increase of oxygen species in polymer surface, which rise the wettability. In particular, the ultraviolet ozone treatment shows a higher change in the oxygen/carbon ratio, resulting however in the weakest adhesion between the coating and substrate, due to the generation of low molecular weight compounds weakly bonded to the surface. Furthermore, regardless of the surface treatment employed, the PMMA substrate presented lower film adhesion than PC.