Surface adsorption and wetting properties of amorphous diamond-like carbon thin films for biomedical applications

Diamond-like carbon (DLC) thin films have unique properties for biological and medical applications due to their excellent bio-compatibility, chemical inertness, and superior mechanical properties. It is important to understand the surface properties of DLC thin films for these applications. In this work, we showed that after DLC deposition, NiTi surfaces became much smoother by choosing suitable deposition conditions. Adsorption and wetting properties of DLC films were studied. The adsorption properties of DLC films were unusual in that a hysteresis was found in the adsorption/desorption isotherms, which cannot be interpreted using the conventional theory of capillary condensation in pores. The model proposed in this work for this unusual hysteresis characteristic is that the hysteresis results from the non-wetting property of DLC surfaces in the nano-scale. The nano-sized droplets formed on the DLC surfaces may require significantly higher energy to evaporate than the formation energy. Argon plasma treatment resulted in a small decrease of the contact angles. After oxygen plasma treatment, the wetting contact angles reduced significantly due to the increase of carbon-oxygen sites on the surfaces, suggesting that the low concentration of carbon-oxygen sites on the surfaces of DLC films contributed to the adsorption hysteresis observed in this work.