Effect of temperature on the surface free energy of amorphous carbon films

Diamond-like carbon (DLC) and tetrahedral amorphous carbon (ta-C) have attracted much attention recently for biomedical and antifouling applications due to their excellent biocompatibility and nonstick properties. It has been demonstrated that the solid surface free energy is a dominant factor in cellular or fouling adhesion. However, few data for surface free energy of DLC and ta-C coatings at temperatures in the range 37–95 °C are available. In this study DLC and ta-C coatings on stainless steel 304 sheets were prepared using an unbalanced sputtering system and a filtered cathodic vacuum arc respectively. The contact angles of water, diiodomethane and ethylene glycol on the coated surfaces at temperatures in the range 20–95 °C were measured using a Dataphysics OCA-20 contact angle analyzer. The surface free energy of the coatings and their components (e.g dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the total surface free energy and dispersive surface free energy of the ta-C coatings, DLC coatings, stainless steel 304 and titanium decreased with increasing temperature, while the acid–base SFE component increased with increasing temperature.