Wettability of plasma-treated nanocrystalline diamond films

The wetting behavior of plasma-treated nanocrystalline diamond films is studied for biocoating applications. The films are prepared from Ar-rich/N2/CH4 and Ar-rich/H2/CH4 mixtures by microwave plasma-enhanced chemical vapor deposition, and further treated by microwave hydrogen and oxygen plasma exposures separately. The hydrogen plasma treatment increases the surface roughness only slightly without a perceptible change in surface morphology and composition, and shows little improvement in wettability. In contrast, the oxygen plasma treatment produces fine protrusions and increases the oxygen concentration near the surface to ~ 11 at.%, and then the contact angle of polar water and apolar 1-bromonaphthalene is drastically reduced from 92° and 4.7°–6.9° to almost zero degree, respectively. The extremely hydrophilic behavior of the oxygen-containing film is exclusively attributed to a great increase in the polar component of the apparent surface free energy up to ~ 34 mJ/m2.

► The wetting behavior of plasma-treated nanocrystalline diamond films is studied for biocoating applications.
► Both the as-deposited and hydrogen plasma treated films are hydrophobic.
► The oxygen plasma treated film is extremely hydrophilic such that the contact angle is reduced down to almost zero degree.