Water-repellency and surface free energy of a-C:H films prepared by heat-treatment of polymer precursor

Amorphous hydrogenated carbon (a-C:H) films with high water-repellency were prepared on Si substrates by a simple heat-treatment of the poly(phenylcarbyne) polymer at various temperature in Ar atmosphere. The contact-angle (CA) was measured by the sessile-drop technique. The use of CA for different liquid (water, ethylene glycol, and formamide) analysis for the evaluation of surface energy including the dispersion and polar components was described. The influences of surface roughness, chemical composition, and microstructure of carbon films on water CA and surface energy were investigated by atomic force microscopy (AFM), Fourier transforms infrared spectrometry (FTIR), and Raman spectroscopy, respectively. As the results, the a-C:H films exhibit good hydrophobicity and low surface free energy. The CA of a-C:H films slight increases and the surface free energy of a-C:H films reduces with the increase of the heat-treatment temperature. The a-C:H films are hydrophobic for not only pure water but also corrosive liquids, such as acidic and alkali solutions. The roughness of the films has no obvious effect on the CA and the reduction of surface energy with the increase of heat-treatment temperature is related to increase of sp2 content in the film.