Thermal Stability Of Superhydrophilic Carbon Films

Plasma polymerisation in atmospheric pressure is an emerging method of creating highly hydrophilic surfaces, with water contact angles below 10 degrees. Unlike low-pressure plasma polymerisation, it is cheaper, faster and can be done inline, but requires larger amounts of precursor. Unlike plasma activation, the increase of wettability does not show an aging effect. In our experiments, we deposited hydrocarbon films from low concentration propane-butane in nitrogen plasma at atmospheric pressure on c-Si 2 cm x 3 cm large, 0.6 mm thick substrates from distance 0.1 mm. We used three different concentrations of propane-butane. Using thermal desorption spectroscopy, we have systematically analysed the thermal stability of all these films. The samples were slowly heated in high vacuum at constant speed to various temperatures, up to 1000 degrees C. Thermally desorbed gases from the sample were analysed using a mass spectrometer. The dependences of partial pressures on particle mass and temperature were rendered into colour maps. We have found that reactions begun to occur at temperatures about 100 degrees C, releasing hydrocarbon gases. Contact angle measurements have shown that the hydrocarbon films progressively lost their hydrophilic effect in temperatures from 100 degrees C to 300 degrees C. At temperatures around 850 degrees C, a strong reaction occurs, leading to a massive release of hydrocarbon gases, but the film itself remains on the substrate. Samples before and after annealing were analysed by means of common laboratory tests.