Résumé
In this paper we report on a study of the composition and growth rate of anti scratch silica-like coatings deposited on polycarbonate (PC) in an atmospheric pressure dielectric barrier discharge using a low frequency (28 kHz) high voltage generator in the tetraethoxysilane/He/O-2 system. For the first time for this purpose the discharge was sustained between upper metal mesh and lower insulated solid electrodes and this reactor design had shown good results in uniformity of the scratch resistive films on plastic substrates. It has been shown that plasma pretreatment in pure helium leads to the 2.5-fold increase of PC surface energy in comparison to an untreated PC and provides a high adhesion of films deposited even at low deposition temperature (110 degrees C). Scratching experiments were carried out using standard test method for film hardness by pencil scratch test. The variations of coating hardness with the process parameters have been studied. It was found that despite some positive changes in the composition of the films, the introduction of oxygen had no significant improvement in the coatings' properties.