Polystyrene thin films treatment under DC pulsed discharges conditions in oxygen

Abstract

A systematic parameters study is performed in a DC pulsed glow discharge in oxygen in order to improve the wettability of thin polystyrene layers. The experimental parameters considered are the pressure P, the gas flow rate Q, the interelectrode voltage V, the frequency ν of the pulsed power supply and the treatment time t_t. The wettability is characterized by the contact angle technic and evaluated by the determination of the $\Delta\Theta/\Theta_{\rm i}= (\Theta_{\rm i}-\Theta_{\rm f})/\Theta_{\rm i}$ ratio ($\Theta_{\rm i}$ and $\Theta_{\rm f}$ are respectively the initial and final contact angles). In the first part of the paper, the relative contact angle variations $\Delta\Theta/\Theta_{\rm i}$ as a function of the treatment duration time t_t are investigated. In the second part, the specific energy ε and the economical criterion γ are introduced to deduce the best running conditions through a chemical engineering approach. Taking into account the weak duty factor of the power supply (1% ), it is shown that the polymer surface is treated with a minimum of energy. Finally, it is deduced that the duration time necessary to reach the same $\Delta\Theta/\Theta_{\rm i}$ value is shorter for an oxygen plasma than for a nitrogen plasma.