Polystyrene thin films treatment under DC pulsed discharges conditions in nitrogen

A systematic parameters study is performed in a DC pulsed glow discharge in nitrogen in order to improve the wettability of thin polystyrene layers. The experimental parameters considered are the pressure P, the interelectrode voltage V, the frequency nu of the pulsed power supply and the treatment time t(t). The wettability is characterized by the contact angle technic. The (Theta (i) - Theta (f))/Theta (i) = Delta Theta/Theta (i) ratio is measured, where Theta (i) and Theta (f) are respectively the initial and final contact angles. In the first part of the paper, the variations of Delta Theta/Theta (i) as a function of the electrical energy E are investigated, the variations of E being obtained by modifying the parameters V, nu and/or t(t). In the second part, the specific energy epsilon and the economical criterion gamma 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.