Effect of Electron Density and Temperature in Oxygen Plasma Treatment of Polystyrene Surface

A plasma treatment of polymeric materials has become one of the most important methods to enhance the surface wettability without affecting the bulk material features. Oxygen plasma treatment of polystyrene surfaces deposited on a QCM sensor was evaluated by relating the plasma parameters, surface roughness, and the wettability. The internal plasma parameters investigated in this work were the electron temperature (T_e ) and the electron density (n_e ). The oxygen plasma was generated using an RF power generator. The power was varied by applying a voltage from 60 volts to 100 volts. An Optical Emission Spectroscopy (OES) was used to determine the plasma species, the T_e and the n_e during the plasma oxygen process. The dominant species in the plasma was excited atomic oxygen or activated oxygen (OI) which was detected from the 774 nm and 842 nm emissions. The higher applied RF voltage resulted in the higher T_e and n_e . The effect of the T_e and n_e on the polystyrene surface was observed on the change of the surface roughness. The surface roughness significantly related to the surface wettability observed with a contact angle measurement. Furthermore, the plasma treatment greatly changed the surface from hydrophobic to hydrophilic via reactive processes by the excited atomic oxygen species. This was confirmed by the increase in C = C and C = O functional groups observed using a Fourier transform infrared (FTIR) spectroscopy. The T_e and n_e may also affected the character of the plasma in terms of its reactivity.