INFLUENCE OF GAS-PRESSURE ON THE PLASMA REACTION ON POLYETHERSULFONE

Different gases (Ar, H-2, N-2 and O-2) were used for plasma treatments of polyethersulphone (PES) performed in an electron cyclotron resonan ce (ECR) plasma. The effect of the gas pressure on the chemical modifi cation of the PES surface during plasma treatment was investigated by X-ray photoelectron spectroscopy (XPS). The experimental set-up of the plasma chamber connected via an ultra high vacuum transfer to a surfa ce analysis system allows to measure well-defined surface modification s. The experiments have shown that the plasma-polymer interaction in t he topmost surface region of the polymer increase with decreasing gas pressure. At low gas pressures (p < 10(-3) mbar) the plasma attacks fi rst the polar bonds of the sulphonic group, this results in the reduct ion to sulphide of all sulphonic groups (-SO2- --> -S-) in the study s tate. This effect decreases progressively for higher gas pressures(p > 10(-3) mbar) and is no more observable at p = 10(-1) mbar. In additio n to the amount of sulfide formation also the time scale of sulfide fo rmation varies with the gas pressure. The time constant for the sulfid e formation change from tenth of seconds to about one minute for 10(-4 ) to 10(-2) mbar gas pressure, respectively. The thickness of the surf ace layer in which sulphide is formed depends on the pressure and is a t least equal to the XPS probing depth of about 100 Angstrom for p < 1 0(-3) mbar. The incorporation of new chemical functionalities by react ive gas plasma treatments is similar for all gas pressures. Difference s were observed in the amount of adsorbed species at the top most surf ace layer. The higher the gas pressure is, the higher the content of a dsorbed species. The results are discussed in function of the flux phi (i), and the kinetic energy E(kin) of the ions interacting with the po lymer surface.