Modification of polysulfone membranes: 3. Effect of nitrogen plasma

The paper considers properties of porous membranes modified by action of nitrogen plasma. The membrane material was polysulfone — the polymer most frequently used in production of ultrafiltration membranes. It is shown that 2.45 GHz nitrogen plasma generates various kinds of surface functionalities both of acidic and basic character. The surface changes during the first week after plasma treatment, some groups disappear some others are shifted towards surface. In consequence, surface hydrophilicity gained during plasma treatment decreases but does not disappears completely. It is shown that modified ultrafiltration membranes are less prone to protein fouling than their untreated analogues. This protection is extended on a wide range of retentate pH-values. Plasma action alters also morphology of membranes. During first 2 min of action, polymer ablation seems to dominate. Pore diameter becomes larger and pores size distribution wider. Longer exposition to plasma does not affect pores any more — the rates of ablation and deposition seem to be balanced.