Surface modification of poly(tetrafluoroethylene) films via plasma treatment and graft copolymerization of acrylic acid

For surface modification of poly(tetrafluoroethylene) (PTFE), a two-step procedure based on a low-pressure plasma treatment followed by acrylic acid (AAc) grafting copolymerization was used. The influences of AAc concentration and grafting temperature on the hydrophilicity of film surface were studied. The wettability of the PTFE membrane surface was characterized by water contact angle, and the surface microstructures and compositions of the AAc-modified PTFE film were characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Contact angle measurements revealed that the hydrophilicity of the PTFE film surface was greatly enhanced by the grafting of the AAc chains, and the surface contact angle decreased from 126° to 64.8° after 6-h grafting of AAc under the condition of 30% (v/v) AAc at 70°C. The PTFE surface with a low contact angle was very effective in immobilization of chitosan. The amount of chitosan covalently immobilized on the carboxylic acid group-grafted PTFE was 64.5 μg/cm2 membrane as determined with the ninhydrin method and the water contact angle further decreased with the immobilization of chitosan.