Electrochemical properties of polypropylene membranes modified by the plasma polymerization coating of SO₂/acetylene

Polypropylene membranes were modified by the plasma etching of SO 2 , SO 2 O 2 , or SO 2 H 2 O, followed by the plasma polymerization coating of SO 2 /acetylene. The conditions for SO 2 plasma etching were optimized by the measurement of the ion‐exchange capacity (IEC) as a function of the plasma‐etching power (10–30 W), gas pressure (40–60 mTorr), and treatment time (15–120 s). For the plasma etching of SO 2 O 2 and SO 2 H 2 O, only the pressure ratio (SO 2 /O 2 and SO 2 /H 2 O) was optimized under the optimized conditions determined from SO 2 plasma etching. Plasma etching was then combined with the plasma polymerization coating of SO 2 /acetylene, for which the conditions were again optimized by the measurement of the IEC as a function of the plasma power (10–40 W), chamber pressure (50–200 mTorr), SO 2 /acetylene ratio (15/135–60/90), and treatment time (0–10 min). Next, the electrical resistance and water uptake were evaluated. The modified membranes were also analyzed with scanning electron microscopy, whereas plasma polymer coatings were characterized with Fourier transform infrared/attenuated total reflection.