The glow and no glow zone effect on surface wettability modified in O2 or hexamethyldisilazane cold plasma treatment

Small cold plasma zone treatment is an important modification technique in modern industry. In this study, the effect of gas flow direction on plasma treatment was investigated. In order to decrease the plasma zone area, we added a separate cylinder to surround the upper electrode. Separate cylinder is effective to limit plasma discharge area, and we could find a light and dark area in the vacuum chamber. After O2 plasma treatment, the result shows that only PP non-woven in the discharge area became hydrophilic, but other position away from the plasma zone was not affected. The water adsorption of PP non-woven increased from 34.8% to 537.4%. When sample is more far from the plasma zone, near the up stream of gas flow, the surface property is less hydrophilic. Water contact angle analysis of PS and glass shows the same results as those of PP non-woven. But PET in plasma zone or dark zone (plasma zone: 75–31°, dark zone: 75–52°) both shows hydrophilic property. The wettability effect in dark zone may be due to the UV-light irradiation in the process of plasma excitation.