Polyimides were treated to generate hydrophilic surfaces using an atmospheric pressure O-2-Ar mixed gas plasma. Treatments were carried out in the upstream region of the plasma with the aim of achieving high speed processing without altering the characteristic properties of samples due to high temperatures. Various parameters of the generated plasma were assessed to better understand the processing environment. Using these plasma parameters, the axial variations of constituent species in the plasma were calculated so as to determine the optimum sample position. Moreover, the absolute value of the oxygen atom number density, which is thought to play an important role in the surface treatment, was measured using a heated platinum catalytic probe. Experimental results were used to determine the relationship between the water contact angle on treated surfaces and the oxygen atom fluence and the data were in good agreement with the hydrophilic characteristics obtained during our previous research using surface wave plasma. The effect of oxygen atoms during hydrophilic treatment using an atmospheric pressure microwave-excited plasma source was thus elucidated and high speed surface treatment was demonstrated.
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