Plasma treatment of poly(dimethylsiloxane) surfaces using a compact atmospheric pressure dielectric barrier discharge device for adhesion improvement

Results of the treatment of poly(dimethylsiloxane) (PDMS) surfaces using novel atmospheric pressure pulsed dielectric barrier discharge plasmas are presented. Different gases (argon, helium, nitrogen) as well as their mixtures with water vapor were compared in terms of the improvement of adhesion between two PDMS samples after processing by plasma. The plasma was characterized by optical emission spectroscopy to identify the emitting species and determine the plasma temperatures. For all the gases studied, plasma processing resulted in increase of adhesion between PDMS samples if long exposure time (larger than 150 s) is applied. However, for very short treatment times (20 plasma pulses, total processing time about 3 s) the highest efficiency was found for helium plasmas. Water contact angles at PDMS surfaces as function of plasma processing time was analyzed. Atomic force microscopy analysis was performed to show reduction in the surface roughness after plasma treatment, which is likely to be the responsible for increase of the surface contact area and thus the adhesion between two PDMS surfaces. The role of the two mechanisms in the improvement of adhesion (enhanced wettability and changes in the surface morphology), for different time scales, is discussed. Interestingly, for the minimum processing time (20 plasma pulses), the improvement in adhesion and reduction of surface roughness are observed although the changes in the water contact angle are insignificant. (C) 2016 The Japan Society of Applied Physics