Surface analysis of poly(ethylene naphthalate) (PEN) films treated at atmospheric pressure using diffuse coplanar surface barrier discharge in air and in nitrogen

Changes in Surface Characteristics of BOPP Foil after Treatment by Ambient Air Plasma Generated by Coplanar and Volume Dielectric Barrier Discharge

Biaxially oriented polypropylene (BOPP) is a highly transparent polymer defined by excellent mechanical and barrier properties applicable in the food packaging industry. However, its low surface free energy restricts its use in many industrial processes and needs to be improved. The presented study modifies a BOPP surface using two different atmospheric-pressure plasma sources operating in ambient air and capable of inline processing. The volume dielectric barrier discharge (VDBD) and diffuse coplanar surface barrier discharge (DCSBD) were applied to improve the wettability and adhesion of the 1-10 s treated surface. The changes in morphology and surface chemistry were analyzed by SEM, AFM, WCA/SFE, and XPS, and adhesion was evaluated by a peel force test. Comparing both plasma sources revealed their similar effect on surface wettability and incorporation of polar functional groups. Additionally, higher surface roughness in the case of VDBD treatment contributed to slightly more efficient adhesion in comparison to DCSBD. Although we achieved comparable results for both plasma sources in the term of enhanced surface wettability, degree of oxidation, and stability of induced changes, DCSBD had less effect on the surface deterioration than VDBD, where surface structuring caused an undesirable haze.

Plasma Treatment of Thermally Modified and Unmodified Norway Spruce Wood by Diffuse Coplanar Surface Barrier Discharge

This work deals with the treatment of wood surfaces by diffuse coplanar surface barrier discharge (DCSBD) generated at atmospheric pressure. The effect of the distance of the sample from the electrode surface and the composition of the working gas in the chamber was studied. Norway spruce (Picea abies) wood, both unmodified and thermally modified, was chosen as the investigated material. The change in the surface free energy (SFE) of the wood surface was investigated by contact angles measurements. Chemical and structural changes were studied using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Activation at a 0.15 mm gap from the electrode led in all cases to an increase in the SFE. The largest change in SFE components was recorded for wood thermally modified to 200 °C. At a 1 mm gap from the electrode increase of SFE occurred only when oxygen (O2) and argon (Ar) were used as working gas. Treatment in air and nitrogen (N2) resulted in an anomalous reduction of SFE. With the growing temperature of thermal modification, this hydrophobization effect became less pronounced. The results point out the importance of precise position control during the DCSBD mediated plasma treatment. A slight reduction of SFE on thermally modified spruce was achieved also by short term ultra-violet (UV) light exposure, generated by DCSBD.

Adhesive Properties of Silicone-Coated Release Liner Paper Enhanced by Atmospheric Pressure Plasma Pre- and Post-Treatment

For release-liner preparation, coating stabilization of the silicone layer on base paper often requires pre- and post-treatment. In this study, we used atmospheric pressure diffuse coplanar surface barrier discharge in roll-to-roll configuration. The results of prepared coating showed that the A4 size clay-coated paper sprayed with silicone oil (0.25–0.50 mL) gradually decreased the tape peeling force (180°) with prolonged and repeated air plasma post-treatment. Best results showing increased hydrophobicity and significantly enhanced release factor of the coating were obtained after the plasma treatment in a nitrogen atmosphere. The silicone coating on the clay-coated paper reduced the reference release force from 5.5 N/cm to less than 1.5 N/cm after the repeated silicone spraying and short nitrogen plasma post-treatment. The results of X-ray photoelectron spectroscopy and scanning electron microscopy indicate silicone curing by plasma post-treatment and pore-closing of base paper without changes of the bulk material. The aging test lasting 3 months revealed the stability of the prepared coating.

Investigation of Wettability, Drying and Water Condensation on Polyimide (Kapton) Films Treated by Atmospheric Pressure Air Dielectric Barrier Discharge

In this study, we report on the investigation of influence of air atmospheric pressure dielectric barrier discharge on polyimide (Kapton) films. It is shown that plasma treatment causes a significant increase of Kapton wettability that is connected with alterations of its chemical composition (oxidation) induced by dielectric barrier discharge. Observed variations in the wettability of Kapton were also found to be accompanied by changes in the dynamics of water droplets drying on plasma-treated Kapton, namely by the reduction of the constant contact angle phase of the droplet drying. This effect may be ascribed to the higher surface heterogeneity of plasma-treated Kapton that causes pinning of the edges of drying droplet on the Kapton surface. Finally, the differences in wettability induced by the plasma treatment led to a different way, how the water condensates on the Kapton surface: while the condensing water forms large amount of small droplets on untreated Kapton, much bigger water structures were found on the Kapton exposed to atmospheric plasma.

Dual RGD-immobilized poly(L-lactic acid) by atmospheric pressure plasma jet for bone tissue engineering

Surface treatment on PLA substrates by atmospheric pressure plasma jet (APPJ) for polymerization of dual RGD-peptides were investigated. Peptide-modified surfaces have been highlighted as the most promising approach to improve the integration of implants into surrounding bones. By varying the RF power, PLA substrates treated by APPJ process have a tendency to form a hydrophobic surface. The effects on the proliferation and differentiation of MG63 cells were evaluated and osteocalcin (OCN) expression was analyzed using RT-PCR. The water contact angle of the W/APPJ process PLA was approximately 54% of that of the W/O APPJ process PLA substrates. W/APPJ process significantly increased cell proliferation, improved the functionality of the material without using a complicated procedure. We believe that pretreatment using the APPJ processes and dual RGD grafting can be more appropriate than traditional surface modification methods, with more potential for application to bone materials.

Fast low-temperature plasma reduction of monolayer graphene oxide at atmospheric pressure

We report on an ultrafast plasma-based graphene oxide reduction method superior to conventional vacuum thermal annealing and/or chemical reduction. The method is based on the effect of non-equilibrium atmospheric-pressure plasma generated by the diffuse coplanar surface barrier discharge in proximity of the graphene oxide layer. As the reduction time is in the order of seconds, the presented method is applicable to the large-scale production of reduced graphene oxide layers. The short reduction times are achieved by the high-volume power density of plasma, which is of the order of 100 W cm^-3. Monolayers of graphene oxide on silicon substrate were prepared by a modified Langmuir-Schaefer method and the efficient and rapid reduction by methane and/or hydrogen plasma was demonstrated. The best results were obtained for the graphene oxide reduction in hydrogen plasma, as verified by x-ray photoelectron spectroscopy and Raman spectroscopy.