Abstract
Localized functionalization of polymer surface with an atmospheric-pressure plasma jet was investigated at various treatment conditions. Polystyrene samples were treated with the plasma jet sustained in argon under direct or remote conditions. The two-dimensional evolution of surface wettability and the spot size of the treated area was determined systematically by measuring apparent water contact angles. Modification of surface chemistry and the formation of functional groups were investigated by X-ray photoelectron spectroscopy (XPS). The saturation of surface wettability and functional groups was observed even after a second of treatment providing the sample was placed close to the exhaust of the discharge tube. The spot diameter of the modified area increased logarithmically with increasing treatment time. However, it decreased linearly when increasing the distance. At the edge of the glowing plasma, however, the modification of surface properties was more gradual, so even 30 s of treatment caused marginal effects. With a further increase in the distance from the edge of the glowing plasma, however, there were no further treatment effects. The results are explained by significant axial as well as radial gradients of reactive species, in particular hydroxyl radicals.
Highlights
The modification of surface properties of polymers has attracted significant attention from the scientific community because of numerous applications
The results show that vacuum ultraviolet (VUV) photons and reactive oxygen species, such as O atoms, O3, O2 (a), and OH molecules are the key species in atmospheric-pressure plasma jets (APPJ); it is important to know their fluxes as well as radial and axial gradients of their densities
We present the results of a comprehensive investigation of the evolution of surface wettability versus distances as well as plasma treatment time for the case of polystyrene
Summary
The modification of surface properties of polymers has attracted significant attention from the scientific community because of numerous applications. A commonly used technique for tailoring surface properties of polymer materials is treatment by gaseous plasma. Low-pressure plasma is characterized by its uniformity in a large volume, high dissociation fraction of gaseous molecules, and relatively low power density. Opposite to low-pressure plasmas, the atmospheric pressure plasmas are limited to a rather small volume, where a large electric field is present and the power density is much larger. Atmospheric pressure plasmas are characterized by large gradients in reactive particles’ density. Gaseous plasma at atmospheric pressure can be sustained in the air or any other reactive gas, but the preferred configuration employs noble gases. Other reactive gases such as oxygen can be added in small concentrations to enhance the surface chemistry.
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