Investigation of Surface Modification of Polystyrene by a Direct and Remote Atmospheric-Pressure Plasma Jet Treatment

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.

Melimine-Modified 3D-Printed Polycaprolactone Scaffolds for the Prevention of Biofilm-Related Biomaterial Infections

“…Several authors have described a strong axial gradient of reactive oxygen radicals limiting the penetration depth of plasma and, therefore, the homogeneous surface modification on deeper layers of the sample. 21,23 In order to address this gradient and ensure plasma treatment of the top and bottom layers of the 3D-printed mPCL samples, each scaffold was plasma-treated twice, once on each side. A toluidine blue (TBO) assay was used to determine the surface charge and, therefore, the carboxyl group density on the surface of the modified scaffolds (Figure 2B).…”

“…By comparison, positively charged ions, which are responsible for the surface modification, move randomly at similar velocities to the neutral species until they approach the surface, at which point the attracting potential accelerates them toward the material until they eventually reach the surface. At the surface, these ions transfer their kinetic and potential energy to the surface in the form of increased temperature and can leave the surface as neutral species. , It is important to stress that not all of the reactive oxygen and argon ions that approach the surface are able to interact with it, as ions can encounter other particles and undergo elastic collisions that will reflect them back to the gaseous plasma. These interactions between particles lower the probabilities of positively charged ions reaching and modifying the polymer surface .…”

“…This is even more significant in the case of 3D samples, where the deeper layers are less exposed to the plasma than the top layers, and therefore, the probability of ions reaching them is much lower. Several authors have described a strong axial gradient of reactive oxygen radicals limiting the penetration depth of plasma and, therefore, the homogeneous surface modification on deeper layers of the sample. , In order to address this gradient and ensure plasma treatment of the top and bottom layers of the 3D-printed mPCL samples, each scaffold was plasma-treated twice, once on each side.…”

“…At the surface, these ions transfer their kinetic and potential energy to the surface in the form of increased temperature and can leave the surface as neutral species. 20 , 21 It is important to stress that not all of the reactive oxygen and argon ions that approach the surface are able to interact with it, as ions can encounter other particles and undergo elastic collisions that will reflect them back to the gaseous plasma. These interactions between particles lower the probabilities of positively charged ions reaching and modifying the polymer surface.…”

Different Radial Modification Profiles Observed on APPJ-Treated Polypropylene Surfaces according to the Distance between Plasma Outlet and Target

“…This enhanced interest is caused by the fact that CAPPs are able to perform both chemical and physical action on the treated surfaces by creating/removing functional groups and changing the surface roughness [ 1 , 2 , 3 , 4 ]. For a large quantity of materials, surface modifications are required or desired to facilitate the occurrence of other processes, such as adhesion, or to enhance another surface property [ 5 , 6 , 7 , 8 , 9 , 10 ].…”