Model polymer etching and surface modification by a time modulated RF plasma jet: role of atomic oxygen and water vapor

Abstract

The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O 2 and 1% air plasma and OH for Ar/1% H 2 O plasma, play an essential role for polymer etching. For O 2 containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzlesurface distance increases. The etching reaction probability of an O atom ranging from 10 −4 to 10 −3 is consistent with low pressure plasma research. We also find that adding O 2 and H 2 O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O 2 /H 2 O plasma.

Role of adsorbed water on PEEK surfaces prior to − and after − atmospheric plasma activation

“…Figure shows that there is no difference anymore in the plateau‐values between 1 and 2 scans when drying the PEEK surface in a 15% RH atmosphere before plasma treatment, as pointed out by the superimposition of the two curves. The surface energy values for the samples treated with one scan ranging from 71.6 ± 1.2 to 78 ± 1 mJ · m −2 are indeed nearing the values of the surface energy of the samples treated with two scans (from 70 ± 2 to 79.4 ± 1.2 mJ · m −2 ), corresponding both to exposure times between 0.2 and 1 s. This would imply that the water adsorbed on the PEEK surface acts as a shield to the treatment, as it has been shown that water acts as a quencher for plasma‐activated particles . This means that for a wet polymer surface, the main effect of the first scan with an atmospheric plasma torch could be the desorption of water.…”

Polymer etching by atmospheric‐pressure plasma jet and surface micro‐discharge sources: Activation energy analysis and etching directionality

“…Two primary plasma sources were utilized in this work. They were chosen due to their completely different principles of operation and operating environment, and the variances in surface effects such as modification and etching seen from previous work …”

“…Details of how the power was calculated for this source can be found in previous work . Operating conditions were kept as close to previous work as possible to make the conditions comparable …”

“…Additionally we found that the total amount of surface modification is significantly higher for the SMD than for the MHz APPJ, consistent with the plasma surface interaction mechanism being very different between these two sources. It has been assumed previously that all the etching seen at room temperature is due to short‐lived highly reactive chemical neutral species which travels from the plasma source to the sample when there is no visible contact between them . This work seeks to explain these differences by investigating the behavior of the species that are responsible for etching and surface modification by looking at directionality and activation energy.…”

“…We seek to compare a MHz APPJ source with a SMD source that between these two types have shown fundamentally different behavior with respect to their interactions with polymers surfaces. The MHz APPJ has been well characterized to determine which gas phase species it produces and these have been correlated to the amount of etching of polymer films . The SMD has also been characterized and shown to produce some similar gas phase species however it does not cause significant etching of polymer films at room temperature.…”