Self-organization phenomena in cold atmospheric pressure plasma slit jet

Abstract

The RF plasma slit jet, which produces 150 mm wide streaming plasma outside the jet body, exhibits exciting self-organization phenomena that resemble the self-organized patterns of dielectric barrier discharge (DBD) filaments. Similarly, as in DBD, the filaments are surrounded by an inhibition zone that does not allow two filaments to come closer to each other. With fast camera imaging, we observed the filamentary character of the discharge in all the studied gas feeds (Ar, Ar/N2, and Ar/O2). Still, the visual appearance of the filaments in the plasma and their interaction with a dielectric surface depended significantly on the gas feed. As the breakdown voltage in pure Ar is relatively low compared to the applied one, new filaments form frequently. Such newly created filaments disrupted the characteristic inter-filament distance, forcing the system to rearrange. The frequent ignition and decay processes in Ar led to short filament lifetimes (0.020–0.035 s) and their high jitter speed (0.9–1.7 m/s), as determined with an image processing custom code based on Gwyddion libraries. The number of filaments was lower in the Ar/O2 and Ar/N2 mixtures. It was attributed to a loss of energy in the excitation of rotational and vibrational levels and oxygen electronegativity. Since the probability of low-current side discharges transitioning into the full plasma filaments was limited in these gas mixtures, the self-organized pattern was seldom disrupted, leading to lesser movement and longer lifetimes. Unlike in Ar or Ar/O2, the constricted filaments in Ar/N2 were surrounded by diffuse plasma plumes, likely connected to the presence of long-lived nitrogen species. We demonstrated in the polypropylene treatment that the self-organization phenomena affected the treatment uniformity.

Electric field and higher harmonics of RF plasma slit jet measured by antennas and VI probes

“…Most crucially, the PSJ filaments formed self-organized patterns characterized by inter-filament distance. The behavior resembles the self-organizing patterns of a quasi-1D dielectric barrier discharge (DBD) [43,45].…”

“…The recalculation ratio from electric field E a at the antenna position to E p inside the sheath was then obtained as the ratio of electric fields inside the extended dipole and at the antenna position. The effective geometry of the dipole was obtained using previous results of filament fast camera video analysis [43]. Because of rapid horizontal filament movement and many repetitions in the antenna measurements, a simple rectangular cuboid geometry was used to represent the mean of all possible filament states.…”

Enhanced Adhesion of Electrospun Polycaprolactone Nanofibers to Plasma-Modified Polypropylene Fabric

“…However, in contrast to DBD, the properties of PSJ discharge can be controlled by simple adjustment of sample placement distance. Moreover, compared to stationary filaments of DBDs, the PSJ filaments changed positions over time, shuffling along the length of the slit at the jitter speeds in orders of m/s [ 41 ]. This constant motion ensures higher treatment homogeneities even for higher sample movement speeds, i.e., low treatment times.…”

“…At atmospheric pressure, the PP fabric was treated with RF PSJ [ 40 , 41 ] with a working frequency of 13.56 MHz at a power of 500 W in ambient air. Two gas feeds were used: Ar and Ar+N .…”

“…The excellent adhesion between the functional nanofibrous and supporting composite parts is a key property, especially for wound dressing development. On that account, our work aimed to enhance the adhesion of PCL NFs to spunbond PP fabric modified by the radio-frequency (RF) low-pressure capacitively coupled plasma discharge and the low-temperature atmospheric-pressure RF plasma slit jet (PSJ) [ 40 , 41 ]. In a few studies [ 24 , 25 , 33 , 34 , 35 , 38 , 42 ], adhesion between NFs and textile support is evaluated, and all of them have employed tensile T-peel tests requiring a rather thick nanofibrous mat.…”