Electrical and optical properties of an argon plasma jet were characterized. In particular, effects of an additive gas, namely nitrogen or oxygen, on these properties were studied in detail. The plasma jet was found to be of a glow-like discharge, which scarcely changed upon the injection of an additive gas, either directly or through a glass capillary. Optical emission spectroscopy characterization revealed that excited argon atoms were the predominant active species in this plasma jet. Metastable argon atoms were highly quenched, and N2(C 3 u ) became the main energy carrier following nitrogen injection. When oxygen was added to the afterglow zone through a glass capillary, no significant quenching effect was observed and the number of oxygen atoms decreased with the increase in oxygen concentration. Finally, to demonstrate an application of this plasma jet, a high-density polyethylene surface was treated with argon, argon/nitrogen, and argon/oxygen plasmas.

In this study, a high-density polyethylene (HDPE, 5-mm-thick, 0.95 g/cm 3) surface was treated using an RF capacitive atmospheric pressure cold Ar plasma jet. By using this Ar plasma jet, a hydrophilic HDPE surface was formed during the plasma treatment. In particular, the effects of an additive gas (N2 or O2) on the HDPE surface treatment were investigated in detail. It was shown that the addition of N2 or O2 gas had an important influence on the HDPE surface treatment. Compared to pure Ar plasma treatment, a lower value of water contact angle (WCA) was obtained when a trace of N2 or O2 gas was added. It was also found that besides the quantities of active species in the plasma jet, the treatment temperature played an important role in the HDPE surface treatment. This is because surface molecular motion is not negligible when the treatment temperature is close to the melting point of the polymer.

In this study, we conducted experiments to investigate the electrical and optical characteristics of a non-equilibrium Ar-N2 plasma discharge at atmospheric pressure. To obtain the plasma discharge we used our indigenously designed plasma generating device named CAPPLAT (Cold Atmospheric Pressure Plasma Torch) which was manufactured by Cresur Corporation. The plasma discharge obtained with only Ar gas was quite filamentary. So, to achieve a homogeneous discharge N2 gas was admixed. The effects of different volumes of admixed N2 gas were also studied. The optical emission spectroscopy was used to study the active charged species in the plasma discharges. The further increased volume of N2 gas further suppressed the emission intensity of Ar metastables but at the same time the emission intensity of the second positive system of nitrogen molecules (N2(C3Πu) enhanced significantly. It can be concluded that in Ar- plasma discharge, argon metastables are the main energy carriers but when N2 gas is added to the feeding gas (Ar) for plasma generation, the second positive system of nitrogen molecules (N2(C3Πu) become the main energy carriers. On the other hand the addition of the N2 gas doesn’t change the electrical characteristics of plasma discharge significantly. To identify the effectiveness of the CAPPLAT as a tool for sterilization, highly environmental stress resistant bacterial (Bacillus subtilis) endospores were treated for different durations. We could successfully deactivate the population of 1.0X107 to 4.0X107 Bacillus endospores/ml. The details of this experiment are discussed in our next paper.

In this study, we conducted experiments to investigate the effectiveness of a non-equilibrium Ar-N2 plasma jet generated by a Cold Atmospheric Pressure Plasma Torch (CAPPLAT) at a sinusoidal voltage of 20 kV, frequency of 30 kHz with 10 slm of Ar gas and 100 sccm of N2 gas. Highly environmental stress resistant bacterial endospores of Bacillus subtilis, dried on an agar disc were exposed to the plasma discharge from the CAPPLAT for different durations. The viability of spores after plasma exposure was checked by counting CFUs by serial dilution method. We also measured the amount of released DPA (dipicolinic acid, pyridine-2, 6-dicarboxylic acid), which is exclusively found in endospore protoplast (cortex), to confirm the disintegration of the cortex. We could successfully inactivate a population of Bacillus endospores of about 1.0 × 107 to 4.0 × 107 spores/ml.

A non-equilibrium atmospheric pressure plasma was applied for the polymerization of the methacrylic monomers such as (2-hydroxyethyl methacrylate (HEMA), methacrylic acid (MAA) and butyl methacrylate (BMA)). These monomers were successfully polymerized with retaining the functional groups of ester or acid. The polymerization mechanism was discussed on the basis of the optical emission spectroscopy (OES) of the plasma. It was strongly suggested that the functional groups could be retained in the polymerization proceeds when the HOMO-LUMO gap of the monomer is close to the energy of Ar metastable atom, which initiates the polymerization.