Search

Using Ar/Air mixture microwave plasma, we investigated the effects of air and gas temperature on the generation of electrons, ozone (O3), and nitric oxide (NO) through experiments and chemical kinetics simulation. The global model (GM) chemical kinetics simulation was used to validate and complement experimental observations. As the air percentages in Ar plasma increase, electrons are mainly generated by reactive oxygen species (ROS), but electron densities decrease. This is why plasma jet length becomes shorter with the mixture of air to Ar plasma at the same power. The profile of O3 densities has a maximum point because these are affected by oxygen (O2) molecules and gas temperature. O3 densities increase because these are generated via recombination of atomic oxygen (O) and O2 radicals as the air percentages increase. As the gas temperature increases, O3 densities decrease and O3 radicals are mainly destroyed by ROS such as O2−, excited O2, and O, although air percentages increase. NO radicals increase continually with the addition of air mixture and increase in gas temperature. With respect to biomedical applications, in the case of Ar/Air plasma treatment, it takes just 2 d, which has reduced the wound area to 30% because of faster scab formation over the wound and mRNA activation. Abundant NO radicals with ROS in Ar/aAir plasma strongly enhance IL-6 and TGF-β1, which facilitate collagen remodeling and wound recovery effectively.

Using surface type air atmospheric pressure plasma, we investigated the amount of ozone and other reactive species generation with variations of the surface temperature of an electrode through an optical emission spectrum and a tube type gas detector. Reduced version of global model (GM) was employed to complement these experimental observations. The results of the model matched well with the experimental data. The amount of ozone generated from the surface type air plasma device was dramatically reduced with increasing temperature. Atomic oxygen (O) and nitric oxide (NO) radicals, which are important agents for biomedical applications, proportionally increased with increasing temperature. We also elucidated the dominant reaction related to the generation or loss of these radicals based on temperature variation through our GM.

Oral cavity and teeth are important organs of human body. The attention and cost for dental treatments increase every year. In dental clinics, the most common diseases are dental caries, periodontal disease, and stomatitis. Dental aesthetics such as tooth whitening is one of important part of dental clinics. However, conventional treatment methods in dental clinics have limitations by pain and long-time treatment. Nonthermal plasmas have shown great potential as noble techniques to dental applications due to safety and multi-functional effects achieved by the abundant plasma components including charged particles, radiation, and reactive species. Reactive oxygen species generated from plasmas can effectively inhibit pathogen activity. The use of nonthermal plasmas is efficient in treating oral diseases because the construction of the plasma devices allows easy access to the oral cavity. However, few studies have been conducted on the use of plasmas in oral disease. Tooth aesthetics, as well as treatment of oral diseases, are important in determining the quality of human life. Recent studies have shown nonthermal plasmas to have strong tooth-bleaching effects. Studies on oral care using nonthermal plasmas will significantly contribute to oral health in the future.

Energy-based surgical devices are widely used to fuse tissues and seal vessels, but tissue adhesion to the instrument complicates the procedure. We deposit a robust non-stick coating on the jaws of LigaSure tissue fusion devices by employing an atmospheric pressure RFdriven plasma with hexamethyldisiloxane (HMDSO) entrained in argon carrier gas. The hydrophobicity, surface energy, surface topography, and chemical characteristics of deposited films are characterized by water contact angle measurements, surface energy test pens, atomic force microscopy, and Fourier transform infrared spectroscopy, respectively. We demonstrate significantly reduced tissue adhesion to HMDSO polymer film-coated instruments during the tissue fusion procedure in comparison with uncoated and chromium nitride-coated instruments.

Radio frequency (RF) driven hybrid gaswater plasma for tooth whitening was developed and the plasma chemical reactions with de-ionized (DI) water were studied. Plasma operating conditions, such as RF input power and argon flow rate were correlated with plasma lengths. The operation of hybrid gaswater plasma changed both the electrical conductivity and pH concentration of the DI water. OH and H2O2 densities were measured to determine the dominant species generated by plasma. The major chemical reaction pathways and known rate constants are given in support of the analysis of major chemical reaction pathways. Finally, we demonstrated that the hybrid gaswater configuration achieved porcine tooth whitening.

Atmospheric pressure plasmas have attracted great interests and been widely used in biomedical applications such as sterilization, coagulation, wound healing, and cancer cells treatment. The reactive oxygen species (ROS) generated in atmospheric pressure plasmas have been believed to play a crucial role in these biomedical applications. The experimental measurement of the atomic oxygen density showed that the highest density was measured at an admixture of 0.5% of O2. The similar trend of the atomic oxygen density varying the concentration of O2 was reproduced through a global model of He/O2 in atmospheric pressure plasmas. The evolution of the dominant production and loss reactions for the atomic oxygen was analyzed. With increase in the concentration of O2, the atomic oxygen was produced mainly by the dissociation of O2 and lost through the recombinations with themselves and oxygen molecules.

Three-electrode plasma jet system consisting of a perforated dielectric tube with two outer and one floating inner electrodes was developed and employed for tooth bleaching. Lowered gas breakdown voltage and increased discharge current were achieved by using the floating inner electrode. Optical emission spectra analysis showed that the rotational temperature of the second positive nitrogen bands was ≈290 K and vibrational temperature was ≈2 500 K, which means this plasma is in highly non-quilibrium state and nonthermal. The presence of excited He, N2, N and O in the plasma plume was revealed. The plasma jet was used in combination with hydrogen peroxide (H2O2) to remove stains from extracted teeth stained by either coffee or red wine. Combining the plasma jet and H2O2 improved the bleaching efficacy by a factor of 3.1 (coffee) and 3.7 (red wine) compared with using H2O2 alone.

The results of simulations using a fluid model and a PIC-MCC model are compared, and the PIC-MCC is used to explore the kinetics of energetic ions and electrons in microplasmas. The kinetics are studied under helium discharges at 760 Torr and Ne/Xe DBD discharges at 300 Torr with various driving currents and geometries. While EEPFs of microplasmas at high pressure show strong nonequilibrium behavior near the sheath region, EEDFs on the powered and grounded electrodes have qualitatively different features depending on input power. The effective temperature and energy flux of charged particles can be obtained from the slopes in EEPFs and IEPFs. The effects of input power, discharge length, and mixture gas concentration on the IEDFs on each electrode are discussed.

Atmospheric pressure glow discharges (APGDs) have widespread applications, including sterilization, cancer cell treatment, deposition, and surface modification due to their rather simple configurations, thanks to no need for vacuum system and their great capability to generate reactive species such as radical oxygen species. Helium and argon are widely used as feeding gases, achieving stable operations for wide ranges of parameters in atmospheric pressure, and oxygen is added into these gases to generate more reactive oxygen species (ROS), which play a significant role in sterilization. As the measurements of species densities and electron temperature in APGDs are difficult, we have developed the zero-dimensional global model of He/O 2 and Ar/O 2 APGDs to calculate the densities of several kinds of species and electron temperature. It was shown that even though small fraction of oxygen less than 1% was added to helium or argon, electrons dissipated most of their energy through collisions with oxygen molecules rather than helium or argon atoms. The densities of electron, atomic oxygen, and ozone of Ar/O 2 were higher than those of He/ O 2 ; however, the electron temperature of He/O 2 was higher than that of Ar/O 2 . When the pulsed power is applied, the time-averaged electron temperature for the shorter pulse period and the larger duty ratio increased, and the electron density decreased as the duty ratio increased.

Thanks to their portability and the non-equilibrium character of the discharges, microplasmas are finding application in many scientific disciplines. Although microplasma research has traditionally been application driven, microplasmas represent a new realm in plasma physics that still is not fully understood. This paper reviews existing microplasma sources and discusses charged particle kinetics in various microdischarges. The non-equilibrium character highlighted in this manuscript raises concerns about the accuracy of fluid models and should trigger further kinetic studies of high-pressure microdischarges. Finally, an outlook is presented on the biomedical application of microplasmas.

Pulsed microwave driven microplasma at atmospheric pressure is proposed as an efficient source of energetic electrons for low-temperature biomedical applications. Energetic electrons are required to break the covalent bonds of nitrogen, oxygen, and water molecules in humid air and produce reactive species. Particle-in-cell (PIC) simulations demonstrate that the energetic electrons with energy greater than 10 eV (capable of breaking the bond of nitrogen molecules) can be produced much more efficiently in pulsed microwave helium plasmas than in pulsed DC or continuous microwave plasmas. In particular, fast heating and cooling of electrons are observed at the rising edge and the falling edge of the pulse, respectively. This phenomenon is consistent with the fluid analysis showing the electrons’ energy gain via collective motion and collisional loss to the neutral particles.

A study was conducted on the dependence of discharge efficiency upon discharge voltage, its spatial distribution, and distribution of electron beam injected in Ne-Xe mixture discharge lamp through 2-D fluid simulation and 1-D particle-in-cell simulation combined with a fluid model, respectively. Based on the simple calculation from cross-section and electron beam energy, the optimum energy of the injected electron beam for high efficient light source is about 14∼16eV in the case of pure Xe. The simulation results also show the similar characteristics to the estimated data in discharge efficiency.

An efficient stereoselective route for the preparation of stereoisomeric aminocyclopentitols 3- 5 was achieved using a six-step sequence starting from the corresponding D-sugars. Key steps of the synthesis of the title compounds involved the regioselective and diastereoselective amination of cinnamylic 1,2- ANTI- or 1,2- SYN-tribenzyl ethers using chlorosulfonyl isocyanate (CSI), intramolecular olefin metathesis, and diastereoselective dihydroxylation.

The first observation of striation in plasma display panel (PDP) cell by kinetic and fluid simulations is presented. The striation phenomenon in the kinetic simulation is clearer than that in fluid simulation. The striation is due to the self-consistent interaction of plasma, dielectric wall, and applied voltages. Simulation results indicate that the phenomenon occurs due to the non-uniform accumulation of surface charges on the sustain electrodes, which consequently deform the local potential profile. The surface and space charges locally create multiple-tier potential distribution near anode region that makes plasma bunches. The discharge in this region is governed by ionization process, but the cathode discharge depends on the secondary-electron emission process on the dielectric surface. Based on these discharge characteristics, 80 % efficiency increase of PDP cell is obtained due to triggered striation by the modification of front dielectric material and MgO protective-layer.