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- ItemMicrowave plasma discharges for biomass pretreatment: Degradation of a sodium carboxymethyl cellulose model(New York, NY : American Inst. of Physics, 2020) Honnorat, B.; Brüser, V.; Kolb, J.F.Biogas production is an important component of an environmentally benign renewable energy strategy. However, the cost-effectiveness of biogas production from biomass is limited by the presence of polymeric structures, which are recalcitrant to digestion by bacteria. Therefore, pretreatments must often be applied prior to anaerobic fermentation to increase yields of biogas. Many physico-chemical pretreatments have a high energy demand and are generally costly. An alternative could be the ignition of a plasma directly in the biomass substrate. The reactive species that are generated by plasma-liquid interactions, such as hydroxyl radicals and hydrogen peroxides, could contribute significantly to the disintegration of cell walls and the breakage of poorly digestible polymers. With respect to economic, processing, and other potential benefits, a microwave instigated and sustained plasma was investigated. A microwave circuit transmitted 2-kW pulses into a recirculated sodium carboxymethyl cellulose solution, which mimicked the rheological properties of biomass. Each microwave pulse had a duration of 12.5 ms and caused the ignition of a discharge after a vapor bubble had formed. Microwaves were absorbed in the process with an efficiency of ∼97%. Slow-motion imaging showed the development of the discharge. The plasma discharges provoked a decrease in the viscosity, probably caused by the shortening of polymer chains of the cellulose derivative. The decrease in viscosity by itself could reduce processing costs and promotes bacterial activity in actual biomass. The results demonstrate the potential of microwave in-liquid plasma discharges for the pretreatment of biomass. © 2020 Author(s).
- ItemTreatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet(College Park, MD : Institute of Physics Publishing, 2010) Koban, I.; Matthes, R.; Hübner, N.-O.; Welk, A.; Meisel, P.; Holtfreter, B.; Sietmann, R.; Kindel, E.; Weltmann, K.-D.; Kramer, A.; Kocher, T.Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% Chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log 10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemParticles as probes for complex plasmas in front of biased surfaces(College Park, MD : Institute of Physics Publishing, 2009) Basner, R.; Sigeneger, F.; Loffhagen, D.; Schubert, G.; Fehske, H.; Kersten, H.An interesting aspect in the research of complex (dusty) plasmas is the experimental study of the interaction of micro-particles with the surrounding plasma for diagnostic purposes. Local electric fields can be determined from the behaviour of particles in the plasma, e.g. particles may serve as electrostatic probes. Since in many cases of applications in plasma technology it is of great interest to describe the electric field conditions in front of floating or biased surfaces, the confinement and behaviour of test particles is studied in front of floating walls inserted into a plasma as well as in front of additionally biased surfaces. For the latter case, the behaviour of particles in front of an adaptive electrode, which allows for an efficient confinement and manipulation of the grains, has been experimentally studied in terms of the dependence on the discharge parameters and on different bias conditions of the electrode. The effect of the partially biased surface (dc and rf) on the charged micro-particles has been investigated by particle falling experiments. In addition to the experiments, we also investigate the particle behaviour numerically by molecular dynamics, in combination with a fluid and particle-in-cell description of the plasma. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
- ItemBehavior of a porous particle in a radiofrequency plasma under pulsed argon ion beam bombardment(College Park, MD : Institute of Physics Publishing, 2010) Wiese, R.; Sushkov, V.; Kersten, H.; Ikkurthi, V.R.; Schneider, R.; Hippler, R.The behavior of a single porous particle with a diameter of 250 μm levitating in a radiofrequency (RF) plasma under pulsed argon ion beam bombardment was investigated. The motion of the particle under the action of the ion beam was observed to be an oscillatory motion. The Fourier-analyzed motion is dominated by the excitation frequency of the pulsed ion beam and odd higher harmonics, which peak near the resonance frequency. The appearance of even harmonics is explained by a variation of the particles's charge depending on its position in the plasma sheath. The Fourier analysis also allows a discussion of neutral and ion forces. The particle's charge was derived and compared with theoretical estimates based on the orbital motion-limited (OML) model using also a numerical simulation of the RF discharge. The derived particle's charge is about 7-15 times larger than predicted by the theoretical models. This difference is attributed to the porous structure of the particle. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.