Abstract: This paper reports on the incorporation of three commercial fluorescent dyes, i.e., rhodamine 6G, fluorescein, and fluorescent brightener 184, in plasma coatings, by utilizing a dielectric barrier discharge (DBD) reactor, and the subsequent monitoring of the coatings homogeneity based on the emitted fluorescent light. The plasma coatings are qualitatively characterized with fluorescence microscopy, UVvis spectroscopy and profilometry for the determination of the coating thickness. The emitted fluorescent light of the coating correlates to the amount of dye per area, and deviations of these factors can hence be observed by monitoring the intensity of this light. This allows monitoring the homogeneity of the plasma coatings in a fast and simple way, without making major adjustments to the process.

Abstract: Simulations and experiments are performed to obtain a better insight in the plasma enhanced chemical vapor deposition process of SiO2 by SiCl4/O2/Ar plasmas for introducing a SiO2-like coating in wafer processing reactors. Reaction sets describing the plasma and surface chemistry of the SiCl4/O2/Ar mixture are presented. Typical calculation results include the bulk plasma characteristics, i.e., electrical properties, species densities, and information on important production and loss processes, as well as the chemical composition of the deposited coating, and the thickness uniformity of the film on all reactor surfaces. The film deposition characteristics, and the trends for varying discharge conditions, are explained based on the plasma behavior, as calculated by the model.

Abstract: Electrical breakdown by the application of an electric field occurs more easily in hot gases than in cold gases because of the extra electron-species interactions that occur as a result of dissociation, ionization and excitation at higher temperature. This paper discusses some overlooked physics and clarifies inaccuracies in the evaluation of the effective ionization coefficients and the critical reduced breakdown electric field of CO2 at elevated temperature, considering the influence of excited states and ion kinetics. The critical reduced breakdown electric field is obtained by balancing electron generation and loss mechanisms using the electron energy distribution function (EEDF) derived from the Boltzmann transport equation under the two-term approximation. The equilibrium compositions of the hot gas mixtures are determined based on Gibbs free energy minimization considering the ground states as well as vibrationally and electronically excited states as independent species, which follow a Boltzmann distribution with a fixed excitation temperature. The interaction cross sections between electrons and the excited species, not reported previously, are properly taken into account. Furthermore, the ion kinetics, including electron–ion recombination, associative electron detachment, charge transfer and ion conversion into stable negative ion clusters, are also considered. Our results indicate that the excited species lead to a greater population of high-energy electrons at higher gas temperature and this affects the Townsend rate coefficients (i.e. of electron impact ionization and attachment), but the critical reduced breakdown electric field strength of CO2 is only affected when also properly accounting for the ion kinetics. Indeed, the latter greatly influences the effective ionization coefficients and hence the critical reduced breakdown electric field at temperatures above 1500 K. The rapid increase of the dissociative electron attachment cross-section of molecular oxygen with rising vibrational quantum number leads to a larger electron loss rate and this enhances the critical reduced breakdown electric field strength in the temperature range where the concentration of molecular oxygen is relatively high. The results obtained in this work show reasonable agreement with experimental results from literature, and are important for the evaluation of the dielectric strength of CO2 in a highly reactive environment at elevated temperature.

Abstract: Plasma catalysis is gaining increasing interest for various environmental applications. Catalytic
material can be inserted in different shapes in the plasma, e.g., as pellets, (coated) beads, but also
as honeycomb monolith and 3DFD structures, also called ‘structured catalysts’, which have high
mass and heat transfer properties. In this work, we examine the streamer discharge propagation
and the interaction between plasma and catalysts, inside the channels of such structured catalysts,
by means of a two-dimensional particle-in-cell/Monte Carlo collision model. Our results reveal
that plasma streamers behave differently in various structured catalysts. In case of a honeycomb
structure, the streamers are limited to only one channel, with low or high plasma density when
the channels are parallel or perpendicular to the electrodes, respectively. In contrast, in case of a
3DFD structure, the streamers can distribute to different channels, causing discharge
enhancement due to surface charging on the dielectric walls of the structured catalyst, and
especially giving rise to a broader plasma distribution. The latter should be beneficial for plasma
catalysis applications, as it allows a larger catalyst surface area to be exposed to the plasma.

Abstract: Industry needs a flexible and efficient technology to convert CO2 into useful products, which fits in the Carbon Capture and Utilization (CCU) philosophy. Plasma technology is intensively being investigated for this purpose. A promising candidate is the gliding arc plasmatron (GAP). Waste streams of CO2 are often not pure and contain N2 as important impurity. Therefore, in this paper we provide a detailed experimental and computational study of the combined CO2 and N2 conversion in a GAP. Is it possible to take advantage of the presence of N2 in the mixture and to combine CO2 conversion with N2 fixation? Our experiments and simulations reveal that N2 actively contributes to the process of CO2 conversion, through its vibrational levels. In addition, NO and NO2 are formed, with concentrations around 7000 ppm, which is slightly too low for valorization, but by improving the reactor design it must be possible to further increase their concentrations. Other NO-based molecules, in particular the strong greenhouse gas N2O, are not formed in the GAP, which is an important result. We also compare our results with those obtained in other plasma reactors to clarify the differences in underlying plasma processes, and to demonstrate the superiority of the GAP.

Abstract: We studied the plasma-catalytic production of NH3 from H2 and N2 in a dielectric barrier discharge plasma reactor using five different Co-based catalysts supported on Al2O3, namely Co/Al2O3, CoCe/Al2O3, CoLa/Al2O3, CoCeLa/Al2O3 and CoCeMg/Al2O3. The catalysts were characterized via several techniques, including SEM-EDX, and their performance was compared. The best performing catalyst was found to be CoLa/Al2O3, but the dif-ferences in NH3 concentration, energy consumption and production rate between the different catalysts were limited under the same conditions (i.e. feed gas, flow rate and ratio, and applied power). At the same time, the plasma properties, such as the plasma power and current profile, varied significantly depending on the catalyst. Taken together, these findings suggest that in the production of NH3 by plasma catalysis, our catalysts act as plasma modifiers, i.e., they change the discharge properties and hence the gas phase plasma chemistry. Importantly, this effect dominates over the direct catalytic effect (as e.g. in thermal catalysis) defined by the chemistry on the catalyst surface.

Abstract: The phase transition processes induced by ultrashort, 100 fs pulsed laser irradiation of Au, Cu, and Ni are studied by means of a combined atomistic-continuum approach. A moderately low absorbed laser fluence range, from 200 to 600 J/m2 is considered to study phase transitions by means of a local and a nonlocal order parameter. At low laser fluences, the occurrence of layer-by-layer evaporation has been observed, which suggests a direct solid to vapor transition. The calculated amount of molten material remains very limited under the conditions studied, especially for Ni. Therefore, our results show that a kinetic equation that describes a direct solid to vapor transition might be the best approach to model laser-induced phase transitions by continuum models. Furthermore, the results provide more insight into the applicability of analytical superheating theories that were implemented in continuum models and help the understanding of nonequilibrium phase transitions.

Abstract: This paper outlines two different numerical simulation approaches, carried out by our group, used for describing hydrocarbon plasmas in their applications for either nanoparticle formation in the plasma or the growth of nanostructured thin films, such as nanocrystalline diamond (NCD). A plasma model based on the fluid approach is utilized to study the initial mechanisms giving rise to nanoparticle formation in an acetylene plasma. The growth of NCD is investigated by molecular dynamics simulations, describing the interaction of the hydrocarbon species with a substrate.

Abstract: Selective etching allows for obtaining carbon nanotubes with a specific chirality. While plasma-assisted etching has already been used to separate metallic tubes from their semiconducting counterparts, little is known about the nanoscale mechanisms of the etching process. We combine (reactive) molecular dynamics (MD) and force-bias Monte Carlo (tfMC) simulations to study H-etching of CNTs. In particular, during the hydrogenation and subsequent etching of both the carbon cap and the tube, they sequentially transform to different carbon nanostructures, including carbon nanosheet, nanowall, and polyyne chains, before they are completely removed from the surface of a substrate-bound Ni-nanocluster.We also found that onset of the etching process is different in the cases of the cap and the tube, although the overall etching scenario is similar in both cases. The entire hydrogenation/etching process for both cases is analysed in detail, comparing with available theoretical and experimental evidences.

Abstract: Synthetic glucocorticoids (GC) are the mainstay therapy for treatment of acute and chronic inflammatory disorders. Due to the high adverse effects associated with long-term use, GC pharmacology has focused since the nineties on more selective GC ligand-binding strategies, classified as selective glucocorticoid receptor (GR) agonists (SEGRAs) or selective glucocorticoid receptor modulators (SEGRMs). In the current study, GSK866 analogs with electrophilic covalent-binding warheads were developed with potential SEGRA properties to improve their clinical safety profile for long-lasting topical skin disease applications. Since the off-rate of a covalently binding drug is negligible compared to that of a non-covalent drug, its therapeutic effects can be prolonged and typically, smaller doses of the drug are necessary to reach the same level of therapeutic efficacy, thereby potentially reducing systemic side effects. Different analogs of SEGRA GSK866 coupled to cysteine reactive warheads were characterized for GR potency and selectivity in various biochemical and cellular assays. GR- and NFκB-dependent reporter gene studies show favorable anti-inflammatory properties with reduced GR transactivation of two non-steroidal GSK866 analogs UAMC-1217 and UAMC-1218, whereas UAMC-1158 and UAMC-1159 compounds failed to modulate cellular GR activity. These results were further supported by GR immuno-localization and S211 phospho-GR western analysis, illustrating significant GR phosphoactivation and nuclear translocation upon treatment of GSK866, UAMC-1217, or UAMC-1218, but not in case of UAMC-1158 or UAMC-1159. Furthermore, mass spectrometry analysis of tryptic peptides of recombinant GR ligand-binding domain (LBD) bound to UAMC-1217 or UAMC-1218 confirmed covalent cysteine-dependent GR binding. Finally, molecular dynamics simulations, as well as glucocorticoid receptor ligand-binding domain (GR-LBD) coregulator interaction profiling of the GR-LBD bound to GSK866 or its covalently binding analogs UAMC-1217 or UAMC-1218 revealed subtle conformational differences that might underlie their SEGRA properties. Altogether, GSK866 analogs UAMC-1217 and UAMC-1218 hold promise as a novel class of covalent-binding SEGRA ligands for the treatment of topical inflammatory skin disorders.

Abstract: Cold atmospheric plasma (CAP) is a promising new agent for (selective) cancer treatment, but the underlying cause of the anti-cancer effect of CAP is not well understood yet. Among different theories and observations, one theory in particular has been postulated in great detail and consists of a very complex network of reactions that are claimed to account for the anti-cancer effect of CAP. Here, the key concept is a reactivation of two specific apoptotic cell signaling pathways through catalase inactivation caused by CAP. Thus, it is postulated that the anti-cancer effect of CAP is due to its ability to inactivate catalase, either directly or indirectly. A theoretical investigation of the proposed theory, especially the role of catalase inactivation, can contribute to the understanding of the underlying cause of the anti-cancer effect of CAP. In the present study, we develop a mathematical model to analyze the proposed catalase-dependent anti-cancer effect of CAP. Our results show that a catalase-dependent reactivation of the two apoptotic pathways of interest is unlikely to contribute to the observed anti-cancer effect of CAP. Thus, we believe that other theories of the underlying cause should be considered and evaluated to gain knowledge about the principles of CAP-induced cancer cell death.