arXiv subjects

Davide Mariotti

Publications and source records attributed to Davide Mariotti.

7 recordsLinked to original sources

arXiv2025

Negative charge acquisition by isolated single microdroplets from plasma exposure at atmospheric pressure

Charged liquid microdroplets have generated significant interest recently due to the observation of chemical reaction rate enhancement by orders of magnitude. Droplet charging by plasma irradiation has been observed along with significantly enhanced reaction rates in liquid. In this paper we measure the charge on fixed size (47 $\mu$m) individual droplets, exposed for approximately 4 ms to a low temperature RF-driven plasma operated at atmospheric pressure. The measured charge values (0.8 - 2.0 $\times 10^{7}$ electrons) approached the Rayleigh limit for the given droplet diameter. Results were compared with finite element simulations of plasma charging which provided estimates of surface electric fields and charge fluxes to the droplet surface and helps advance the development of a theoretical framework for plasma-charged microreactors.

physics.plasm-ph↗

arXiv2025

Free electron charging of microdroplets in a plasma at atmospheric pressure

Gas-phase microdroplets have recently demonstrated exceptional chemical properties via suspected mechanisms such as contact electrification and surface charge pinning, producing high surface electric fields. Here, microdroplets are injected into a low-temperature atmospheric-pressure plasma and exposed to an excess free-electron flux. We report the first measurements of droplet charge in a fully collisional plasma, with averages up to 2.5 $\times 10^{5}$ electrons for 15 $\mu$m droplets, dependent on absorbed power. Simulations indicate solid particles under similar conditions acquire $\sim$40\% less charge, likely due to low-mobility water cluster ion formation around evaporating droplets, and predict surface electric fields up to $10^{7}$ V m$^{-1}$ for the smallest droplets (3 $\mu$m). Plasma exposure also produces H$_{2}$O$_{2}$ in the liquid, with concentrations up to 33 mM, corresponding to remarkable generation rates exceeding 275 M s$^{-1}$. The system involves complex, not yet fully elucidated mechanisms. A controlled plasma environment enables defined charge levels and exposure times, allowing systematic study and enhancing droplet properties.

physics.plasm-ph↗

arXiv2022

Generation and delivery of free hydroxyl radicals using a remote plasma

We demonstrate a new gas-based OH generation source using a low power RF-driven atmospheric pressure plasma configured to deliver the radical flux into the far effluent region, well away from interference from other plasma factors such as electric fields, currents, and UV radiation. Using He-H2O gas chemistry isolated from the laboratory air, the plasma generated flux consists of H2O2 and OH, varying with H2O vapour content and absorbed power density. Peak flux values were 2.3 nmol s-1 and 0.23 nmol s-1 for H2O2 and OH respectively at a distance of 50 mm from the plasma, with 790 ppmv H2O and a power density of 1E8 W m-3. The maximum OH flux density was 4.5 x 1E19 m-2 s-1 falling to 1.7 x 1E19 m-2 s-1 at 110 mm, equivalent to generation rates of 74 uM s-1 and 28 uM s-1. Despite high OH recombination rates at the plasma exit, the escaping flux is still significant, indicating a viable delivery capability to downstream targets. Its performance with regard to OH generation rates compares well with traditional OH generation techniques such as radiolysis, advanced oxidation processes and enhanced Fenton-chemistry approaches where OH production rates are sub-uM s-1. Delivering precisely quantifiable OH fluxes provides new opportunities for scientific studies and technological opportunities in cell biology, atmospheric chemistry, protein unfolding and systematic dose studies for plasma-based and other OH related potential medical treatments.

physics.plasm-ph↗

arXiv2022

Methane detection to 1 ppm using machine learning analysis of atmospheric pressure plasma optical emission spectra

Optical emission spectroscopy from a small-volume, 5 uL, atmospheric pressure RF-driven helium plasma was used in conjunction with Partial Least Squares Discriminant Analysis (PLS-DA) for the detection of trace concentrations of methane gas. A limit of detection of 1 ppm was obtained and sample concentrations up to 100 ppm CH4 were classified using a nine-category model. A range of algorithm enhancements were investigated including regularization, simple data segmentation and subset selection, VIP feature selection and wavelength variable compression in order to address the high dimensionality and collinearity of spectral emission data. These approaches showed the potential for significant reduction in the number of wavelength variables and the spectral resolution/bandwidth. Wavelength variable compression exhibited reliable predictive performance, with accuracy values > 97%, under more challenging multi-session train - test scenarios. Simple modelling of plasma electron energy distribution functions highlights the complex cross-sensitivities between the target methane, its dissociation products and atmospheric impurities and their impact on excitation and emission.

physics.plasm-ph↗

arXiv2010

Method to determine argon metastable number density and plasma electron temperature from spectral emission originating from four 4p argon levels

A simple model and method is proposed here to determine argon metastable number densities and electron temperature with the assumption of a Maxwell-Boltzmann electron energy distribution. This method is based on the availability of experimental relative emission intensities of only four argon lines that originate from any of the 4p argon levels. The proposed model has a relatively wide range of validity for laboratory plasmas that contain argon gas and can be a valuable tool for the emerging field of atmospheric microplasmas, for which diagnostics is still limited.

physics.plasm-ph↗

arXiv2010

Nonequilibrium and effect of gas mixtures in an atmospheric microplasma

The gas and effective electron temperatures have been estimated for atmospheric microplasma by means of optical emission spectroscopy. The results have shown that the microplasma exhibits nonequilibrium and, as its size is reduced, the two temperatures depart from each other, enhancing the nonequilibrium characteristic. The effect of methane and oxygen concentrations has also been studied, showing that gas mixtures have an important effect on the microplasma state.

physics.plasm-ph↗

arXiv2010

Experimental study of a planar atmospheric-pressure plasma operating in the microplasma regime

Electrical characterization of a nonthermal radio-frequency atmospheric-pressure microplasma in a parallel plate configuration has shown that reducing electrode gap into the submillimeter range increases current and power density at a reduced voltage as compared to similar plasmas at larger electrode gaps which have no gap dependence. Calculation of sheath thickness and electric fields in the sheath and in the bulk demonstrate a dependence on the electrode gap as it is reduced into the submillimeter regime, indicating a distinct regime of operation.

physics.plasm-ph↗