Thomson scattering on non-thermal atmospheric pressure plasma jets

To characterize non-thermal atmospheric pressure plasmas experimentally, a large variety of methods and techniques is available, each having its own specific possibilities and limitations. A rewarding method to investigate these plasma sources is laser Thomson scattering. However, that is challenging. Non-thermal atmospheric pressure plasmas (gas temperatures close to room temperature and electron temperatures of a few eV) have usually small dimensions (below 1 mm) and a low degree of ionization (below 10^-4). Here an overview is presented of how Thomson scattering can be applied to such plasmas and used to measure directly spatially and temporally resolved the electron density and energy distribution. A general description of the scattering of photons and the guidelines for an experimental setup of this active diagnostic are provided. Special attention is given to the design concepts required to achieve the maximum signal photon flux with a minimum of unwanted signals. Recent results from the literature are also presented and discussed.

Deposition of thin films by a non-equilibrium atmospheric pressure Plasma Jet: a poly-diagnostic study

The use of atmospheric pressure plasmas for thin film deposition on thermo-sensitive materials is currently one of the main challenges of the plasma scientific community. Despite the growing interest in this field, the existing knowledge gap between gas-phase reaction mechanisms and thin film properties is still one of the most important barriers to overcome for a complete understanding of the process. In this work, thin films surface characterization techniques, combined with passive and active gas-phase diagnostic methods, were used to provide a comprehensive study of the Ar/TEOS deposition process assisted by an atmospheric pressure plasma jet. SiO2-based thin films exhibiting a well-defined chemistry, a good morphological structure and high uniformity were studied in detail by FTIR, XPS, AFM and SEM analysis. Furthermore, non-intrusive spectroscopy techniques (OES, filter imaging) and laser spectroscopic methods (Rayleigh scattering, LIF and TALIF) were employed to shed light on the complexity of gas-phase mechanisms involved in the deposition process and discuss the influence of TEOS admixture on gas temperature, electron density and spatial-temporal behaviours of active species. The poly-diagnostic approach proposed in this work opens interesting perspectives both in terms of process control and optimization of thin film performances.

Development and optimization of techniques and design parameters for the engineering of atmospheric pressure plasma devices for biomedical applications and plasma medicine

In the last decades, the possibility to generate plasma at atmospheric pressure gave rise to a new emerging field called plasma medicine; it deals with the application of cold atmospheric pressure plasmas (CAPs) or plasma-activated solutions on or in the human body for therapeutic effects. Thanks to a blend of synergic biologically active agents and biocompatible temperatures, different CAP sources were successfully employed in many different biomedical applications such as dentistry, dermatology, wound healing, cancer treatment, blood coagulation, etc.… Despite their effectiveness has been verified in the above-mentioned biomedical applications, over the years, researchers throughout the world described numerous CAP sources which are still laboratory devices not optimized for the specific application. In this perspective, the aim of this dissertation was the development and the optimization of techniques and design parameters for the engineering of CAP sources for different biomedical applications and plasma medicine among which cancer treatment, dentistry and bioaerosol decontamination. In the first section, the discharge electrical parameters, the behavior of the plasma streamers and the liquid and the gas phase chemistry of a multiwire device for the treatment of liquids were performed. Moreover, two different plasma-activated liquids were used for the treatment of Epithelial Ovarian Cancer cells and fibroblasts to assess their selectivity. In the second section, in accordance with the most important standard regulations for medical devices, were reported the realization steps of a Plasma Gun device easy to handle and expected to be mounted on a tabletop device that could be used for dental clinical applications. In the third section, in relation to the current COVID-19 pandemic, were reported the first steps for the design, realization, and optimization of a dielectric barrier discharge source suitable for the treatment of different types of bioaerosol.

Biomedical and industrial applications of atmospheric pressure non-equilibrium plasmas

This dissertation will be focused on the characterization of an atmospheric pressure plasma jet source with an application oriented diagnostic approach and the description of processes supported by this plasma source. The plasma source investigated is a single electrode plasma jet. Schlieren images, optical emission spectra, temperature and heat flux profiles are analyzed to deeply investigate the fluid dynamic, the chemical composition and the thermal output of the plasma generated with a nanosecond-pulsed high voltage generator. The maximum temperature measured is about 45 °C and values close to the room temperature are reached 10 mm down the source outlet, ensuring the possibility to use the plasma jet for the treatment of thermosensitive materials, such as, for example, biological substrate or polymers. Electrospinning of polymeric solution allows the production of nanofibrous non-woven mats and the plasma pre-treatment of the solutions leads to the realization of defect free nanofibers. The use of the plasma jet allows the electrospinnability of a non-spinnable poly(L-lactic acid) (PLLA) solution, suitable for the production of biological scaffold for the wound dressing.

Determination of the species generated in atmospheric-pressure laser-induced plasmas by mass spectometry techniques

We present temporal information obtained by mass spectrometry techniques about the evolution of plasmas generated by laser filamentation in air. The experimental setup used in this work allowed us to study not only the dynamics of the filament core but also of the energy reservoir that surrounds it. Furthermore, valuable insights about the chemistry of such systems like the photofragmentation and/or formation of molecules were obtained. The interpretation of the experimental results are supported by PIC simulations.

Surface modification of siloxane containing polyurethane polymer by dielectric barrier discharge at atmospheric pressure

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Modification of polyethylene terephthalate by atmospheric pressure dielectric barrier discharge (DBD) in view of improving the polymer wetting properties

Surface treatment of polymers by discharge plasmas has increasingly found industrial applications due to its capability of modifying uniformly the surface without changing the material bulk properties. This work deals with surface modification of polyethylene terephthalate (PET) by a dielectric barrier discharge (DBD) at atmospheric pressure. The treatments were conducted in air, nitrogen or argon plasma. The polymer surface was characterized by contact angle measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results show that the plasma treatment introduces oxygen-and nitrogen-related polar groups on the polymer surface and promotes the surface roughening. Both plasma-induced surface modifications contribute to the enhancement of the polymer wettability.

Surface Modification of Polycarbonate by Atmospheric-Pressure Plasma Jets

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Treatment of polycarbonate by dielectric barrier discharge (DBD) at atmospheric pressure

Generally most plastic materials are intrinsically hydrophobic, low surface energy materials, and thus do not adhere well to other substances. Surface treatment of polymers by discharge plasmas is of great and increasing industrial application because it can uniformly modify the surface of sample without changing the material bulk properties and is environmentally friendly. The plasma processes that can be conducted under ambient pressure and temperature conditions have attracted special attention because of their easy implementation in industrial processing. Present work deals with surface modification of polycarbonate (PC) by a dielectric barrier discharge (DBD) at atmospheric pressure. The treatment was performed in a parallel plate reactor driven by a 60Hz power supply. The DBD plasmas at atmospheric pressure were generated in air and nitrogen. Material characterization was carried out by contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The surface energy of the polymer surface was calculated from contact angle data by Owens-Wendt method using distilled water and diiodomethane as test liquids. The plasma-induced chemical modifications are associated with incorporation of polar oxygen and nitrogen containing groups on the polymer surface. Due to these surface modifications the DBD-treated polymers become more hydrophilic. Aging behavior of the treated samples revealed that the polymer surfaces were prone to hydrophobic recovery although they did not completely recover their original wetting properties.

Eradication and phenotypic tolerance of Burkholderia cenocepacia biofilms exposed to atmospheric pressure non-thermal plasma.

Chronic lung infection with bacteria from the Burkholderia cepacia complex (BCC), and in particular B. cenocepacia, is associated with significant morbidity and mortality in patients with cystic fibrosis (CF). B. cenocepacia can spread from person to person and exhibits intrinsic broad-spectrum antibiotic resistance. Recently, atmospheric pressure non-thermal plasmas (APNTPs) have gained increasing attention as a novel approach to the prevention and treatment of a variety of hospital-acquired infections. In this study, we evaluated an in-house-designed kHz-driven plasma source for the treatment of biofilms of a number of clinical CF B. cenocepacia isolates. The results demonstrated that APNTP is an effective and efficient tool for the eradication of B. cenocepacia biofilms but that efficacy is highly variable across different isolates. Determination of phenotypic differences between isolates in an attempt to understand variability in plasma tolerance revealed that isolates which are highly tolerant to APNTP typically produce biofilms of greater biomass than their more sensitive counterparts. This indicates a potential role for biofilm matrix components in biofilm tolerance to APNTP exposure. Furthermore, significant isolate-dependent differences in catalase activity in planktonic bacteria positively correlated with phenotypic resistance to APNTP by isolates grown in biofilms.

Quantification of free mycophenolic acid by high-performance liquid chromatography-atmospheric pressure chemical ionisation tandem mass spectrometry

To facilitate the investigation of free mycophenolic acid concentrations we developed a high-performance liquid chromatography tandem mass spectrometry method using indomethacin as an internal standard. Free drug was isolated from plasma samples (500 mul) using ultrafiltration, The analytes were extracted from the ultrafiltrate (200 mul) using C-18 solid-phase extraction. Detection was by selected reactant monitoring of mycophenolic acid (m/z 318.9-->190.9) and the internal standard (m/z 356.0-->297.1) with an atmospheric pressure chemical ionisation interface. The total chromatographic analysis time was 12 min. The method was found to be linear over the range investigated, 2.5-200 mug/l (r>0.990, n=6). The relative recovery of the method for the control samples studied (7.5, 40.0 and 150 mug/l) ranged from 95 to 104%. The imprecision of the method, expressed in terms of intra- and inter-day coefficients of variation, was

Temperature and atmospheric pressure may be considered as predictors for the occurrence of bacillary dysentery in Guangzhou, Southern China

Introduction The control of bacillary dysentery (BD) remains a big challenge for China. Methods Negative binomial multivariable regression was used to study relationships between meteorological variables and the occurrence of BD during the period of 2006-2012. Results Each 1°C rise of temperature corresponded to an increase of 3.60% (95%CI, 3.03% to 4.18%) in the monthly number of BD cases, whereas a 1 hPa rise in atmospheric pressure corresponded to a decrease in the number of BD cases by 2.85% (95%CI = 3.34% to 2.37% decrease). Conclusions Temperature and atmospheric pressure may be considered as predictors for the occurrence of BD in Guangzhou.

Steam Curing of Portland Cement Concrete at Atmospheric Pressure, HR-40, 1962

The primary reason for using steam in the curing of concrete is to produce a high early strength. This high early strength is very desirable to the manufacturers of precast and prestressed concrete units, which often require expensive forms or stress beds. They want to remove the forms and move the units to storage yards as soon as possible. The minimum time between casting and moving the units is usually governed by the strength of the concrete. Steam curing accelerates the gain in strength at early ages, but the uncontrolled use of steam may seriously affect the growth in strength at later ages. The research described in this report was prompted by the need to establish realistic controls and specifications for the steam curing of pretensioned, prestressed concrete bridge beams and concrete culvert pipe manufactured in central plants. The complete project encompasses a series of laboratory and field investigations conducted over a period of approximately three years.

Radicals from the atmospheric pressure pyrolysis and oxidative pyrolysis of hydroquinone, catechol, and phenol

The burning of tobacco creates various types of free radicals that have been reported to be biologically active. Some radicals are transient but can initiate catalytic cycles that generate other free radicals. Other radicals are environmentally persistent and can exist in total particulate matter (TPM) for extended periods. In spite of their importance, little is known concerning the precursors of these radicals or under what pyrolysis/combustion conditions they are formed. We performed studies of the formation of radicals from the gas-phase pyrolysis and oxidative pyrolysis of hydroquinone (HQ) and catechol (CT) between 750 and 1000 °C and phenol from 500 to 1000 °C. The initial electron paramagnetic resonance (EPR) spectra were complex, indicating the presence of multiple radicals. Using matrix annealing and microwave power saturation techniques, phenoxyl, cyclopentadienyl, and peroxyl radicals were identifiable, but only cyclopentadienyl radicals were stable above 750 °C.