37 research outputs found
Organic coatings from acetylene at atmospheric pressure: UV light versus plasma
ABSTRACT: A versatile pilot-scale reactor has been designed in such a way that it can be readily converted from a dielectric barrier discharge âPECVDâ operating mode into a photoinitiated âPICVDâ one; in the latter, low-pressure mercury (Hg) lamps replace the high-voltage glow discharge plasma. Both processes operate at ambient temperature and atmospheric pressure, 100âkPa, using acetylene (C2H2) monomer. In both sets of experiments, it was found that efficient gas-to-solid conversion can occur in the form of a nanoparticulate amorphous hydrocarbon polymer-like material. It was found that in the PICVD case, great care was required to exclude even traces of O2 contamination, because it not only reduced the growth rate of solid, but the latter then became highly oxidized ([O] ~50âat.%) and water-soluble
Nanoporous sponges as carbon-based sorbents for atmospheric water generation
Water scarcity threatens more and more people in the world. Moisture adsorption from the atmosphere represents a promising avenue to provide fresh water. Nanoporous sponges (âNPSsâ ), new carbon-based sorbents synthesized from the pyrolysis of resorcinol-formaldehyde resin, can achieve comparable performance to metal organic framework-based systems, but at a significantly lower cost. Oxygen and nitrogen functionalities can be added to the NPS surface, through oxidation and addition of phenanthroline to the initial reagent mixture, respectively. The resulting NPS sorbents have high specific surface areas of 347 to 527 m2·gâ1 and an average capillary-condensation-compatible pore size of 1.5 nm. When oxidized, the NPS can capture up to 0.28 g of water per gram of adsorbent at a relative pressure of 0.90 (0.14 g·gâ1 at P/Psat = 0.40) and maintain this adsorption capacity over multiple adsorption/desorption cycles. Scaled-up synthesis of the NPS was performed and tested in an experimental water capture setup, showing good agreement between small- and larger-scale adsorption properties. Water adsorption isotherms fitted with the theoretical model proposed by Do and Do demonstrate that hydroxyl functionalities are of key importance to NPS behavior
Atmospheric pressure plasma synthesis of biocompatible poly(ethylene glycol)-like coatings
The role of a protein-repelling coating is to limit the interaction between a device and its physiological environment. Plasma-polymerized-PEG (pp-PEG) surfaces are of great interest since they are known to avoid protein adsorption. and cell attachment. However, in all the studies previously published in the literature, the PEG coatings have been prepared using low pressure processes. <p>In this thesis, we synthesize biocompatible pp-PEG coatings using atmospheric pressure plasma. Two original methods are developed to obtain these pp-PEG films. 1. Atmospheric pressure plasma liquid deposition (APPLD) consists in the injection of the precursor, tetra(ethylene glycol)dimethylether (tetraglyme), by means of a liquid spray, directly in the post-discharge of an atmospheric argon plasma torch. 2. In atmospheric pressure plasma-enhanced chemical vapor deposition (APPECVD), tetraglyme vapors are brought in the post-discharge trough a heating sprinkler. The chemical composition, as well as the non-fouling properties of the APPLD and APPECVD films, are compared to those of PEG coatings synthesized by conventional low pressure plasma processes.<p>In the first part of the study, the effect of the power on the chemical composition of the films has been investigated by infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and secondary ions mass spectroscopy (SIMS). <p>The surface analysis reveals that for the APPECVD samples, the fragmentation of the precursor increases as the power of the treatment is increased. In other terms, the lower the plasma power is, the higher the âPEG characterâ of the resulting films is. Indeed, the C-O component (286.5 eV) of the XPS C 1s peak is decreasing while the hydrocarbon component (285 eV) is increasing as the power of the plasma is increased. The same conclusion can be drawn from the signature ToF-SIMS peaks (m/z = 45 (CH3&61485;O&61485;CH2+ and +CH2CH2&61485;OH), 59 (CH3&61485;O&61485;CH2&61485;CH2+), 103 (CH3&61485;(O&61485;CH2&61485;CH2)2+)) that are decreasing in the case of high power treatments. Accordingly, IRRAS measurements show that the C-O stretching band is decreasing for high power plasma deposition. This is in agreement with the observations made from the analysis of the LP PECVD coatings and from the literature.<p>The films deposited by the APPLD process do not show the same behavior. Indeed, whatever the power injected into the discharge is, we are able to achieve films with a relatively high PEG character (&61566;83 %).<p>The second part of this study is dedicated to the evaluation of the non-fouling properties of the coatings by exposing them to proteins (bovine serum albumin and human fibrinogen) and cells (mouse fibroblasts (L929 and MEF)) and controlling the adsorption with XPS (proteins) and SEM (cells).<p>For the APPECVD samples, a low plasma power (30 W) leads to an important reduction of protein adsorption and cell adhesion (over 85%). However, higher-powered treatments tend to reduce the non-fouling ability of the surfaces (around 50% of reduction for a 80 W deposition). <p>The same order of magnitude (over 90% reduction of the adsorption) is obtained for the APPLD surfaces, whatever is the power of the treatment. <p>Those results show an important difference between the two processes in terms of power of the plasma treatment, and a strong relationship between the surface chemistry and the adsorption behavior: the more the PEG character is preserved, the more protein-repellent and cell-repellent is the surface. / Le rĂŽle dâune couche empĂȘchant lâadsorption de protĂ©ines est de limiter les interactions entre un implant et le milieu physiologique auquel il est exposĂ©. Les films de poly(Ă©thylĂšne glycol) polymĂ©risĂ©s par plasma (pp-PEG) sont dâintĂ©rĂȘt majeur car ils sont connus pour empĂȘcher lâadsorption de protĂ©ines ainsi que lâattachement cellulaire. Cependant, dans toutes les Ă©tudes publiĂ©es prĂ©cĂ©demment, les couches de type PEG ont Ă©tĂ© rĂ©alisĂ©es sous vide.<p>Dans cette thĂšse de doctorat, nous synthĂ©tisons des couches de type pp-PEG biocompatibles par plasmas Ă pression atmosphĂ©rique. A cette fin, deux mĂ©thodes originales ont Ă©tĂ© dĂ©veloppĂ©es. 1. La premiĂšre mĂ©thode consiste en lâinjection du prĂ©curseur, le tetra(Ă©thylĂšne glycol) dimĂ©thyl Ă©ther (tetraglyme), en phase liquide, en nĂ©bulisant ce dernier au moyen dâun spray, directement dans la post-dĂ©charge dâune torche Ă plasma atmosphĂ©rique fonctionnant Ă lâargon. En anglais, nous appelons ce procĂ©dĂ© « Atmospheric pressure plasma liquid deposition (APPLD) ». 2. Dans la deuxiĂšme mĂ©thode, appelĂ©e en anglais « Atmospheric pressure plasma-enhanced chemical vapor deposition (APPECVD)», le tetraglyme est amenĂ© en phase vapeur dans la post-dĂ©charge, au moyen dâun diffuseur chauffant. La composition chimique des dĂ©pĂŽts de type APPLD et APPECVD, ainsi que leurs propriĂ©tĂ©s dâanti-adsorption sont Ă©valuĂ©es, et comparĂ©es aux dĂ©pĂŽts pp-PEG obtenus par les mĂ©thodes Ă basse pression conventionnelles.<p>Dans la premiĂšre partie de cette Ă©tude, nous nous focalisons sur la composition chimique des films dĂ©posĂ©s, et plus particuliĂšrement sur lâinfluence de la puissance injectĂ©e dans le plasma sur cette composition chimique. A cette fin, nous avons fait appel Ă des techniques dâanalyse telles que la spectroscopie de rĂ©flexion-absorption infrarouge (IRRAS), la spectroscopie des photoĂ©lectrons X (XPS) et la spectromĂ©trie de masse des ions secondaires (SIMS). <p>Il en ressort que les films de type APPECVD perdent progressivement leur « caractĂšre PEG » Ă mesure que la puissance de la dĂ©charge plasma est Ă©levĂ©e. Cela serait dĂ» Ă une plus grande fragmentation du prĂ©curseur dans la post-dĂ©charge dâun plasma plus Ă©nergĂ©tique. Cette tendance est cohĂ©rente avec ce que nous avons observĂ© pour les dĂ©pĂŽts Ă basse pression ainsi que dans la littĂ©rature.<p>Dans le cas des films de type APPLD, un tel comportement nâa pas Ă©tĂ© mis en Ă©vidence :quelle que soit la puissance dissipĂ©e dans le plasma, les films prĂ©sentent un « caractĂšre PEG » relativement Ă©levĂ©.<p>La deuxiĂšme partie de cette thĂšse est dĂ©diĂ©e Ă lâĂ©valuation des propriĂ©tĂ©s dâanti-adsorption des films synthĂ©tisĂ©s, en les exposant Ă des protĂ©ines (albumine de sĂ©rum bovin et fibrinogĂšne humain) et des cellules (fibroblastes de souris, L929 et MEF). Lâadsorption de protĂ©ines est contrĂŽlĂ©e par XPS tandis que lâattachement cellulaire est contrĂŽlĂ© par imagerie SEM.<p>Pour les Ă©chantillons de type APPECVD, un dĂ©pĂŽt Ă faible puissance (30 W) mĂšne Ă une importante rĂ©duction de lâadsorption de protĂ©ines et de cellules (> 85%) tandis quâĂ de plus hautes puissances (80 W), lâanti-adsorption est sensiblement diminuĂ©e (50% de rĂ©duction). Dans le cas des dĂ©pĂŽts de type APPLD, quelle que soit la puissance du plasma, une forte diminution de lâadsorption de protĂ©ines et de cellules est observĂ©e (> 90 %).<p>Ces rĂ©sultats montrent une diffĂ©rence majeure entre les deux procĂ©dĂ©s quant Ă lâinfluence de la puissance du plasma ainsi quâune forte relation entre la composition chimique de la surface synthĂ©tisĂ©e et son pouvoir dâanti-adsorption :plus le « caractĂšre PEG » du dĂ©pĂŽt est conservĂ©, plus la surface empĂȘchera lâinteraction avec les protĂ©ines et les cellules. <p><p>Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe
Challenges in the characterization of plasma polymers using XPS
Organic coatings synthesized using plasma techniques, often called plasma polymers, are very frequently characterized routinely using X-ray photoelectron spectroscopy. In this paper, we show that, due to the intrinsic chemistry and structure of plasma polymers, such characterization is not trivial and should be carefully driven. Some routes to improve the characterization are proposed, and we show also that XPS, combined with other gas phase or solid state characterization techniques can successfully help to improve the structure, chemistry, and polymerization process of the coatings.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Easy Synthesis of Ageing-Resistant Coatings with Tunable Wettability by Atmospheric Pressure Plasma
This study presents a simple and dry approach to synthesize stable, thin organic coatings with tunable wettability by injecting appropriate quantities of propargyl methacrylate (propaMA) and acrylic acid (AA) into a dielectric barrier discharge operating at atmospheric pressure. Deposition rates of up to 11 nm sâ1 can be achieved, thanks to the high reactivity of the propaMA monomer in the discharge. The AA monomer exhibits a weaker reactivity but, as evidenced by IRRAS and XPS analyses, allows introducing polar groups into the coating, thereby modifying the surface wettability. The surface is thus shown to be tunable from highly hydrophobic (WCA = 140°, pure propaMA coatings) to highly hydrophilic (WCA = 15°, pure AA coatings) by adjusting the monomer ratio in the discharge. These coatings have been deposited on polypropylene (PP) substrates, and the resulting WCA is shown to remain constant for at least 64 days, ageing that is remarkably slow compared with plasma functionalization that usually leads to rapid hydrophobic recovery.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Energetics of reactions in a dielectric barrier discharge with argon carrier gas: VIII hydrofluoromethanes
Use of remote atmospheric mass spectrometry in atmospheric plasma polymerization of hydrophilic and hydrophobic coatings
This paper shows that, to a certain extent, remote atmospheric mass spectrometry can be used to identify signature fragments, which are able to predict the final surface chemistry of plasma-deposited organic hydrophilic or hydrophobic coatings, to propose polymerization mechanisms and to predict coating contamination. Examples are given for the plasma polymerization of anhydrides and organic acids for polar coatings and for the polymerization of fluorinated precursors for hydrophobic coatings. To predict the final surface chemistry of hydrophilic coatings, we show that by tracking the evolution of the CO+ and CO2 + fragments in the plasma phase, one can deduce the relative amount of polar functions on the final coating surface. Similarly, the change in intensities of the various CFx + fragments during the plasma polymerization of hydrophobic coatings is correlated with the relative amount of such CFx groups in the coating. For the same coatings, when CO2 +, COF+, and COF2 + fragments are detected in the gas phase, the final coating will be contaminated. The possibilities, as well as some limits of this approach, are discussed.SCOPUS: ar.jinfo:eu-repo/semantics/publishe