Patrick Choquet

Robust bio-inspired antibacterial surfaces based on the covalent binding of peptides on functional atmospheric plasma thin films

Here, we describe a robust process aiming at conferring antibacterial properties on stainless steel through the covalent grafting of nisin, a natural antimicrobial peptide, onto a functional plasma thin film deposited by an atmospheric pressure dielectric barrier discharge process. The three different steps of the procedure, namely the deposition of a carboxyl rich thin layer, the surface activation by using a zero-length crosslinking agent and the nisin immobilisation, are reported and thoroughly characterised. A correlation between the carboxylic group surface concentration and the surface roughness onto the antibacterial properties of the layers is evidenced. Finally, IR analyses appear as a powerful analytical tool allowing us to validate the different chemical surface modifications, to confirm the relevance of the activation step to achieve a stable and homogenous peptide grafting over all the surfaces, as well as to investigate the secondary structure of immobilized peptides.

A simple and scalable approach towards the preparation of superhydrophobic surfaces – importance of the surface roughness skewness

A simple and easily up-scalable approach towards the preparation of fluorine-free superhydrophobic surfaces is proposed. Surfaces with water contact angle (WCA) as high as 170° and contact angle hysteresis (CAH) down to 5° are obtained on industrial metallic foils (cold-rolled aluminium foils and electrodeposited copper foils) coated thanks to an atmospheric pressure plasma-enhanced chemical vapour deposition method. Nano- and micro-scale roughness characterisation of the surface, performed by atomic force microscopy (AFM) and confocal microscopy, provided evidence for the substrate surface skewness as the major parameter influencing the WCA for identical nano-rough plasma-polymerised PDMS coatings. A symmetric height distribution, Rskm = 0, is shown to be more desirable to achieve superhydrophobic surfaces.

Atmospheric pressure plasma-initiated chemical vapor deposition (AP-PiCVD) of poly(diethylallylphosphate) coating: a char-forming protective coating for cellulosic textile.

An innovative atmospheric pressure chemical vapor deposition method toward the deposition of polymeric layers has been developed. This latter involves the use of a nanopulsed plasma discharge to initiate the free-radical polymerization of an allyl monomer containing phosphorus (diethylallylphosphate, DEAP) at atmospheric pressure. The polymeric structure of the film is evidence by mass spectrometry. The method, highly suitable for the treatment of natural biopolymer substrate, has been carried out on cotton textile to perform the deposition of an efficient and conformal protective coating.

Luminescent lanthanide-based hybrid coatings deposited by atmospheric pressure plasma assisted chemical vapour deposition

A new atmospheric pressure plasma route toward the formation of smart hybrid coatings is presented. As an example, luminescent lanthanide-containing coordination polymers were embedded in a silica matrix.

Photocatalytic Anatase TiO2 Thin Films on Polymer Optical Fiber Using Atmospheric-Pressure Plasma

Due to the undeniable industrial advantages of low-temperature atmospheric-pressure plasma processes, such as low cost, low temperature, easy implementation, and in-line process capabilities, they have become the most promising next-generation candidate system for replacing thermal chemical vapor deposition or wet chemical processes for the deposition of functional coatings. In the work detailed in this article, photocatalytic anatase TiO2 thin films were deposited at a low temperature on polymer optical fibers using an atmospheric-pressure plasma process. This method overcomes the challenge of forming crystalline transition metal oxide coatings on polymer substrates by using a dry and up-scalable method. The careful selection of the plasma source and the titanium precursor, i.e., titanium ethoxide with a short alkoxy group, allowed the deposition of well-adherent, dense, and crystalline TiO2 coatings at low substrate temperature. Raman and XRD investigations showed that the addition of oxygen to the precursors carrier gas resulted in a further increase of the films crystallinity. Furthermore, the films deposited in the presence of oxygen exhibited a better photocatalytic activity toward methylene blue degradation assumedly due to their higher amount of photoactive {101} facets.

Formation of ammonium in saline solution treated by nanosecond pulsed cold atmospheric microplasma: a route to fast inactivation of E. coli bacteria

He/N2 cold atmospheric plasma treatment of E. coli suspension leads to a fast and efficient inactivation process. Significant generation of ammonium is reported. The formation of NH4+ species in saline solution treated by cold atmospheric plasma is proposed for the first time as the main process responsible for the fast bacterial inactivation in pH-buffered solutions, at ambient temperature and physiological pH.

Interstitial boron-doped anatase TiO2 thin-films on optical fibres: atmospheric pressure-plasma enhanced chemical vapour deposition as the key for functional oxide coatings on temperature-sensitive substrates

Temperature sensitive poly(methyl methacrylate) (PMMA) optical fibres were coated with boron doped-anatase crystalline TiO2 thin films in a one-step atmospheric pressure-plasma enhanced chemical vapour deposition (AP-PECVD) process. Both the undoped and interstitial boron-doped TiO2 thin films showed photoactivity under UV irradiation, with the boron-doped thin films presenting higher photodegradation rates when compared to the undoped samples.

Influence of temperature on oxidation mechanisms of fiber-textured AlTiTaN coatings.

The oxidation kinetics of AlTiTaN hard coatings deposited at 265 °C by DC magnetron sputtering were investigated between 700 and 950 °C for various durations. By combining dynamic secondary ion mass spectrometry (D-SIMS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) investigations of the different oxidized coatings, we were able to highlight the oxidation mechanisms involved. The TEM cross-section observations combined with XRD analysis show that a single amorphous oxide layer comprising Ti, Al, and Ta formed at 700 °C. Above 750 °C, the oxide scale transforms into a bilayer oxide comprising an Al-rich upper oxide layer and a Ti/Ta-rich oxide layer at the interface with the coated nitride layer. From the D-SIMS analysis, it could be proposed that the oxidation mechanism was governed primarily by inward diffusion of O for temperatures of ≤700 °C, while at ≥750 °C, it is controlled by outward diffusion of Al and inward diffusion of O. Via a combination of structural and chemical analysis, it is possible to propose that crystallization of rutile lattice favors the outward diffusion of Al within the AlTiTa mixed oxide layer with an increase in the temperature of oxidation. The difference in the mechanisms of oxidation at 700 and 900 °C also influences the oxidation kinetics with respect to oxidation time. Formation of a protective alumina layer decreases the rate of oxidation at 900 °C for long durations of oxidation compared to 700 °C. Along with the oxidation behavior, the enhanced thermal stability of AlTiTaN compared to that of the TiAlN coating is illustrated.

Temperature-dependent wear mechanisms for magnetron sputtered AlTiTaN hard coatings

AlTiTaN coatings have been demonstrated to have high thermal stability at temperatures up to 900 °C. It has been speculated that the high oxidation resistance promotes an improved wear resistance, specifically for dry machining applications. This work reports on the influence of temperature up to 900 °C on the wear mechanisms of AlTiTaN hard coatings. DC magnetron-sputtered coatings were obtained from an Al(46)Ti(42)Ta(12) target, keeping the substrate bias at -100 V and the substrate temperature at 265 °C. The coatings exhibited a single-phase face-centered cubic AlTiTaN structure. The dry sliding tests revealed predominant abrasion and tribo-oxidation as wear mechanisms, depending on the wear debris formed. At room temperature, abrasion leading to surface polishing was observed. At 700 and 800 °C, slow tribo-oxidation and an amorphous oxide formed reduced the wear rate of the coating compared to room temperature. Further, an increase in temperature to 900 °C increased the wear rate significantly due to fast tribo-oxidation accompanied by grooving. The friction coefficient was found to decrease with temperature increasing from 700 to 900 °C due to the formation of oxide scales, which reduce adhesion of asperity contacts. A relationship between the oxidation and wear mechanisms was established using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, surface profilometry, confocal microscopy, and dynamic secondary ion mass spectrometry.

Computational Study of Acidic and Basic Functionalized Crystalline Silica Surfaces as a Model for Biomaterial Interfaces.

In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been carried out by means of a density functional approach based on a gradient-corrected functional to provide insight into the characterization of experimentally functionalized surfaces via a plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm(2)) mimic an amorphous silica interface as unsubstituted material. To functionalize the silica surface we transformed the surface Si-OH groups into Si-CH2COOH and Si-CH2NH2 moieties to represent acidic/basic chemical character for the substitution. Structures, energetics, electronic, and vibrational properties were computed and compared as a function of the increasing loading of the functional groups (from 1 to 4 per surface unit cell). Classical molecular dynamics simulations of selected cases have been performed through a Reax-FF reactive force field to assess the mobility of the surface added chains. Both DFT and force field calculations identify the CH2NH2 moderate surface loading (1 group per unit cell) as the most stable functionalization, at variance with the case of the CH2COOH group, where higher loadings are preferred (2 groups per unit cell). The vibrational fingerprints of the surface functionalities, which are the ν(C═O) stretching and δ(NH2) bending modes for acidic/basic cases, have been characterized as a function of substitution percentage in order to guide the assignment of the experimental data. The final results highlighted the different behavior of the two types of functionalization. On the one hand, the frequency associated with the ν(C═O) mode shifts to lower wavenumbers as a function of the H-bond strength between the surface functionalities (both COOH and SiOH groups), and on the other hand, the δ(NH2) frequency shift seems to be caused by a subtle balance between the H-bond donor and acceptor abilities of the NH2 moiety. Both sets of data are in general agreement with experimental measurements on the corresponding silica-functionalized materials and provide finer details for a deeper interpretation of experimental spectra.