Personne :
Laroche, Gaétan

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Adresse électronique
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Structures organisationnelles
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Université Laval. Département de génie des mines, de la métallurgie et des matériaux
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Résultats de recherche

Voici les éléments 1 - 7 sur 7
  • Publication
    Accès libre
    Characterization of argon dielectric barrier discharges applied to ethyl lactate plasma polymerization
    (Institute of Physics Publishing Ltd, 2017-11-03) Laroche, Gaétan; Desjardins, Edouard; Naudé, Nicolas; Meichelboeck, Maximilian; Laurent, Morgane; Stafford, Luc; Gherardi, Nicolas
    The influence of the input voltage frequency (35 and 150 kHz), interelectrode gap (1 and 2 mm) and precursor concentration (250, 350, and 450 ppm) on the electron temperature (Te), number density of metastable Ar atoms (n(Arm)), and discharge current density (proportional to the electron density ne) is studied in an argon-ethyl lactate dielectric barrier discharge (DBD). An argon-ammonia Penning mixture is also considered as reference. These results are correlated to the chemistry (XPS, IR) and topography (AFM) of the ethyl-lactate-based plasma polymer coatings. Low Te values from 0.3 to 0.5 eV were obtained for all discharges. This observation, in addition to resemblances with the Ar–NH3 mixture, suggested that the ionization kinetics of ethyl lactate-based discharges is driven by Penning reactions. Among the investigated parameters, the dissipated power obtained through changes of the excitation frequency had the largest impact on both the coatings properties and the discharge behavior.
  • Publication
    Accès libre
    Time-resolved study of the electron temperature and number density of argon metastable atoms in argon-based dielectric barrier discharges
    (IOP Publishing, 2018-01-24) Desjardins, Edouard; Laroche, Gaétan; Naudé, Nicolas; Durocher-Jean, Antoine; Laurent, Morgane; Gherardi, Nicolas; Stafford, Luc
    A combination of optical emission spectroscopy and collisional-radiative modelling is used to determine the time-resolved electron temperature (assuming Maxwellian electron energy distribution function) and number density of Ar 1s states in atmospheric pressure Ar-based dielectric barrier discharges in presence of either NH₃ or ethyl lactate. In both cases, Te values were higher early in the discharge cycle (around 0.8 eV), decreased down to about 0.35 eV with the rise of the discharge current, and then remained fairly constant during discharge extinction. The opposite behaviour was observed for Ar 1s states, with cycle-averaged values in the 10¹⁷ m−³ range. Based on these findings, a link was established between the discharge ionization kinetics (and thus the electron temperature) and the number density of Ar 1s state.
  • Publication
    Accès libre
    Influence of a square pulse voltage on argon-ethyl lactate discharges and their plasma-deposited coatings using time-resolved spectroscopy and surface characterization
    (AIP Publishing, 2018-10-15) Laroche, Gaétan; Desjardins, Edouard; Naudé, Nicolas; Meichelboeck, Maximilian; Belinger, Antoine; Laurent, Morgane; Stafford, Luc; Gherardi, Nicolas
    By comparing time-resolved optical emission spectroscopy measurements and the predictions of a collisional-radiative model, the evolutions of electron temperature (Te) and number density of argon metastable atoms [n(Arm)] were determined in argon-ethyl lactate dielectric barrier discharges. The influence of a square pulse power supply on Te, n(Arm), and discharge current is evaluated and correlated with the chemistry and the topography of plasma-deposited coatings. Pulsed discharges were found to have shorter (100 ns) but stronger (1 A) current peaks and higher electron temperatures (0.7 eV) than when using a 35 kHz sinusoidal power supply (2 μs, 30 mA, 0.3 eV). The n(Arm) values seemed to be rather stable around 1011 cm−3 with a sinus power supply. In contrast, with a pulse power supply with long time off (i.e., time without discharge) between each pulse, a progressive increase in n(Arm) from 1011 cm−3 up to 1012–1013 cm−3 was observed. When the time off was reduced, this increase was measured in sync with the current peak. The chemical composition of the coatings was not significantly affected by using a pulse signal, whereas the topography was strongly influenced and led to powder formations when reducing the time off.
  • Publication
    Accès libre
    Response surface methodology as a predictive tool for the fabrication of coatings with optimal anti-fogging performance
    (Lausanne Elsevier Sequoia, 2020-12-15) Laroche, Gaétan; Profili, Jacopo; Rodríguez Durán, Iván; Stafford, Luc
    In this study, response surface methodology was applied to optimize the anti-fogging performance of coatings deposited on commercial glass samples from 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)/N2O mixtures by atmospheric pressure plasma enhanced chemical vapor deposition. The effect of the dissipated power (DP), [N2O]/[TMCTS] ratio, and sample scroll speed on the anti-fogging performance was investigated by means of a Box-Behnken experimental design. The regression model relating transmittance of the coated glasses to these deposition parameters revealed that the anti-fogging performance strongly depends on the second-order interaction of the dissipated power and [N2O]/[TMCTS] ratio (i.e., DP × [N2O]/[TMCTS]). Contour plots showed that the dissipated power required to prepare optimal anti-fogging coatings should be of at least 0,7, 0,5 or 0,4 W cm−2, if the [N2O]/[TMCTS] ratio in the plasma is 20, 30, or 40, respectively. When placed over water at 50°C, the coated glass samples allowed 80% (or more) of 590-nm light to pass through, thus meeting the minimal anti-fogging requirement for alpine skier goggles and faceshields. Despite not having a significant impact on the anti-fogging performance, the sample scroll speed is key to fabricating coatings with the desired thickness during in-line manufacturing.
  • Publication
    Accès libre
    Atmospheric pressure townsend discharges as a promising tool for the one‐step deposition of antifogging coatings from N2O/TMCTS mixtures
    (Wiley, 2020-02-13) Laroche, Gaétan; Durocher-Jean, Antoine; Rodríguez Durán, Iván; Profili, Jacopo; Stafford, Luc
    The need to ensuring the “see‐through” property of transparent materials when exposed to sudden temperature changes or very humid conditions has encouraged the development of antifogging strategies, such as the deposition of (super)hydrophilic coatings. However, despite the effectiveness of these coatings in combating the effects of fogging, most of the coating techniques explored to date are typically time‐consuming and environment‐unfriendly. Bearing this in mind, we demonstrate that the application of dielectric barrier discharges operated at atmospheric pressure proves to be successful in preparing antifogging coatings on glass samples from 1,3,5,7‐tetramethylcyclotetrasiloxane (TMCTS) and nitrous oxide (N2O). The antifogging performance of the coatings was found to be governed by the [N2O]/[TMCTS] ratio and not by the [N2O] + [TMCTS] sum. Coatings prepared under a [N2O]/[TMCTS] = 30 were superhydrophilic (water contact angles ≈ 5°–10°) due to surface silanol groups and endowed glass samples with a superior antifogging property, as revealed by the ASTM F 659‐06 test. In contrast, because of the lesser hydrophilicity (water contact angles ≈ 60°), coatings prepared under a [N2O]/[TMCTS] = 10 did not endow glass samples with antifogging property. Regardless of the deposition conditions, the plasma‐deposited coatings displayed crack‐free smooth surfaces (Rrms = 2−4 nm).
  • Publication
    Accès libre
    Deposition of anti-fog coatings on glass substrates using the jet of an open-to-air microwave argon plasma at atmospheric pressure
    (Wiley-VCH-Verl., 2020-04-22) Durocher-Jean, Antoine; Rodríguez Durán, Iván; Asadollahi, Siavash; Laroche, Gaétan; Stafford, Luc
    This study reports a one-step process for the formation of anti-fog coatings on commercial glass substrates using the jet of an open-to-air microwave argon plasma at atmospheric pressure with hexamethyldisiloxane (HMDSO) as the precursor for plasma-enhanced chemical vapor deposition. Optical microscopy and broadband light transmittance measurements revealed significant precursor fragmentation and gas phase association reactions when HMDSO was injected close to the tube outlet, resulting in powder-like, hydrophobic, and semiopaque glass surfaces. On the contrary, injection of HMDSO close to the substrate led to smoother, homogeneous, hydrophilic, and transparent glass surfaces. In addition, transmittance measurements at 590 nm in humid air according to American Society for Testing and Materials standard tests revealed superior antifogging properties to plasma-treated glass substrates. On the basis of the optical emission and absorption spectroscopy measurements, electrons, metastable argon atoms, and hot neutral argon atoms were mostly responsible for the significant precursor fragmentation close to the tube outlet, whereas the contribution of hot neutrals and ultraviolet photons became important close to the substrate.
  • Publication
    Beyond microelectronics with 1,3,5,7-tetramethylcyclotetrasiloxane : a promising molecule for anti-fogging coatings
    (Elsevier Sequoia, 2019-12-04) Laroche, Gaétan; Profili, Jacopo; Rodríguez Durán, Iván; Stafford, Luc
    Over the past few years, a growing number of studies have focused on designing coatings for use in applications dealing with the fogging phenomenon such as endoscopes, automobile side view mirrors, and protective goggles. However, because of the long manufacturing times, the implementation on an industrial scale of most of the coating techniques used thus far is still a pending issue. Bearing this in mind, we report on the use of atmospheric pressure dielectric barrier discharges (AP-DBDs) operated in the presence of nitrous oxide (N2O) and 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS), as a reliable coating strategy for the one-step fabrication of anti-fogging glass. An increase in either the [N2O]/[TMCTS] ratio or the dissipated power resulted in coatings with such hydrophilic groups on the surface as Si–OH, C–O, and OC–O; and a structure similar to that of SiO2. Because of their “water-loving” characteristics (WCA < 40°), coatings deposited under a [N2O]/[TMCTS] ratio ≥ 30 and a dissipated power ≥ 0.25 W cm−2 conferred a remarkable anti-fogging performance to glass samples when placed over water at 80 °C. After 30 s of exposure to water vapor at 50 °C (ASTM F 659-06), the coated glasses exhibited a light transmittance greater than that of the uncoated glass (90% vs. 55%). These results illustrate how by controlling the dissipated power and the [N2O]/[TMCTS] ratio in the plasma anti-fogging glass can readily be fabricated.