Remote atmospheric pressure plasma for improving acid-base surface properties of PEEK polymer: relevance to coating adhesion

Our study focuses on a remote atmospheric pressure plasma for the improvement of polymer surface reactivity. From the perspective of linking surface modifications to adhesives performances, wettability measurements are made using two models (Owens-Wendt-Rabel-Kaelble and Van Oss-Good-Chaudhury). This study is a contribution to correlate wettability with adhesion results obtained with three-point bending test. Acid-base properties of the treated polymeric surfaces are discussed according to the Lewis’s theory

Alimentation électrique des dispositifs à décharge à barrière diélectrique (DBD)

L’utilisation d’une Décharge contrôlée par Barrière Diélectrique (DBD) permet d’obtenir un plasma froid à pression atmosphérique dont une des utilisations est le traitement de surface. Actuellement, de tels dispositifs sont alimentés par des sources de tension variable (amplitude, fréquence) : la décharge obtenue est le plus souvent filamentaire (défavorable à la qualité du traitement de surface), notamment lorsque l’on souhaite transmettre une puissance élevée. Des études récentes menées pour l’alimentation de lampes à excimères [1] ont montré l’intérêt de remplacer la source de tension par une source de courant, afin d’obtenir la décharge sur une plus grande plage de puissance et de fréquence, de disposer de degrés de liberté permettant le contrôle de la puissance transmise. Cet article est dédié à l’étude théorique et expérimentale d’une structure d’alimentation électrique de ce type

Characterization of argon dielectric barrier discharges applied to ethyl lactate plasma polymerization

The influence of the input voltage frequency (35 and 150 kHz), interelectrode gap (1 and 2mm) 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

Role of substrate outgassing on the formation dynamics of either hydrophilic or hydrophobic wood surfaces in atmospheric-pressure, organosilicon plasmas

This work examines the influence of substrate outgassing on the deposition dynamics of either hydrophilic or hydrophobic coatings on wood surfaces in organosilicon, dielectric barrier discharges. Sugar maple and black spruce wood samples were placed on the bottom electrode and the discharge was sustained in N2–HMDSO (hexamethyldisiloxane) gas mixtures by applying a 24 kV peak-to-peak voltage at 2 kHz. Current–voltage characteristics revealed a transition from a filamentary to a homogeneous discharge with increasing plasma treatment time, t. Based on opticalemission spectroscopy, the filamentary behaviorwas ascribed to the release of air and humidity from the wood substrate following discharge exposure which produced significant quenching of N2 metastables. This effect vanished at longer treatment times due to the nearly complete “pumping” of products from the wood substrate and the progressive deposition of a “barrier” layer. Analysis of the surface wettability through static, water contact angles (WCAs) and of the surface composition through Fourier-Transform-Infra-Red-Spectroscopy and X-ray-Photoelectron-Spectroscopy indicated that for t b 10 min, the wood surface was more hydrophilic due to the formation of a SiOx layer, a typical behavior for HMDSO deposition in presence of oxygen. On the other hand, for t > 10 min, the static WCA increased up to ~140° due to the deposition of hydrophobic Si(CH3)3-O-Si(CH3)2, Si(CH3)3, and Si(CH3)2 functional groups

Milkweed scaffold : a new candidate for bone cell growth

This study aims to evaluate the potential of milkweed as potential candidate to construct biodegradable scaffold for bone regeneration. A mat made of milkweed, polyethylene, and polypropylene was treated with an atmospheric pressure plasma to functionalize the surface of the polymer assembly with carboxylic acid groups, which enable to conjugate bioactive molecules, while accelerating the degradation of milkweed. Degradation tests demonstrated substantial decrease of the weight of the treated polymer mat as compared to untreated one. Biological assays revealed that the polymer assembly promoted preosteoblast MC3T3 cells recruitment with a significant enhancement observed on the RGD-grafted polymer mat

Fine-tuning of chemical and physical polymer surface modifications by atmospheric pressure post-discharge plasma and its correlation with adhesion improvement

Our study focuses on the use of a remote atmospheric pressure plasma process for the improvement of polymer surface reactivity. Indeed, surface activation of carbon-fiber-reinforced polymers that use a polyetheretherketone matrix is required to achieve strong and long-term adhesion of paint on the composite. Emphasis will be placed on the contribution of gas plasma used on surface modification. We use two techniques to characterize adherence improvement: a qualitative and industrial approach with a cross-cut test and a quantitative approach with a three-point bending test. However, to provide a better understanding of the plasma-induced modifications using air or nitrogen gas, diagnostics of the surface are also necessary. The wettability improvement, chemical surface modifications, and topography are analyzed by using contact angle measurement, X-ray photoelectron spectroscopy, and atomic force microscopy, respectively. The combination of these diagnostics highlights the capability of plasma treatment to tune the plasma/surface interactions depending on gas plasma, which results in improved adhesion

Etude électrique de la physique d'une décharge de Townsend à la pression atmosphérique et de son interaction avec un générateur : Modèle et Expérience

Recent works showed that the Atmospheric Pressure Townsend Discharge (APTD) is compatible with online surface treatment process like polymers surface activation or thin films deposit. Nevertheless, the conditions to get this dielectric barrier discharge are still too limited for the development of an industrial process: the dissipated power being too low the treatment time is too long for industrial applications. The aim of this work is to improve the APTD physics understanding in order to determine the origin of the different observed destabilizations which limit the power transmitted to the discharge. The approach consists in a fine study of the coupling between the power supply and the discharge, by means of an electrical model based on experimental observations of both the APTD and the power supply. The electrical model of the APTD allows to have a macroscopic view of the discharge. We have highlighted the importance of the secondary emission variation during the discharge, as well as the memory effect from one discharge to the following one and of the gas temperature increase, determined by a resistance thermometer and rotational temperature measurements. It appears that the increase of the gas temperature is always proportional to the mean power, even during the transients. Thus, the developed model describes the electrical behavior of the discharge on its entire domain. The coupling of this model with the power supply model shows that a reason of the APTD destabilization come from oscillations due to the parasitic elements of the power supply. This understanding allowed to find two solutions to increase the discharge power. The first consists in decreasing the ratio between the gas capacity and the solid dielectric capacity which avoids the transition to the arc, in order to avoid the appearance of the oscillations. The second, studied only in simulation, is based on the use of a square-wave current inverter source in order to maintain a constant current during the discharge and to increase the duration of the discharge ignition.Des travaux récents ont montré que la Décharge de Townsend à la Pression Atmosphérique (DTPA) est compatible avec les procédés de traitement en ligne de matériaux comme, par exemple, l'activation de surfaces polymères ou le dépôt de couches minces. Néanmoins, les conditions d'obtention de cette décharge contrôlée par barrière diélectrique sont encore limitées pour développer un procédé industriel, ce qui se traduit par une puissance trop faible et donc des temps de traitement trop longs pour des applications industrielles à grande échelle. Ainsi, l'objectif de ce travail est d'améliorer la compréhension de la physique de la DTPA afin de définir en particulier l'origine des différentes causes de sa déstabilisation qui limite la puissance transmise à la décharge. Pour cela, la démarche adoptée consiste en une étude fine du couplage entre le générateur et la décharge, par le biais d'une modélisation électrique de type circuit de l'alimentation électrique et de la DTPA basée sur des observations expérimentales. Le modèle électrique de la DTPA permet d'avoir une vision macroscopique de la décharge. Nous avons pu mettre en évidence l'importance de la variation de l'émission secondaire durant la décharge, ainsi que le rôle de l'effet mémoire d'une décharge à la suivante et celui de l'élévation de la température du gaz, déterminée par un thermocouple et par des mesures de température rotationnelle. Il apparaît que l'élévation de la température du gaz est proportionnelle à la puissance moyenne, y compris pendant les transitoires. Nous avons ainsi mis au point un modèle qui décrit le comportement électrique de la décharge sur toute sa plage de fonctionnement. Le couplage de ce modèle avec celui de l'alimentation montre qu'une cause de déstabilisation de la DTPA est liée à des oscillations dues aux éléments parasites de l'alimentation. Ainsi, l'étude du couplage entre l'alimentation et la décharge a permis de définir deux solutions permettant d'augmenter la puissance transmise. La première consiste à éviter l'apparition d'oscillations en diminuant le rapport de la capacité du diélectrique solide qui évite la transition à l'arc sur la capacité du gaz. La seconde, étudiée uniquement en simulation, est basée sur l'utilisation d'une source de courant de type commutateur de courant afin de maintenir un courant constant durant la décharge et d'accroître la durée d'allumage de la décharge

Transition from diffuse to self-organized discharge in a high frequency dielectric barrier discharge

Depending on the operating conditions, different regimes can be obtained in a dielectric barrier discharge (DBD): filamentary, diffuse (also called homogeneous) or self-organized. For a plane-to-plane DBD operated at high frequency (160 kHz) and at atmospheric pressure in helium gas, we show that the addition of a small amount of nitrogen induces a transition from the diffuse regime to a self-organized regime characterized by the appearance of filaments at the exit of the discharge. In this paper, we detail mechanisms that could be responsible of the transition from diffuse mode to this self-organized mode. We point out the critical role of the power supply and the importance of the gas memory effect from one discharge to the following one on the transition to the self-organised mode. The self-organized mode is usually attributed to a surface memory effect. In this work, we show an additional involvement of the gas memory effect on the self-organized mode

Experimental investigations of a remote atmospheric pressure plasma by electrical diagnostics and related effects on polymer composite surfaces

Surface activation of Carbon Fiber Reinforced Polymers (CFRP) using (Poly-EtherEtherKetone) (PEEK) matrices is required to achieve strong and long-term adherent painting on the composite. Among the different techniques, an industrial atmospheric pressure remote plasma has been used in this work to treat PEEK CFRP surfaces. The characterization of this device by means of electrical diagnostics related to the effect of such post-discharge on the surface modifications is discussed. Firstly, electrical characteristics of the discharge show fairly high currents associated to high voltages which suggest a nonestablished and cold arc. Power consumed by the electrical supply associated to post-discharge length and surface temperatures allowed a better understanding of the industrial device. Secondly, the effects of plasma on surface chemistry and topography are analyzed by water contact angle measurements, X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). Investigations showed that treated surfaces exhibited better hydrophilicity mainly due to an incorporation of oxygen containing groups (up to 8.4% more) under air plasma whereas an increase of the nanoroughness and specific surface is preponderant under nitrogen plasma. Different hydrophilic capabilities of the surface obtained in air and nitrogen gas plasmas highlight a potential optimization of activation performances according to industrial specification