CHANICHANI

Plasma tailoring of surfaces and surface spectroscopies

Research

The research areas of the CHANI Plasma Team are focused on COLD ATMOSPHERIC PLASMAS and SURFACE TREATMENTS. Here is a short overview of our activities.

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DEVELOPMENT AND VALIDATION OF INNOVATING MATERIALS COMPONENTS FOR FUEL CELLS USING PROTON EXCHANGE MEMBRANES  (D. Merche - INNOPEM)


• Atmospheric plasmas are investigated to develop at lower cost electrodes and proton exchange membranes for fuel cells using hydrogen or methanol.

• Electrodes
Catalyst nanoparticles are grafted on porous carbon substrates in order to synthesize electrodes. This grafting can be achieved:
-    By a dedicated plasma treatment of a "carbon/ Pt organometallic" mixture.
-    By spraying an organometallic or a Pt colloidal solution in the post-discharge of an atmospheric RF plasma torch.
Then, our work is to evaluate in which extent the plasma conditions can influence the size, the dispersion and the amount of the grafted catalyst nanoparticles but also their chemical state and the nature of the C-metal interface. For this purpose, the treated substrates are investigated by SEM, TEM, XPS and SIMS.

• Membranes
The sulfonated polystyrene thin membranes are synthesized in one step in a home-made DBD (Dielectric Barrier Discharge) chamber, by plasma copolymerization of two monomers simultaneously injected in the discharge. The membranes are synthesized on Si wafers or on electrodes loaded with platinum to develop Membrane-Electrode Assembly. They are chemically characterized by XPS, SIMS (static and dynamic), and FTIR (IRRAS). The thickness and the morphology are investigated by SEM. The analytical tools show that the sulfonic acids groups, necessary for the proton conductivity present a good in-depth homogeneity in the polystyrene matrix. An electrochemical characterization of the elements of the cell realized by plasma is underway.


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Procedure to synthesize half membrane electrode by plasma.







FUNDAMENTAL STUDY OF THE INTERACTION MECHANISMS OCCURING AT THE PLASMA/POLYMER INTERFACE (T. Dufour – ULB, IAP/7)


• Polymers are ubiquitous and play an essential role in everyday life due to the tremendous diversity of their properties and to successful research aimed at manufacturing products with desired mechanical and chemical properties. The plasma modification of polymer surfaces has further increased their fields of applications (barrier functionalities added to food packaging films, biocompatibility measurements, biocompatibility applications self-cleaning coatings, …).

• The activation mechanisms on polymer surfaces are fairly well mastered, but the understanding of the etching mechanisms occurring at the plasma/polymer interface is still not well established, particularly in atmospheric plasmas using O2 as reactive gas. Our researches aim to find out interaction mechanisms between polymer surfaces such as HDPE, PVF, PVDF, PTFE, FEP, PFA and Nafion with the post-discharge emitted by an RF atmospheric plasma torch supplied in helium as carrier gas. Several reactive gases can be investigated: O2, H2 or N2. As an example illustrated in the following figure, etching models occurring at the post-discharge/polymer interface are proposed after analyzing the results obtained from mass losses measurements, XPS spectra, WCA observations and AFM imaging.



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Models representing the etching mechanisms occurring on the HDPE and PTFE surfaces, either by a pure helium post-discharge or by a helium-oxygen post-discharge at atmospheric pressure.




GROWTH OF CARBON NANOTUBES FORESTS FROM METALLIC NANOPARTICLES BY ATMOSPHERIC PLASMA (C. De Vos - ULB, IAP/7)


• The aim of this fundamental research is to achieve a new type of multi-functional layer, i.e. a "forest" of carbon nanotubes vertically grown so as to reproduce a "fakir" biomimetic morphology. This predicted effect would prevent macromolecular contaminants and larger particles (dust, aerosol) from adsorption on this layer. Growing carbon nanotube forests requires a nanoscale metal catalyst - such as nanoparticles - homogeneously dispersed on the surface of a substrate.

• For this purpose, silver nanoparticles are synthesized by dissolving different salts in an aqueous solution. Then, the resulting mixture is treated with an atmospheric microplasma jet supplied in argon. This plasma treatment allows the ignition of electrochemical reactions and the nucleation of particles without reducing agents. These metal nanoparticles can be stored in a colloidal solution to be subsequently nebulized in the post-discharge of an atmospheric RF plasma torch. Finally, carbon nanotubes can be initiated on the deposited metal catalysts and grow by PECVD, perpendicularly to the surface.

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DEPOSITION OF MULTIFUNCTINOAL COATINGS ON METAL SURFACES BY ATMOSPHERIC PLASMA PROCESSING (B. Nisol - GREENCOAT)


• The main goal of the GREENCOAT II project is to develop "all-in-one" hybrid surface coating procedures based on atmospheric plasma processing for the creation of metal surfaces with multifunctional properties, in an eco-friendly and a time efficient way.

• In GREENCOAT II we go beyond GREENCOAT I, by up-scaling to industrial level processing, diversifying and the further creation and enhancement of multifunctional property coatings. We specifically aim at two types of coatings, deposited by an all-in-one co-deposition atmospheric plasma process, with dedicated functional properties:
- For outdoor metal exposure: a primer type coating with good adherence to the metal, good bonding with the overlying paint finish, durable barrier properties and active durable corrosion protection.
- For indoor metal applications: a surface finishing coating with functional appearance, hydrophobicity for easy-cleaning, and active durable corrosion protection.

• This project will result in innovative products, which will be protected by patents, and extended innovative knowledge that will support our atmospheric plasma coatings expertise center, namely CAPCOAT, which we are setting up during the course of this second phase project.

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STUDY OF THE WATER REACTIVITY AT THE PLASMA/POLYMER INTERFACE (S. Collette – ULB, IAP/7)


• Water vapor is rarely used as a reactant in plasma chemistry or merely for the functionalization of surfaces. Usually, gases such as N2, O2, CO2, NH3 are preferred as they are easier to implement and disturb the discharge less than water vapor. However, the great reactivity of the OH radical makes it a prime candidate for surface functionalization.

• This project aims to a better understanding of the OH radicals reactivity occurring at the interface between polymer surfaces (PE, PVF, PVDF, PTFE) and atmospheric plasma sources. For this purpose, the water vapor is injected in two distinct plasma sources: a DBD (Dielectric Barrier Discharge) and an RF plasma torch.

• The plasma phase and the exposed surfaces are both characterized and correlated:
-    The plasma phase is investigated by atmospheric mass spectrometry, spatially resolved Optical Emission Spectroscopy (OES) and Laser Induced Fluorescence spectroscopy (LIF).
-    The treated polymer surfaces (PE, PVF, PVDF, PTFE) are characterized by dynamic water contact angle measurements (DWCA),by Angle Resolved monochromatized X-ray Photoelectron Spectroscopy (ARXPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The first technique gives an information on the surface energy (more specifically its polar component), whereas the two others determine the surface chemistry, as well as its in-depth distribution.

• Another sight of the project is to evaluate the synergetic effects between water and oxygen in the gas phase.


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CARBON DIOXIDE VALORIZATION BY PLASMA TREATMENT (G. Arnoult, T. Bieber - Projet GAZTON)


• Due to its high chemical stability, carbon dioxide is poorly used as a reactant. It is usually considered as a waste, an unavoidable end-product of many industrial processes. Dry reforming of carbon dioxide by plasma has attracted significant interest to reuse it for generating carbon monoxide which presents an interesting energetic value [1], [2].

• The Gazton project is a joined initiative of industrial and academic partners focused on carbon dioxide valorization by plasma treatment. In the framework of this project, dry reforming of CO2 by atmospheric pressure Dielectric Barrier Discharge (DBD) is investigated. Several reactors prototypes have been developed and key parameters (gas mixture, input power, flow rate, reactor dimension and geometry, frequencies) are under study so as to optimize the efficiency of the prototypes.
The post-treatment gas mixture is analyzed by two new equipments:
-    An Agilent Technologies 7890A gas chromatography system
-    A Hiden Analytical QGA atmospheric pressure mass spectrometer

[1] R. Li, Q. Tang, S. Yin, et T. Sato, « Plasma catalysis for CO2 decomposition by using different dielectric materials », Fuel Processing Technology, vol. 87, no 7, p. 617–622, 2006.

[2] S. Paulussen, B. Verheyde, X. Tu, C. De Bie, T. Martens, D. Petrovic, A. Bogaerts, et B. Sels, « Conversion of carbon dioxide to value-added chemicals in atmospheric pressure dielectric barrier discharges », Plasma Sources Science and Technology, vol. 19, p. 034015, 2010.





IMPROVEMENT OF BARRIER PROPERTIES OF POLYMERS (USED IN FOOD PACKAGING) BY PLASMA TREATMENTS (S. Abou Rich, P. Leroy, EVERWALL)


• Many materials require surface protection for their use or storage. The barrier layers are used to prevent the diffusion, into or through a solid, a liquid or a gas such as CO2, water vapor or oxygen.
The barrier properties have a commercial interest in a wide variety of applications such as food packaging, opto-electronics and protection against corrosion. In the case of food packaging, oxygen and water vapor are in some cases ban to preserve food. An excellent packaging prolongs significantly the life of fresh food (shelf life) and warranties a organoleptic, nutritional, and hygienic protection.
• The organic coatings (SiOx and SiNx) are already recognized for their barrier properties and used in the food packaging sector. SiOx films, deposited onto a polymer, allow the reduction of up to 40 times the permeability to oxygen.
• The interface coating- substrate influences strongly the properties of the deposited layer. In addition, the deposition of an inorganic layer on an organic substrate is a real challenge. For this purpose, a surface pretreatment of the substrate assigns the appropriate chemical functionalities. This pretreatment is performed in Dielectric Barrier Discharge (DBD) at sub-atmospheric or atmospheric pressure. The deposition of the thin films is performed in a PECVD chamber at low pressure.
• The aim of the project is to develop a control line (roll to roll system) plasma chamber at the industrial scale. This control line is composed by two compartments (DBD and PECVD) separated by a SAS to reduce the pressure from sub-atmospheric (10-100 mTorr) to a lower one (1 mTorr).

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SPIN-OFF IN BRUSSELS FUNDED BY INNOVIRIS (N. Vandencasteele, APSInt)


• Since October 2012 the Brussels region (INNOVIRIS) is funding the APSInt spin-off project. The aim of this project is to start the Spin-off company in October 2014. APSInt stands for: Atmospheric Plasma Solution Integrator. It will help industries to identify the best available plasma technique available for their needs and to smoothly integrate the plasma solution on their production lines. It will provide recommendations on how to replace traditional surface treatments by more environmentally friendly cold atmospheric plasma process. As the plasma is cold this technology can be used on most types of substrates and is able to deposit a great variety of complex molecules. The use of atmospheric pressure plasmas greatly reduces the treatment cost compare to traditional low pressure plasma. No vacuum chamber and no pumping system are needed anymore. As the technology does not required sealed off chambers it can be directly implemented on continuous process line. With help from the Capcoat expertise center the spin-off will also be able to propose innovative functional coatings to its clients, broadening the possible applications of their products. With stricter environmental laws, some traditional processes must be changed in order to comply with the new laws. The clients themselves are becoming more and more concerned about the environmental responsiveness of the products they buy. Therefore using a cutting edge environmentally friendly process becomes a strong sales argument.

• Several companies have already shown an interest in the implementation of atmospheric plasma solutions on their production line. Some of them have accepted to sponsor the APSInt project: AGC, ARCEO, MACTAC and Surfx.

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FUNDAMENTAL STUDY OF THE SYNTHESIS MECHANISMS AND TEXTURIZATION PROCESS OF (SUPER)HYDROPHOBIC FLUORINATED COATINGS BY ATMOSPHERIC PLASMA
 (J. Hubert, FNRS)


• This research project aims to study fundamentally the mechanisms involved in the synthesis of fluorinated coatings and to understand the texturization processes required for the achievement of (ultra)hydrophobic coatings, at atmospheric pressure.

• This study is managed in two parts; the first one is dedicated to the understanding of texturization processes of the model substrate: polytetrafluoroethylene (PTFE) and the second one, to the optimization and texturization of fluorinated coatings. The research is focused on the understanding of the mechanisms governing at the interface plasma/polymer by correlation between surface modifications and the gas phase characterization, at atmospheric pressure. Our approach is totally different from those described in the literature where the texturization is achieved by “addition” of material, as we are removing material rather than adding it.


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Surface treatment for pre-painted steel
 (F. BOYDENS, DAO Project)


• A special surface treatment of the metallic parts of buildings in order to optimize their functional properties while maintaining the original “look” of the surface, is much sought after within the field of metal construction. With such a surface treatment, which prevents fouling and enables self-cleaning by rain, the initial aesthetics of the building can be preserved longer and maintenance costs can be reduced.

• The goal of the Durable Aesthetic Outdoor (DAO) project is to develop such a surface treatment for pre-painted steel. Two different approaches are applied in order to obtain this goal.

- A first approach is the deposition of superhydrophilic and/or photocatalytic thin films on pre-painted steel. Superhydrophilic thin films have very low contact angles, meaning that water droplets get smeared out over the surface. Combining this with photocatalytic activity, which stimulates the decomposition of organic pollutants, would result in an auto-cleaning surface. Previous research projects have shown that TiO2 thin films deposited using a vacuum technique show interesting results. To further optimize the photocatalytic properties and increase the deposition rate it is investigate whether these TiO2 films can be deposited with an atmospheric plasma treatment (DBD setup). The feasibility of other deposition techniques are investigated as well, such as post-discharge deposition and using an RF torche.
- A second approach is the investigation of superhydrophobic thin films based on organic fluorides. As these prevent the adhesion of contaminants, they can be of interest for anti-fouling purposes. Again an atmospheric plasma (DBD or RF torche) is used to deposit these films.

• The deposited thin films are analyzed by XPS in order to correlate the contact angle to the chemical composition of the surface and provide us with a better understanding of the fundamental processes governing the self-cleaning process.



Plasma Team
Group Meetings

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