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Plasma technology

Introduction to atmospheric plasma technology using a Dielectric Barrier Discharge reactor:

  • Since a few years, great effort has been put on the development of atmospheric plasma systems able to modify surfaces and to deposit (in) organic coatings. The obvious practical advantage is that it combines the environmental friendly aspect of the existing low pressure plasma systems, with a reduction of cost (no need of vacuum chamber anymore, no energy loss due to pumping), and an increase of speed (no transfer necessary any more). Similarly, all the above mentioned steps can be done in one single chamber, in a simple continuous process; one only needs to change the feeding gas of the plasma.
  • Whereas at low pressure the main mechanism for molecular activation is a collisional process between a molecule (the monomer) and an electron, at high atmospheric pressure, one has to take into account also the molecule–molecule collisions, as well as collisions with metastable species from the main plasma gas, which make the understanding of the kinetics and the polymerisation process much more complicated. Similarly, due to Paschen’s Law and to the relationships between current, pressure and voltage applied, the technology to maintain a plasma, without going to arc, is also different. Contrary to usual polymerisation, radicals are always created in the plasma gas phase, even if the starting building block contains no unsaturated bonds, which opens the field to new compounds. One of the potential disadvantages of the techniques is inherent to the electron impact in the gas phase: a too high fragmentation, resulting in the loss of the chemical function of interest. For this reason, tuning of the plasma conditions needs dedicated attention.
  • Atmospheric plasma systems can be used to clean and functionalise the substrate surface, and to create the (co-)deposition of organic and hybrid coatings. The technology to be used is High Frequency Dielectric Barrier Discharge (HF DBD). The atmospheric plasma is initiated between two parallel plate metal electrodes, covered by a dielectric.


Static DBD reactors

DBD reactor with rotating electrode: New rotating bottom electrode setup in the DBD reactor for higher film uniformity.
A lab-scale reactor was constructed to deposit coatings on relatively small substrates.  Its operation has been optimized to perform homogenous depositions.  Its optimization was based on the correct position of the inlet of the precursor and the rotation of the substrate during the deposition.  Since the discharge is completely isolated from the atmospheric air, it can deposit coatings with practically no contamination from the atmospheric air.




NEW: Dynamic DBD reactor


The large-scale reactor was developed for the deposition on large panels, simulating an industrial process. This reactor could deposit coatings with good uniformity in a relatively good area providing enough material for the evaluation of the performance of the plasma coatings. 
The large-scale reactor can deposit various precursors either by the transfer of their vapors or by spraying their droplets in the discharge. In its current condition it can deposit multiple layers of combination of two precursors, creating gradients of them while it can be easily upgraded even more sophisticated depositions. It is an important research tool for future research since it can be used for the study of the deposition of different precursors, on different substrates and can be easily modified for continuous deposition on textiles or foils. Thanks to its versatility, this setup can be easily modified to physically simulate industrial plasma processes. 


The following scheme shows how the new dynamic reactor works.


The basic parts of  the plasma reactor are shown in the following image:


Dynamic DBD reactor while depositing methacrylate based coatings: