An atmospheric pressure plasma chemical vapor deposition process designed for the site‐selective deposition of organic functional materials with a sub‐millimetric lateral resolution is presented in this study. Injecting methyl methacrylate vapor in plasma post‐discharge allowed to synthesize plasma‐polymerized methyl methacrylate (ppMMA) coatings on metallic, dielectric, and polymer substrates at close to room temperature (40°C). A circular dot, as small as 400 µm in diameter, of ppMMA is deposited and characterized by Fourier‐transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and high‐resolution mass spectrometry. Oligomeric species of poly‐MMA up to n = 18 have been detected, evidencing the particularly “soft” polymerization offered by the presented process.
Photocatalytic surfaces have the potentiality to respond to many of nowadays societal concerns such as clean H2 generation, CO2 conversion, organic pollutant removal or virus inactivation. Despite its numerous superior properties, the wide development of TiO2 photocatalytic surfaces suffers from important drawbacks. Hence, the high temperature usually required (> 450 °C) for the synthesis of anatase TiO2 is still a challenge to outreach. In this article, we report the development and optimisation of an ECWR-PECVD process enabling the deposition of anatase TiO2 thin films at low substrate temperature. Scanning of experimental parameters such as RF power and deposition time was achieved in order to maximise photocatalytic activity. The careful selection of the deposition parameters (RF power, deposition time and plasma gas composition) enabled the synthesis of coatings exhibiting photocatalytic activity comparable to industrial references such as P25 Degussa and Pilkington Activ at a substrate temperature below 200 °C. In addition, to further decrease the substrate temperature, the interest of pulsing the plasma RF source was investigated. Using a duty cycle of 50%, it is thus possible to synthesise photocatalytic anatase TiO2 thin films at a substrate temperature below 115 °C with a deposition rate around 10 nm/min.
A coaxial shaped atmospheric pressure plasma torch has been used to deposit the millimetric scale plasma polymer. A detailed experiment has revealed the appearance of three different kinetic regimes with distinct coating morphology: no deposition, circular dot and circular ring formation. The ratio of precursor carrier gas flow to the plasma species carrier gas flow has been identified as crucial factor to separate the three regimes. Further experiments regarding the influence of precursor mass fraction on the dimension and deposition rates has been performed for a circular dot regime to get more insights into the coating shape, size and volume and its relation to gas flow dynamics. A side by side computational fluid dynamic simulation coupled with species transport module has been performed to understand the influence of flow dynamics on coating morphology. The appearance of recirculatory vortices in-between the nozzle and substrate and its role on confinement of precursor at specific region and mixing of plasma species to precursor has been highlighted. A good correlation in between the diameter of thus coated plasma polymer in circular dot regime and the simulated confinement zone is here reported.
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