EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The adjustment of surface free energy of various substrates plays a major role in coating technology and is perceived as an important part in the design of microfluidic devices for medical applications. Here we present a deposition strategy for two different organosilicon substances, vinyltrimethoxysilane (VTMO) and hexamethyldisiloxane (HMDSO), and the impact of process parameters on plasma chemistry and film formation, especially their hydrophobic and hydrophilic properties and the formation of coatings w/o dust. For this purpose, we used an atmospheric pressure cold plasma deposition device (Inocon Techonologie GmbH) to guarantee fast and gentle treatment of thermal sensitive substrates (polypropylene, polyethylene terephthalate). Different characterization methods such as FTIR, EDX, REM, profilometric- and contact angle measurements were applied for chemical and structural analysis of the layers. By using different process parameters, but also different process gases, we reached water contact angles between 15° and 80°, whereby especially the deposition of dust-free, hydrophilic surfaces appeared to be a great challenge. The formation of dust is a common problem in plasma technology and often leads to falsification of results by showing super-hydrophobic to super-hydrophilic characteristics. In this work, we identify the dust as nanoparticle agglomerates of silicate nature and its formation could be avoided by changing over from a HMDSO to VTMO precursor. The deposition of the latter resulted in nearly dust-free surfaces with different surface free energies compared to the former. Differences in the plasma are explained including simulation and spectroscopic validation. While HMDSO leads to more hydrophobic layers with high carbon content, VTMO generates more hydrophilic ones with low carbon content. Finally, the atmosphere around the plasma plume has an influence on layer building processes, since a reduction of oxygen in the environment seems to inhibit oxidation of precursors and thus, leads to more hydrophobic films.