The properties of plasma-enhanced chemical vapour deposition (PECVD) coatings on polymer materials depend to some extent on the surface and material properties of the substrate. Here, isotactic polypropylene (PP) substrates are coated with silicon oxide (SiOx) films. Plasmas for the deposition of SiOx are energetic and oxidative due to the high amount of oxygen in the gas mixture. Residual stress measurements using single Si cantilever stress sensors showed that these coatings contain high compressive stress. To investigate the influence of the plasma and the coatings, residual stress, silicon organic (SiOCH) coatings with different thicknesses between the PP and the SiOx coating are used as a means to protect the substrate from the oxidative SiOx coating process. Pull-off tests are performed to analyse differences in the adhesion of these coating systems. It could be shown that the adhesion of the PECVD coatings on PP depends on the coatings’ residual stress. In a PP/SiOCH/SiOx-multilayer system the residual stress can be significantly reduced by increasing the thickness of the SiOCH coating, resulting in enhanced adhesion.

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Thin plasma polymerized gas barrier coatings were applied on PET films using low-pressure microwave excited hexamethyldisiloxane plasma. Oxygen and water vapor transmission rates were determined for the same barrier coating of varying thickness and correlated with the coating porosity. The porosity was quantified on different scales with two complementary methods. A plasma etching process with subsequent high-resolution SEM imaging and an automated defect detection as well as an overall porosity measurement by means of cyclic voltammetry. This method combination can be used to assign and classify Knudsen diffusion and Knudsen diffusion for different coatings and defect distributions applied. Film growing process could be observed with correlating defect distributions and it could be determined that almost no macro defects with a radius rd > 150 nm are present while growing process. With visually closed coatings, the entire oxygen and water vapor permeation could be attributed to Knudsen and solid body diffusion, although it is difficult to divide the proportions of these two processes.

Oxygen and water vapour permeation through plastic films in food packaging or other applications with high demands on permeation are prevented by inorganic barrier films. Most of the permeation occurs through small defects (<3 µm) in the barrier coating. The defects were visualized by etching with reactive oxygen in a capacitively coupled plasma and subsequent SEM imaging. In this work, defects in SiO x -coatings deposited by plasmaenhanced chemical vapour deposition on polyethylene terephthalate (PET) are investigated and the mass transport through the polymer is simulated in a 3D approach. Calculations of single defects showed that there is no linear correlation between the defect area and the resulting permeability. The influence of adjacent defects in different distances was observed and led to flow reduction functions depending on the defect spacing and defect area. A critical defect spacing where no interaction between defects occurs was found and compared to other findings. According to the superposition principle, the permeability of single defects was added up and compared to experimentally determined oxygen permeation. The results showed the same trend of decreasing permeability with decreasing defect densities.

Thin SiNwOxCyHz coatings were deposited from hexamethyldisilazane as a precursor in a microwave driven low pressure plasma enhanced chemical vapor deposition process, in order to investigate their suitability as silicon based separating layers in membranes for gas separation. Polydimethylsiloxane composite membranes were used as substrate, as they have a dense and defect free surface and by this provide a smooth surface to ensure a homogenous and defect free coating. To evaluate correlations between process parameters, coating properties and permeation/selectivity performance, the influence of different compositions of the feed gas (auxiliary gas and monomer) on the chemistry and structure of the coatings and subsequently on permeability were investigated. For this, auxiliary gas was varied (N2, none and Ar) and coatings/membranes were analysed regarding their structural properties with atomic force microscopy and cyclic voltammetry as well as their chemical properties with x-ray photoelectron spectroscopy. Correlations between those properties and the permeation properties were examined. The investigations reveal that coating and gas transport properties can be adjusted by changing the auxiliary gas type. Membrane selectivities could be produced that are above Knudsen selectivity, especially for the gas pairings CO2/N2 (up to 15), He/N2 (up to 9) and CO2/CH4 (up to 8) at 30 °C.