Hexamethyldisiloxane (HMDSO)‐ and hexamethyldisilazane (HMDSN)‐based plasma polymeric coatings are compared as elements of multilayer barrier coatings, consisting of an alternating structure of organosilicon and silicon oxide layers. Furthermore, these coatings are examined with regard to their deposition rate, critical layer thickness, surface roughness, atomic composition, and gas permeability. It is investigated how these attributes correlate in the overall barrier performance of a multilayer coating system. The concluded examinations show that HMDSN delivers best overall barrier performances as a precursor at high energy densities. For lower energy densities, the use of HMDSO is preferable. Intermediate layer thickness should not exceed six nanometers for best barrier performance in the given experiment configuration.

Thin SiN _w O _x C _y H _z 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 (N _2, 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 CO ₂ /N ₂ (up to 15), He/N ₂ (up to 9) and CO ₂ /CH ₄ (up to 8) at 30 °C.

This study tracks the physical aging behavior of coated and uncoated ultra‐thin poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) films on silicon wafers based on the refractive index using ellipsometry. The measured refractive index directly correlates with the free volume and hence the physical aging progression. Plasma‐enhanced chemical vapor deposition (PECVD) creates coatings with different thicknesses and oxidation degrees onto PTMSP films. Compared to uncoated PTMSP films, the PECVD‐coated films show a reduction of the refractive index increase of more than two orders of magnitude for less than 10 nm thin SiOx coatings. In contrast, SiOCH films show only a minor impact. The results reveal the superior physical aging behavior of PECVD‐coated films compared to untreated PTMSP films.

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 r _d > 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.

Selective, nanometer-thin organosilica layers created by plasma-enhanced chemical vapor deposition (PECVD) exhibit selective gas permeation behavior. Despite their promising pure gas performance, published data with regard to mixed gas behavior are still severely lacking. This study endeavors to close this gap by investigating the pure and mixed gas behavior depending on temperatures from 0 °C to 60 °C for four gases (helium, methane, carbon dioxide, and nitrogen) and water vapor. For the two permanent gases, helium and methane, the studied organosilica membrane shows a substantial increase in selectivity from αHe/CH₄ = 9 at 0 °C to αHe/CH₄ = 40 at 60 °C for pure as well as mixed gases with helium permeance of up to 300 GPU. In contrast, a condensable gas such as CO₂ leads to a decrease in selectivity and an increase in permeance compared to its pure gas performance. When water vapor is present in the feed gas, the organosilica membrane shows even stronger deviations from pure gas behavior with a permeance loss of about 60 % accompanied by an increase in ideal selectivity αHe/CO₂ from 8 to 13. All in all, the studied organosilica membrane shows very promising results for mixed gases. Especially for elevated temperatures, there is a high potential for separation by size exclusion.