On the Mixed Gas Behavior of Organosilica Membranes Fabricated by Plasma-Enhanced Chemical Vapor Deposition (PECVD)

Abstract

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.

PECVD and PEALD on polymer substrates (part II): Understanding and tuning of barrier and membrane properties of thin films

“…Rubner et al also observed a significant and irreversible drop in permeance for both He and CO 2 when exposed to water vapor, although the ideal He/CO 2 selectivity increases. [104] Overall, the investigated organosilica membrane demonstrates promising mixed gas behavior for separating permanent gases with small kinetic diameters from larger gas molecules. [104] Besides the separation properties of the films deposited by PECVD, Rubner et al also investigated the mitigation of physical aging of ultrathin polymer films with intrinsic microporosity.…”

“…Rubner et al also observed a significant and irreversible drop in permeance for both He and $${\text{CO}}_{2}$$ when exposed to water vapor, although the ideal $${\text{He}/\text{CO}}_{2}$$ selectivity increases. [ 104 ] Overall, the investigated organosilica membrane demonstrates promising mixed gas behavior for separating permanent gases with small kinetic diameters from larger gas molecules. [ 104 ]…”

“…[ 104 ] Overall, the investigated organosilica membrane demonstrates promising mixed gas behavior for separating permanent gases with small kinetic diameters from larger gas molecules. [ 104 ]…”

“…[17] With the gained knowledge about the dependence of the PECVD fabrication parameters on the membrane properties, the best-performing parameter set of the two mentioned publications of Kleines et al was chosen for the production of membranes for in-depth investigations of the permeation properties of the deposited film. [17,22] Rubner et al [104] showed that PECVD-fabricated organosilica membranes have the potential to combine the benefits of silica and polymeric membranes, offering both high permeabilities and selectivities comparable to silica membranes and as low production costs as polymeric membranes. The comprehensive investigation of the chosen organosilica membrane, using pure and mixed gas feeds at different temperatures, reveals promising nonideal permeation behavior.…”

On the role of defects in modelling approaches for thin film gas barrier coatings on polymer substrates: I. Model development

“…Adjusting the permeability of plastics is an important task in many applications such as food or pharma packaging, membrane technology or water-sensitive OLED displays, and thus the subject of ongoing research activities [1][2][3]. Besides many other approaches, the plasma-enhanced deposition of thin film coatings stands out due to its versatility, low material usage and long-term stability [4].…”