Enhancing the separation properties of plasma polymerized membranes on polydimethylsiloxane substrates by adjusting the auxiliary gas in the PECVD processes
Abstract: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 pa… Show more
“… Robeson plot for He/CO 2 with a variety of organosilica membranes fabricated via PECVD by the authors (filled circles) [ 21 , 22 ] and the uncoated PDMS substrate membrane. As reference, the plot displays two commercially available polymers (Matrimid [ 36 ] and P84 [ 37 ]) with an assumed thickness of 1 µm.…”
Section: Figurementioning
confidence: 99%
“…It allows the fabrication of tailored coatings with regard to mechanical and chemical properties and, at the same time, enables low coating thicknesses in the nanometer range. The formation of organosilica layers by PECVD utilizing hexamethyldisiloxane (HMDSO) as a precursor results in membranes with gas separation characteristics [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Inorganic [ 24 , 25 , 26 , 27 ] or organic substrate membranes [ 15 , 21 , 22 , 23 , 28 , 29 , 30 , 31 , 32 , 33 ] function as support for the thin organosilica layer.…”
Section: Introductionmentioning
confidence: 99%
“…The formation of organosilica layers by PECVD utilizing hexamethyldisiloxane (HMDSO) as a precursor results in membranes with gas separation characteristics [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Inorganic [ 24 , 25 , 26 , 27 ] or organic substrate membranes [ 15 , 21 , 22 , 23 , 28 , 29 , 30 , 31 , 32 , 33 ] function as support for the thin organosilica layer. Besides, PECVD enables the combination of advantages of different membrane materials.…”
Section: Introductionmentioning
confidence: 99%
“…The solid line in Figure 1 represents the Robeson upper bound [ 4 ]. The filled circles show the permeation characteristics of our composite membranes with selective PECVD coatings fabricated with varying coating parameters (refer to Kleines et al [ 21 , 22 ]). Additionally, the characteristics of the used PDMS substrate for the PECVD coating and two commercially available polymers (Matrimid [ 36 ] and P84 [ 37 ]) are plotted as reference.…”
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.
“… Robeson plot for He/CO 2 with a variety of organosilica membranes fabricated via PECVD by the authors (filled circles) [ 21 , 22 ] and the uncoated PDMS substrate membrane. As reference, the plot displays two commercially available polymers (Matrimid [ 36 ] and P84 [ 37 ]) with an assumed thickness of 1 µm.…”
Section: Figurementioning
confidence: 99%
“…It allows the fabrication of tailored coatings with regard to mechanical and chemical properties and, at the same time, enables low coating thicknesses in the nanometer range. The formation of organosilica layers by PECVD utilizing hexamethyldisiloxane (HMDSO) as a precursor results in membranes with gas separation characteristics [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Inorganic [ 24 , 25 , 26 , 27 ] or organic substrate membranes [ 15 , 21 , 22 , 23 , 28 , 29 , 30 , 31 , 32 , 33 ] function as support for the thin organosilica layer.…”
Section: Introductionmentioning
confidence: 99%
“…The formation of organosilica layers by PECVD utilizing hexamethyldisiloxane (HMDSO) as a precursor results in membranes with gas separation characteristics [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ]. Inorganic [ 24 , 25 , 26 , 27 ] or organic substrate membranes [ 15 , 21 , 22 , 23 , 28 , 29 , 30 , 31 , 32 , 33 ] function as support for the thin organosilica layer. Besides, PECVD enables the combination of advantages of different membrane materials.…”
Section: Introductionmentioning
confidence: 99%
“…The solid line in Figure 1 represents the Robeson upper bound [ 4 ]. The filled circles show the permeation characteristics of our composite membranes with selective PECVD coatings fabricated with varying coating parameters (refer to Kleines et al [ 21 , 22 ]). Additionally, the characteristics of the used PDMS substrate for the PECVD coating and two commercially available polymers (Matrimid [ 36 ] and P84 [ 37 ]) are plotted as reference.…”
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.
“…[25][26][27][28][29][30][31] Coatings are typically deposited on inorganic [32][33][34][35] or on organic substrate membranes. [27,[36][37][38][39][40][41][42] Up to now, the influence of PECVD coatings on the aging behavior of the underlying polymer has not been studied.…”
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.
Vapor phase infiltration (VPI) has emerged as a promising tool for fabrication of novel hybrid materials. In the field of polymeric gas separation membranes, a beneficial impact on stability and membrane performance is known for several polymers with differing functional groups. This study for the first time investigates VPI of trimethylaluminum (TMA) into poly(1‐trimethylsilyl‐1‐propyne) (PTMSP), featuring a carbon–carbon double bond as functional group. Saturation of the precursor inside the polymer is already attained after 60 s infiltration time leading to significant densification of the material. Depth profiling proves accumulation of aluminum in the polymer itself, but a significantly increased accumulation is visible in the gradient layer between polymer and SiO2 substrate. A reaction pathway is proposed and supplemented by density‐functional theory (DFT) calculations. Infrared spectra derived from both experiments and simulation support the presented reaction pathway. In terms of permeance, a favorable impact on selectivity is observed for infiltration times up to 1 s. Longer infiltration times yield greatly reduced permeance values close or even below the detection limit of the measurement device. The present results of this study set a strong basis for the application of VPI on polymers for gas‐barrier and membrane applications in the future.
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