Gas Permeation Properties Research Articles

A hydrostable mesoporous γ-Al2O3 membrane modified with Si–C–H organic-inorganic hybrid derived from polycarbosilane

Excellent hydrophobicity of polycarbosilane (PCS)-derived Si–C–H organic-inorganic hybrid was characterized by measuring water vapor adsorption-desorption isotherms at room temperature. Modification with the PCS-derived Si–C–H successfully improved hydrostability in terms of stable gas permeation property of sol gel-derived hydrophilic mesoporous γ-Al2O3 membrane formed on a macroporous α-Al2O3 support: even under saturated water vapor partial pressure at 50 °C, the modified membrane exhibited high gas permeances of helium, hydrogen and nitrogen ranging from 1.2 to 3.0 × 10−6 mol m−2 s−1·Pa−1. The improved gas permeability under the humid condition achieved for the Si–C–H-modified mesoporous γ-Al2O3 membrane in this study was discussed aiming to prepare a gas permeable hydrophobic mesoporous intermediate layer essential for developing H2-permselective ceramic-based multilayered composite membranes with applications to novel solar hydrogen production system.

Exploration of hybrid nanocarbon composite with polylactic acid for packaging applications

Polylactic acid (PLA) nanocomposite films were fabricated with graphene oxide (GO) and single-walled carbon nanotubes (CNT) as a hybrid-co-filler with GOCNT fraction varying from 0.05 to 0.4% by weight. The effect of the GOCNT on the physical, thermal, morphological, gas permeation, and optical properties was investigated. The X-ray diffraction test reveals no restacking and coagulation of GOCNT in the composite films. Differential Scanning Calorimetry analysis shows an insignificant shift of glass transition and melting temperature but enhanced crystallization resulting from the existence of GOCNT as a nucleating agent. Scanning Electron Microscope scans indicate GOCNT embedded homogeneously without considerable aggregates in the PLA. Transmission of ultraviolet-visible radiation decreases to 30% with increasing fraction of GOCNT while Oxygen Transmission Rate diminishes to 67% in the film. These are attributed to the tortuous pathways provided by the well-dispersed hybrid GOCNT in the PLA. Compared to the pristine PLA film, the composite film shows an increase of 75% and 130% in the tensile strength and Young's modulus, respectively. Taken together, all of these improvements observed in the hybrid GOCNT-PLA composites should provide useful guidelines in customizing designs for applications across a range of fields including packaging, life sciences, cosmetics, and conventional synthetic plastics.

Investigation of the gas permeability properties from polysulfone/polyethylene glycol composite membrane

In this research, the effect of polyethylene glycol (PEG) molecular weight on permeability and selectivity of polysulfone/polyethylene glycol (PSF/PEG) composite membrane is investigated. Polyethylene glycol with molecular weights of 4000, 6000, and 10,000 is applied. It is shown from the results that PEG applied in composite membranes with molecular weight of 1000 had the best diffusivity in comparison with the other composite membranes containing PEG with lower molecular weights. In addition, it is perceived that the permeability of CO2 from PSF/PEG10000 composite membranes has increased with enhancing weight percent. CO2 permeability into PSF/PEG composite membranes containing 20 wt% PEG10000 is calculated 7.64 barrer (1 barrer = 10−10 cm3 (STP) cm/cm2 s cmHg). The ideal selectivity for CO2/N2 gas pair in PSF pure membrane and composite membranes containing 10 wt% and 20 wt% PEG10000 are calculated 26.57, 30.61, and 32.12, respectively. Finally, the morphology and membrane structure of the membrane were evaluated with infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile strength test.

Superior interfacial design in ternary mixed matrix membranes to enhance the CO2 separation performance

The design of high performance mixed matrix membranes (MMMs) with new chemistry was the main challenge of membranologists in recent years. In this paper, extra high-performance MMMs were fabricated by incorporating the nickel zinc iron oxide nanoparticles and 1-Methyl-3-Octylimidazolium Hexafluorophosphate ionic liquid simultaneously into the Pebax®1657 polymer matrix. The influence of operating pressure (2–10 bar), IL blending (2–8 wt.%), and filler loading (0.5–2 wt.%) on gas permeation properties of each of prepared blend and ternary MMMs were investigated at 35 °C. Moreover, prepared membranes were evaluated by SEM, EDX, FTIR-ATR, DSC, XRD and Tensile analyses.Results showed that the membrane containing 6.5 wt.% ionic liquid and 1.5 wt.% nanoparticle was the optimum. Indeed, a superior combination of Ni2+, Zn2+ and Fe3+ in NiZnFe4O4 as a filler and a unique ionic liquid [OMIM][PF6] with superior CO2 solubility caused an excellent interfacial design and compatibility in MMM structure, which was very effective on gas transport results and mechanical properties of fabricated MMMs. Comparing the results with the pristine membrane, CO2 permeability of the optimum membrane was 300 Barrer (with more than 145% improvement) at 10 bar while the CO2/CH4 and CO2/N2 selectivities were 97.5 (with 369% improvement) and 248.6 (with 281% improvement), respectively. Finally, it was concluded that the fabricated membranes was easily surpassed the Robeson upper bound.

Characterization and enhancement of the gas separation properties of mixed matrix membranes: Polyimide with nickel oxide nanoparticles

Here, we report for the first time the fabrication of a glassy polymer/nickel oxide hybrid membrane as a gas separation membrane. A PI (Matrimid) is used as a continuous phase, and nickel oxide nanoparticles (NiO) were utilized as a dispersed phase. The structure of mixed matrix (MMMs) and pure Matrimid membranes are investigated by employing various characterization techniques including scanning electron microscopy (SEM), Fourier transforms infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and tensile stress-strain to characterize the NiO nanoparticles. The effect of NiO nanoparticles content (0–5wt%) on gas permeability of pure CO2, CH4, O2, and N2 gases at different operating temperatures (24–40°C) and feed pressures (1–5bar) were surveyed. The results revealed that the CO2 permeability almost did not change and CO2/CH4 selectivity of PI was enhanced with low-level loadings of NiO while the gas permeability of N2, CH4, and O2 was reduced. Our results indicated that since NiO nanoparticles have high interaction with CO2 as Lewis pairs, they have high potential to improve the gas permeability properties of polymer-based membranes. This approach allows predicting the gas transport properties, structure/solubility quantitative relationships of different gases, especially CO2 through the MMMs system.

Experimental investigation on effects of calcined bentonite on fresh, strength and durability properties of sustainable self-compacting concrete

With the current focus on sustainable development in the civil engineering field, it is necessary to develop construction and building materials with reasonable costs and low environmental impacts in order to reduce CO2 emissions during the production of concrete, and from the cement industry as a whole. This research studies the effect of using calcined bentonite (CB) as partial replacement of Ordinary Portland Cement (OPC) on the sustainability of self-compacting concrete (SCC). The cement in SCC mixes has been replaced with two different types of CB at 0, 5, 10, 15, 20, 25 and 30% by weight. Slump flow, V-funnel flow time, L-box test and sieve stability tests are performed to evaluate the fresh properties of SCC mixtures. Various tests are used to assess the performance of SCC mixtures in hardened states, such as compressive strength, porosity accessible to water, chloride-ions penetration and gas permeability. The results showed that the use of CB in SCC mixes reduced the fresh properties of SCC and the slump flows, flow times, and segregation tests are good enough for SCC production. At a hardened state, SCC with 10–15% of CB had a higher compressive strength up to 90 days, as well as improved porosity, chloride-ions penetration and gas permeability properties. These results indicate that a CB solution will reduce CO2 emissions and make durable and eco-friendly SCC at a low cost.

Gas permeation properties and preparation of carbon membrane by PECVD method using indene as precursor

This work could demonstrate a new approach to the fabrication of gas separation membrane using indene as polymeric precursor for low pressure PECVD system. Membrane characterization was done by taking Scanning Electron Microscopy (SEM) and FTIR measurements. For membrane performance testing, permeability and selectivity of the membrane were evaluated with pure gases of H2, N2, and CO2 using a differential permeation technique. PECVD-derived polyindene membrane showed selectivities of 8.2 and 4.0 for H2/CO2 and H2/N2, respectively, at room temperature. Polyindene (PIn) membrane was successfully fabricated onto a zeolite 5A substrate via radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at room temperature.

The effect of poly(alkyl (meth)acrylate) segments on the thermodynamic properties, morphology and gas permeation properties of poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) triblock copolymer membranes

The structure-property relationship of the poly(alkyl (meth)acrylate)-b-poly(dimethyl siloxane) (PA-b-PDMS) triblock copolymers were studied for membrane application. The effect of PA segments with different main-chain flexibility and side chains such as poly(benzyl methacrylate) (PBzMA), poly(ethyl methacrylate) (PEMA) and poly(methyl acrylate) (PMA) were studied on the properties of PA-b-PDMS block copolymer membranes. The block copolymers were synthesized via atom transfer radical polymerization (ATRP). The morphology structure of the synthesized block copolymers was changed from spherical to the cylindrical type by changing the structural segments from PMA and P(EMA-b-PEMA) to PEMA, respectively. The morphological feature of the PA-b-PDMS block copolymers was discussed according to their thermodynamic properties (surface energy, the solubility parameter of the constituent segments, and binary interaction parameters). The glass transition temperature of the hard segments of PA-b-PDMS block copolymers was increased by increasing poly(alkyl methacrylate) segments. CO2 permeability of the P(EMA-co-MA)-b-PDMS-b-P(EMA-co-MA) block copolymers was increased (from 7.2 Barrer to 908 Barrer) by increasing MA repeating units which correlated to the higher main chain flexibility of MA compared to the EMA repeating units. Permeability of CO2 was increased 27% by substitution of BzMA repeating units of P(BzMA-co-MA)-b-PDMS-b-P(BzMA-co-MA) block copolymer with EMA and correlated with the lower fractional free volume of BzMA repeating units.

Synthesis, characterization and gas permeability properties of a novel nanocomposite based on poly(ethylene-co-vinyl acetate)/polyurethane acrylate/clay

In this paper, nanocomposites of poly(ethylene-co-vinyl acetate) (PEVA)/polyurethane acrylate(PUA)/clay (Cl25A) (PEVA/PUA/Cl25A) are synthesized through a novel in situ method of polymerization. Isophorone-diisocyanate (IPDI) and 2-hydroxyethyl methacrylate (HEMA) are mixed with Cloisite 25A (Cl25A) nanofiller, at different percentage of weights. Organo modified montmorillonite clay like Cl25A are used with PEVA/PUA matrix for their liberal compatibility. The main characteristic peaks of the nanocomposite materials are observed in FT-IR spectra. The changes in the intensity and the position validate the strong interaction between clay and polymer. The nanocomposites were investigated by thermogravimetric analysis (TGA) and have exhibited a better thermal stability than the pure pristine PEVA/PUA. Thermal stability in the sample with 5wt.% of PEVA/PUA/Cl25A matrix has improved up to ∼60°C. The morphology of the nanocomposites is studied by scanning electron microscope (SEM) and X-ray diffraction (XRD). The XRD results have confirmed the penetration of clay into the PEVA/PUA matrix, as the d-spacing (2θ=4.79°) increases with the increase in different weight percentage of clay. The dispersion of nanoclay in PEVA/PUA nanocomposites was investigated by scanning electron microscope. The mechanical property associated with tensile strength, elongation at break and Young's modulus has showed a dramatic increase by varying Cloisite 25A, the filler loading, when compared to the pure PEVA/PUA matrix polymer. The barrier properties of the PEVA/PUA/Cl25A nanocomposite membrane with 5wt.% of Cloisite 25A loading has decreased by 51%. The results have suggested that these nanocomposite materials have great potential for applications in packing materials films with superior properties.

Gas Permeability of Cellulose Aerogels with a Designed Dual Pore Space System.

The gas permeability of a porous material is a key property determining the impact of the material in an application such as filter/separation techniques. In the present study, aerogels of cellulose scaffolds were designed with a dual pore space system consisting of macropores with cell walls composing of mesopores and a nanofibrillar network. The gas permeability properties of these dual porous materials were compared with classical cellulose aerogels. Emulsifying the oil droplets in the hot salt–hydrate melt with a fixed amount of cellulose was performed in the presence of surfactants. The surfactants varied in physical, chemical and structural properties and a range of hydrophilic–lipophilic balance (HLB) values, 13.5 to 18. A wide range of hierarchical dual pore space systems were produced and analysed using nitrogen adsorption–desorption analysis and scanning electron microscopy. The microstructures of the dual pore system of aerogels were quantitatively characterized using image analysis methods. The gas permeability was measured and discussed with respect to the well-known model of Carman–Kozeny for open porous materials. The gas permeability values implied that the kind of the macropore channel’s size, shape, their connectivity through the neck parts and the mesoporous structures on the cell walls are significantly controlling the flow resistance of air. Adaption of this new design route for cellulose-based aerogels can be suitable for advanced filters/membranes production and also biological or catalytic supporting materials since the emulsion template method allows the tailoring of the gas permeability while the nanopores of the cell walls can act simultaneously as absorbers.

Study on Deformation and Permeation Properties of Gas-Containing Fractured Rock

In this paper, we investigated the gas permeation properties of fractured rock during the process of stage load axial stress and cyclic load and unload confining pressure and come to some conclusions as follows: (1) the relationship between radial strain and deviatoric stress satisfied the quadratic polynomial function, and the relationship between permeability and deviatoric stress satisfied the exponential function under different axial stress levels; (2) in the staged load axial stress process, the axial strain-deviatoric curves of specimens conform to the quadratic polynomial function. The axial strain-deviatoric curves of specimens conform to linear function when confining pressure is 8.6 MPa or 2.0 MPa at different axial stress levels; (3) we used the permeability damage rate and maximum permeability damage rate to evaluate the recovery degree and reduction extent of permeability; (4) we used the volume expansion ratio and the maximum volume expansion ratio to evaluate the expansion degree and increase extent of rock samples’ volume.

Effects of surface pretreatment and deposition conditions on the gas permeation properties and flexibility of Al2O3 films on polymer substrates by atomic layer deposition

The effects of surface pretreatment and deposition conditions on the gas permeation properties—including permeability of He, O2, and H2O; the size; and the density of permeation-enhancing defects—and mechanical flexibility of Al2O3 films on polymer substrates by atomic layer deposition (ALD) were investigated to develop flexible gas barrier films for organic and flexible electronics. Pretreating polyimide (PI) and poly(ethylene terephthalate) (PET) substrates with an aqueous KOH solution greatly lowered the gas permeability of the ALD Al2O3 films as a result of improved affinity between the substrate surface and the ALD precursors. Varying the ALD conditions—including lengthening the precursor exposure, elevating the deposition temperature, and changing the precursor sequence—enhanced physisorption of ALD precursors on the polymer substrate, which improved nucleation of the ALD films to reduce defects in the films and lower their gas permeability. Activation energy for permeation determined from the temperature dependence of the permeability of the ALD films indicated that the ALD films deposited under the optimized condition contained smaller and few permeation-enhancing defects. The optimized ALD films possessed a low water vapor transmission rate of ~ 10−6 g/m2 day that met the stringent requirement of organic and flexible electronics, while also exhibiting excellent mechanical flexibility by withstanding repeated bending with small increases in gas permeability. Our results provide valuable insights into the development of flexible barrier thin films for the encapsulation of organic and flexible electronics.

Development of multilayer films with improved aroma barrier properties for durian packaging application

The symmetrical A/B/A structure of multilayer blown films was fabricated in this study. The immiscible low‐density polyethylene/polylactic acid (LDPE/PLA) blend was set as a core (B) layer and LDPE was used as skin (A) layers. The compositions of PLA in the core layer were varied from 20 to 50 wt%. The thickness of each layer was 10 μm (total film thickness of ~ 30 μm). In a blown film co‐extrusion process, the morphology of the fiber/ribbon‐like structures of LDPE/PLA blend was developed. Such structures had interesting effects on gas permeability and aroma barrier properties of the films. For instance, multilayer LDPE films containing 40 and 50 wt% PLA (P40 and P50) showed the reduction of oxygen permeability (PO2) approximately 20% and 43%, respectively, compared with the neat LDPE film. A long tortuous path for gas and aroma transportation through film thickness was created from the developed ribbon‐like structures of the PLA minor phase. For durian packaging application, fresh‐cut durian of 300 g was packed in the developed multilayer films, LDPE, and HDPE (Control), stored at 4°C for 7 days. Results demonstrated that the steady‐state condition of 10% to 13% O2 and 8% to 10% CO2 was achieved in all packages except in the HDPE. Moreover, the P40 and P50 films exhibited an outstanding aroma barrier property for three major durian volatiles: diethyl sulfide, ethyl propanoate, and 2‐ethyl‐1‐hexanol. Overall results clearly indicated that the multilayer LDPE films containing PLA exhibited a significantly improved aroma barrier performance with optimum gas permeability desirable for modified atmosphere packaging to retain quality of fresh‐cut durian throughout the storage period.

Preparation and Permeation Properties of PESU-Based Mixed Matrix Membranes with Nano-Sized CHA Zeolites

CHA-type SAPO-34 and SSZ-13 zeolites with different homogeneous crystal sizes were prepared and used as fillers for fabricating polyethersulfone (PESU) based mixed matrix membranes (MMMs). These CHA-type crystals and the obtained MMMs were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). H2, N2, CO2 and CH4 gas permeation properties of MMMs with 20% and 30% zeolite weight loadings were investigated at 35°C under the pressure drop of 0.3 MPa. All gas permeabilities were enhanced after filling these zeolites into PESU polymer. The defective MMMs were formed when using the smallest 100 nm SAPO-34 crystals. High permselectivity MMMs were obtained with 200 nm SAPO-34 crystals, and high gas permeability MMMs were obtained when filled with 400 nm SSZ-13 zeolites.

Thermal crosslinking of a novel membrane derived from phenolphthalein-based cardo poly(arylene ether ketone) to enhance CO2/CH4 separation performance and plasticization resistance

A novel gas separation membrane was fabricated from a commercially available polymer of phenolphthalein-based cardo poly (arylene ether ketone) (PEK-C). Thermal treatment was employed to improve the gas permeability and anti-plasticization property of PEK-C polymeric membrane via inducing interchain crosslinking. The changes of chemical structure, thermal crosslinking reaction, interchain distance, gas separation performance and anti-plasticization properties of PEK-C membranes were investigated by the FT-IR, XPS, TG-MS, XRD and gas permeation tests. Results show that the gas separation performance and anti-plasticization properties of PEK-C membranes are significantly enhanced after the thermal crosslinking, which is induced by the decomposition of the lactone rings in cardo moieties and crosslinking with the formation of biphenyl linkages. The dramatic enhancement in gas permeability for the crosslinked membrane is attributed to the enlargement of the interchain distance and free volume cavity, and the great improvement on the anti-plasticization property is due to the formation of a rigid crosslinked network structure. Compared to PEK-C polymeric membrane, the CO2 permeability of the crosslinked membrane increased by more than 110 times with an adequate CO2/CH4 selectivity, especially for the separation of CO2/CH4 mixed gas (50:50 mol%). The CO2 plasticization pressure substantially increased from 2 atm to the highest tested pressure of 30 atm. The gas separation performance of the crosslinked membrane surpassed the 2008 upper bound for CO2/CH4, exhibiting that the thermal crosslinking membrane derived from PEK-C membrane material is an attractive candidate for the natural gas purification.

Influence of spherical porous aggregate content on microstructures and properties of gas-permeable mullite-corundum refractories

Abstract In this study, six gas-permeable mullite-corundum refractories with 45–95 wt% spherical porous mullite aggregates were prepared. The influence of the spherical porous aggregate content (SPAC) on the microstructure, gas permeability, and mechanical properties was analysed by XRD, SEM, EDS and image analysis method, etc. It's found that the SPAC affected the pore characteristics and mechanical properties through changing the packing and sintering behaviours of the aggregate and matrix in the refractories. When the SPAC was 45–65 wt%, the refractories had higher strengths as well as two gas-permeable channels in the aggregate and matrix respectively. Whereas, when the SPAC increased to 75–95 wt%, the refractories had lower strength as well as one gas-permeable channel in the matrix. The optimized product contained 65 wt% spherical porous aggregate and combined a high gas permeability of 4.9 × 10 −12 m 2 , a high compressive strength of 18.5 MPa, a good thermal shock resistance and well-distributed gas-permeable channels.

A novel analytical method for prediction of gas permeation properties in ternary mixed matrix membranes: Considering an adsorption zone around the particles

Mixed Matrix Membranes (MMMs) are composed of dispersed (nano) particles into a continuous polymer matrix with a complex structure. Here, we present a new analytical model for calculation of gas concentration in the MMMs. In this regard, it is determined the gas concentration in the two zones of an MMM including the polymer matrix and the outer surface of a dense nanoparticle which is called adsorption zone. Therefore, mass transfer equations developed for polymer matrix/nanoparticles interface. A 3D model for MMM considered in which the spherical shape dense nanoparticles are randomly dispersed in the polymer matrix. In the vicinity of a nanoparticle, gas molecules attract to the adsorption zone. Achieved results indicated that when a gas molecule passing from up- to downstream side of an MMM, its concentration changes linearly through the polymer matrix, however changes nonlinearly near to the adsorption zone. Indeed, gas molecules pass the adsorption zone much faster than the polymer matrix and abandon the membrane non-uniformly. It was also concluded that penetrant concentration at the adsorption zone is directly related to the gas diffusion coefficient at the nanoparticle surface (Dadsorp) which is two orders of magnitude higher than gas diffusion coefficient in the polymer matrix (Dp). Moreover, the results showed that at the nanoparticle surface where the theta (azimuthal angle) is equal to zero, the gas concentration has its minimum value. The more molecules adsorb on the nanoparticle surface, the higher concentration gradient between the polymer matrix and the nanoparticle surface is achieved. Gas concentration gradient in the polymer matrix deviates from its linear behavior on the upper hemispherical of nanoparticle surface (which is first facing point of the gas-adsorption zone). In addition, it is observed that the gas concentration at the bottom of the adsorption zone (the lower hemispherical of nanoparticle surface) is higher than that of the polymer matrix in a same width of the membrane because at this zone the gas molecules are desorbed in the polymer matrix again. An important result obtained here is that the concentration gradient in the adsorption zone is much higher than that for the polymer matrix along the membrane width. This makes mass transfer in the absorption zone to be greater than the polymer matrix.

Tailoring fibre lengths to fabricate a highly permeable SiC fibre porous medium for more efficient combustion

Traditional ceramic foam and metal fibre media combustion were usually restricted owing to their intrinsic brittleness and easy corrosion, respectively. In order to obtain higher gas permeability, longer durability, and less noxious gas emissions for gas flame combustion, a novel SiC fibre porous medium (FPM) is investigated in this study. SiC fibre mat were firstly produced from chopped SiC fibres using solution dispersion and vacuum filtration, then a boron nitride interphase for antioxidation and subsequent SiC coating for rigidity were deposited by chemical vapor infiltration, resulted in the formation of self-supporting SiC FPM. Findings demonstrate that the microstructure, gas permeability, thermal physical and combustion properties of SiC FPM can be improved by tailoring fibre length. As the fibre length was 4.5 mm, the density of SiC FPM was 0.113 g/cm3, and it exhibited excellent properties in permeability and utilization of fuel gas, pollutant emissions and combustion temperature accompanied by slight reduction in thermal conductivity. Such ultra-light SiC FPM could respond fast during the heating process and help gas mixture burn off.

Tailoring the molecular sieving properties and thermal stability of carbonized membranes containing polyhedral oligomeric silsesquioxane (POSS)-polyimide via the introduction of norbornene

Two types of POSS (polyhedral oligomeric silsesquioxane)-polymers, (POSS-polyimide-phenyl (POSS-PI-Ph) and POSS-polyimide-phenyl-norbornene (POSS-PI-Ph-Norbornene)), were utilized for the fabrication of highly permeable gas-separation membranes. POSS-PI-Ph and POSS-PI-Ph-Norbornene separation layer for selective gas separation were successfully formed on porous intermediate layer. A POSS-derived membrane calcined at 250–350 °C under N2 showed approximately the same levels of selectivity for He/N2 and CO2/N2 as conventional polyimide membranes, which shows there was no formation of large pores that decreases gas selectivity. The introduction of norbornene, which forms a cross-linked structure by thermally inducing cross-linking at 500 °C under N2, improved gas permeance without decreasing the gas-permeance ratio. A POSS-PI-Ph-Norbornene membrane heat treated at 500 °C showed increases in He permeance that ranged from 1.2 × 10−7 to 4.6 × 10−7 mol m−2 s−1 Pa−1 with He/N2, CO2/N2, He/CF4, and He/SF6 permeance ratios of 38; 8; 2700; and 14000, respectively. The relationship between the activation energy of H2 permeation and the He/H2 permeance ratio in POSS-derived, organosilica, and polymer (polyimide, polyamide, polysulfone) membranes suggests that gas permeation properties depend on the concentration of organic groups (C/Si ratio) in networks, because networks become more flexible when carbon concentration increases and dominates the permeation properties, which corresponds to a solution-diffusion mechanism.

Colorless and Transparent Copolyimides and Their Nanocomposites: Thermo-Optical Properties, Morphologies, and Gas Permeabilities.

A series of linear aromatic copolyimides (Co-PIs) were synthesized by reacting 4,4′-biphthalic anhydride (BPA) with various molar contents of 2,2′-bis(trifluoromethyl)benzidine (TFB) and p-xylylenediamine (p-XDA) in N,N′-dimethylacetamide (DMAc). Co-PI films were fabricated by solution casting and thermal imidization with poly(amic acid) (PAA) on glass plates. The thermo-optical properties and gas permeabilities of Co-PI films composed of various molar ratios of p-XDA (0.2–1.0 relative to BPA) were investigated. Thermal properties were observed to deteriorate with increasing p-XDA concentration. However, oxygen-transmission rates (O2TRs) and optical transparencies improved with increasing p-XDA concentration. Co-PI hybrids with a 1:0.2:0.8 molar ratio of BPA:TFB:p-XDA and organically modified hectorite (STN) were prepared by the in situ intercalation method. The morphologies and the thermo-optical and gas permeation properties of the hybrids were examined as functions of STN loading (5–50 wt %). XRD and TEM revealed substantial increases in clay particle agglomeration in the Co-PI hybrid films as the clay loading was increased from 5 to 50 wt %. The coefficient of thermal expansion (CTE) and the O2TR of a Co-PI hybrid film were observed to improve with increasing STN concentration; however, its optical transparency decreased gradually with increasing STN concentration.