Preparation of novel fluorinated block copolyimide membranes for gas separation

We synthesized novel fluorinated block copolyimides with various diamine compositions and block chain lengths by chemical imidization in a two‐pod procedure. We describe the gas‐transport properties of the novel block copolyimide membranes. We demonstrate that the gas‐transport properties of the copolyimide membranes strongly depended on the block chain lengths. The gas permeabilities of the copolyimide membranes increased with increasing block chain length, and the gas selectivities increased with decreasing lengths. We clarify that the gas diffusivity of the block copolyimide membrane dominated the gas‐transport properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2436–2442, 2006     

Facile preparation and separation performances of cellulose nanofibrous membranes

Ultrafiltration (UF) is a size selective pressure‐driven membrane separation process increasingly required for high efficient water treatment and suspended solids removal in many industrial applications. This study examined the morphology of as‐prepared cellulose nanofibers and then utilized the nanofibers dispersion to fabricate nanofibrous nanoporous membranes with potential wide applications in various fields including water treatment. The nanofibers were prepared using a simple and powerful mechanical high intensity ultrasonication following a pre‐chemical treatment of α‐cellulose. The cellulose nanofibers’ morphology, crystallinity, and yield were found to be influenced by pre‐chemical treatment. Cellulose nanofibrous membranes were fabricated from cellulose nanofibers dispersion on a porous support. A nanoporous structure with an extensive interconnected network of fine cellulose nanofibers was formed on the support substrate. The resulting membranes exhibited typical and high‐efficient UF performances with high water fluxes of up to 2.75 10³ L/m²/h/bar. The membranes also displayed high rejections for ferritin and 10 nm gold nanoparticles with a reactive surface area capable of rapidly decolorizing methylene blue from its aqueous solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43544.     

Rigid and microporous polymers for gas separation membranes

Microporous polymers are a class of microporous materials with high free volume elements and large surface areas. Microporous polymers have received much attention for various applications in gas separation, gas storage, and for clean energy resources due to their easy processability for mass production, as well as microporosity for high performance. This review describes recent research trends of microporous polymers in various energy related applications, especially for gas separations and gas storages. The new classes of microporous polymers, so-called thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs), have been developed by enhancing polymer rigidity to improve microporosity with sufficient free volume sizes. Their rigidity improves separation performance and efficiency with extraordinary gas permeability. Moreover, their solubility in organic solvents allows them to have potential use in large-scale industrial applications.     

Structure and gas permeation properties of asymmetric polyimide membranes made by dry–wet phase inversion: Influence of the polyimide molecular weight

In this article, we report the influence of the polyimide molecular weight (1.2 × 10⁵, 2.6 × 10⁵, and 4.1 × 10⁵) on the structure and the gas permeation properties of asymmetric polyimide membranes made by the dry–wet phase‐inversion process. The apparent skin layer thickness of the asymmetric membrane increased with increasing molecular weight, and the thicknesses of the membranes prepared from the three polyimides with a casting polymer solution containing 8.0 wt % butanol were 132, 350, and 739 nm, respectively. That is, the gas permeance in the asymmetric membranes increased with decreasing molecular weight. In contrast, the gas selectivity of the asymmetric membranes did not depend on the skin layer thickness. The solvent evaporation in the dry phase‐inversion process and the nonsolvent diffusion in the dry process were important factors that determined the formation of the asymmetric membrane. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of cooling temperature and aging treatment on the morphology of nano‐ and micro‐porous poly(ethylene‐co‐vinyl alcohol) membranes by thermal induced phase separation method

Poly(ethylene‐co‐vinyl alcohol) (EVOH 32) / 1,3‐propanediol mixtures are processed by thermally induced phase separation for the formation of porous membranes. The crystallization line was determined both by the cloud‐point and DSC methods. Two precursor solution compositions, four quench temperatures and various aging times were explored. It is found possible to generate both polymer‐crystallization controlled morphologies (for high quenches and/or sufficiently aged dopes), especially globular microporous ones, and novel nano‐scale porous morphologies dominated by intra‐binodal phase separation (for low quenches and limited or no precursor solution aging). Structural characterization of the membranes was accomplished via application of scanning electron microscopy and wide angle X‐ray diffraction. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40374.     

Gas permeation and separation properties of polyimide/ZSM‐5 zeolite composite membranes containing liquid sulfolane

The preparation, characterization, and gas permeation properties of novel composite membranes containing polyimide (PI), liquid sulfolane (SF), and zeolite (ZSM‐5) were investigated to address the interface defects between the PI and the zeolite. The free‐standing composite membranes were prepared by the solvent casting method. The gas permeability of the PI+ZSM‐5 membrane was higher than that of PI, whereas its gas selectivity was significantly reduced, suggesting that these results are attributed to the interface defects. The CO₂ selectivity of PI+ZSM‐5+SF was higher than those of the PI+ZSM‐5 membranes because of the introduction of liquid SF into the interface defects. Furthermore, liquid SF enhanced the CO₂/H₂ selectivity near the recent upper bound. Therefore, the use of liquid SF could be an effective approach to preventing interface defects and increasing the CO₂ selectivity, particularly for CO₂/H₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of inorganic fillers on the structural and transport properties of mixed matrix membranes

In this study, three types of inorganic fillers—fumed nano‐SiO₂, synthesized mesoporous MCM‐41, and zeolite 4A—were incorporated into P84 matrix to prepare mixed matrix membranes. The structural characteristics and transport properties of the resulting composite membranes were investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the dispersion of the filler particles in the composite membranes. TEM micrographs verified that there were no nonselective pores at the particle–polymer interfaces of the composite membranes. Differential scanning calorimetry tests were conducted to investigate the structure of the composite membranes. The glass transition temperatures (T_g) of the P84/MCM‐41 and P84/4A composite membranes were 11 and 30°C, respectively, above that of pure P84 membrane. But, the T_g value for the P84/SiO₂ composite membrane decreased by 22°C when compared with that of the P84 membrane. The density of the composite membrane was also measured to calculate its fractional free volume. Gas permeation tests showed that, among the three synthesized composite membranes, the P84/SiO₂ membrane had the best performance in terms of gas separation. P84/SiO₂ membrane exhibited 20, 63, 59, and 45% increases in the permeabilities of He, O₂, N₂, and CO₂, respectively, above those for the P84 membrane whilst maintaining comparable good selectivities. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of highly selective nanofiltration composite membranes based on a novel soluble rigidly contorted monomer

Nanofiltration composite membranes with high selectivity are one of the most critical cores in water treatment, and regulating the surface charge and pore structure of active separation layers in thin film composite membranes is one of the most effective means to improve the selectivity of composite membranes. This article synthesized a novel monomer with positive charge and a rigid twisted Tröger's base structure (named TBDA-SO₃), which was manipulated to improve the microporous structure and surface charge of the composite membrane. By interfacial polymerization, TBDA-SO₃, and piperazine were co-reacted with trimesoyl chloride to successfully prepare positively charged, highly selective, and strongly microporous polyamide composite nanofiltration membranes. The best-performing composite nanofiltration membrane in this article has a permeability similar to that of the control group's poly(piperazine amide) (PPA) membrane (pure water flux, 7.8 L m⁻² h⁻¹ bar⁻¹), but has excellent divalent cation selectivity (52.57), which is 4.4 times that of the control group's PPA membrane.     

Effect of the microscopic morphology of a filler on its dispersion in a PI matrix: Calculation and analysis

The preparation of crosslinked polyimide (PI) composites via a blending technique is reported. Different kinds of organic or inorganic silicon-based nanofillers have been used for this purpose. A comparison is made between carefully chosen pairs of fillers, the choice depending on the compatibility of the crosslinked PI with the filler, to study the effects of the crosslinked PI matrix structure and fillers with different micromorphology. The dispersion of the filler is characterized with SEM as uniformly dispersed or gelled. It is found that with different micromorphology of filler, the PI matrix can be loaded with different mass fractions of filler, and the point at which gelation occurs is not the same. In order to study this behavior, these fillers are subjected to a quadratic mean equation calculation and analysis. Compared to pure PI, all obtained crosslinked composites have a higher glass-transition temperature and a lower dielectric constant. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46875.     

Influence of electrochemical copolymerization conditions of 3‐methylthiophene and biphenyl on the morphology and nanomechanical properties of the films

The aim of this work is to synthesize novel 3‐methylthiophene (3MTh)/biphenyl (Biph) copolymer films by electropolymerization and study their mechanical properties through nanoindentation. The morphology, the chemical structure as well as the electrical conductivity of the copolymer films depended strongly on the electropolymerization conditions. It was found that the polymer deposition follow an instantaneous, two‐dimensional nucleation and growth mechanism leading to homogenous films. The copolymer films had higher Young modulus and nanohardness than poly(3‐methylthiophene) (3PMTh), indicating that the incorporation of Biph units within the P3MTh chain leads to a more densely packed structure and a more brittle polymer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42575.     

Investigating the thermal,mechanical, and electrochemical properties of PVdF/PVP nanofibrous membranes for supercapacitor applications

Polyvinylidene fluoride and polyvinylpyrrolidone polymers incorporated with carbon black nanoparticles (50 nm) were electrospun to fabricate nanofibrous membranes for supercapacitor separators. Different weight percentages (0, 0.25, 0.5, 1, 2, and 4 wt %) of carbon black nanoparticles were dispersed in N,N‐dimethylacetamide and acetone prior to the electrospinning processes at various voltage, pump speed, and tip‐to‐collector distances. The morphology, thermal, mechanical, hydrophobic, and electrochemical characterization of nanofibrous membrane were analyzed using different techniques, such as scanning electron microscopy, differential scanning calorimetry, capacitance bridge, thermogravimetric analysis, dynamic mechanical analyzer, and water contact angle. Effects of annealing and UV irradiation exposures on the nanofibrous membranes were investigated in detail. Test results revealed that the physical properties of the nanocomposite separators were significantly enhanced as a function of carbon black inclusions in the polymeric structures, which may be useful for the applications of supercapacitor separators and other energy storage devices. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43707.     

Synthetic 6FDA-ODA copolyimide membranes for gas separation and pervaporation: Functional groups and separation properties

Copolyimides were prepared from one-step polymerization of 6FDA and ODA with four diamines DBSA, DABA, DAPy and DANT as the third monomers. Polymers were characterized with GPC, FTIR, NMR, DSC and TGA. Surface free energies and membrane-water interfacial free energies were calculated from contact angles, and results indicated that DABA, DBSA and DAPy moieties helped to increase the hydrophilicity. Gas permeation was measured for N₂, O₂, H₂, He and CO₂. Linear moiety contribution method was proposed to study the moiety effects on gas selectivities. The selectivities of O₂/N₂, H₂/N₂, and He/N₂ were greatly affected by the steric effects from the monomer moieties, but permeation of CO₂ was controlled by its solubility in polymers as well as the interactions with the functional groups. Water permeation and dehydration of isopropanol were carried out in pervaporation processes. Concentration coefficients were proposed for feed concentration effects on permeation flux, and permeation activation energies were used to study the temperature dependence of flux. Linear moiety contribution method was applied to quantitatively compare the effects of monomer moieties. Functional groups could change the sorption and diffusion properties in pervaporation, and moiety contribution factors indicated that feed concentrations mainly affected sorption properties, whereas temperatures influenced diffusion properties.     

Mixed gas and pure gas transport properties of copolyimide membranes

Copolyimides were synthesized from dianhydride of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamine contents of 4,4′‐oxydianiline (ODA) and 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (TeMPD) by chemical imidization in a two‐step procedure. Polyimides (PIs) were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, as well as specific volume and free volume. The gas transport properties for pure gas and blends of CO₂ and CH₄ for the homopolymers and 6FDA‐ODA/TeMPD copolymers were investigated at 35°C and 150 psi pressure. In pure gas permeation, permeability of CO₂ and CH₄ increased with increasing TeMPD content in the diamine moiety, whereas the ideal selectivity decreased with increasing TeMPD content. In the mixed gas permeation, permeabilities and separation factor were measured as a function of CO₂ feed molar fraction for five PI membranes. The behavior of pure gas and mixed gas permeabilities and separation factor of CO₂/CH₄ mixtures as the chemical nature of the diamine and the CO₂ molar fraction in the feed gas were varied and are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Effects of phenylenediamines and alkoxysilanes on gas transport properties of polyimide - silica hybrid membranes

Gas transport properties of polyimides (PIs) and their silica hybrids were investigated. The PIs synthesized with several methyl-substituted phenylenediamines were hybridized with silica via a sol–gel process with different alkoxysilanes. The prepared hybrid membranes showed controlled gas permselectivity, depending on the selected phenylenediamines and alkoxysilanes. It was worth noting that the hybrids prepared with tetraethoxysilane possessed improved CO₂ permselectivity with increasing silica content, which tended to exceed the upper-bound trade-off line. This fact suggested the additional formation of free volume holes especially favorable for the CO₂/CH₄ separation around the polymer/silica interfacial area.     

Influence of the dilute‐solution properties of cellulose acetate in solvent mixtures on the morphology and pervaporation performance of their membranes

The pervaporation performance of cellulose acetate (CA) membranes prepared from acetone (AC), acetone/tetrahydrofuran (AC/THF), acetone/chloroform (AC/CF), and acetone/cyclohexane (AC/CYH) was studied for separating MeOH/MTBE (methyl tert‐butyl ether) mixture with 5 (wt) % MeOH. The dilute‐solution properties and Huggins constant (K_H) of CA dissolved in AC and AC/solvent mixtures with 15 vol % of the second solvent (tetrahydrofuran, chloroform, or cyclohexane) were examined. J and α of the CA membranes were affected by the types of solvent mixtures used to prepare the casting solutions. Under the same conditions, the membrane with AC/CYH had the highest J value and the lowest α value, and it was followed by the membranes with AC/CF, AC/THF, and AC. The increasing value of J and decreasing value of α for the CA membranes from different solvent mixtures were in good agreement with the increasing value of K_H of CA in corresponding solvent mixtures. Furthermore, differences in the morphology from scanning electron microscopy images of the cross sections or from atomic force microscopy photographs of the surfaces of the membranes existed, and they provided proof of the different pervaporation performances of the CA membranes prepared from AC and AC/solvent mixtures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97:1891–1898, 2005     

Gas‐separation properties of amine‐crosslinked polyimide membranes modified by amine vapor

The modification of a polyimide (PI) membrane by aromatic amine vapor was performed in this work to increase the crosslinking of the membrane and to study the effect on gas permeability and the corresponding selectivity. The single‐gas permeability of the membranes at 35 °C was probed for H₂, O₂, N₂, CO₂, and CH₄. From the relationship between the combinations of gases and ideal permselectivities, this study showed that amine‐crosslinked PI membranes tended to increase gas permselectivities exponentially with the increasing difference in gas kinetic diameter. Moreover, this study illustrated that the permeability of the membranes was influenced by the formation rate of amine‐crosslinked networks or chemical structures after the reaction. The membranes had the highest level of permselectivities among crosslinked PI membranes for O₂/N₂, and the H₂/CH₄ permselectivity increased 26 times after vapor modification. Furthermore, the modification method that used aromatic amine vapor produced thin and strongly modified layers. These findings indicate that modification is an advantageous technique for improving gas‐separation performance, even considering thinning. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44569.     

Soluble polyimides with propeller shape triphenyl core for membrane based gas separation

This article reports the synthesis and characterization of a series of new aromatic polyimides (PIs) having bulky tert butyl group containing propeller shaped triphenylamine unit in its structure. The PIs were prepared by the reaction of 4,4′‐diamino‐4″‐(2,4,6‐tri‐tert‐butylphenoxy) triphenylamine with different commercially available aromatic dianhydrides through the formation of corresponding poly(amic acid)s and subsequent thermal cycloimidization. The PIs showed high glass transition temperature (T_g up to 270 °C) and thermal stability (T_d10 up to 475 °C). The PI membranes showed good mechanical properties with tensile strength up to 70 MPa, excellent separation performance [P(CO₂) = 100.8, P(O₂) = 40.4 barrer], and good permselectivity [P(CO₂)/P(CH₄) = 50.9, P(O₂)/P(N₂) = 7.6]. The membranes exhibited extremely high solubility selectivity for the CO₂/CH₄ gas pair due to the strong affinity between CO₂ and nitrogen atoms of tertiary amine in triphenylamine. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46658.     

Reversible photochromic nanofibrous membranes with excellent water/windproof and breathable performance

Electrospun nanofibrous membranes (NFMs) with outstanding photochromic property, waterproof, and breathability have attracted considerable interest owing to their multifunctional applications in intelligent clothing, self‐cleaning, and protection. However, great challenges still remain in creating such functional materials. A novel waterproof–breathable membrane with robust photochromic property is fabricated by introducing photochromic microcapsule (PM) into electrospun thermoplastic polyurethanes (TPU) membranes. Compared with the pristine TPU NFMs, the composite TPU/PM membranes are endowed with reversible photochromic properties. In addition, the composite membranes not only exhibited a water contact angle of 137° and a milk contact angle of 130°, but also had integrated properties of modest water vapor transmittance rate of 19,278 g m^?2 day^?1, high air permeability of 962 mm s^?1, low waterproofness of 2.813 kPa, and comparable tensile strength of 12.08 MPa. Furthermore, the convenience and efficiency of this fabrication process will allow for large‐scale production of the multifunctional NFMs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46342.     

Influence of residual solvent on the gas transport properties of dense Hyflon® AD 60X gas separation membranes

The solvent retention by dense Hyflon AD 60X membranes were studied. The effect of the residual solvent on the transport properties of the membranes was evaluated. The permeability, diffusion coefficient and solubility of six permanent gases in membranes prepared under different conditions were determined and compared with the results of simulation studies.     

Relationship between the separation performances and free volume distributions of polyimide/Ag3O4 composite membranes

First, water, methanol, ethanol, acetone, and methyl t‐butyl ether were used as molecular probes to measure the free volume distribution of a type of polyimide membrane material (HQDEA–DMMDA). The methods were equilibrium swelling and separation membrane technologies. From the Kirchheim theory of free volume distribution, a Gaussian distribution function was determined. The Gaussian distribution function was confirmed with tensile testing and wide‐angle X‐ray diffraction of the polyimide films. Second, polyimide/Ag₃O₄ composite hollow‐fiber membranes were prepared by dry/wet phase inversion. The separation performances of the composite membranes were characterized with a methanol/methyl t‐butyl ether mixture. The change in the separation performances was explained by the free volume distribution function very well. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 871–879, 2005