Polyimide Composite Membranes Research Articles

Modulating dielectric properties of polyimide composite membranes with hydrophobic mesoporous silica via ball milling processing

This research work investigated the impact of the ball-milling (BM) process on the dielectric properties of polyimide (PI) composite membranes incorporating hydrophobic mesoporous silica (HMS) particles. Initially, HMS particles were synthesized through base-catalyzed sol-gel reactions among APTES, MTMS, and TEOS, utilizing D-(−)-Fructose as a template. Following synthesis, the HMS particles underwent ball-milling to fine-tune corresponding specific surface area and average particle size. Three distinctive ball-milled HMS variants (referred to as BMS) were thoroughly characterized using FTIR, 13C NMR, 29Si-NMR spectra, DLS, BET, CA, TGA, SEM, and TEM techniques. Subsequently, a series of PI composite membranes were fabricated and subjected to characterization via FTIR, EDS, CA, and TGA analyses. It should be noted that the three distinctive BM treated HMS was found to exhibit higher specific surface area and hydrophobicity as compared to non-BM treated HMS based on the data of BET and CA, respectively. Moreover, the surface area and hydrophobicity of ball-milled HMS exhibited the upward trend of BMS1 < BMS2 < BMS3. Subsequently, the dielectric constant (Dk) and dielectric loss (Df) of PI and its composite membranes containing HMS particles measured at frequency of 10 GHz was found to show the downward trend. For example, the Dk of PI composite membranes: PI/BMS3 (3.34) < PI/BMS2 (3.41) < PI/BMS1 (3.55) < PI/HMS (3.58) < PI (3.66). On the other hand, the Df of PI composite membranes: PI-BMS3 (0.0113) < PI/BMS2 (0.0114) < PI/BMS1(0.0115) < PI/HMS (0.0121) < PI (0.0123). This resulting decreasing trend of dielectric constant of as-prepared composite membranes may be attributed to the incorporated of HMS particles in PI membrane exhibiting lower moisture absorption (Dk of water = 80) and higher surface area (Dk of air = 1) based on the TGA and CA, respectively.

Thermally rearranged OH-containing polyimide composite membranes with enhanced gas separation performance and physical aging resistance

Gas separation membranes play a pivotal role in various industrial processes, demanding continuous improvement in their efficiency and durability. This study focuses on thin-film composite (TFC) membranes based on polyimide, utilizing a hydroxyl-containing polyimide selective layer for its processability and selectivity. A complete and smooth surface for the selective layer in the composite membranes was achieved by exclusively selecting a 10% concentration of the polyimide spin-coating solution. Subsequent thermal rearrangement at 430°C induced the formation of a rigid polybenzoxazole structure, enhancing gas permeance. Optimal separation performance was achieved through a two-hour rearrangement, resulting in a more than 30-fold increase in gas permeance while preserving selectivity. The study also delved into anti-physical aging performance. The thermally treated PI-10 wt%−2 h membrane exhibited a 10% reduction in CO2 and O2 permeance over 90 days, with O2/N2 and CO2/N2 selectivities nearly maintaining their initial levels. This research provides valuable insights for the development of efficient and durable gas separation membranes.

Construction of transfer-free regular through-pore polyimide composite microfiltration membranes via amphiphilic dendron-assisted breath-figure method for water treatment

Regular through-pore membranes exhibit extremely high productivity and size-selective capabilities. Previous studies have demonstrated that the use of a polymer alone on a solid substrate surface hinders the formation of regular through-pore membranes. In this study, amphiphilic dendrons were used as surfactants to concentrate the functional groups and strengthen the weak bonding forces between the molecules, which is conducive to the formation of regular through-pores in the membrane. The amphiphilic dendrons were mixed with commercial-grade polyimide (PI) using chloroform as the solvent, and the solution was evenly coated on the surface of the filter paper. Using the breath-figure method, an ultrathin regular through-pore PI layer was formed directly on the surface of the filter paper. The SEM image shows that regular through-pores were formed only on the surface of the substrate. The preparation process used in this study eliminates the need to transfer ultrathin and weak membranes to the substrate surface, which simplifies the membrane-making process. Pure water and yeast solution filtration tests were conducted on the composite membrane prepared with a 5 mg/ml dendron solution. A pure water permeance of 118,826 L m-2h−1 bar−1 (LMH/bar) was obtained, the yeast solution permeance and rejection are 17,410 LMH/bar and 92.85 %, respectively. The yellow, turbid, muddy water was successfully purified to clean water. The original performance of the fouled membrane was restored after only 30 s of water flushing. This study proposes a new approach to fabricate high-efficiency regular through-pore PI composite microfiltration membranes.

Effects of different amine-functionalized graphene oxide on the mechanical and thermal properties of polyimide composites

The utilization of functionalized graphene oxide as nanofillers has attracted significant attention in the development of high-performance composite materials. In this study, amine-functionalized graphene oxide (AFGO) by different amines, including p-phenylenediamine- (PPD-GO) and 4, 4’-diaminodiphenyl ether (ODA-GO), respectively, was prepared and used to synthesize a series of polyimide (PI) composite membranes via in situ polymerization method. The PPD-GO/PI and ODA-GO/PI composite membranes exhibited much higher mechanical and thermal properties than that of neat PI, owing to the diverse interfacial interaction and the surface architecture behavior. Compared to neat PI, the tensile strengths were enhanced 14.6% and 14.5%, the tensile modulus were enhanced 26.9% and 23.2%, and the Tg increased by 9°C and 17.5°C of the PI composite membrane containing 0.3 wt% PPD-GO or ODA-GO, respectively. This study provides a guidance for the development of high-performance PI composite materials through the regulated interfacial structure via the moderate chain length.

Preparation and Properties of Polyimide Composite Membrane with High Transmittance and Surface Hydrophobicity for Lightweight Optical System.

Polyimide membranes have excellent physiochemical properties which make them valuable materials for optical area. However, common aromatic polyimide membrane trend to show low transmittance in visible region because of the charge-transfer complex (CTC) in molecular structures. Moreover, it’s trending to show high moisture uptakes because of the hydrophilic imide rings in molecular structure. In this work, a polyimide composite membrane with SiO2 antireflective membrane on both sides was prepared. High transmittance (93% within 500~800 nm) and surface hydrophobicity was realized simultaneously. The polyimide composite membrane showed great optical homogeneity. The SiO2 antireflective membranes on polyimide substrate were prepared through a simple and efficient sol-gel method. The surface roughness of polyimide membrane substrate on each side has been improved to 1.56 nm and 3.14 nm, respectively. Moreover, the excellent thermal stability and mechanical property of polyimide membrane has been preserved, which greatly improves the range of applications for the composite membrane. It is a good candidate for light weight optical system.

Novel sulfonated polyimide-nafion nanocomposite membranes: Fabrication, morphology and physiochemical investigations for fuel cell applications

Herein, Nafion/sulfonated polyimide (SPI-x) composite membranes have been fabricated using different ratios of Nafion and SPI. The SPI was synthesized using 1, 4, 5, 8-Napthalenetetracarboxylic dianhydride (NTDA) via a one-step high-temperature imidization method in an inert atmosphere. The incorporation of SPI membrane with ion exchange capacity (IEC) of about 1.0 mmol−1 in Nafion showed improvement in physicochemical properties, such as IECs, hydrolytic/oxidative stability, water uptake, and dimensional changes (3.61). Nafion/SPI-x composite membranes showed good proton exchange nature i.e. proton conductivity and thermal stability. Scanning electron micrographs (SEM) reveals that the Nafion/SPI-x nanocomposites membranes display well defined micro-phase separation morphology based on SPI content in the composites. Fourier-transform infrared spectroscopy (FT-IR) confirmed the presence of important functional groups in synthesized membranes. The protons present in membranes were studied by nuclear magnetic resonance (1H NMR) spectroscopy, carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy, and X-ray diffraction analysis (XRD) investigated the nature of polymer material. The thermal stability of the synthesized membranes was found up to be 500–550 °C by thermogravimetric analysis (TGA), a clear indication of good thermal stability of synthesized membranes. Among all Nafion/SPI composites with 60 and 80 wt.% of SPI show good morphology for membranes because of cross-linking between Nafion and SPI. In conclusion, the findings revealed that Nafion/SPI-x membrane could be used as a polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs) applications.

Molecular level understanding of CO2 capture in ionic liquid/polyimide composite membrane

Ionic liquid (IL)/polyimide (PI) composite membranes demonstrate promise for use in CO2 separation applications. However, few studies have focused on the microscopic mechanism of CO2 in these composite systems, which is important information for designing new membranes. In this work, a series of systems of CO2 in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide composited with 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based PI, 6FDA-2,3,5,6-tetramethyl-1,4-phenylene-diamine, at different IL concentrations were investigated by all-atom molecular dynamics simulation. The formation of IL regions in PI was found, and the IL regions gradually became continuous channels with increasing IL concentrations. The analysis of the radial distribution functions and hydrogen bond numbers demonstrated that PI had a stronger interaction with cations than anions. However, the hydrogen bonds among PI chains were destroyed by the addition of IL, which was favorable for transporting CO2. Furthermore, the self-diffusion coefficient and free energy barrier suggested that the diffusion coefficient of CO2 decreased with increasing IL concentrations up to 35 wt-% due to the decrease of the fractional free volume of the composite membrane. However, the CO2 self-diffusion coefficients increased when the IL contents were higher than 35 wt-%, which was attributed to the formation of continuous IL domain that benefitted the transportation of CO2.

Ionic Liquid/Sulfonated Polyimide Composite Membranes: Effect of Polyimide Sequence on CO2 Transport Properties

The carbon dioxide capture and storage (CCS) plays an important role in reducing greenhouse gases, but its high energy cost is a critical issue. The CO2 separation is recognized as a key process for reducing cost, and a membrane separation method is one of the promising candidates with a low energy cost. Ion gels comprising polymer networks and ionic liquids (IL), which exhibit unique properties such as non-volatility and CO2 absorption selectivity, have attracted attention as environmentally friendly separation membranes. Previous work in our group has shown that sulfonated polyimide (SPI) with an imidazolium cation exhibits good compatibility with an IL. SPI can hold high content of IL (~75 wt%) and form a uniform, flexible, tough (~10 MPa of Young’s modulus) and thin composite membrane.[1-3] This SPI was synthesized by random copolymerization of a sulfonated ionic monomer and a non-ionic monomer. The composite membranes separated into bicontinuous two phases of ionic and non-ionic domains, which contribute to the formation of gas diffusion path and mechanically tough network, respectively. By using multiblock copolymers of SPI, it is expected that the size and connectivity of each domain are improved, which could lead to the increase of the CO2 permeability and mechanical toughness of the membrane. In this study, we fabricated an 1-buty-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2])/SPI composite membranes composed of multiblock-type SPI (mb-SPI) and compared their property with those of random-type SPI (r-SPI).75 wt%[C4mim][NTf2]/mb-SPI composite membranes exhibited higher CO2 permeability (372 barrer) than the corresponding r-SPI (235 barrer) while the gas selectivity (CO2/N2) is 26, which is of the same magnitude as that of r-SPI (CO2/N2 is 28). The mb-SPI can hold higher IL content up to 80 wt% than r-SPI, resulting in higher CO2 permeability (480 barrer; CO2/N2 is 27). The higher ionic conductivity also suggested the higher connectivity of ionic domains in mb-SPI system. On the other hand, from tensile tests, it was found that the mb-SPI membrane was less ductile than the r-SPI membrane. The result of dynamic mechanical analysis (DMA) indicates that the difference of internal structure between the membranes composed of mb-SPI and r-SPI is one of the reasons of the poor mechanical property.To fabricate more strong membrane, we used SPI with more rigid polymer backbone. Rigid mb-SPI exhibits high CO2 permeability (450 barrer) and gas selectivity (CO2/N2 is 24), comparable with the conventional one, and the mechanical property was superior to the conventional one. From these results, we concluded that the mb-SPI membrane having high CO2 permeability and toughness was successfully fabricated.

Novel sulfonated polyimide membrane blended with flexible poly[bis(4-methylphenoxy) phosphazene] chains for all vanadium redox flow battery

To improve SPI stability, poly[bis(4-methylphenoxy) phosphazene] (PMPP) was designed and synthesized using polyphosphazene's unique and strong flexibility. A novel sulfonated polyimide (SPI) composite membrane embedded with flexible PMPP chains was prepared for all vanadium redox flow battery applications. SPI/PMPP composite membrane characterizations, such as proton conductivity, vanadium ion permeability, stability, and single cell performance, were thoroughly investigated. PMPP's unique properties not only allow the membrane to exhibit excellent anti-hydrolysis and anti-oxidation stability, but also maintain high proton conductivity and low vanadium ion permeability (as low as 4.81 × 10−7 cm2 min−1). It can also form a rigidity-flexibility network with SPI to improve membrane mechanical properties. It can be deduced that introducing PMPP has achieved many things in one stroke. Results show that the hydrolysis and oxidation stabilities of SPI/PMPP membrane were significantly improved. The SPI/2% PMPP membrane exhibits higher columbic efficiency (CE: 97.52%), voltage efficiency (VE: 84.88%), and energy efficiency (EE: 82.21%) than that of the N212 membrane (CE: 94.97%, VE: 82.04%, EE: 76.99%) at a high current density of 100 mA cm−2. In addition, the charging capacity loss of a battery with a SPI/2% PMPP membrane has also significantly decreased by about 206.70 mAh after 110 cycles at 100 mA cm−2 with the same electrolyte volume compared to a pristine SPI. Meanwhile, the high temperature resistance of SPI/PMPP membrane also shows the possibility of being applied with fuel cells.

Preparation and application of a high-temperature–resistant EVOH-SO3Li/PI fiber membrane with self-closing pores

A lithium ethylene-vinyl alcohol copolymer sulfate (EVOH-SO3Li)/polyimide (PI) composite fiber membrane prepared via high-voltage electrospinning and impregnation was used as a lithium-ion battery separator for research purposes. The polyamic acid spinning solution was synthesized from 3,3′′,4,4′′-benzophenone tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether. The PI fiber membrane was prepared via high-voltage electrospinning and thermal imidization, and EVOH-SO3Li was then coated on the surface of the PI fiber to prepare an EVOH-SO3Li/PI composite fiber membrane material (t-EVOH-SO3Li/PI). Overall, the EVOH-SO3Li/PI membrane exhibits excellent basic physical properties, given the clear three-dimensional network microstructure. When compared with EVOH-SO3Li/PI composite fiber membrane prepared via the cospinning method (s-EVOH-SO3Li/PI), its electrolyte uptake and tensile strength can increase to 739% and 17.56 MPa, respectively. Additionally, the EVOH-SO3Li/PI composite fiber membrane prepared via high-voltage electrospinning and impregnation exhibits better heat shrinkage stability, electrochemical performance, and high-temperature self-closing pores function. The electrochemical stability window, electrochemical impedance, and ionic conductivity correspond to 5.8 V, 310 Ω, and 3.753 × 10−3 S cm−1, respectively. Specifically, at 200°C, the internal pores can close effectively, and this is extremely important for the safety of lithium-ion batteries.

Role of Cation Structure in CO2 Separation by Ionic Liquid/Sulfonated Polyimide Composite Membrane.

The development of suitable separation technologies for the separation of carbon dioxide is a pressing technological requirement. The application of ion gel membranes for this purpose continues to stimulate a great deal of research, and in this study we focus on the chemical structure of the ionic liquid component in the ion gel, and its interactions with the sulfonated polyimide polymer. Whilst such membranes are known to give promising carbon dioxide separation properties together with mechanical strength and thin-film-processability, we further elaborate on how changing the cation of the ionic liquid from a typical imidazolium cation to a protic variant effects the physicochemical, thermal, and structural properties of the membranes, and how these changes further influence the carbon dioxide separation properties. We compare and contrast our findings with our earlier study on protic and aprotic ammonium-based ionic liquids, and highlight that for CO2 absorption behavior in the imidazolium systems, the importance of directionality of interactions (ion pairs exhibit a large energy stabilization only for a specific geometrical arrangement of cation and anion, e.g., hydrogen bonding rather than Coulombic interaction) between cation and anion applies not only to the protic system, but also to the nominally aprotic cation. Finally, we demonstrate that the phase separation behavior in the ion gels is an important factor in determining the carbon dioxide separation behavior.

Application of Protic Ionic Liquids to CO2 Separation in a Sulfonated Polyimide-Derived Ion Gel Membrane

It is of great interest to determine whether a relatively easily prepared and inexpensive protic ionic liquid (PIL) could be used in place of an aprotic ionic liquid (AIL) in a composite membrane for CO2 separation. We prepared mechanically reliable sulfonated polyimide (SPI) composite membranes with a PIL, [N124][NTf2] (N,N,N-butylethylmethylammonium bis(trifluoromethylsulfonyl)amide) by a solution casting method, and their mechanical, thermal, and gas separation (CO2 and N2) properties were compared with those of membranes incorporating an isomeric AIL, [N1123][NTf2] ([N1123]+, N,N,N,N-ethyldimethylpropylammonium). We discussed the influence of the presence or absence of active protons in the ILs on CO2 separation characteristics and the applicability of the PIL to a CO2 separation membrane. The SPI/PIL membrane exhibited a slightly lower selectivity, but higher permeability, than the SPI/AIL membrane. It is supposed that these differences originate from the difference in membrane structure and CO2 inte...

Graphene oxide/cross-linked polyimide (GO/CLPI) composite membranes for organic solvent nanofiltration

Purification and recovery of polar organic solvents such as dimethylformamide (DMF) with high chemical separation speed and low energy cost nanofiltration membranes has been widely investigated, while it is still a difficult challenge that high permeability of solvents and rejection of solutes are achieved simultaneously. In this study, a novel organic solvent nanofiltration (OSN) membranes was obtained via coating a thin selective graphene oxide (GO) layer on top of the polyimide porous substrate (PI) which was cross-linked to improve the stability in polar solvents. The resultant GO/cross-linked PI (GO/CLPI) composite membranes feature remarkable sieving capability of >94% for RBss molecules (1018 Da), accompanying high pure solvent permeability of 11.1 L h−1 m−2 bar−1, 4.9 L h−1 m−2 bar−1 and 1.0 L h−1 m−2 bar−1 for water, IPA and DMF, respectively. Different from conventional method of characterization, low field nuclear magnetic resonance technology (LF-NMR) was utilized to confirm that the GO/CLPI membrane shows a higher adsorption capacity for IPA than DMF. This newly technique can be effectively utilized to evaluate the affinity between organic solvents and the surface of membranes.

Improved performance of sulfonated polyimide composite membranes with rice husk ash as a bio-filler for application in direct methanol fuel cells

The main problem with using membranes in a direct methanol fuel cell is the proton conductivity and methanol permeability that reduces the performance of the membrane. In addition, the cost of the membrane is very high and remains the main issue for the commercialization of Direct Methanol Fuel Cell (DMFC). To solve this problem, this study introduces rice husk ash (RHA) as a bio-filler in sulfonated polyimide (SPI) composite membranes. The bio-filler is expected to reduce the cost of the membrane and at the same time increase the performance of the membrane. In this work, agricultural rice husk waste was subjected to oxidation to produce RHA. The composite membrane displayed maximum values for the ion exchange capacity (0.2829 mmol g−1) and water uptake (55.24%). It was observed that the proton conductivity (0.2058 S cm−1) was higher than that in the pristine SPI membrane. The methanol permeability of the SPI-RHA membranes was reduced to 24 times lower than that of the pristine SPI membrane. In the DMFC passive single-cell test, the maximum power density was increased from 8.0 mW cm−1 to 13.0 mW cm−1 using a composite membrane with 15 wt % RHA. These composite membranes have proven that the addition of RHA enhanced the performances of the fuel cell and have a very high potential to act as an alternative bio-filler for the membranes used in a direct methanol fuel cell.

Sulfonated Polyimide/Ionic Liquid Composite Membranes for CO2 Separation: Transport Properties in Relation to Their Nanostructures

The transport properties of ionic liquid (IL)/sulfonated polyimide (SPI) composite membranes for CO2 separation were explored in relation to their nanostructures. 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2]), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([P14][NTf2]) were selected as the ILs. These composite membranes enable favorable CO2 separation and superior mechanical properties. SPI is plasticized by the IL, which induces a decrease in the elastic modulus; however, due to the formation of bicontinuous nanostructures of IL-rich and SPI-rich phases, a modulus of >10 MPa is retained even with the incorporation of 75 wt % IL. [C4mim][NTf2] and [C4mim]PF6 exhibit stronger plasticization effects on SPI than [P14][NTf2]. The diffusion coefficients of CO2 and N2, which were measured by the time-lag method, abruptly increase with increasing IL content in the [C4mim][NTf2]/SPI composite memb...

Sulfonated polyimide/ionic liquid composite membranes for carbon dioxide separation

A series of composite membranes (SPI-NTf2 and SPI-PF6) consisting of a sulfonated polyimide (SPI) and an ionic liquid (IL), either [C4mim][NTf2] or [C4mim]PF6, where [C4mim] and [NTf2] stand for 1-butyl-3-methylimidazolium and bis(trifluoromethanesulfonyl)amide, respectively, were prepared, and their thermal, mechanical and gas (carbon dioxide (CO2) and N2) permeation properties were systematically investigated. The ILs functioned as plasticizers of the SPI, making the composite membranes softer (lower Young’s modulus and larger elongation at break). However, SPI-NTf2 (75), containing 75 wt% [C4mim][NTf2], still exhibited a Young’s modulus higher than 10 MPa, which is much higher than that reported for common IL/polymer composites. The SPI membrane behaved as a gas barrier membrane; however, the addition of IL greatly enhanced gas permeability. Consequently, SPI-NTf2 (75) exhibited CO2 permeability ( ) of 412 Barrer at 30 °C and selectivity against N2 ( ) of 27. The SPI-PF6 composite membranes showed similar behavior; however, gas permeability exhibited by these membranes was lower than that exhibited by the SPI-NTf2 composite membranes. In permeation tests under mixed-gas conditions, the value decreased than that under single-gas conditions, whereas increased, and decreased (from the range 29−27 to 12–16). Ionic liquid (IL)/sulfonated polyimide (SPI) composite membranes exhibit high carbon dioxide (CO2) permeability with good CO2/N2 selectivity. CO2 permeation coefficients (PCO2) are higher than 400 Barrer at 30 °C when the composite membranes include 75 wt% of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. The IL/SPI composite membranes also exhibits excellent mechanical properties (Young’s modulus ⩾10 MPa) and can be processed into thin and uniform membranes. These characteristics are preferable as CO2 separation membranes.

Study on the electromechanical properties of polyimide composites containing TiO 2 nanotubes and carbon nanotubes

New polyimide composite membranes were prepared by physical incorporation of different amounts of TiO2 nanotubes (TNTs) and carbon nanotubes (CNTs) into a poly(amic acid) solution, followed by film casting and thermal imidization. The poly(amic acid) was synthesized by polycondensation reaction of 4,4′-(1,3-phenylenedioxy)dianiline with 4,4′-oxydiphthalic anhydride, in N-methyl-2-pyrrolidone as solvent. TNTs having outer diameters of approximately 10–12 nm and length of several hundred of nanometers were obtained by hydrothermal method. Their surface was modified by treating with 3-aminopropyltriethoxysilane to enhance organic–inorganic compatibility and to avoid agglomeration. A study of microelectromechanical properties of these membranes was performed. The influence of filler content on nanometric displacements when an electric voltage is applied on the membrane surface was determined. Also, theoretical aspects on the combined effects thermal and electrostrictive actuation are presented. The longitudinal microactuation included only electrothermal effect. The microactuation including electrostrictive effect as well as electrothermal effect was remarkable to the small electric field intensity and to small temperature domain.

Improved performance of PVdF-HFP/PI nanofiber membrane for lithium ion battery separator prepared by a bicomponent cross-electrospinning method

Poly(vinylidene fluoride-co-hexafluoropropylene)/polyimide (PVdF-HFP/PI) composite nanofiber membrane used for lithium ion battery separator was prepared by an electrospinning apparatus equipped with four needles. Two needles were fed with PVdF-HFP solution and the rest with PI solution and the two types of polymer solutions were arrayed alternately, in a straight line to form a composite membrane, which could be referred to as cross-electrospinning, followed by thermal calendering process to improve the mechanical property of the composite membrane via fusing the PVdF-HFP component which has lower melting temperature. PVdF-HFP/PI composite membrane showed positive results in terms of physical properties. Additionally, the cells assembled with the composite separators exhibited better electrochemical stability, lower interfacial resistance and higher ionic conductivity, compared with Celgard 2400 PP separator. Conspicuously, the improved performance of lithium ion battery separator indicated that bicomponent cross-electrospinning method could be potentially applied for designing future lithium ion battery separator.

그라핀을 포함하는 폴리이미드 멤브레인의 미세조직구조 변화

The polyimide composite membranes were prepared with polyimide composite solutions including graphenes by using the phase inversion method. The morphologies of these membranes were significantly changed according to the graphene loadings in composite solutions and the solvent systems of the composite solutions. The finger-like macro-voids were formed in the hollow fiber membranes which were prepared in the NMP solvent system with a small amount of ethanol. As increasing the content of the viscous alcohols such as glycerol or 1,3-propanediol in the composite solution, however, the morphologies of the hollow fiber membranes were changed to sponge-like types. In case of flat membranes, the increase of graphene content in polyimide composites causes that their membranes change from the finger-like macro-porous to sponge-like morphologies.

Preparation and characterization of novel thermoset polyimide and polyimide-peo doped with LiCF3SO3

This paper deals with the synthesis and characterization of a new type of anhydrous ionic conducting lithium doped membranes consist of polyimide (PI), poly (ethylene oxide) (PEO) and lithium trifluoromethanesulfonate (LiCF3SO3) for solid polymer electrolyte (SPE). For this purpose, different molar ratios of lithium salt (Li-salt) solution are added into poly (amic acid) (PAA) intermediate prepared from the reaction of 3,3!,4,4!-benzophenon tetracarboxylic dian- hydride (BTDA) and 4,4!-oxydianiline (ODA). PEO is incorporated into PAA since it forms more stable complexes and possess high ionic conductivities. Then, Li-salt containing PAA solutions are imidized by thermal process. The effect of interaction between host polymer and Li-salt is characterized by FT-IR (Fourier Transform Infrared) spectroscopy and SEM (scanning electron micrsocopy). The conductivities of Li-salt and PEO containing PI composite membranes are in the range of 10 -7 -10 -5 S·cm -1 . The conductivity increases with incorporation of PEO. Thermogravimetric analysis results reveal that the PI/PEO/LiCF3SO3 composite polymer electrolyte membranes are thermally stable up to 500°C.