Porous Polyimide Research Articles

Preparation and characterization of porous polyimide fibers with electromagnetic wave absorption properties

AbstractThe porous polyimide (PI) composite fibers, which exhibit high‐efficiency electromagnetic wave adsorption (EMWA) performance, were successfully fabricated by controlling temperature of the coagulation bath during the wet spinning process. The mechanical properties of composite fiber decreased and average radius of micropores increased gradually with the rise of coagulation bath temperature. In addition, carbon nanotubes (CNTs) and nano‐Fe3O4 were introduced into the system by in situ polymerization. CNTs and nano‐Fe3O4 contribute to the attenuation of electromagnetic wave (EMW) through microwave absorption and reflection loss (RL), and the porous structure was able to provide multiple reflection paths for incident EMW and achieved higher attenuation. Particularly, when the temperature of coagulation bath was 50°C, the minimum RL (RLmin) value of the PI/CNTs/nano‐Fe3O4 (PI/C‐Fe) composite fibers was demonstrated to be −54.61 dB with the matching thickness of 2.10 mm. The successful preparation of PI/C‐Fe composite fiber in this study pointed out a new direction for the application of PI‐based fiber materials in structural EMWA materials.

Highly-Efficient adsorptive separation of Cs+ from aqueous solutions by porous polyimide membrane containing Dibenzo-18-Crown-6

To develop recyclable adsorptive materials for high-efficient separation of cesium (Cs+) from aqueous salt lake brine is of great significance. Herein, a novel polyimide (PI-18C6) with high molecular weight (Mn = 93 kDa) and high thermal stability (Td > 380 °C) was synthesized by the condensation and polymerization of di(aminobenzo)-18-crown-6 (DAB18C6) and 4,4′- (hexafluoro-isopropylidene) diphthalic anhydride. Simultaneously, porous membranes for Cs+ selective adsorption were prepared by non-solvent induced phase separation (NIPs) method. Results suggested that the adsorption of Cs+ on PI-18C6 membrane is the monolayer chemical adsorption as confirmed by fitting its adsorption data using pseudo-second-order adsorption model and Langmuir isotherm model, respectively. PI-18C6 membranes displayed a high adsorption capacity up to 54.08 mg g−1 combined with a higher selectivity of coexisting ions such as K+, Na+, Mg2+ and Rb+. Theoretical calculation results showed that the PI-18C6 has a higher adsorption energy for Cs+ (-395.72 kJ mol−1) than K+ and Rb+. The significant higher adsorption energy at the crown-ether sites is largely attributed to the fact that the cavity diameter cavity of DB18C6 (2.6–3.2 Å) is a closer to Cs+ (3.34 Å). The membrane also exhibited excellent repeatability. In summary, our study paves a facile way to develop functional membrane materials for the selective adsorption separation of Cs+ from aqueous solution.

In Situ Fabrication of Magnetic and Hierarchically Porous Carbon Films for Efficient Electromagnetic Wave Shielding and Absorption.

Carbon-based materials have been recognized as a promising method to eliminate electromagnetic interference (EMI) shielding and electromagnetic (EM) wave absorption. However, developing lightweight, ultrathin, and efficient EM wave-shielding and wave-absorbing materials remains a challenge. Herein, a series of magnetic porous carbon composite films with a hierarchical network structure were fabricated via pyrolysis of porous polyimide (PI) films containing magnetic metallic salts of Fe(acac)3 and Ni(acac)2. After pyrolysis, the obtained uniform porous carbon films (CFs) possess a favorable EMI-shielding efficiency (SE) of 46 dB in the X-band with a thickness of ∼0.3 mm. In addition, a higher EMI SE of 58 dB can be achieved by increasing the thickness of the porous CF-20Ni to 0.53 mm. Moreover, the CF-20Ni composites also present effective EM wave-absorbing performance of RLmin = - 30.2 dB with a loading amount of 20 wt % at 13.0 GHz owing to the hierarchically conductive carbon skeleton, magnetic Ni nanoparticles, and dielectric interlaced carbon nanotube cluster within the micropores. These novel lightweight and ultrathin porous CFs are expected to be attractive candidates for efficient EM wave absorption and EMI shielding.

Multi-Functional Polyimide Separators for Electrochemical Capacitor and Lithium-Ion Cell Applications

Achieving both higher energy and power densities are significant targets for next-generation energy storage devices. This will involve the development of new materials and chemistries, but also optimisation and improvements of all the cell components, such as separators, electrolytes and current collectors. Optimisation of cell separators to move beyond the present industry standard of polyolefin materials has received wider attention in the past few years. Polyolefin materials have poor wettability with electrolytes, resulting in low ionic conductivity and affecting the cell performance at high current densities. Moreover, polyolefin class of separators present a higher safety risk due to their poor thermal-dimensional stability that cannot effectively terminate the thermal runaway. The present solution to improve safety is achieved via a sandwich structure (polypropylene (PP)/polyethene (PE)/polypropylene (PP)). However, this leads to a decrease in the ionic conductivity, sacrificing cell performance.Herein, the polyimide-based separators with superior characteristics, including high thermo-dimensional stability, excellent electrolyte affinity, and ionic conductivity, are fabricated by electrospinning and applied within electrochemical capacitors. The specific capacitance of the cells with this composite separator is approximately 13 F/g at 50 A/g, which is double the achievable value using commercial cellulose separators (TF4030). Furthermore, a thermal shutdown functionality can be added to the composite film after spin-coating a layer of low-density polyethene on the surface to apply within lithium-ion cells. Due to the superior physical properties of polyimide, the composite film can endure high temperature without any shrinkage. Additionally, the specific capacity of the cells using a composite separator is approximately 20 mAh/g higher than that of a commercial separator (Celgard2325, PP/PE/PP). The highly porous polyimide (PI) with controllable thickness and high electrolyte wettability is also applied to lithium-free cells to decrease the overpotentials for nucleation and growth of lithium (Reduced from 175 mV to 130 mV in Cu//Li cells). As a result, the coulombic efficiency of the cells with PI separators is 20% higher than via using PE in 1.2 M LiPF6 (EC/DMC=1/1) electrolyte without any additives. The SEM images also present granular lithium deposition (15~30 μm in diameter) rather than dendritic lithium when the electrospun PI separator is applied to the cells. Due to the relationship between the morphology of lithium deposition and the overpotential required for lithium nucleation/growth from the literature. Experiments confirm that the low overpotential can facilitate large lithium deposition rather than dendritic lithium and this is achieved via improvements in the separator.

A breathable flexible glucose biosensor with embedded electrodes for long-term and accurate wearable monitoring

This paper reports a breathable flexible glucose biosensor with excellent flexibility and moisture/air permeability. The biosensor’s electrodes are embedded in a flexible porous nanofiber polyimide substrate through electrospinning. The porous structure of this nanofiber substrate makes the biosensor breathable, effectively avoiding the body-fluid accumulation that can significantly affect measurement accuracy in long-term wearable monitoring. It also completely embeds the electrodes in the substrate preventing them from falling off, which frequently occurs in a surface-electrode structure, effectively avoiding degradation of sensing performance over time. The air-permeable film substrate was obtained by optimizing the manufacturing parameters, including spinning voltage, flow rate, solution concentration, and electrospinning distance. Three electrodes were then embedded on the flexible air-permeable substrate by inkjet printing to form the breathable glucose biosensor. The fabricated breathable flexible glucose biosensor was found to have excellent moisture (∼3954.8 g/[m2 × 24 h]) and air (∼63.59 mm/s) permeability. A bending test verified the firmness of the embedded structure, and the microscopic connectivity and conductivity of the electrodes were stable. This breathable biosensor can precisely detect glucose in the linear range of 0–25 mM with a detection limit of 0.128 mM.

Carbon-based cathode host derived from crosslinked porous polyimides for lithium-sulfur batteries and their electrochemical properties

Carbon-based porous materials as Li–S batteries cathode hosts have received widespread attention because of the superiority of fine physical confinement, vast accommodation voids and excellent conductive networks, towards realizing the adsorption-diffusion-conversion of lithium polysulfides (LiPSs). However, carbon-based materials are usually non-polar, which can only act as physical barriers to limit polysulfides shuttle behavior during short-term cycling of Li–S batteries, lacking strong chemical entrapment towards the polar polysulfides. Herein, we successfully synthesize two novel carbon-based hierarchical porous materials (CR-PPIs@800) derived from crosslinked porous polyimides (CR-PPIs) via traditional polymerization and crosslinking reaction as well as high-temperature treatment. Because the pre-designed porous architectures, CR-PPIs@800 not only give hierarchical porous structure for accommodating LiPSs, but also afford strong chemisorption interaction from high heteroatom N species for adsorbing LiPSs and buffering shuttle behaviors. The carbon networks of CR-PPIs@800 possess valid ion storage and transportation network for accelerating charge/ion migration of LiPSs. Profiting from above advantages, S/CR-PPIs@800 composites cathodes realize the fast conversion of LiPSs, and show promoted electrochemical properties.

Crosslinked porous porphyrin-based polyimides based on terminal alkynyl groups for high carbon dioxide selectivity

Crosslinked porous porphyrin-based polyimides (CR-PPBPIs) were constructed from 5,10,15,20-tetra(4-aminophenyl)porphyrin (TAPP), 2,5-bis(3,4-dicarboxyphenoxy)-4′- phenylethynyl biphenyl (PEPHQDA) and terminal monoamines (AP, APE, APEP and APEN) via polymerization and alkynyl crosslinking reactions. CR-PPBPIs had permanent porosities and revealed outstanding thermal stabilities. With increasing spatial configuration (molecular sizes and conjugate effect) in terminal monoamines, the BET surface areas of PPBPIs decreased first and then increased (158–42 m2 g−1), whereas, the BET surface areas of CR-PPBPIs increased (505–37 m2 g−1) and subsequently declined. The variation trend of BET surface areas in CR-PPBPIs with increasing spatial configuration in terminal monoamines was derived from molecular sizes and π-stacking effect. The reasonable distribution of terminal alkynyl group was critical key to regulating the porosity parameters of crosslinked terminal-modified polyimides. CR-PPBPIs possessed CO2 uptakes (1.63–2.17 mmol g−1 at 273 K) and Qst values (31.3–29.7 kJ mol−1). In addition, CR-PPBPIs had high CO2/N2 (85.64–40.34) selectivities. This work provides a strategy to tune the porosity parameters of crosslinked materials towards CO2 adsorption and separation.

Mechanical and thermal properties of porous polyimide monoliths crosslinked with aromatic and aliphatic triamines

Mechanical and thermal properties of porous polyimide monoliths crosslinked with aromatic and aliphatic triamines

Constructing Highly Conductive and Thermomechanical Stable Quasi‐Solid Electrolytes by Self‐Polymerization of Liquid Electrolytes within Porous Polyimide Nanofiber Films

AbstractSolid electrolytes are being considered as an effective solution to replace liquid ones for building safer batteries, but they suffer either low ionic conductivity or large contact ohmic impedance. Here, a highly conductive and thermomechanically stable quasi‐solid electrolytes (QSE) by self‐polymerization of a commercially available liquid electrolytes (1,3‐dioxolane (DOL), 1,2‐dimethoxyethane (DME), lithium trifluoromethane sulfonimide (LiTFSI) and LiPF6) at room temperature in a porous polyimide nanofiber film are reported. LiPF6 initiates the ring‐opening reaction of DOL and LiTFSI promotes the self‐polymerization to form poly‐DOL (PDOL), while the plasticizer of DME solidifies the PDOL. On the other hand, polyimide has a great affinity with PDOL that facilitates to form stable QSE network. As a result, the QSE film shows a high room‐temperature ionic conductivity of 2.9 × 10−3 S cm−1, a high mechanical strength of 31 MPa, and high heat resistance to 160 °C. The LiFePO4||QSE||Li batteries with a high cathode loading of ≈18.7 mg cm−2 show great cycling performance and stable electrode/electrolyte interfaces at a high current rate of 0.5 C with a capacity retention of 91.8% over 200 cycles at room temperature.

Preparation of polyimide-metal complexes with tunable Sol-Gel transition by Introduction of Zn(II)-Coordination

Developing fully rigid-chain polyimides with reversible sol-gel/gel-sol transitions is of great interest for designing high-performance materials. To date, few approaches have been employed to construct polyimide gels other than hydrogen bonding. Here, we report a polyimide-Zn(II) complex with thermo-responsive sol-gel/gel-sol transition behavior by introducing supramolecular coordination interactions. The tunable dynamic sol-gel behaviors of polyimide-Zn(II) complexes were confirmed using rheological methods. Microstructure analysis shows that coordination interactions occur between the benzimidazole molecules and Zn(II) ions. As a result, the apparent viscosity of the polyimide-Zn(II) complex even rises approximately four orders of magnitude higher than that of the PI-neat oligomer solution. Based on the 2D-correlation spectra and X-ray diffraction results, we deduced that the formation of dense chain stacking caused by coordination effects plays an essential part in the reversible sol-gel transition. As a preliminary experiment, this work gives a novel strategy to construct polyimide gels, showing application prospects in the fabrication of porous polyimide membranes, high-performance polyimide fibers, and aerogels, etc.

Synthesis of porous polyimide films with low dielectric constant and excellent mechanical properties by ambient pressure drying

Synthesis of porous polyimide films with low dielectric constant and excellent mechanical properties by ambient pressure drying

Characteristic parameter to predict the lubricant outflow from porous polyimide retainer material

The lubrication performance of oil-impregnated porous polyimide retainer depends on the release of lubricant from the pores. The centrifugal effect induced by rotation is one of the important inducements of lubricant outflow. In this paper, molecular dynamics simulations and experiments are conducted to investigate the lubricant outflow process in the porous polyimide material. The results show that the lubricant outflow can be controlled by five features: pore sizes, rotation speeds, radii of rotation, lubricant viscosities, and surface tensions. Inspired by molecular dynamics simulation results and experimental observations, a characteristic parameter is proposed to evaluate the lubricant outflow state. This new understanding may help expand the use of porous material to improve lubrication in space bearing.

Electrocatalytic oxidation of formaldehyde using electrospinning porous zein-based polyimide fibers

In this work, electrode coated with electrospinning porous polyimide fibers were prepared. The fiber is made by electrospinning zein from corn by-products and polyacrylic acid (PAA). The prepared porous fiber film was loaded with copper and prepared as working electrode material.The specific surface area of the porous fiber membrane is 304.6313 m2/g. The Polyimide (PI)-Cu nanoparticle electrochemical sensor was prepared by supporting non-noble metal Cu on the porous polyimide for the oxidation of formaldehyde. The prepared electrode can be used to catalyze the oxidation of formaldehyde, and the oxidation peak potential is around −0.41 V. Catalytic oxidation for 300 s at the oxidation peak potential can consume formaldehyde 0.758 × 10−6g, and the coulombic efficiency reaches 74.96%. Electrodes made of cheap metals can quickly remove formaldehyde in solution through electrochemical catalytic oxidation.

Polymer Concentration and Liquid-Liquid Demixing Time Correlation with Porous Structure of Low Dielectric Polyimide in Diffusion-Driven Phase Separation.

Porous polyimide (PI) films are a promising low-k dielectric material for high-frequency data transmission with low signal attenuation. Pores are generated by non-solvent induced phase separation (NIPS) during phase inversion of polymer solution via non-solvent accumulation and solvent diffusion. In this study, aromatic PI was employed as a matrix for NIPS, and the influence of polymer concentration and liquid—liquid demixing time on the morphology of pores in the PI films was investigated. This ensured control over the porous structure of the PI film and provided desirable dielectric properties in a broad frequency range of 100 Hz–30 MHz (1.99 at 30 MHz) and thermal stability (Td5% > 576 °C, Tg > 391 °C). This study addresses the effect of polymer concentration and coagulation time on the morphology and physical properties of PI sponge films and provides guidance on the design and optimization of architectures for polymeric materials requiring pore modification.

Scalable fabrication of cross-linked porous centrifugally spun polyimide fibers for thermal insulation application

Flexible fibrous thermal insulators with low thermal conductivity are highly demanded to improve energy efficiency in many application fields, especially in the aerospace industry. In the present study, the cross-linked porous polyimide (PI) fibrous insulator was prepared using centrifugal spinning, a scalable and facile technique for fibers production. The influence of PI concentration and solvent composition was evaluated to find the optimum parameters for defect-free fiber fabrication. In the following step, the PI fibers were cross-linked to gain better solvent stability. The morphology, chemical properties, surface wettability, thermal resistance, and thermal conductivity of the obtained fibers were evaluated. The cross-linked fibers exhibit a low thermal conductivity of 0.029 W/mK with thermal stability up to 515 °C, hydrophobicity with a contact angle of 137.7°, and are flexible at high temperature. The successful fabrication of the PI fibers opens a new approach for the scalable fabrication of flexible fibrous insulators for aerospace applications.

Effects of porosity on the tribological and mechanical properties of oil-impregnated polyimide

The porosity of oil-impregnated porous polyimide is closely related to its tribological and mechanical properties, which is critical to determine the application and service life. Herein, polyimides with different porosities are fabricated by mixing different contents of pore-forming agent to investigate the significance of porosity with dimethyl silicone oil as impregnated lubricant. The dynamic porosity was simulated to explain the self-lubricating mechanism. Results show that the increasing porosity results in a higher oil content and the oil can be easily extruded, but leads to a poor bearing capacity and a higher friction coefficient, and vice versa. The friction coefficient reduced by 46.15% with the optimized porosity of 20.05%. This study may provide guidance for the development of high-performance oil-impregnated polymers.

Achieving multiband compatible and mechanical tuning absorber using edge topological defect-induced graphene plasmon

Graphene has been shown to be a high-performance microwave-absorbing material with broadband potential. However, simultaneous realization of multiband compatible strong absorption is still a challenge. In this study, graphene rich in edge topological defects is successfully synthesized, and the effect of defect density on electromagnetic parameters has been investigated. Electrons (π electrons, π+σ electrons) located at edge defects alter the loss paths and plasma absorption frequencies of the graphene aerogels. These improvements in electrical properties give the graphene aerogel a more coordinated impedance matching and attenuation capability, allowing it to achieve strong absorption in multiband (S, X, Ku band) simultaneously. In addition, a mechanically tunable multimode absorber can be further realized by incorporating porous polyimide foam. The strong absorption (>99.9%) of a wide range of variable bands (S, C, X, and Ku bands) can be flexibly adjusted by stress cycling of piezo resistive foam. In addition, self-cleaning, high temperature resistance, and simple processability are expected to deliver solutions for the communication and Internet of Things engineering.

Study on preparation process parameters and tribological properties of porous PI materials

PurposePreviously, the effect of pore-forming agents on the properties of pore size and morphology was studied. In this paper, we determine the optimal combination of parameters by tensile strength and perform tribological tests with optimal combination of parameters.Design/methodology/approachIn this paper, porous polyimide (PI) materials were fabricated using vacuum hot molding technology. The orthogonal experiment was designed to test the mechanical properties of porous PI materials with the process parameters and the content of pore-forming agent as the changing factors. The porous PI oil-bearing materials were obtained by vacuum immersion, and tribological test were carried out.FindingsThe results showed that porous PI oil-bearing materials are suitable for low-speed and low-load conditions. The actual value of the friction coefficient basically match with the theoretical value of the regression analysis, and the errors of the friction coefficient are within 10% and 3%, respectively, which proves that the method used in the study is feasible for the friction coefficient prediction.Originality/valueIn this paper, we have produced a new porous oil-bearing material with good tribological properties. This study can effectively predict the friction coefficient of PI porous material.

Selective photocatalytic CO2 reduction to CH4 over metal-free porous polyimide in the solid-gas mode.

Using a catalyst-free one-pot polycondensation approach, a new donor-acceptor (D-A) based porous polyimide (PeTt-POP) photocatalyst was developed. PeTt-POP produced CH4 (125.63 ppm g-1 in 6 h) from CO2 under visible light irradiation in the gas-solid mode without the use of co-catalysts or sacrificial agents. The progress of the reaction and the corresponding intermediate species involved in the CO2 reduction were identified by operando DRIFTS experiments, from which a plausible reaction mechanism was proposed.

One-pot two-step synthesis of micro- and mesoporous organic fibrils for efficient pseudocapacitors

A porous polyimide with a hexaazatriphenylene triimide group is synthesized from two pre-assembled monomers. Its micro- and mesoporous architecture enables fast ion diffusion for an efficient energy storage material with a high charge capacity.