Polyimide Materials Research Articles

Large π‐Conjugated Structure Strategy for Optimizing Polyimide Film‐Forming Properties and Developing Gas Fluorescence Sensors

ABSTRACTFour different amounts of anthracene groups were introduced into the polyimide (PI) backbone by one‐step polycondensation. This bulky and rigid polycyclic aromatic hydrocarbon structure effectively improved the solubility of the polyimide material. Therefore, the anthracene‐containing polyimides (ANPIs) were easily cast into the films at room temperature. The introduction of anthracene chromophores significantly developed the fluorescence performance of polyimides. It was found that the photoluminescence emission band of ANPIs migrated from the blue to the orange light region as the samples changed from solution to film. This is related to the aggregation of molecular chains in a solid state. Furthermore, ethanol and phenylethanol were selected to investigate the fluorescence response of the ANPI film. Interestingly, the sample displayed a noticeable luminescent “turn‐off” effect on the targets. It could be considered a convenient strategy for the detection of organic gases.

ОСОБЕННОСТИ ПОЛУЧЕНИЯ И ОПРЕДЕЛЕНИЕ ОСНОВНОСТИ АДАМАНТАНСОДЕРЖАЩИХ ЖИРНОАРОМАТИЧЕСКИХ ДИАМИНОВ - ПОТЕНЦИАЛЬНЫХ МОНОМЕРОВ ДЛЯ ОПТИЧЕСКИ ПРОЗРАЧНЫХ ПОЛИИМИДОВ

A series of fatty aromatic adamantane-containing diamines based on acetylated aniline derivatives have been obtained using trifluoroacetic acid, which allows the target products to be obtained selectively with yields of up to 93 % and purities of up to 97,5 % without pretreatment. The pKa values and the charges on the nitrogen atom of the resulting diamines are determined. The synthesized compounds are potential monomers for transparent polyimide materials.

Electrospun fine-diameter polyimide nanofiber membranes via metal wire-based needle-free technique for high-efficiency PM0.3 filtration at high-temperature

Polyimide (PI) nanofiber materials have garnered attention in the field of high-temperature filtration due to their exceptional thermal stability. Enhancing their filtration efficiency for fine particulate matter (PM2.5–0.3) and exploring their performance limits under high-temperature conditions are crucial for high-temperature filtration applications. In this study, a metal wire-based needle-free electrospinning technique was employed to electrospin polyimide (PI) material, successfully fabricating nanofiber membranes with an average fiber diameter of 122 nm within just 10 min at an elevated electrospinning voltage of 80 kV (electric field:333.33 kV/m). The Fine-diameter PI nanofiber membrane achieved a filtration efficiency of 99.99 % for PM0.3 and operated at a low resistance of 189.18 Pa. After continuous treatment at a high temperature of 390 °C for one hour, the Fine-diameter PI nanofiber membrane still maintained a filtration efficiency of 99.96 % for PM0.3 and was capable of completely filtering PM2.5. This demonstrates the excellent stability and reliability of the Fine-diameter PI nanofiber membrane under extreme temperature conditions. Additionally, the membrane exhibited outstanding hydrophobic properties, with a static contact angle of 130 ± 3°, aiding in maintaining its filtration performance in humid environments. The Fine-diameter PI nanofiber membrane developed in this study offers a novel fabrication strategy for PM filtration in high-temperature environments and provides new insights into its limit performance.

Electrostatic self‐assembly of barnacle‐like modified BN@ND hetero‐structured fillers to synergistic enhanced thermal conductivity of PI composite films

AbstractHigh‐integration microelectronic equipment cannot dissipate heat for long periods of time, which enormously damages the efficiency and service life of electronic devices. Developing polymer‐based composite film exhibiting admirable thermal conductivity (TC), mechanical, dielectric and insulation performances has been pursued by researchers. Polyimide (PI) materials are generally used in progressive electronic systems. In this research, we constructed unique thermally conductive fillers to improve the TC of PI composites. Specifically, boron nitride nanosheets (BNNS) and nanodiamond (ND) were modified to impart them different charging properties. The barnacle‐like hetero‐structured fillers (MBN@FND) were assembled by electrostatic self‐assembly, and then introduced into PI to prepare PI composites. MBN@FND‐2 (MBN/FND, 1/1, wt/wt) fillers exhibited optimal morphology. The results showed that MBN@FND formed tightly stacked structure in composites, availing the densification of the thermal network and improving the heat transfer efficiency. Under 25 wt% MBN@FND loading, the in‐plane TC of MBN@FND/PI composite was 9.73 W/mK, and the through‐plane TC was 0.72 W/mK. The MBN@FND/PI composite remained at a low level in terms of dielectric properties. Moreover, MBN@FND/PI composites had flexibility, good tensile strength (47.9 MPa), and volume resistivity of 1.05 × 1013 Ω cm. This work provides a versatile approach for the preparation of hybrid materials.Highlights Hetero‐structured fillers were prepared by electrostatic self‐assembly. The in‐plane TC and through‐plane TC of PI composite was improved. The composites had insulation, flexibility, and low dielectric properties.

Molecular Dynamics Simulations of Lubricant Supply in Porous Polyimide Bearing Retainers

Space bearing retainers are widely made of a porous, oil-impregnated material due to the unmaintainability of spacecraft. Porous polyimide (PI) material with a certain micropore structure can be used as a lubricant storage and migration channel to realize the lubricant circulation supply in the bearing system. In this work, molecular dynamics simulations are adopted to model the lubricant outflow process from the pore of the PI material. Coarse-grained models are constructed to investigate the lubricant migration behaviors with different rotation speeds, rotation radii, and pore sizes. The results show that a lubricant within the pore fails to outflow due to the capillary effect in a static state. However, for the rotating pores, if the centrifugal forces resulting from rotation exceed the capillary forces, the lubricants will begin to flow out. Furthermore, the lubricant in the large pore is easier to outflow due to the smaller capillary force, which is the main mechanism of lubricant outflow from the pores.

Sustainable poly(imide‐imide) vitrimer based on multiple dynamic covalent bonds

AbstractPolyimide materials with high mechanical strength are widely used in various fields, but pose certain challenges in achieving sustainable material utilization. A poly(imide‐imide) vitrimer material (ADTA) based on multiple dynamic covalent bonds (imide, imine, and disulfide bonds) was constructed by preparing vanillin difunctionalized derivatives (DVA) for aldolamine condensation reactions with bis‐amine monomers (ATFA) and tris(2‐aminoethyl) amines (TAEA) with imide structures. The ADTA material has good 5% thermal stability Td5% (278.87°C), high energy storage modulus E (2421.26 MPa), and fast relaxation time (36.39 s). The thermal stability and mechanical properties of the material are enhanced by the more stable alicyclic structure of the imide structure. The material also demonstrated excellent solvent resistance and self‐healing properties. This study provides a new option for the development of sustainable utilization of polyimide materials.

A Recyclable Polyimide Derived Hard Carbon as a High‐Performance Negative Electrode Material for Sodium‐Ion Batteries

AbstractHard carbon, characterized by high ion storage capacity, low operating voltage, and excellent cycling stability, is considered an ideal negative electrode material for sodium‐ion batteries. However, the high cost and low carbon yield of thermosetting precursors limit their practical application in SIBs, while low‐cost and high‐yield raw materials exhibit highly ordered carbon structures and narrow interlayer spacing under high‐temperature carbonization. Discarded polyimide materials are inexpensive, which offer a high carbon yield and possess good thermal stability and thermoplasticity, with functional groups of imide rings (−CO−N−CO−) on their main chains. This study recycled and converted polyimide materials into hard carbon materials from discarded engineering plastics, investigating the influence of carbonization temperature on the degree of graphitization, interlayer spacing, and pore structure of the materials to achieve high reversible sodium storage capacity. After carbonization at 1300 °C, the polyimide material exhibited 319 mAh g−1 reversible capacity and excellent electrochemical performance (with a capacity retention of 91.92 % after 100 cycles at a 0.5 C current rate) and rate performance (up to 242.5 mAh g−1 at 2 C). This study provided a simple, high‐yield, and effective method for the reuse of discarded organic polymers, promoting the sustainable utilization of resources.

Heat‐resistant and transparent polyimides derived from alicyclic dianhydrides and phthalazinone‐based diamine

AbstractAdvanced flexible display materials have drastically sparked considerable interest for heat‐resistant, low dielectric, and transparent polyimide (PI) materials. In light of this, our study aims to develop high‐performance semi‐aromatic PI films, followed by investigate the correlations between bridged‐alkyl/heteroaromatic ring structures and their thermal, dielectric, optical, and mechanical properties. Such PI films, namely AP‐PIs, were synthesized with a one‐step high‐temperature method between 4‐[4‐(4‐aminophenoxy) phenyl]‐2‐(4‐aminophenyl)‐1(2H)‐phthalazinone (DHPZDA) and various commercial alicyclic dianhydrides. The incorporation of rigid phthalazinone structures significantly enhanced thermal resistance and mechanical flexibility, while simultaneously reducing their dielectric constant (Dk), attributed to the large polymer internal free volume. Impressively, the prepared films exhibit exceptional glass transition temperature (Tg) as high as 419°C (DMTA tanδ peak), low Dk as low as 2.71, and elongation at break (ε %) up to 50.4%. Furthermore, AP‐PI films demonstrate reasonable solubility and optical transparency within the UV–visible region. The maximum optical transmittance at 550 nm (T550 nm) could reach 83.01%. These desirable properties position these materials as promising candidates for flexible substrate applications.

Solar energy harvesting using nanostructured ultrawideband absorber with nearly perfect thermal emission

In this article, nanostructured ultrawideband absorber is proposed for infrared to ultraviolet spectrum. The proposed three layered absorber structure formed of nickel, polyimide and nickel (Ni) material. The proposed unit cell volume is 90nm × 90 nm × 10.62 nm (0.0484λL× 0.0484λL× 0.00571λLnm3 where, λL is wavelength at lowest operating frequency). Absorption (A)≥ 90 % is achieved from 161.48 THz (1857.81 nm) to 3894.58 THz (77.03 nm) which covers infrared, visible and ultraviolet frequency bands. The average absorption 98.08 % is achieved over the entire operating frequency band. The absorption is also analyzed in different resonating patch geometry and using different substrate material. Due to the symmetricity of the octagonal patch geometry, the proposed structure is polarization insensitive and has incident angle (θ◦) stability up to 60° for absorption more than 80 %. The proposed solar absorber achieves 96.82 % solar absorption efficiency (ηA) and also achieves 94.61 %, 95.78 %, 96.31 % & 96.62 % thermal emission efficiency (ηE) at temperature 2000K, 2500K, 3000K & 3500K respectively. The suggested nanostructure absorber design works well across infrared, visible, and ultraviolet (UV) light, making it an efficient absorber for various uses like solar panels, detectors, solar energy harvesters, thermal devices, cloaking, solar power, sensors, and UV protection.

Electrical Conductivity Characteristic of Polyimide under Long-Term Combined Electron Irradiation and Thermal Cycle in Vacuum.

During long-term operation, low-earth-orbit spacecraft are exposed to a severe environment of electron irradiation and thermal cycle. This affects the electric properties of polyimide, an essential insulation material for spacecraft electrical transmission equipment, particularly the conductivity characteristic. Therefore, this paper investigates the conductivity and its evolution of polyimide after the combination of 20 keV, 8 nA/cm2 electron irradiation, and 243-343 K, 5 K/min thermal cycle in a vacuum environment for 432 h. The results show that the conductivity increases by about 2 orders of magnitude over 432 h, with the threshold field for electric-field-dependent conductivity decreasing. The conductivity growth rate varies, rising during the first 192 h, then increasing in the midelectric field, and decreasing in the high electric field regions. The thermally stimulated depolarization current method demonstrates that increases in γ, β1, and β2 trap densities, associated with enhanced motility of end groups, diamines, and dianhydrides after long-chain breaks, lead to higher conductivity and growth rate. Additionally, increases in β3 and α trap densities, related to increased C═O bonds and free radicals, reduce the threshold field and the conductivity growth rate in the range of 57.0-100.0 kV/mm after 192 h. These findings provide a reference for the performance evaluation and enhancement of spacecraft polyimide materials.

A strategy for the preparation of low dielectric FGQD/PSPI composite films in wafer-level packaging

Advancement of wafer-level packaging (WLP) has heightened the requirements for photosensitive polyimide (PSPI) materials, where the low dielectric property is a key element to realize high frequency communication. Herein, a poly(amidate) (PAE) was prepared using Pyromellitic Dianhydride, 4,4’-diaminodiphenyl ether, and hydroxyethyl methacrylate as the photosensitive group. Specifically, the fluorinated graphene quantum dots (FGQD) was introduced into the PAE resin by in situ polymerization, and the prepared composite films of photosensitive polyimide-fluorinated graphene quantum dots (PSPI-FGQD) showed excellent dielectric constants and other comprehensive properties. Compared with pure PSPI, the dielectric constant of PSPI-FGQD decreases from 3.8 to 3.0 at 1 MHz; the tensile strength increases from 84.5 to 110.1 MPa, the elongation at break raises from 5.24 % to 17.3 %, and the Young's modulus increases from 2.68 GPa to 2.88 GPa. The glass transition temperature (Tg) is also increased to 420 °C with the introduction of FGQD. Apart of these, the fine patterning ability was observed for the FGQD/PSPI composite film, achieving a high photolithography resolution of 10 μm (L/S). To conclude, the preparation method of low dielectric FGQD/PSPI materials has promising potential applications in advanced packaging.

Atomic oxygen erosion mechanism of polyimide via reactive molecular dynamics simulation and density functional theory calculation

Atomic oxygen (AO) causes serious oxidative degradation on polymeric materials in the space environment, yet understanding its reaction mechanism is a challenging task. Herein, we primarily investigate the reaction sites and reaction paths of pure polyimide material to AO erosion and propose a modification strategy involving electron-withdrawing groups to enhance the material's resistance to AO with density functional theory (DFT) and reactive force field molecular dynamics (ReaxFF MD). DFT calculations reveal that AO erosion is an electrophilic reaction, which preferentially interacts on the benzene ring with pronounced electron density distribution on the third part of the polyimide molecule. ReaxFF MD simulations validate this finding and provide additional reaction pathways that are divided into the early-stage reactions and later secondary reactions. In the early stage, only small number of AOs take part in the reactions that include the formation of CO bonds and ring opening processes. These reactions are relatively slow and majorly determine the AO resistance of the material. In the subsequent stage, AO predominantly reacts with reactive species and radicals generated from earlier reactions, leading to fast degradation. With these findings, we propose a strategy to enhance the AO resistance by introducing electron-withdrawing functional groups in the polyimides. As exemplified, the polyimide with -CF3 group shows 21.1% lower erosion yield than unmodified polymer. The present study gives a deep insight for the mechanism of AO erosion on polyimide by exploring its reaction sites and provides valuable theoretical guidance for improving the material's resistance to erosion.

Adhesion and Transparency Enhancement between Flexible Polyimide-PDMS Copolymerized Film and Copper Foil for LED Transparent Screen.

With the increasing demand for innovative electronic products, LED transparent screens are gradually entering the public eye. Polyimide (PI) materials combine high temperature resistance and high transparency, which can be used to prepare flexible copper-clad laminate substrates. The physical and chemical properties of PI materials differ from copper, such as their thermal expansion coefficients (CTEs), surface energy, etc. These differences affect the formation and stability of the interface between copper and PI films, resulting in a short life for LED transparent screens. To enhance PI-copper interfacial adhesion, aminopropyl-terminated polydimethylsiloxane (PDMS) can be used to increase the adhesive ability. Two diamine monomers with a trifluoromethyl structure and a sulfone group structure were selected in this research. Bisphenol type A diether dianhydride is a dianhydride monomer. All three of the above monomers have non-coplanar structures and flexible structural units. The adhesion and optical properties can be improved between the interface of the synthesized PI films and copper foil. PI films containing PDMS 0, 1, 3, and 5 wt% were analyzed using UV spectroscopy. The transmittance of the PI-1/3%, PI-1/5%, PI-2/3%, and PI-2/5% films were all more than 80% at 450 nm. Meanwhile, the Td 5% and Td 10% heat loss and Tg temperatures decreased gradually with the increase in PDMS. The peel adhesion of PI-copper foil was measured using a 180° peel assay. The effect of PDMS addition on peel adhesion was analyzed. PIs-3% films had the greatest peeling intensities of 0.98 N/mm and 0.85 N/mm.

Integrated Fibrous Iontronic Pressure Sensors with High Sensitivity and Reliability for Human Plantar Pressure and Gait Analysis.

Flexible sensing systems (FSSs) designed to measure plantar pressure can deliver instantaneous feedback on human movement and posture. This feedback is crucial not only for preventing and controlling diseases associated with abnormal plantar pressures but also for optimizing athletes' postures to minimize injuries. The development of an optimal plantar pressure sensor hinges on key metrics such as a wide sensing range, high sensitivity, and long-term stability. However, the effectiveness of current flexible sensors is impeded by numerous challenges, including limitations in structural deformability, mechanical incompatibility between multifunctional layers, and instability under complex stress conditions. Addressing these limitations, we have engineered an integrated pressure sensing system with high sensitivity and reliability for human plantar pressure and gait analysis. It features a high-modulus, porous laminated ionic fiber structure with robust self-bonded interfaces, utilizing a unified polyimide material system. This system showcases a high sensitivity (156.6 kPa-1), an extensive sensing range (up to 4000 kPa), and augmented interfacial toughness and durability (over 150,000 cycles). Additionally, our FSS is capable of real-time monitoring of plantar pressure distribution across various sports activities. Leveraging deep learning, the flexible sensing system achieves a high-precision, intelligent recognition of different plantar types with a 99.8% accuracy rate. This approach provides a strategic advancement in the field of flexible pressure sensors, ensuring prolonged stability and accuracy even amidst complex pressure dynamics and providing a feasible solution for long-term gait monitoring and analysis.

Effect of the molar mass of polyimide based on pyromellitic dianhydride and 4,4′‐oxydianiline on dielectric and mechanical properties of nonwoven oriented polyimide materials

AbstractThis work is dedicated to the development and investigation of the properties of low‐dielectric‐constant nonwoven materials obtained by electrospinning from a polyimide‐based polymer, PMDA‐ODA, which is composed of pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The influence of the molar mass of PMDA‐ODA on the structural, mechanical, and dielectric properties of the resulting samples has been investigated. The molar mass of the polyimide has been determined through light scattering and viscosity measurements of polyamic acid solutions. As the molar mass of PMDA‐ODA increases from 13.400 to 49.300 g/mol, the glass transition temperature of the produced nonwoven samples increases, and their tensile mechanical properties are improved. The dielectric constant of PMDA‐ODA nonwoven polyimide materials varies from 1.55 to 1.91 at a temperature of 30°C in a frequency range from 1 Hz to 1 MHz, depending on the molar mass of the polymer used.

Nano-structuration influence on the polyimide-based spatial light modulator’s parameters

The classical and the nano-structured spatial light modulators (SLMs) especially based on the polyimide photosensitive layers, as the key element of the optoelectronic devices, display, and telecommunications schemes are considered. The main emphasis is placed on the device with a polyimide photo-layer due to its high sensitivity and acceptable performance. A modulator’s basic characteristics are studied taken into account the comparison with the different types of the photo-layers, such as: ZnSe, ZnS, a-Si:H. Liquid crystal (LC) media is considered as the modulation system. It is indicated that the different methods and approaches are applied for investigation of the basic SLM parameters, such as: Z-scanning technique, third harmonic generation, four-wave mixing set-up, etc. In the current paper the laser holographic technique is used to investigate the resolution, sensitivity, and speed of the LC-SLM devices. The influence of the fullerene doping on the organic photo-layers based on the polyimide materials is presented. This influence of this nano-structuration process on the modulator’s basic parameters is discussed.

The Discharge Behavior and Mechanism of Polyimide Aerogel under Electron Irradiation.

The response and mechanism of polyimide aerogel under electron irradiations were investigated. The experimental results indicated that electron irradiation could not damage the skeleton polyimide in the aerogel due to its high stability, but could result in a discharge within. The morphology of the discharge shows some dendritic discharge patterns, and the material surrounding the discharge channels was carbonized. The numerical simulation results indicated that the incident electrons, and also large amount induced secondary electrons, would be deposited inhomogeneously within the nano-porous polyimide aerogel. This would result in forming an ultra-high electrical potential of up to about 8.5 × 1010 V/m (which is far higher than the breakdown strength (2 × 108 V/m) of bulk polyimide materials) in a local region. This may be the leading cause of the obvious discharge in the materials. Furthermore, it was found that the actual reason for the discharge is related to the residual gas within the nano-porous structure; namely, the more internal residual gas (as a shorter-time vacuum pumping in the irradiated chamber), the more serious the discharge phenomenon. Correspondingly, the phenomenon may largely consist of both residual-gas discharge and surface flashover due to ultra-high local potentials induced by unevenly deposited charges in the porous aerogel.

Three-dimensional porous polyimide anode for high-rate lithium ion batteries

Polymeric electrode materials are widely used in many applications but still suffer from poor electrical conductivity and slow transport kinetics, especially poor performance at high current densities. Herein, a polyimide electrode structure with 3D-ordered interconnected gradient pores was developed to improve the lithium-ion transport efficiency. The homogeneous mixed PMTA-PMMA composite was prepared by a simple one-pot method, followed by removal of PMMA (polymethyl methacrylate) spherical porogenic agent during the synthesis of polyimide material at high temperatures to form a low curvature gradient-pore structure. The large pores in the electrode enhanced the ion transport ability and improved the electrolyte infiltration rate, while the small pores improved the active specific surface area and guided the deposition of lithium ions. As a result, a high specific capacity reaching 907 mAh/g was maintained even after 1000 cycles at 5 A/g, a value about 3-fold that of un-pored electrode materials. The experimental studies and DFT calculations were used to develop a 24Li storage mechanism of PMTA, and the active electrode material was fully electrochemically activated by the constructed three-dimensional porous electrode structure. Overall, the proposed porous material with a high active area and porosity looks potential for use as an ultra-fast charging and discharging electrode of lithium-ion batteries with high specific capacity and excellent cycling performance.

Bifunctional Sulfhydryl-Based Polyimides for Highly Active Cathodes of Li-S Batteries.

Sulfhydryl-based polyimides were synthesized by the nucleophilic ring-opening reaction of thiolactone monomers (BPDA-T, ODPA-T, BTDA-T) with polyethylenimine (PEI), and they were coated on carbon nanotubes as host materials (BPTP@CNT, ODTP@CNT, and BTTP@CNT) of the sulfur cathode. BPTP@CNT/S, ODTP@CNT/S, and BTTP@CNT/S as cathode materials not only promote the covalent bonding of sulfur and polysulfide with sulfhydryl-based polyimides but also reduce the shuttle effect of soluble polysulfide in the redox process. Moreover, sulfhydryl-based polyimides can help improve the compatibility and interfacial contact between sulfur and conductive carbon while alleviating the volume expansion of the cathode. In addition, the conductive network of carbon nanotubes improves the electronic conductivity of the cathode materials. The BTTP@CNT/S cathode showed superior stability (the initial capacity was 902 mAh g-1 at 1C, and the capacity retention rate was 88.58% after 500 cycles) and the initial capacity could reach 718 mAh g-1 when the sulfur loading was 4.8 mg cm-2 (electrolyte/sulfur ratio: 10 μL mg-1), which fully proves the feasibility of the large-scale application of sulfhydryl-based polyimide materials.

Metal- and binder-free dual-ion battery based on green synthetic nano-embroidered spherical organic anode and pure ionic liquid electrolyte

Dual-ion batteries (DIBs) have attracted extensive attention and investigations due to their inherent wide operating voltage and environmental friendliness. Nevertheless, the vast majority of DIBs employ metal-based anode active materials or electrolytes, which are relatively costly and unsustainable. Moreover, the utilization of binders and current collectors in the preparation of cathodes and anodes reduces the energy density to a certain extent, which weakens the advantages of DIBs. Here, we synthesized three types of binder-free nano-embroidered spherical polyimide anode materials composed entirely of renewable elements, paired with pure ionic liquid electrolyte without metal elements and flexible self-supporting independent graphite paper cathode without current collector, to construct a class of totally metal and binder-free DIBs. It significantly improves specific discharge capacity, energy density, cyclic stability, and fast charging performance while remarkably reducing costs and self-discharge rate. Additionally, we overcame the drawbacks of conventional synthesis methods and innovatively prepared nanoscale polyimide materials by a green and facile hydrothermal method, which effectively minimizes synthesis costs and avoids risks. This novel battery system design strategy will promote the advancement of low-cost, high-performance DIBs and could be a promising candidate for large-scale energy storage applications.