Search

The thermal hazard assessment of polyimide (PI) synthesis, including polyamide acid (PAA) and PAA imidization, was investigated owing to its uncontrolled viscosity and heat release. The thermal behavior of PAA with different viscosities investigated using a laboratory-scale setup and auto-reaction calorimetry (SIMULAR). The reaction enthalpy of PAA ranged from − 154.54 to − 156.82 kJ mol−1 as the viscosity increased from 7000 to 104,200 Pa s, indicating that heat release and viscosity increment were two opposite processes during PAA synthesis. The thermal behavior of PAA imidization was investigated using differential scanning calorimeter (DSC). The imidization of PAA was found to be an endothermic reaction with a heat absorption of 105.77 J g−1. Hence, the two-step PI synthesis is an exothermic reaction that concentrates on the synthesis of PAA. Second, the decomposition characteristics of PI in the isothermal mode were analyzed using DSC. The decomposition of PI occurred in the temperature range of 842.89–981.28 K, with a heat release of − 380.07 J g−1. The apparent activation energy of PI, calculated using the Ozawa model, ranged from 179.74 to 308.26 kJ mol−1. Finally, the thermal hazard level of PI was found to be Level 1 based on the Stoessel criticality diagram. This suggests that controlling the dosage can avoid implosion during PI synthesis because an increase in viscosity leads to a higher hazard. [ABSTRACT FROM AUTHOR]

Design idea diagram of the BT@PDA/PI nanocomposite film. [Display omitted] • The scale-like barium titanate (BT) ceramic fillers were prepared from the layered K 0.8 Li 0.27 Ti 1.73 O 4 crystals using solid-phase and hydrothermal processes. • The scale-like BT@Polydomine (PDA) nanoparticles were horizontally ordered distribution in the polyimide (PI) matrix using orientation engineering. • The horizontally ordered BT@PDA can increase the tortuosity of the breakdown path and construct effective conduction barriers, restricting the charges migration and the electron trees growth. • Horizontally ordered BT@PDA/PI nanocomposite films show the highest energy storage density and efficiency comparing with the other BT/PI in past reports. High-temperature ceramics polymer dielectric nanocomposite materials have broad application prospects in energy storage. The barium titanate (BT) plays an important role as one of outstanding representative ceramics in the dielectric nanocomposite materials. However, there is little known for the effects of two-dimensional (2D) BT morphology and layout on the properties of high-temperature nanocomposite materials. Hence, 2D scale-like BT ceramic fillers were prepared from layered K 0.8 Li 0.27 Ti 1.73 O 4 crystals as precursors using a combined solid-state and hydrothermal process. 2D scale-like BT@polydopamine (PDA) core-shell nanocomposites were prepared via coating PDA on the BT. BT@PDA/polyimide(PI) nanocomposite films were fabricated by horizontally oriented distribution of BT@PDA in the PI matrix. The BT@PDA/PI nanocomposite films exhibit a high energy density (3.34 J/cm3) and high charge-discharge efficiency (83.68 %) at 150 °C. It is currently the highest energy storage performance in the BT/PI nanocomposite films at 150 °C. The excellent properties are due to preventing upward breakdown of electrical pathways and promoting dispersion and entanglement of the electrical pathway routes. Additionally, strong electrostatic interactions between the different polymer chains (PDA and PI) restricts the movement of space charges. This work demonstrates that introducing horizontally oriented, organically shell-modified and 2D small-sized BT nanoparticles into a PI matrix is an effective method for improving energy storage performance. [ABSTRACT FROM AUTHOR]

This paper investigates the properties of 100-nm ZnO thin films prepared by radio frequency (RF) sputtering technique on polyethylene terephthalate (PET) and polyimide (PI) plastic substrates using X-ray diffraction (XRD) patterns to show the proper formation of hexagonal ZnO (002) structure, with ZnO on PET plastic substrate recording higher peak and FWHM compared to ZnO on PI plastic substrate. AFM reveals smooth surface morphologies on both substrates with a root-mean-square (RMS) roughness of below 10 nm. Optical transmittance measures values exceeding 80% in the visible and infrared (IR) regions on each substrate. ZnO on PET records 3.33 eV, and ZnO on PI measures 3.35 eV of optical band gap (Eg) from the Tauc plot. The photoelectrochemical cell (PEC) parameter measurement study shows that ZnO thin films on PET and PI plastic substrates have efficiencies (η = 0.93) and (η = 0.88), respectively. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is a special engineering plastic, widely involved in mechanical components, instruments, and petrochemicals. However, single PI material is inevitably subject to wear and tear in practice, which leads to weakened material properties. In this work, Ti3C2Tx@SiO2 was prepared to enhance the wear resistance and lubrication properties of PI by intercalating SiO2 into the interlayer of Ti3C2Tx sheets. Ti3C2Tx@SiO2/PI composites were fabricated in two steps to test the tribological performances. SiO2 particles change the form of interfacial friction from sliding to rolling, thus relieving direct friction between material and steel ball. So, the composites have a minimum COF (COF = 0.33) when the content of Ti3C2Tx@SiO2 is 0.80 wt%. Moreover, the average value of wear rate was 0.24 × 10−5 mm3/(N·m) when Ti3C2Tx@SiO2 content was 1.60 wt%, which was 91.0% lower compared to the PI matrix. During the friction process, the abrasive chips of the material migrate to the surface of the steel ball to form a transfer film, which protects the material and thus reduces the wear rate. Therefore, the hybrids Ti3C2Tx@SiO2 are effective and important wear‐resistant agents and solid lubricants to improve the wear resistance and lubricity of PI or other polymer materials. Highlights: SiO2 insert Ti3C2Tx is a key factor in changing sliding friction into rolling friction, effectively reducing the COF.The average wear rate was 91.0% lower than that of the polyimide matrix when Ti3C2Tx@SiO2 content was 1.60 wt%.The minimum COF of Ti3C2Tx@SiO2/PI composites reached 0.33 when the content of Ti3C2Tx@SiO2 was 0.80 wt%.The transfer film effectively reduces further wear of the material during friction. [ABSTRACT FROM AUTHOR]

Graphene with an atomically thin structure is considered to be a highly sensitive transducer capable of converting diverse external stimuli into measurable electrical signals. The generated signals, such as current and resistance, can be extracted through electrical contact to graphene. Conventional methods for contact formation are usually based on physical deposition of conductive materials on the target graphene. Here, we propose a method for in situ chemical synthesis of electrical contacts to graphene as an alternative approach that complements conventional physical methods. CO2 laser irradiation on a polyimide film with monolayer graphene on top can convert the polyimide surface to conductive electrodes of laser-induced graphene (LIG) that electrically connect to the existing graphene channel. Laser-scribing conditions, such as the power and scan rate, can modulate the contact resistance of the LIG–graphene junction. Various arbitrary shapes of in situ LIG contacts can be scribed to the direct writing ability of the laser. The proposed in situ LIG contact method can be extended to other carbon nanomaterials, such as carbon nanotubes and PEDOT:PSS. As a proof of concept of the in situ LIG contacts to graphene for electronic device applications, graphene field-effect transistors were demonstrated on a graphene-supported polyimide substrate with LIG–graphene junctions as source/drain electrodes. Our approach will pave the way for the simple and low-cost fabrication of versatile graphene electronic devices by utilizing the existing LIG technology specialized for energy devices and sensors. [ABSTRACT FROM AUTHOR]

The incorporation of a "graphene-carbon nanotube-graphene" structure as a filler in polyimide composites to enhance their mechanical and thermal properties was investigated. The performance of the composites was evaluated by molecular dynamics simulations. Findings revealed that this arrangement significantly enhanced the mechanical strength and stiffness of the composites, improving their tensile and shear properties. [ABSTRACT FROM AUTHOR]

The effect of adding texture to increase the deformation of a bilayer actuator by a factor of over 100 was demonstrated. A bilayer actuator is driven by the difference in thermal deformation. Therefore, two films or plates with a large difference in thermal expansion coefficient are required. The newly developed textured film actuator (TFA) obtained large deformation even in a case involving a combination of two films with a small difference in thermal expansion coefficient. The TFA was fabricated by transferring the texture when laminating two PI films with different coefficients of thermal expansion. A TFA with thin‐film electrodes was heated by applying electric power. Thereby, it unfolded from a curled state. The maximum generated force and curvature of the TFA were 7.4 mN and 0.19 mm−1, respectively, at 0.38 W. The manufacturing process for the TFA is simple and convenient, as it does not require adhesives or special materials. In thermal drive bilayer actuator fabrication, the range of material selection is expanded substantially. In addition, large deformations are generated with less energy. Therefore, the energy consumption is likely to be reduced. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Polymer materials with a low dielectric constant and low dielectric loss have the potential to be applied to high-frequency signal transmissions, such as mobile phone antennas and millimeter wave radars. Two types of diamines, 4,4′-diamino-p-tetraphenyl (DPT) and crown ether diamine (CED), were prepared for ternary copolymerization with BPDA in this study. Cross-links with molecular chains were formed, increasing molecular chain distance by utilizing rings of CED. The MPI films exhibit a good thermal performance with the increase in CED addition, with Tg > 380 °C and CTE from −4 × 10−6 K−1 to 5 × 10−6 K−1. The Young's modulus can reach 8.6 GPa, and the tensile strength is above 200 MPa when 5% and 7% CED are introduced. These MPI films exhibit good mechanical performances. The dielectric constant of PI−10% film can go as low as 3.17. Meanwhile, the relationship between dielectric properties and molecular structure has been demonstrated by Molecular Simulation (MS). PI molecules are separated by low dielectric groups, resulting in a decrease in the dielectric constant. [ABSTRACT FROM AUTHOR]

In this paper, stannous oxide (SnO) was synthesized by hydrothermal method, and then the obtained SnO was introduced into polyimide matrix by in-situ polymerization method to prepare SnO/PT composite films. The contents of SnO have significant influence on the dielectric constant, dielectric loss, tensile strength and breakdown strength of the film. When the contents of SnO was 1 Owt%, the dielectric constant of the SnO/PT composite film was as high as 456, the dielectric loss was only 0.034, the tensile strength was 65 MPa, and the breakdown strength was 146.9 MV/m, respectively. The introduction of SnO into PT could greatly improve the dielectric properties of the composite PT films, so that it has a good application prospect in energy storage, aerospace, insulation and other fields. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Polymer Materials Science & Engineering is the property of Sichuan University, Polymer Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Polyimide (PI) aerogels, renowned for their nano-porous structure and exceptional performance across a spectrum of applications, often encounter significant challenges during fabrication, primarily due to severe shrinkage. In this study, we innovatively incorporated ceramic fibers of varying diameters into the PI aerogel matrix to enhance the shape stability against shrinkage. The structure of the resulting ceramic fiber-reinforced PI (CF-PI) aerogel composites as well as their performance in thermal decomposition, thermal insulation, and compression resistance were characterized. The results revealed that the CF-PI aerogel composites dried by supercritical ethanol achieved greatly reduced shrinkage as low as 5.0 vol.% and low thermal conductivity ranging from 31.2 mW·m−1·K−1 to 35.3 mW·m−1·K−1, showcasing their excellent performance in shape stability and thermal insulation. These composites also inherited the superior residue-forming ability of ceramic fibers and the robust mechanical attributes of PI, thereby exhibiting enhanced thermal stability and compression resistance. Besides, the effects of different drying conditions on the structure and properties of CF-PI aerogels were also discussed. The coupling use of supercritical ethanol drying with the addition of ceramic fibers is preferred. This preferred condition gives birth to low-shrinkage CF-PI aerogel composites, which also stand out for their integrated advantages include high thermal stability, low thermal conductivity, and high mechanical strength. These advantages attribute to CF-PI aerogel composites substantial potential for a wide range of applications, particularly as high-performance thermal insulation materials for extreme conditions. [ABSTRACT FROM AUTHOR]

Copyright of China Plastics / Zhongguo Suliao is the property of Journal Office of CHINA PLASTICS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Considering the extensive resources, flexible structural designability, and abundant active sites, organic electrodes have been considered as the ideal sodium storage materials. However, organic materials generally face the limitations of unstable and dissolved characteristic, leading to a poor cyclic stability. In this work, we proposed a carbon nanotube (CNT) modified polyimide as the anode for sodium‐based dual‐ion battery (SDIB). The polyimide remains well the structure and morphology of monomer with a stable conjugated structure and high degree of crystallinity, effectively enhancing the electrochemical performance of the SDIBs. Also, the cooperation with CNT particularly improves the ion conductivity of the anode and advances the rate performance. Combined with an ionic liquid electrolyte, the constructed dual‐ion battery exhibits excellent rate capability, high specific discharge capacity and stable cycling performance. It delivers a specific discharge capacity of 119.3 mA h g−1 at 0.2 C (1 C=100 mA g−1) and still has a specific discharge capacity of 82.3 mA h g−1 even after 1000 cycles at 10 C. Besides, the system displays a low self‐discharge rate and stable fast charging performance, which is expected to be applied in the large‐scale electrochemical energy storage devices and inspire the future development of SDIBs. [ABSTRACT FROM AUTHOR]

Polymer dielectrics with high dielectric constant are urgently demanded for potential electrical and pulsed power applications. The design of polymers with side chains containing dipolar groups is considered an effective method for preparing materials with a high dielectric constant and low loss. This study synthesizes and comprehensively compare the dielectric properties of novel polyimides with side chains containing urea (BU‐PI), carbamate (BC‐PI), and sulfonyl (BS‐PI) functional groups. The novel polyimides exhibit relatively high dielectric constant and low dielectric loss values due to the enhanced orientational polarization and suppressed dipole‐dipole interactions of dipolar groups. In particular, BU‐PI containing urea pendant groups presents the highest dielectric constant of 6.14 and reasonably low dielectric loss value of 0.0097. The strong γ transitions with low activation energies derived from dielectric spectroscopy measurements have been further evaluated to demonstrate the enhanced free rotational motion of urea pendant dipoles. In energy storage applications, BU‐PI achieves a discharged energy density of 6.92 J cm−3 and a charge‐discharge efficiency above 83% at 500 MV m−1. This study demonstrates that urea group, as dipolar pendant group, can provide polymers with better dielectric properties than the most commonly used sulfonyl groups. [ABSTRACT FROM AUTHOR]

Based on a novel phenylacetylene capped polyimide (PI) with unique high-temperature resistance, its curing kinetics and thermal decomposition behavior were investigated. The curing mechanism and kinetics were studied by differential scanning calorimetry (DSC), and the activation energy (Ea) and pre-exponential factor (A) of the curing reaction were calculated based on the Kissinger equation, Ozawa equation, and Crane equation. According to the curve of conversion rate changing with temperature, the relationship between the dynamic reaction Ea and conversion rate (α) was calculated by the Friedman equation, Starink equation, and Ozawa–Flynn–Wall (O-F-W) equation, and the reaction Ea in different stages was compared with the results of molecular dynamics. Thermogravimetric analysis (TGA) and a scanning electron microscope (SEM) were used to analyze the thermal decomposition behavior of PI resins before and after curing. Temperatures at 5% and 20% mass loss (T5%, T20%), peak decomposition temperature (Tmax), residual carbon rate (RW), and integral process decomposition temperature (IPDT) were used to compare the thermal stability of PI resins and cured PI resins. The results display that the cured PI has excellent thermal stability. The Ea of the thermal decomposition reaction was calculated by the Coats–Redfern method, and the thermal decomposition behavior was analyzed. The thermal decomposition reaction of PI resins at different temperatures was simulated by molecular dynamics, the initial thermal decomposition reaction was studied, and the pyrolysis mechanism was analyzed more comprehensively and intuitively. [ABSTRACT FROM AUTHOR]

As an excellent polymer material, polyimide (PI) plays an important role in practical applications. However, traditional filler doping modification is hard to simultaneously improve the dielectric properties and mechanical properties of the film. Here, PI–boron nitride (BN) nanosheets/PI–sodium titanate nanotubes (STNs)/PI–BN composite films with sandwich structure are prepared by in situ polymerization and multilayer coating processes, which significantly enhance the electrical and mechanical properties of dielectric films. With only 0.5 wt% fillers doping, the AC breakdown strength of the composite film can reach 183.7 kV mm−1, which is 16.41% higher than that of pure PI. When the filler doping is 1.5 wt%, the corona aging time of the composite film achieves 311.7% higher than that of pure PI film. In addition, the composite film exhibits outstanding elongation at break (58%) and tensile strength (138.92 MPa) performance. The 2D BN of the outer layer and 1D STNs of the middle layer effectively block the injection of charge carriers while improving the internal polarization response. A mechanism related to microstructure and interface is proposed to explain the improvement of electrical and mechanical properties in detail. This work provides a useful idea for the accurate design of high‐performance dielectric films. [ABSTRACT FROM AUTHOR]

In order to meet the requirements of highly integrated and miniaturized electronic components, there is an urgent need for low dielectric materials with high mechanical properties and optical transparency in the field of microelectronics. In this study, a series of novel polyimide films (FPI) containing fluorenyl were prepared, and the effects of the fluorenyl content on the thermal, mechanical, and dielectric properties of the copolymerized films were investigated and discussed. The results demonstrate a significant decrease in the dielectric constant of the FPI films following the introduction of fluorenyl into polyimide (PI) chain segment. The FPI films also exhibited high mechanical properties, including tensile strengths between 92 and 106 MPa and elongation at break in the range of 8.4%–13.0%. Additionally, the introduction of the noncoplanar fluorenyl considerably improved the optical transparency and solubility of the FPI film. It is noteworthy that the FPI‐3 has the best dielectric properties, with a low dielectric constant of 2.61 at 10 MHz and shows low water absorption (0.49%). The results show that we have prepared a novel low dielectric PI material film with excellent mechanical properties and optical transparency by introducing fluorenyl into the PI chain segment. These FPI films with satisfactory properties may be good candidates for dielectric materials for electronic components. [ABSTRACT FROM AUTHOR]

With the booming of telecommunication and microelectronics, it is essential to develop electromagnetic interference (EMI) shielding materials with low reflectivity characteristics to avoid the secondary pollution from electromagnetic waves (EMWs). Herein, we fabricated a series of hierarchical polypyrrole/carbon nanofiber (PPy/CF) composites with multilayer PPy films. The EMI shielding performance can be adjusted by attaching different layered PPy films. The EMI shielding efficiency (SE) of PPy/CF composite films can reach to 74.59 dB with an electrical conductivity of 3.02 × 10–3 S/mm. Moreover, in order to make the composite film have excellent strength and flexibility, we specially designed an acetone-soluble polyimide (PI) resin to encapsulate PPy/CF. After packaging with PI, the composite films are imparted with high flexibility and mechanical properties with the tensile strength and modulus of 4.65 and 153.03 MPa, respectively. Moreover, the resultant PI/PPy/CF composite films also possess favorable Joule heating performance and sensing monitoring. The Joule heating temperature of PI/PPy/CF films reaches 131.0 °C within 15 s when the applied voltage is 5 V. The fabricated composite films are promising for applications in the fields of aerospace, telecommunication, and microelectronic engineering and multifunctional wearable devices. [ABSTRACT FROM AUTHOR]

In order to prepare polymer dielectric materials with high energy storage density, a series of polyimide (PI) based Janus composite films were prepared by metal–organic frameworks (MOFs) material (UiO‐66) with high dielectric constant (ɛr) and boron nitride nanosheets (BNNSs) with high breakdown strength (Eb). As reported, the UiO‐66 can significantly improve the ɛr of the composites. The ɛr of 20 wt% UiO‐66/PI film is 10.51 at 103 Hz, which is 3.1 times that of pure PI film (3.39 at 103 Hz). However, the Eb of 20 wt% UiO‐66/PI is only 58 MV m−1, which is only 16.51% of pure PI (352 MV m−1). The sharp decline in Eb reduces the energy storage capacity of the composites. To solve this problem, first, BNNSs with an average diameter of 2 μm and a thickness of 1.36 nm (about 4–5 layer) were obtained by hydrothermal reflux stripping. BNNSs/PI//UiO‐66/PI Janus composite films with double‐layer structure were prepared by directly casting BNNSs/PI on the surface of UiO‐66/PI. For 0.3 wt% BNNSs/PI//10 wt% UiO‐66/PI, the calculated energy storage density (Ue) is 5.75 J cm−3 at 140 MV m−1, which is 3.57 times that of pure PI film (1.61 J cm−3 at 140 MV m−1). Meanwhile, the charge discharge efficiency is 82.55% (at 140 MV m−1). Highlights: BNNSs prepared by hydrothermal reflux stripping have fewer layers.BNNSs/PI composites improve the Eb of UiO‐66/PI composites by Janus structure.The Ue of BP‐0.3//UP‐10 composites with Janus structure was 5.75 J cm−3. [ABSTRACT FROM AUTHOR]

The inherent low dielectric constant of polyimide (PI) dielectrics restricts their applications to become a component of high energy density film capacitors. In this work, double core–shell structured barium titanate@magnesium oxide@polydopamine (BaTiO3@MgO@PDA) nanoparticles were synthesized successfully and utilized as high dielectric constant functional fillers for PIs, in which the insulating MgO layer meliorated dielectric constant difference between BaTiO3 and PI matrix, and the organic PDA layer improved the compatibility between the inorganic fillers and PI matrices. Then, a series of sandwich‐structured PI‐based hybrid films was prepared through a layer‐by‐layer solution casting method. The middle layer of pure PI with excellent insulating properties effectively suppressed charge injection. With the combination of sandwich structure and the BaTiO3@MgO@PDA nanoparticles, the PI hybrid film containing 15 wt% fillers in the outer layers achieved the maximum breakdown strength of 425.68 kV/mm and the maximum energy density of 5.132 J/cm3, which was 68.3% and 413% higher than those of pure PI film, respectively, meanwhile maintained a low dielectric loss value of 0.0083 at 1 kHz. The introduction of BaTiO3@MgO@PDA enhanced the interfacial polarization due to the high barrier energy between adjacent layers preventing the transfer of electrons and weakening the leakage current in the sandwich‐structured composite film. This work demonstrates that an appropriate combination of high dielectric hybrid fillers and multilayer structure can effectively increase the energy storage density of PI substrate for high‐temperature energy storage applications. Highlights: The double core–shell structured BaTiO3@MgO@PDA was synthesized successfully.The sandwich‐structured hybrid films were prepared by layer‐by‐layer method.The energy density of hybrid films reached a high value of 5.132 J/cm3. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) are a class of smart materials that have the ability of transform shape in response to external stimuli, such as heat, light, electricity and magnetic. To design suitable macromolecules and crosslinking mode of polyimide to obtain shape memory polymer with high transition temperature, high strength for application of aerospace, high temperature and other harsh environment is very important. Herein, using well-dispersed graphene oxide (GO) as the reinforced phase, polyhexahydrotriazine crosslinked polyimide/graphene shape memory composite (PI-PHT) was prepared by solvent volatilization and high temperature cyclization. The structure of the materials was characterized by nuclear magnetism and infrared spectrum demonstrating the successful preparation of composites. The mechanical properties tested by universal testing machine showed that after introduction of graphene, the strength, toughness, thermo-mechanical properties and shape memory properties of the composite were significantly improved. When the mass fraction of GO was 5%, the tensile strength and toughness of PI-PHT reached 105.7 MPa and 12.4 MJ/m3 , respectively (1.3 times and 2 times higher than that of PI-PHT without adding GO, respectively) duo to the strong interaction between the well-dispersed grapheme and polyimide. The shape memory properties and shape recovery force were detected by dynamic thermo-mechanical analyzer. The results showed that the shape fixation rate, recovery rate and recovery stress of PI-PHT-5% reached 97.2%, 92.6% and 9.46 MPa, respectively [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Porous materials impregnated with lubricants can be used in conditions where limited lubricant is desirable. In this work, three porous polyimides (PPI) with different densities were prepared. Polyalphaolefin (PAO) impregnated PPI (iPPI) discs were rubbed against steel and sapphire balls. In operando observations of the iPPI–sapphire contacts show that oil is released under an applied load, forming a meniscus around contacts. Cavitation at the outlet is created at high sliding speeds. The amount of released oil increases with increasing PPI porosity. Contact moduli, E*, estimated based on the actual contact size show that trapped oil in iPPIs contributes to load support. At higher speeds, tribological rehydration of the contact occurs in low density iPPI, with that E* rises with speed. For high density PPIs, high speeds give a constantly high E* which is limited by the viscoelastic properties of the PPI network and possibly the rate of oil exudation. Friction of iPPI–steel contacts is governed by the mechanical properties of the PPI, the flow of the lubricant, and the roughness of the PPI surfaces. For low- and medium- density (highly porous, high roughness) PPIs, large amount of oil is released, and lubrication is mainly via lubricant restricted in the contact in the pores and possibly tribological rehydration. For high density (low porosity) PPI, with lower roughness, hydrodynamic lubrication is achieved which gives the lowest friction. Our results show that polymeric porous materials for effective lubrication require the optimization of its surface roughness, stiffness, oil flow, and oil retentions. [ABSTRACT FROM AUTHOR]

Integration of controllable deformation with excellent thermal stability, mechanical, and insulation properties can greatly expand the versatility of smart polyimides (PIs). However, the unique molecular structure of PI makes it difficult for its molecular chain to move, which is not conducive to the reversible transformation of highly stable PI under environmental conditions. In this study, a PI film integrating shape memory and photo deformation is prepared by constructing a chemical network with PI oligomer as the hard, hexamethylene diisocyanate (HDI) as the soft, and azobenzene as the functional chain segment. The PI films still have a high glass transition temperature Tg ~ 225°C, a high Young's modulus E ~ 3.5 GPa, and a good breakdown strength Eb ~ 176 kV/mm. Moreover, as the network point of the chemical network, the trifunctional crosslinking agent makes the PI produce the shape memory effect induced by light and heat. UV light can drive crosslinked photoresponsivity PI film to have special shape transformation under specific conditions, using azobenzene as photoresponsivity group. This study provides a new idea for the preparation of multifunctional PI, which makes it potentially applicable in the field of smart electric and electronic engineering. [ABSTRACT FROM AUTHOR]

AbstractThis article has investigated the friction behavior of a tribological system composed of a liquid crystal and polyimide. In this tribological system, ZrO2 and PMDA-ODA polyimide film used as a friction pair, and the liquid crystals used as lubricants including the single liquid crystal 5CB and the mixed liquid crystals LCs1 (5CB-5CEPO2), LCs2 (5CB-3CEPC3), LCs3 (5CB-2CEPPN), and conducted friction coefficient comparison experiments with n-hexadecane. It was found that the average friction coefficient of the LCs3 (90% 5CB + 10% 2CEPPN) is the smallest at the load of 5 N and the velocity of 200 rpm, which is 0.00113. Load and velocity selection experiments were investigated of LCs3, as well as polyimide film’s surface analysis including scanning electron microscope, white-light interference, polarization microscope, and surface-enhanced Raman scattering spectra. The results of the surface analysis indicated that some groups in the main chain and branch chain of the polyimide molecules are oriented parallel to the polyimide surface after rubbing. [ABSTRACT FROM AUTHOR]

Polyimide (PI) has excellent resistance to high or low temperatures due to its unique molecular structure, and is widely used in advanced electronics and power systems in extreme environments. In recent years, a small amount of studies have been published to modulate the dynamic behavior of PI such as self‐healable, recyclable, and degradable abilities by adjusting the structure of molecular chains and the composition of monomers. However, the conceptual design, formation conditions, and application prospects of dynamic PI are still unclear. In this paper, the new concepts and systems of dynamic PI are introduced from the perspective of the design of molecular structure, the development of regulating performance area, and the application of extreme insulation, based on recent work and other representative work. Specifically, this work appeals to researchers involved in PI synthesis, smart, dielectric, energy storage, and extreme insulation. [ABSTRACT FROM AUTHOR]

Joint replacements provide pain free movement for the injured or our aging population. Current prothesis mainly consist of hard metal on metal, or ceramic femoral head on ultra-high-molecular weight polyethylene (UHMWPE). In this study, a rodent fracture model was used to test the influence of wear debris from a high-performance polymer (polyimide MP-1™). Saline, MP-1™ Low Dose in Saline (1%), or MP-1 High Dose (2%) in Saline was injected directly into a standard closed unilateral femoral fracture in 12-week old Sprague Dawley rats (n = 25) for 1, 3 and 6 weeks. Endpoints included radiography, micro-computed tomography, mechanical testing and paraffin histology. No adverse effects from the wear particles were observed from the current study based on radiology, mechanical or histological data. Although the particles were present, histological analysis revealed a progression in healing between the Polyimide treated groups and the non-treated saline control groups over the duration of 1, 3, and 6 weeks, with no inhibition from the particles. The MP-1™ wear debris generated are larger than 1 µm thus are not able to be engulfed by macrophages and cause osteolysis. This family of polymers (polyimides) may be an ideal material to consider for articulating joints and other implants in the human body. [ABSTRACT FROM AUTHOR]

In this work, diamondoid metal-organic frameworks (MOFs) were efficiently prepared by sonochemical synthesis and grown on polyimide (PI), aiming to improve the anti-wear performance of the PI matrix. By introducing MOFs into the PI matrix, the free movement of PI molecular chains were restricted, and its hardness and elastic modulus were improved. It was found that the wear rate of the 3 wt.% MOFs/PI composites was reduced by 72.6% compared to pure PI at a load of 4 N after tribological testing by using a ball-on-disk tribometer. This can be attributed to the excellent load-bearing and shear resistance of the fourfold-interpenetrated diamondoid networks, in which the transition metal elements can favor the formation of transfer films. It is worth noting that the 3 wt.% MOFs/PI composites still exhibited great tribological properties under high loads or high speeds. The findings of the present study indicate that diamondoid metal-organic frameworks can be used as efficient modifiers to enhance the tribological properties of PI. [ABSTRACT FROM AUTHOR]

With the policy tilt and increased investment in research and development in the world, new energy vehicle technology continues to progress and the drive motor power density continues to improve, which puts forward higher requirements for the comprehensive performance of the core insulating material enameled wire enamel for drive motors. Polyimide (PI) has excellent electrical insulation properties, and heat resistance is often used to drive the motor winding insulation. To further improve the corona resistance and insulating properties of PI wire enamel varnish, in this paper, firstly, fluorene groups with a rigid conjugated structure were introduced into the molecular chain of the PI film by molecular structure modulation, and then uniformly dispersed alumina nanoclusters (AOCs) were introduced into the PI matrix by using an in situ growth process to inhibit the migration of high-energy electrons. The quantum size effect of the alumina nanoclusters was exploited to synergistically enhance the suppression and scattering of energetic moving electrons by PI-based composite films. The results show that the breakdown field strength of the PI-based composite film (MPI/1.0 vol% AOC) reaches 672.2 kV/mm, and the corona resistance life reaches 7.9 min, which are, respectively, 1.55 and 2.19 times higher than those of the initial PI film. A PI-based composite film with excellent insulating and corona resistance properties was obtained. [ABSTRACT FROM AUTHOR]

A cross-linked hybrid poly Schiff-base (PSB) was synthesized and characterized through spectroscopic, morphological, and structural approaches. The BET surface area (SBET) of the PSB is 20.33 m2/g, the pore volume (Vp) is 0.024 cm3/g, and the pore diameter (Dp) is 4.13 nm. The current study elucidates PSB's strong chemical and thermal stability, as well as the remarkable capacity to adsorb CO2 with perfect selectivity. This property is accomplished by the synergistic interaction of the polymer's physicochemical and structural features when exposed to CO2, N2 and CH4 molecules. This mesoporous polymer exhibits a CO2/N2 = 60 and CO2/CH4 = 10.5 selectivity, and can adsorb 3.22 mmol/g CO2 (at 298 K/1 bar). Furthermore, the isotherms of CO2 gas adsorption and desorption in the porous polymer are reversible. The use of PSB having effective imide, imine, and meta-hydroxyl functional groups in the adsorption and selectivity of CO2 gas produced excellent results, which make it a suitable candidate for CO2 storage and separation applications. [ABSTRACT FROM AUTHOR]

In this study, four novel aromatic polyimides (PIs) with twisted backbone and bulky side substituents were prepared via chemical imidization reaction and two‐step condensation polymerization at reduced reaction temperature. The number‐average and weight‐average molecular weights of the resulting PIs are in the range of 1.98 × 104–4.10 × 104 and 2.66 × 104–5.32 × 104 g mol−1, respectively, while maintaining polydispersity indices consistently below 2.0. In addition, the obtained PIs showed excellent solubility in most common solvents, even in low‐boiling solvents, such as chloroform, dichloromethane, and tetrahydrofuran. The films casted from these PIs also displayed optical transparency with a cutoff wavelength in the range of 335–360 nm. Among the PIs, PAPOT‐OPDA, derived from 3,3′‐Diisopropyl‐4,4′‐diaminodiphenyl‐3″‐phenoxybenzylmethane (PAPOT) and 3,3′,4,4′‐diphenylethertetracarboxylic dianhydride (OPDA), exhibited the highest transparency of T450 = 81% and T500 = 85%, and the best solubility without compromising its thermal properties. [ABSTRACT FROM AUTHOR]

Polyimide (PI) has the inherent defect of poor intrinsic thermal conductivity and cannot meet the increasing demand for rapid heat dissipation in the thermal management introduction. To improve the thermal conductivity of PI, in this study, thick sheet graphene‐ionic liquid (TSG‐IL) functionalized graphene has been prepared by a one‐step ultrasonic‐chemical method. Under the action of mechanical force, IL is successfully modified on the surface of TSG, and TSG is peeled to some extent. TSG‐IL/PI has been prepared the typical method of solution casting followed by thermal imidization. The structure, morphology, thermal conductivity, and mechanical properties of the composites are evaluated by Fourier‐transform infrared spectroscopy, x‐ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, and Hot Disk thermal conductivity tests. When the amount of TSG‐IL is 0.3 wt%, the thermal conductivity of TSG‐IL/PI (0.18 W·m−1·k−1) than pure PI and TSG (ultrasonication)/PI increased by 50.0% and 28.6%, respectively. Moreover, it can maintain good mechanical properties, and its tensile strength (121.5 MPa) is 6.5% and 3.5% higher than that of pure PI and TSG (ultrasonication)/PI, respectively. The potential for application in the preparation of composites with high‐thermal conductivity is promising. [ABSTRACT FROM AUTHOR]

Two semi-alicyclic thermoplastic polyimides (PI) have been prepared from stereoisomeric hydrogenated pyromellitic dianhydrides, including 1S,2R,4S,5R-hydrogenated pyromellitic dianhydride (ccHPMDA or H-PMDA) and 1R,2S,4S,5R-hydrogenated pyromellitic dianhydride (ctHPMDA or Hʹʹ-PMDA) and a fluorine-containing diamine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF), respectively. The derived PI-1 (ccHPMDA-BDAF) and PI-2 (ctHPMDA-BDAF) resins were easily soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc) and meanwhile they also exhibited good thermoplasticities. Thus, the PI films (thickness: ~25 μm) and sheets (thickness: ~3 mm) were separately prepared from the PI solutions in DMAc and the PI powders, respectively. The stereoisomeric effects in the ccHPMDA-derived PI-1 and the ctHPMDA-derived PI-2 apparently affected the melt-flowability of the polymers. PI-2 exhibited lower melting viscosities than that of the PI-1 counterpart. The PI sheets exhibited obviously reduced optical transparency compared with those of the PI films; however better optical transparency than those of the common thermoplastic PI sheets. For example, PI-2 sheet showed the optical transmittance value at the wavelength of 760 nm (T760) of 69.6%, which was 19.5% lower than that of the analogous PI-2 film (T760 = 89.1%), however 50.3% and 65.7% higher than those of the commercially available PI-ref1 sheet (T760 = 19.3%) derived from 3,3ʹ,4,4ʹ-oxydiphthalic dianhydride (ODPA) and 4,4ʹ-oxydianiline (ODA) and the PI-ref2 sheet (T760 = 3.9%, Aurum® PL450C, Mitsui Chem. Co, Ltd., Japan), respectively. Meanwhile, the PI-1 and PI-2 sheets showed the heat deflection temperatures (HDT) of 261.0 °C and 265.0 °C, respectively, which were obviously higher than those of the referenced PIs. At last, the PI sheets exhibited good mechanical properties, including high flexural strength (130.0 ~ 132.0 MPa), flexural modulus (2.87 ~ 2.96 GPa), compression strength (124.4 ~ 149.3 MPa), compression modulus (1.49 ~ 1.59 GPa), and impact strength (129.0 ~ 139.6 KJ/m2). [ABSTRACT FROM AUTHOR]

Polyimide (PI) film have been synthesized and used extensively in energy transmission, wind power generation, new energy vehicles, lidar, and high-power weapons, et al. Nevertheless, it is still challenge to further improve the breakdown strength and dielectric constant of PI film. After the powders of Al0.5xNb0.5xSi1-xO2 (NASO (x mol%)) have been fabricated, it was analyzed that the effect of doping elements Al3+ and Nb5+ on the surface chemistry and microstructure of the NASO powder. And then a small amount of NASO powder was polymerized in situ with PI matrix material, and the effects of NASO on dielectric properties and breakdown strength of the NASO/PI composites were analyzed. The results showed that the introduction of the doping elements Al3+ and Nb5+ favors could be conductive to the formation of oxygen vacancies on the surface of the NASO particle, which improved the surface activity and chemical reactivity of the NASO particle. The PI matrix can efficiently capture additional charges and enhance the insulating characteristics of the NASO/PI composite by properly doping NASO fillers with specific defect concentrations. In the results the breakdown strength of 1 vol% NASO (1 mol%)/PI composites reaches 334.38 kV/mm, which is a 19.6% higher than that of PI. Because the traps in the fillers capture and suppress the carrier transport to enhance the insulating properties of the composites. This work offers a novel synthesis method to simultaneously produce polymer dielectrics with high insulation and high polarization. [ABSTRACT FROM AUTHOR]

High-performance co-polyimide (co-PI) fibers derived from 3,3'4,4'-biphenyldianhydride (BPDA), p-phenylenediamine (p-PDA) and 2-(4-aminophenyl)-5-amino-benzimidazole (BIA) were prepared via the wet spinning and dry-jet wet spinning method, respectively. The distinctions between wet spinning and dry-jet wet spinning processes on the structures and properties of co-PI fibers were systematically investigated. The co-PI fibers prepared by dry-jet wet spinning exhibited smoother surface morphology and higher mechanical properties than those of co-PI prepared by wet spinning. Wide-angle X-ray diffraction (WAXD) results showed that the co-PI fibers prepared by dry-jet wet spinning exhibited highly oriented structure along the fiber direction along with a low degree of lateral packing order in the transverse direction. Small-angle X-ray scattering (SAXS) revealed that the radius, length, misorientation and internal surface roughness of the microvoids in the co-PI fibers prepared by the dry-jet wet spinning are lower than those in co-PI fibers prepared by wet spinning. Moreover, the effect of air layer height, as well as the heat treatment on the structure and properties of fibers during the dry-jet wet spinning process, was also studied. The tensile strength and modulus of co-PI fibers prepared by dry-jet wet spinning reached 2.72 GPa and 114.29 GPa, respectively, with an air layer height of 10 mm and a heat stretching temperature of 440°C. [ABSTRACT FROM AUTHOR]

Polyimide (PI) nanofibrous aerogels (NFAs) have garnered significant attention for their exceptional mechanical and thermal properties, making them promising materials for heat insulation applications. However, there is a lack of comprehensive research on heat transfer of PI NFAs on the modeling and prediction. Therefore, three modified unit cells with the features of PI NFA backbone were constructed for the finite element simulation. Subsequently, the comparisons of our results with experimental data from available literature were conducted. It indicated that the cubic unit cell fitted well with the experimental values when the density was lower than 50 kg / m 3 , while the Weaire–Phelan unit cell demonstrated good agreement when the density was higher than 50 kg / m 3 . A series of parametric studies were performed and indicated that the thermal conductivity is proportional to the nanofiber diameter, whereas inversely proportional to the pore size and porosity. Our research will provide novel insights to the selection of parameters for industrial manufacturing of thermal insulation materials in aerospace, energy, protection, etc. [ABSTRACT FROM AUTHOR]

Composite films of polytetrafluoroethylene (PTFE) and polyimide (PI) combine the advantages of both materials like excellent inertness to chemicals and thermal stability, which provide great potential in applications under harsh environments. However, strong adhesion between PTFE and PI layers still remains a big challenge. In this study, fluorinated ethylene propylene (FEP) as an intermediate layer was found to significantly enhance the adhesion of PTFE films to PI film, with peel strength up to 350 N/m in the manufactured direction comparing to the value of 0 for PTFE/PI composite film without FEP. It's superior to that of commercially available products (25 N/m) under the same test conditions. The improved performance is attributed to the formation of interlocks of molecules at the interfaces between the PTFE and FEP layers, and FEP and PI layers as observed in the images obtained by atomic force microscope (AFM) and scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

Undoped and In‐doped ZnSb thin films are deposited on rigid glass and flexible polyimide (Kapton) by physical vapor deposition. Detailed structural and chemical characterization is performed along with measurement of electrical and optical properties. These properties are very similar for films on glass and Kapton. Flexible ZnSb films show remarkable stability of electrical and optical properties, which are unchanged after 104 cycles of linear bending with surface strain 0.18%. Only severe flexing after this treatment (torsional bending with surface strain 1.7%) causes progressive degradation of conductivity over tens to hundreds of cycles. The ZnSb optical direct gap is determined to be 0.89 ± 0.05 eV. The optical direct gap of β Zn4Sb3 was 1.07 ± 0.05 eV. Other absorption features in the films, including smaller indirect gaps, are discussed. [ABSTRACT FROM AUTHOR]

Thin film materials used in flexible electronics are deposited on polymer substrates and must withstand a variety of static and dynamic mechanical loading conditions to ensure adequate reliability of the device. Tribological loads are also among these loading conditions, and suitable characterization methods and strategies are required for analyzing friction and wear for a variety of tribological contact situations. In the present work, Mo films were deposited on polyimide substrates by high-power impulse magnetron sputtering and then pre-conditioned by straining to several strain levels, including crack onset strain and strains within the crack saturation regime. Subsequently, ball-on-disk tests against different counterpart materials, namely glass, steel, and polymer, were performed to evaluate different tribological contact situations. The comparison of the results of morphologies and characteristics of the films using surface images for strained and unstrained samples provide insight into how increasing straining of the films and crack formation affect the enhanced fracture of the deposited Mo films, which served as a model system in these investigations. [ABSTRACT FROM AUTHOR]

Polyimide (PI) film have been synthesized and used extensively in energy transmission, wind power generation, new energy vehicles, lidar, and high-power weapons, et al. Nevertheless, it is still challenge to further improve the breakdown strength and dielectric constant of PI film. After the powders of Al0.5xNb0.5xSi1-xO2 (NASO (x mol%)) have been fabricated, it was analyzed that the effect of doping elements Al3+ and Nb5+ on the surface chemistry and microstructure of the NASO powder. And then a small amount of NASO powder was polymerized in situ with PI matrix material, and the effects of NASO on dielectric properties and breakdown strength of the NASO/PI composites were analyzed. The results showed that the introduction of the doping elements Al3+ and Nb5+ favors could be conductive to the formation of oxygen vacancies on the surface of the NASO particle, which improved the surface activity and chemical reactivity of the NASO particle. The PI matrix can efficiently capture additional charges and enhance the insulating characteristics of the NASO/PI composite by properly doping NASO fillers with specific defect concentrations. In the results the breakdown strength of 1 vol% NASO (1 mol%)/PI composites reaches 334.38 kV/mm, which is a 19.6% higher than that of PI. Because the traps in the fillers capture and suppress the carrier transport to enhance the insulating properties of the composites. This work offers a novel synthesis method to simultaneously produce polymer dielectrics with high insulation and high polarization. [ABSTRACT FROM AUTHOR]

Copyright of Fire Safety Science is the property of Fire Safety Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the rapid development of wireless communication technology and electronic devices, the issue of electromagnetic interference (EMI) is becoming increasingly severe. Developing a new and flexible electromagnetic interference shielding material has become a challenging task. Here, a sandwich-structured EMI shielding composite film was prepared using electrospinning and vacuum filtration methods. In this process, a porous MXene was synthesized through a reaction with cobalt acetate and served as the intermediate layer in the composite film to shield electromagnetic waves. The electrospun polyimide (PI) fibers were used as the top and bottom layers of the composite film, which can protect the porous MXene from oxidation. This lightweight and flexible composite film integrates electromagnetic interference shielding and thermal insulation capabilities, showing excellent comprehensive performance. The composite film achieves an EMI shielding effectiveness of 48.8 dB in X-band (8.2–12.4 GHz), and absolute shielding effectiveness of the composite film reached a satisfying 4142.43 (dB·cm2)/g. Owing to the design of a multi-layer porous structure, the density of the composite film is 0.65 g/cm3. Furthermore, the thermal conductivity of the film is 0.042 W/(m·K) due to the clamping of electrospun PI fibers, showing excellent thermal insulation performance. Additionally, the composite film exhibits excellent high and low-temperature resistance. In summary, this work provides a feasible strategy for preparing a lightweight polymer-based EMI shielding film. [ABSTRACT FROM AUTHOR]

Humidification of polymer electrolyte membranes in fuel cells is essential for high proton conductivity and lifetime, therefore often membrane humidifier modules are used. We report about the degradation of polyimide humidifier membranes under the influence of airborne ozone traces: during operation we tracked the membranes humidifier performance in 5 modules for up to 1000 h with trace levels of ozone (100 ppb) and conducted characterization tests at 200 h intervals. Operating the humidifier with ozone resulted in a linear decrease in the membrane's ability to transfer moisture over time. Moreover, the glass transition temperature of the membrane material decreases linearly with longer exposure to ozone, while the mechanical strength in terms of breaking force and elongation at break decreases too. Infrared spectra of the tested fibers showed no changes. The reduced water vapor flux would limit fuel cell performance, while the reduced mechanical properties of the membrane can lead to rupture.

Dust removal coatings for polyimide (PI)-based photovoltaic modules used in lunar rovers were fabricated successfully through the blade-coating method using silicon dioxide (SiO2) nanoparticles and γ-aminopropyltriethoxysilane (KH550). The dust removal performance, morphology, transparency, and adhesive force of the coating can be optimized by adjusting the pH and the mass ratios of SiO2 and KH550. The designed coating demonstrates excellent dust removal performance, achieving an percentage of over 85 %. Moreover, the coating has minimal impact on the transparency of the PI substrate and exhibits strong adhesion to it. Additionally, the coating shows remarkable resistance to both high and low temperatures. Even after undergoing five cycles of thermal treatment ranging from −196 to 160 °C, there were no significant changes in the morphology or dust removal performance of the coating. Therefore, this coating exhibits tremendous potential for application in the dust removal of photovoltaic modules in lunar rovers.

Low-dielectric polymers face prominent development challenges at high frequency. Particularly, the relationship between the high-frequency dielectric loss and polymer structures remains not clear enough. Besides, the strategies for achieving low dielectric loss usually have to scarify other important materials properties, e.g., heat resistance or dimensional stability. Herein, fluorine-containing aromatic polyimides were systematically investigated. Among them, simple fluorine atom (-F) substituted polyimides exhibit remarkable low dielectric loss at high frequency (10 GHz) as well as comprehensive advantages, including near-zero thermal expansion coefficient, extremely high thermal decomposition stability, high optical transmittance and excellent mechanical properties. The fundamental mechanisms of low dielectric loss are fully discussed. Benefiting from the unique electric effect and compact size of -F group, -F substituted polyimides display low dipolar density and strongly restricted dipolar motion, contributing to a reduced permanent dipolar polarization loss. Moreover, the concept of induced dipolar polarization was introduced to illustrate the nontrivial impact of F-substituted effect on conjugated electron cloud polarization loss in aromatic polymer system. This work not only provides valuable insights for understanding the mechanism of dielectric loss at high frequency for aromatic polymers, but also opens up broader application possibilities of polyimides in microelectronic and wireless communications industries.

This research presents a new approach to developing an optical window film, leveraging the concept of charge‐transfer complex (CTC) intensification of colorless polyimide The window film demonstrates exceptional characteristics, including a tensile modulus of 8.4 GPa, a high total light transmittance of approximately 90%, and a yellow index below 3. This is the best‐recorded balance between mechanical strength and optical properties for a highly flexible optical film. Furthermore, the resulting film exhibits a pencil hardness grade surpassing 2H, alongside remarkable folding reliability, sustaining over 200,000 cycles of folding and unfolding. The excellent properties are ascribed to the unique supramolecular structure characterized by multiple hydrogen bonding and salt complexation interactions, significantly enhancing CTC intensification. [ABSTRACT FROM AUTHOR]

Abstract Porous materials impregnated with lubricants can be used in conditions where limited lubricant is desirable. In this work, three porous polyimides (PPI) with different densities were prepared. Polyalphaolefin (PAO) impregnated PPI (iPPI) discs were rubbed against steel and sapphire balls. In operando observations of the iPPI–sapphire contacts show that oil is released under an applied load, forming a meniscus around contacts. Cavitation at the outlet is created at high sliding speeds. The amount of released oil increases with increasing PPI porosity. Contact moduli, E*, estimated based on the actual contact size show that trapped oil in iPPIs contributes to load support. At higher speeds, tribological rehydration of the contact occurs in low density iPPI, with that E* rises with speed. For high density PPIs, high speeds give a constantly high E* which is limited by the viscoelastic properties of the PPI network and possibly the rate of oil exudation. Friction of iPPI–steel contacts is governed by the mechanical properties of the PPI, the flow of the lubricant, and the roughness of the PPI surfaces. For low- and medium- density (highly porous, high roughness) PPIs, large amount of oil is released, and lubrication is mainly via lubricant restricted in the contact in the pores and possibly tribological rehydration. For high density (low porosity) PPI, with lower roughness, hydrodynamic lubrication is achieved which gives the lowest friction. Our results show that polymeric porous materials for effective lubrication require the optimization of its surface roughness, stiffness, oil flow, and oil retentions.

Polyimide (PI) is a promising electronic packaging material, but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer. Herein, a series of all-organic PI hybrid films were successfully prepared by introducing the covalent organic framework (COF), which could induce the formation of the cross-linking structure in the PI matrix. Due to the synergistic effects of the COF fillers and the cross-linking structure, the PI/COF hybrid film containing 2 ​wt% COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss (tan δ) of 0.0077 ​at 1 ​MHz. It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI. Besides, the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume (FFV). The molecular dynamics simulation results are well consistent with the dielectric properties data. Furthermore, the PI/COF hybrid film with 5 ​wt% COF showed a significant enhancement in breakdown strength, which increased to 412.8 ​kV/mm as compared with pure PI. In addition, the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient (CTE). It also exhibited excellent thermal, hydrophobicity, and mechanical performance. The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.

Optically transparent polyimide (PI) films with good atomic oxygen (AO) resistance have been paid extensive attention as thermal controls, optical substrates for solar cells or other components for low Earth orbit (LEO) space applications. However, for common PI films, it is usually quite difficult to achieve both high optical transparency and AO resistance and maintain the intrinsic thermal stability of the PI films at the same time. In the current work, we aimed to achieve the target by using the copolymerization methodology using the fluorinated dianhydride 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylic dianhydride (6FCDA), the fluorinated diamine 2,2-bis [4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) and the polyhedral oligomeric silsesquioxane (POSS)-containing diamine N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS) as the starting materials. The fluoro-containing monomers were used to endow the PI films with good optical and thermal properties, while the silicon-containing monomer was used to improve the AO resistance of the afforded PI films. Thus, the 6FCDA-based PI copolymers, including 6FCPI-1, 6FCPI-2 and 6FCPI-3, were prepared using a two-step chemical imidization procedure, respectively. For comparison, the analogous PIs, including 6FPI-1, 6FPI-2 and 6FPI-3, were correspondingly developed according to the same procedure except that 6FCDA was replaced by 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Two referenced PI homopolymers were prepared from BDAF and 6FDA (PI-ref1) and 6FCDA (PI-ref2), respectively. The experimental results indicated that a good balance among thermal stability, optical transparency, and AO resistance was achieved by the 6FCDA-PI films. For example, the 6FCDA-PI films exhibited good thermal stability with glass transition temperatures (Tg) up to 297.3 °C, good optical transparency with an optical transmittance at a wavelength of 450 nm (T450) higher than 62% and good AO resistance with the erosion yield (Ey) as low as 1.7 × 10−25 cm3/atom at an AO irradiation fluence of 5.0 × 1020 atoms/cm2. The developed 6FCDA-PI films might find various applications in aerospace as solar sails, thermal control blankets, optical components and other functional materials.