Polyimide Aerogels Research Articles

High-performance flexible reduced graphene oxide/polyimide nanocomposite aerogels fabricated by double crosslinking strategy for piezoresistive sensor application

Flexible conductive polyimide aerogels used for piezoresistive pressure sensors in harsh environments are often limited by brittleness, structural collapse, low elastic recovery, low sensitivity, and narrow pressure detection range. Herein, we report a simple and green method of ice-templating unidirectional solidification combined with freeze-drying and thermal imidization to obtain a flexible reduced graphene oxide/polyimide (rGO/PI) nanocomposite aerogels with a double crosslinked structure, which achieve a significant transformation of PI aerogels from brittleness to high flexibility. The strong layered structure and dense interlaminar porous network are established by the covalent crosslinking of 1,3,5-triaminophenoxybenzene (TAB) and the hydrogen bonding crosslinking of graphene oxide (GO), imparting the double crosslinked rGO/PI aerogels with unique “porous honeycomb” structure and excellent mechanical properties. Due to the synergistic effect of TAB, rGO, PI, and unidirectional freezing process, the double crosslinked rGO/PI nanocomposite aerogel shows low density (25 mg/cm3), high compression cycle stability (3000 cycles), wide pressure detection range (0–85.1 kPa), extremely short response time (about 129 ms) and excellent environmental resistance (maintaining high structural stability and pressure response even at high temperatures of 180 °C and low temperatures of −50 °C), suitable for detecting various motion signals. It is proved that the elastic double crosslinked rGO/PI nanocomposite aerogels have potential applications serving as candidate materials for piezoresistive sensors and wearable electronic protective equipment in the fields of national defense, military industry, aerospace, and other fields in extreme environments.

Fast and scalable production of crosslinked polyimide aerogel fibers for ultrathin thermoregulating clothes

Polyimide aerogel fibers hold promise for intelligent thermal management fabrics, but their scalable production faces challenges due to the sluggish gelation kinetics and the weak backbone strength. Herein, a strategy is developed for fast and scalable fabrication of crosslinked polyimide (CPI) aerogel fibers by wet-spinning and ambient pressure drying via UV-enhanced dynamic gelation strategy. This strategy enables fast sol-gel transition of photosensitive polyimide, resulting in a strongly-crosslinked gel skeleton that effectively maintains the fiber shape and porous nanostructure. Continuous production of CPI aerogel fibers (length of hundreds of meters) with high specific modulus (390.9 kN m kg−1) can be achieved within 7 h, more efficiently than previous methods (>48 h). Moreover, the CPI aerogel fabric demonstrates almost the same thermal insulating performance as down, but is about 1/8 the thickness of down. The strategy opens a promisingly wide-space for fast and scalable fabrication of ultrathin fabrics for personal thermal management.

Recent Study Advances in Flexible Sensors Based on Polyimides.

With the demand for healthy life and the great advancement of flexible electronics, flexible sensors are playing an irreplaceably important role in healthcare monitoring, wearable devices, clinic treatment, and so on. In particular, the design and application of polyimide (PI)-based sensors are emerging swiftly. However, the tremendous potential of PI in sensors is not deeply understood. This review focuses on recent studies in advanced applications of PI in flexible sensors, including PI nanofibers prepared by electrospinning as flexible substrates, PI aerogels as friction layers in triboelectric nanogenerator (TENG), PI films as sensitive layers based on fiber Bragg grating (FBG) in relative humidity (RH) sensors, photosensitive PI (PSPI) as sacrificial layers, and more. The simple laser-induced graphene (LIG) technique is also introduced in the application of PI graphitization to graphene. Finally, the prospect of PIs in the field of electronics is proposed in the review.

Flexible parallel-type capacitive humidity sensors based on the composite of polyimide aerogel and graphene oxide with capability of detecting water content both in air and liquid

High performance flexible capacitive humidity sensors (FCHS) are desirable due to application potentials in wearable electronics. Herein, we report a self-standing FCHS consisting of a composite of polyimide (PI) aerogel and graphene oxide (GO). Specifically, PI aerogel was modified with NaOH and GO, and treated with laser direct writing to reduce GO to construct electrodes on the surfaces of PI aerogel to fabricate a parallel-type FCHS. Resulting FCHS with 3D interconnected porous structure exhibited capacitance change from ∼10 pF to ∼1000 pF between relative humidity of 11–98 %, showing high sensitivity. Moreover, it displayed good stability against large deformations. The FCHS could monitor respiration and differentiate non-contact finger movement. Of note is that it could detect water content in both ethanol and hydraulic oil with high sensitivity, indicating dual function of measuring water content in both air and liquids. The work provides a facile approach for developing advanced flexible water sensors with broader application prospects.

Low shrinkage polyimide aerogels with excellent thermal insulation: Boosted by “paddle-shaped” benzhydrylidenefluorene-based diamines

Polyimide (PI) aerogels are widely employed as thermal insulating materials in the aerospace and transportation industry in extreme environments. However, there is a lack of research that focused on the development of novel monomers for the preparation of high-performance PI aerogels. In this study, we proposed a “rigid-soft” strategy to design structurally unconventional diamine compounds. These compounds effectively enhance the rigidity of the PI chain, leading to improved thermostability, while still maintaining flexibility and moderate mechanical properties. Accordingly, two brand-new monomers (BDFD and BDFA) incorporating a twisted “paddle-shaped” benzhydrylidenefluorene (BDF)-based diamine were successfully developed. These monomers consisted of a flexible diphenylmethylene moiety coupled to a rigid fluorene building block. Leveraging these distinctive characteristics, two series of PI aerogels were prepared and exhibited exceptional performance, including a low shrinkage rate, high surface area, and uniform pore size. Notably, the PI-D1 aerogel, composed entirely of BDFD, demonstrated the highest surface area of 674.8 m2 s−1. With a molar ratio of 1/3 for BDFA/ODA, PI-A4 demonstrated the ability to achieve high-performance thermal insulation (54.3 mW m−1 K−1 at 200 °C) with excellent thermostability (Td 5% > 580 °C, Tg > 299 °C) and satisfactory dimensional stability (shrinkage at 7.7 %), thanks to its smaller pore size (∼24 nm) and well-balanced rigid and flexible structure property. This research provides an effective method for creating high-performance PI aerogels with an exceptionally low shrinkage rate, which makes them appropriate for thermal management materials that require superior thermal insulation properties.

Deep integration of pyrolysis kinetics and pyrolysis mechanism of polyimide aerogels

As novel advanced organic materials, polyimide aerogels (PI-AER) exhibit high porosity and excellent thermal stability. For the general and safe application of PI-AER, it is imperative to clarify their thermal decomposition process. The kinetic parameters of PI-ARE pyrolysis were calculated using different traditional kinetic methods, and the results showed that the PI-AER pyrolysis process conformed to the Fn-like mechanistic function model with an average activation energy of 143.984 kJ/mol. The pyrolysis mechanism function model of the main pyrolysis stages was optimized and reconstructed to obtain the optimal solution f(α). In addition, the concentration changes of pyrolysis products with increasing temperature were monitored by TG-MS and the PI-AER bond breaking mechanism was analyzed. Finally, the TG curves were fitted piecewise to obtain Ea and lnA for the two pyrolysis processes. Combined with the pyrolysis mechanism and two-stage kinetic parameter analysis, the effects of the two pyrolysis stages of PI-AER on the kinetic parameters were elucidated. It was shown that the activation energies of solvent volatilization and desorption and PI-AER main chain were 60.1 kJ/mol and 147.76 kJ/mol, respectively. This study provides fundamental industrial parameters for the application of polyimide aerogels in extreme conditions.

Ion transport regulation of polyimide separator for safe and durable Li-metal battery

Li-metal battery (LMB) gains enormous attentions because of its high energy and power density. However, the cycling stability of LMB is seriously harmed by the increase of internal temperature and Li-dendrite growth. The development of high-safety thermotolerant separators is urgently desired that can provide advantageous channels for rapid ion transport and simultaneously enable homogeneous Li+ fluxes to inhibit dendrite growth. With superior thermal and electrochemical stability, polyimide-based separator is a good alternative to commercial polyolefin-based separators, but prior design of either nanopores or micropores in polyimide-based separator usually met a dilemma. In this work, we report a polyimide sandwiched separator (denoted as s-PIF) with polyimide fiber (PIF) membrane coated by polyimide aerogels. Significant advancements in terms of mechanical property, electrolyte adsorption/retention and ion conductivity can be achieved for the s-PIF separator, compared with PIF separator. Moreover, the s-PIF separator can render a dendrite-free process of Li plating/stripping for 1400 h. Consequently, the LMB with s-PIF separator shows a remarkable stability with 80 % of its capacity retention after 3000 cycles at 10C.

Moisture resistant polyimide aerogel membranes with low dielectric constant and super thermal insulation for electronic device under harsh environment

Membranes with low dielectric constant and high moisture resistance are the key material for miniaturized and integrated communication equipment as an interlayer dielectric layer. Here, a series of cross-linked PI aerogel membranes were prepared by co-polymerization and scraping coating technology. The introduction of the fluorinated blocks and benzimidazole ring structures can consequently garner novel PI aerogel membranes with fascinating dielectric properties and outstanding moisture resistance. The dielectric constants of the sample membranes are as low as 1.33 at 1 KHz and 1.32 at 1 MHz with dielectric loss as low as 0.0079 at 1 KHz and 0.0035 at 1 MHz. The water contact angle can reach 107.35° with a surface roughness value of 30.428 nm. Moreover, the PI aerogel membranes have high specific surface area and excellent thermal and mechanical properties. The thermal conductivity as low as 35.4 mW m−1 K−1 at room temperature indicates excellent thermal insulation performance. PIAM-2 is suitable as an interlayer dielectric layer for electronic components under harsh environment. In addition, the influence of surface roughness on surface wettability was also elaborated on which can provide a feasible method for the preparation of low dielectric materials with moisture resistance.

Carbon foam-reinforced polyimide aerogel composites for thermal insulation with reduced shrinkage

Carbon foam-reinforced polyimide aerogel composites for thermal insulation with reduced shrinkage

Polyimide aerogel/aramid fiber composite with high mechanical strength and thermal insulation for thermal protective clothing

Polyimide (PI) aerogel, as a new organic aerogel material, has the excellent thermal properties of polyimide and the characteristic of high thermal insulation of aerogels, and has gained increasing attention. In this work, using PI aerogel as the matrix material and aramid fiber as the reinforcement material, controllable flexible PI aerogel/aramid fiber composite insulation materials were successfully prepared by freeze-drying and soft treatment. This study sought to determine how the mass percentage of PI aerogel affected the microstructure, mechanical characteristics, thermal insulation capabilities, and thermal comfort of clothes in PI aerogel/aramid fiber composites. To achieve this, the preparation process of PI aerogel was optimized, and the effects of different mass fractions of PI aerogel on the properties of the composite material were evaluated. The results demonstrated that increasing the mass fraction of PI aerogel led to improvements in the mechanical properties, flexibility, and heat insulation properties of the composite material. Furthermore, the PI aerogel/aramid fiber composite offered enhanced thermal comfort to the wearer in hot and humid environments, indicating that the composite material is particularly suited for thermal insulation applications.

Shape memory polyimide aerogel composites with high programming temperatures and exceptional shape recovery capability

Shape memory polyimide aerogel composites with high programming temperatures and exceptional shape recovery capability

Superelastic bio-based polyimide aerogel with excellent oil/water separation performance and effective visible light photocatalytic activity

Aiming to realize sustainable development and reduce environmental pollution, scientists have been on searching for bio-based materials derived from renewable resources to replace petroleum-based materials. Herein, a bio-based polyimide aerogel derived from 2,5-furandicarboxylic acid was synthesized successfully via supercritical fluid drying. The bio-based polyimide aerogel had mesoporous structure and a large specific surface area (220 m2/g), which were highly advantageous to adsorption and photocatalysis. The bio-based polyimide aerogel possessed fast adsorption behavior (within 1 s), outstanding durability (200 cycles of adsorption and desorption), and a self-cleaning property. The bio-based polyimide aerogel could also realize continuous and rapid separation of organic solvent and water with the aid of a vacuum pump. Importantly, the bio-based polyimide aerogel exhibited superelastic (rapid recovery after 90% strain) and anti-fatigue performance (compressive strength remained 96% after 100 cycles). Moreover, the bio-based polyimide aerogel displayed effective photocatalytic activity under visible light. The possible degradation mechanism was also proposed, and radical quenching tests demonstrated that the generation of h+ and ·O2− was the key to photocatalytic degradation. Considering its environmental friendliness and excellent properties, bio-based polyimide aerogel provides a promising solution for oil/water separation and photocatalysis.

Polyimide aerogels with low thermal conductivity and high-temperature stable properties prepared by lyophilization for flexible thermal protection

Polyimide aerogel, presenting an outstanding new material for lightweight protective thermal insulation, has garnered significant attention in the aerospace field. Despite its potential, due to the high production cost of the supercritical drying method used for its preparation, its widespread application is limited. In this research, a series of lightweight polyimide aerogels (F-PIAs, 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA) and 4,4'-diaminodiphenyl ether (ODA)) with excellent thermal protection properties were prepared by lyophilization. The findings indicated that F-PIAs (Freeze-dried polyimide aerogels) exhibited comparable physical characteristics to S-PIAs (Supercritical-dried polyimide aerogels), while their preparation cost was even more economical. F-PIAs exhibits excellent flexible and compression behavior (compression strength up to 1.16 MPa, modulus up to 12.8 MPa), which provide a great structural basis for the production of molded thermal insulation protective materials. The average pore diameter of F-PIAs is in the range of 7∼11 nm. The nanoporous structure leads to the gas within the pores of the aerogel producing the Knudsen effect, thereby significantly enhancing the thermal insulation performance of the aerogel. The thermal conductivity of F-PIA-4 (Freeze-dried polyimide aerogels with a solid content of 4%) at room temperature is as low as 0.023 W·m−1·K−1, which is superior to the PIAs (0.043 W·m−1·K−1) prepared by lyophilization in literature. Its thermal diffusion coefficient changes from 0.108 mm2·s−1 to 0.18 mm2·s−1 in the temperature range of 27°C to 200°C, demonstrating good thermal insulation performance at high temperatures. Meanwhile, after heating on a 150°C flat plate for 11 min and 41 s, the surface temperature of F-PIA-4 was only 36.2°C, further verifying its excellent thermal insulation performance. The results of the TGA experiment on F-PIA-4 demonstrated the high-temperature stability of aerogel (Td5% is higher than 523°C, Td10% is higher than 566°C). The exceptional properties of F-PIAs hold significant practical reference value in helping to reduce the manufacturing cost of high-performance aerogel thermal insulation materials, thereby enabling their widespread application in aerospace, military, and civil field.

Flexible, Thermally Stable, and Ultralightweight Polyimide-CNT Aerogel Composite Films for Energy Storage Applications.

Polyimide (PI) aerogels are promising in various fields of application, ranging from thermal insulators to aerospace. However, they are typically in the form of a bulk monolith, which suffers from a lack of conformability and drapability. Moreover, their electrical conductivity is limited, and they mainly display an insulative behavior. These shortcomings can limit the applications of PI aerogels in energy storage systems, which require ultralightweight flexible conductive films, which at the same time offer high thermal stability, ultralow density, and high surface area. To overcome these obstacles, the present study reports the fabrication of PI-carbon nanotube (PI-CNT) aerogel composite films with varying CNT content prepared through a sol-gel preparation method, followed by a supercritical drying procedure. Compared to pristine PI aerogels, which displayed a large shrinkage and density of 18.3% and 0.12 g cm-3, respectively, the incorporation of only 5 wt % CNTs resulted in a significant reduction of both shrinkage and density to only 11.5% and 0.10 g cm-3, respectively. This suggests the importance of CNTs in improving the dimensional stability of aerogels and creating a robust network. Further characterizations showed that incorporation of 5 wt % CNTs also resulted in the highest pore volume (1.25 cm3 g-1), highest surface area (324 m2 g-1), highest real permittivity (80), highest electrical conductivity (3 × 10-1 S m-1), and ultrahigh service temperature (575 °C). It was also shown that the aerogel films can withstand a large degree of bending, can be twisted, and can be fully rolled with no obvious cracks propagated in the structure. The combined outstanding properties of the developed aerogel composite films make them promising potential candidates for supercapacitor electrodes. Therefore, the electrochemical performance of the devices based on aerogel electrodes was further studied. The device demonstrated a high energy density of 2.6 Wh kg-1 at a power density of 303.8 W kg-1. The total capacitance after 5000 cycles was 91.8% of the initial capacitance, which indicated excellent stability and durability of the device. Overall, this work provides a facile yet effective methodology for the development of high-performance aerogel materials for energy storage applications.

Upcycling of Waste Fabrics into High-Efficiency Air Filters Using Flexible Polyimide Aerogel Coatings

Upcycling of Waste Fabrics into High-Efficiency Air Filters Using Flexible Polyimide Aerogel Coatings

Polyimide/SiO2 composite aerogels with excellent thermal and sound insulation properties prepared by confined filling method

Aerogels have enormous potential in integrated thermal insulation and noise reduction applications. According to the knowledge of the favorable mechanical and acoustic properties of honeycomb structures. We employed anisotropic “honeycomb-like” polyimide (PI) aerogels as the matrix and utilized a confined filling strategy to directionally filled continuous SiO2 aerogels into the PI aerogel matrix. This resulted in the creation of an exceptional organic–inorganic composite aerogel (PISis) with outstanding thermal and acoustic insulation performance. The radial thermal conductivity of PISis ranged from 22.37 to 27.65 mW·m−1·K−1, and the initial decomposition temperature was approximately 524–557 °C. In the frequency range of 500–6300 Hz, the average sound transmission loss (STL) of the 18 mm thick composite material reached 30.67 ∼ 31.89 dB, and the compressive strength at 10 % strain is 0.416 MPa. The PISis exhibits a density ranging from 0.1012 to 0.1302 g/cm3. These make it an ideal lightweight, high-strength, and efficient material for thermal and acoustic insulation.

Ultrasonic‐Assisted Freeze‐Drying for Polyimide/Carboxylated MWCNTs Aerogel Sensor with Excellent Aging Sensing Performance

AbstractAlong with the rapid development of science and technology, the new demand for flexible strain sensors have been put forward in the field of aerospace and other sophisticated exploration areas. Meanwhile, the high temperature generated during the launch of the aerospace aircraft presents new challenges. The existing high temperature resistant sensors are limited in further development by their inherent defects (stability, high processing costs, etc.). A flexible strain sensor with high‐temperature sensing capability is urgently needed. Therefore, the composite polyimide aerogel flexible strain sensor is prepared by ultrasonic‐assisted freeze‐drying method and thermal imidization. Characterizing the structure and sensing performance of the polyimide/carboxylated MWCNTs (PI/CNTs) composite aerogel, the tunneling effect is innovatively introduced to theoretically calculate the parameters in the sensing path. The prepared composite sensor has a high sensitivity (5.34), a fast response time (187 ms), and long‐term cycling stability (1000 cycles). The composite aerogel sensor, which has undergone high temperature aging, still has good sensing performance. It can be used for sensing under extreme conditions, for example, the peripheral electronic devices of aerial probes are used to sense and detect external deformation or withstand pressure conditions.

Long‐Term Infrared Stealth by Sandwich‐Like Phase‐Change Composites at Elevated Temperatures via Synergistic Emissivity and Thermal Regulation

AbstractThe rapid development of infrared surveillance technologies has attracted great attention for scientists to design advanced functional materials with prominent infrared stealth and thermal camouflage effectiveness. In the current study, a sandwich‐like functional composite based on a crosslinked polyimide aerogel, a meso‐erythritol (mE)‐based phase‐change composite, and an MXene film has been developed to achieve long‐term thermal camouflage at elevated temperatures. In this composite system, the lower aerogel layer can act as a barrier to insulate heat transfer through its layer‐stacking structure under ultralow directional thermal conduction. The introduction of the middle phase‐change composite layer ensures that the composite system obtains a dynamical temperature‐regulation capability through sensible and latent heat absorption of mE as a phase change material, while the upper MXene layer provides a very low emissivity surface for the system. As a result, the developed composite achieves a significant reduction in the thermal radiation temperature of a high‐temperature target. Moreover, the MXene film exhibits good electromagnetic interference shielding effectiveness, making the sandwich‐like composite obtain a thermal camouflage capability in various complicated scenarios. This work provides a promising approach for the design of advanced functional materials to realize long‐term infrared stealth and thermal camouflage of high‐temperature targets in security protection and counter‐surveillance.

A synergistic strategy for fabricating a highly flexible poly(m‐phenylene isophthalamide) nanofiber‐reinforced polyimide aerogel for high‐temperature filtration

AbstractParticulate matter (PM) has a significant impact on air quality, especially the PM produced by automobile exhaust and high temperature environment. Therefore, it is of great significance to develop a technology that can effectively intercept fine PM under high temperature conditions. This study reports the construction of poly(m‐phenylene isophthalamide) (PMIA) nanofiber‐reinforced polyimide aerogel (PPNFAs) filters using freeze‐drying and electrospinning for high temperature filtration. After 100 compression cycles, the maximum compressive stress of PPNFAs is reduced by only 15%. When the content of PMIA is 0.65 wt%, PPNFAs has a high porosity (97.35%), high specific surface area (8.87 m2 g−1) and highest dust holding capacity (124.8 m2 g−1). After 15 days of continuous heating test at 300°C, the filtration efficiency of PPNFAs filter for different diameter particles of impurities remained above 98%. Therefore, the PPNFAs filter prepared in this study provides a new design concept for a new generation of high temperature filters.

Scalable Preparation of Polyimide Sandwiched Separator for Durable High-Rate Lithium-Metal Battery.

The ever-growing demands for efficient energy storage accelerate the development of high-rate lithium-metal battery (LMB) with desirable energy density, power density, and cycling stability. Nevertheless, the practical application of LMB is critically impeded by internal temperature rise and lithium dendrite growth, especially at high charge/discharge rates. It is highly desired but remains challenging to develop high-performance thermotolerant separators that can provide favorable channels to enable fast Li+ transport for high-rate operation and simultaneously homogenize the lithium deposition for dendrite inhibition. Polyimide-based separators with superior thermal properties are promising candidate alternatives to the commercial polyolefin-based separators, but previous strategies of designing either nanoporous or microporous channels in polyimide-based separators often meet a dilemma. Here, a facile and scalable approach is reported to develop a polyimide fiber/aerogel (denoted as PIFA) separator with the microporous polyimide fiber membrane sandwiched between two nanoporous polyimide aerogel layers, which can enable LMBs with remarkable capacity retention of 97.2% after 1500 cycles at 10 C. The experimental and theoretical studies unravel that the sandwiched structure of PIFA can appreciably enhance the electrolyte adsorption and ionic conductivity; while, the aerogel coating can effectively inhibit dendrite growth to realize durable high-rate LMBs.