Polyimide Research Articles

Lightweight Broadband Phased Array Antenna Based on Ultra-Thin Polyimide Film

Lightweight Broadband Phased Array Antenna Based on Ultra-Thin Polyimide Film

Batch-to-Batch Variation in Laser-Inscribed Graphene (LIG) Electrodes for Electrochemical Sensing.

Laser-inscribed graphene (LIG) is an emerging material for micro-electronic applications and is being used to develop supercapacitors, soft actuators, triboelectric generators, and sensors. The fabrication technique is simple, yet the batch-to-batch variation of LIG quality is not well documented in the literature. In this study, we conduct experiments to characterize batch-to-batch variation in the manufacturing of LIG electrodes for applications in electrochemical sensing. Numerous batches of 36 LIG electrodes were synthesized using a CO2 laser system on polyimide film. The LIG material was characterized using goniometry, stereomicroscopy, open circuit potentiometry, and cyclic voltammetry. Hydrophobicity and electrochemical screening (cyclic voltammetry) indicate that LIG electrode batch-to-batch variation is less than 5% when using a commercial reference and counter electrode. Metallization of LIG led to a significant increase in peak current and specific capacitance (area between anodic/cathodic curve). However, batch-to-batch variation increased to approximately 30%. Two different platinum electrodeposition techniques were studied, including galvanostatic and frequency-modulated electrodeposition. The study shows that formation of metallized LIG electrodes with high specific capacitance and peak current may come at the expense of high batch variability. This design tradeoff has not been discussed in the literature and is an important consideration if scaling sensor designs for mass use is desired. This study provides important insight into the variation of LIG material properties for scalable development of LIG sensors. Additional studies are needed to understand the underlying mechanism(s) of this variability so that strategies to improve the repeatability may be developed for improving quality control. The dataset from this study is available via an open access repository.

Decoding high-frequency dielectric loss of Poly(ester imide)s: Molecular simulation and experiment validation

Polyimides (PIs) are essential materials for electronic and high-frequency communication applications, often face challenges with high dielectric loss. Drawing inspiration from low-dielectric-loss liquid crystal polyesters, ester groups have been introduced into PI backbones to develop poly (ester imide)s (PEsIs). This study delved into various PEsIs, aiming to reduce dielectric loss at high frequencies and to understand the molecular mechanisms behind this improvement. Selection and design of PEsIs were based on four key factors: the number of ester groups, substitution positions, side substituents and intermolecular interactions. The results indicated that the high-frequency dielectric loss of PEsIs, specifically at a frequency of 10 GHz, decreases with an increased number of ester groups. For isomeric PEsIs systems, introducing ester groups into the dianhydride part notably reduced the dielectric loss. The modes of bonding between the phenyl ring and the ester group in PI structures also impacted the dielectric loss. The configuration with an O-linked isomer showed a lower value of dielectric loss. On the other hand, introducing hydrogen bonding into PEsIs were observed to contribute a negative impact on the reduction of dielectric loss. Based on these theoretical findings, two PEsIs structures, which were identified as low-dielectric-loss PEsIs candidates, were successfully synthesized. Their dielectric loss factors at 10 GHz were measured experimentally as 0.00153 and 0.00134, thereby confirming the reliability of the theoretical results.

Design of Ultrathin Asymmetric Composite Electrolytes for Interfacial Stable Solid-State Lithium-Metal Batteries.

Ultrathin composite electrolytes hold great promise for high energy density solid-state lithium metal batteries (SSLMBs). However, finding an electrolyte that can simultaneously balance the interfacial stability of the lithium anode and high-voltage cathode is challenging. The present study utilized the both-side tape casting technique to fabricate ultrathin asymmetric composite electrolytes reinforced with polyimide (PI) fiber membrane, with a thickness of 26.8 μm. The implementation of this asymmetric structural design enables SSLMBs to attain favorable interfacial characteristics, such as exceptional resistance to lithium dendrite puncture and compatibility with high voltages. The suppression of lithium dendrite growth and the extension of the cycle life of lithium symmetric batteries by 4000 h are both experimental and theoretically demonstrated under the dual confinement of PI fiber membrane and Li7La3Zr2O12 ceramic fibers. Furthermore, the integration of multicomponent solid electrolyte interphase and cathode electrolyte interface interfacial layers into the lithium anode and high-voltage cathode enhance theirs cycling stability. With a gravimetric/volumetric energy density of 333.1 Wh kg-1/713.2 Wh L-1, the assembled LiNi0.8Co0.1Mn0.1O2 pouch cell demonstrates exceptional safety. The extensive application of this design concept to SSLMBs enables the resolution of electrode/electrolyte interface issues.

Robust all-fabric e-skin with high-temperature and corrosion tolerance for self-powered tactile sensing

Electronic skins (e-skins) for monitoring human and robot activities under extreme circumstances are significant for human-machine interaction in multiple scenarios, which is challenging to realize on fabric/textile materials. Herein, a core filling-encapsulation strategy for multi-layer weaving is explored to achieve a triboelectric triple-layer sandwich woven e-skin (TSW e-skin) for durable self-powered sensing in extreme environments. To construct a robust structure with environment adaptability, ultra-high molecular weight polyethylene (UPE) fibers or polyimide (PI) fibers are integrated into the triple-layer sandwich woven to provide mechanical/thermal/chemical stability, and carbon fibers (CF) are protectively embedded as a core layer for electricity collection, heat management and adaptive sensing. Hydrophobic encapsulation is improved by polydimethylsiloxane (PDMS) thin coating with morphology and mechanical compliances. The TSW e-skin demonstrates excellent mechanical strength (∼20 MPa) and thermal stability (154.5 ℃), durable superhydrophobicity (>150°), and corrosion resistance (pH 1–13), which demonstrates an open-circuit voltage of 53 V and maintains electrically stable at above 150 ℃. The weaving structure enables the e-skin regulatable electrode patterns for sensitive motion perception and touch identification for human and robotic limbs, with real-time tactile feedback even under extreme scenarios. This robust all-fabric e-skin proposes a common strategy for human-robot perception in harsh environments.

CO2 laser-induced porous carbon attached Bi2O3 as highly efficient catalyst for CO2 electroreduction to formate

Electrochemical reduction of carbon dioxide to high-value products is a promising strategy to achieve carbon neutrality, but is hindered by lacking of effective catalysts. Herein, a laser-induced mesoporous carbon (LPC) is quickly prepared by CO2 laser etching commercial polyimide film (PI) without any templates, which proved an artificial support for Bi2O3. The well-defined porous structure and unique nitrogen doping structure synergistically improve the activity and stability of Bi2O3@LPC in catalyzing CO2 electroreduction to formate. The as-made Bi2O3@LPC composite delivers a high faradaic efficiency of 98 % for formate at −150 mA cm−2. DFT calculations reveal the graphitic N in PLC helps stabilize the oxidized state of bismuth under reduction potentials by forming a special N–O–Bi structure. This work provides a new idea for the designing of metal/carbon composite electrocatalysts with nitrogen doped carbon materials as supports.

Super-flexible and low-shrinkage polyimide aerogel composites with excellent thermal insulation: Boosted by SiO2 micron aerogel powder

Polyimide (PI) aerogel composites were synthesized using 4,4′-diaminodiphenyl ether (ODA) and 1,3-bis(4-aminophenoxy)neopentane (BAPN) as diamine monomers, and biphenyl-3,3′,4,4′-tetracarboxylic dianhydride (BPDA) as dianhydride monomers. This study examined the impact of varying proportions of SiO2 micron aerogel powder and the addition of BTC on the properties of the composites. The prepared composites showed ultra-high flexibility (180° folded) with the thickness of 3–4 mm, high thermal stability (95 % weight retention at 501 °C) and thermal insulation performance with ultralow thermal conductivity of 0.033 W/(K·m).

Defect-Engineered Metal-Organic Framework/Polyimide Mixed Matrix Membrane for CO2 Separation.

Defect-engineered metal-organic frameworks (MOFs) with outstanding structural and chemical features have become excellent candidates for specific separation applications. The introduction of structural defects in MOFs as an efficient approach to manipulate their functionality provides excellent opportunities for the preparation of MOF-based mixed matrix membranes (MMMs). However, the use of this strategy to adjust the properties and develop the separation performance of gas separation membranes is still in its early stages. Here, a novel defect-engineered MOF (quasi ZrFum or Q-ZrFum) was synthesized via a controlled thermal deligandation process and incorporated into a CO2-philic 6FDA-durene polyimide (PI) matrix to form Q-ZrFum loaded MMMs. Defect-engineered MOFs and fabricated MMMs were investigated regarding their characteristic properties and separation performance. The incorporation of defects into the MOF structure increases the pore size and provides unsaturated active metal sites that positively affect CO2 molecule transport. The interfacial compatibility between the Q-ZrFum particles and the PI matrix increases via the deligandation process, which improves the mechanical strength of Q-ZrFum loaded membranes. MMM containing 5 wt.% of defect-engineered Q-ZrFum exhibits excellent CO2 permeability of 1308 Barrer, which increased by 99 % compared to the pure PI membrane (656 Barrer) at a feed pressure of 2 bar. CO2/CH4 and CO2/N2 selectivity reached 44 and 26.6 which increased by about 70 and 16 %, respectively. This study emphasizes that defect-engineered MOFs can be promising candidates for use as fillers in the preparation of MMMs for the future development of membrane-based gas separation applications.

Cost-effective strategy for high-temperature energy storage performance of polyimide nanocomposite films

The performance of most polymer-based film capacitors deteriorates severely at high temperatures, while high Tg polymer capacitors, despite their good performance at high temperatures, but their performance still decays severely after prolonged operation at high temperature. This study involves the deposition of a wide bandgap SiO2 inorganic layer on both surfaces of polyimide (PI) films using electron beam thermal evaporation. The findings indicate a substantial enhancement in the breakdown field strength and energy storage density of the composite films at elevated temperature following the deposition of the SiO2 inorganic layer. Specifically, a 100-nm-thick inorganic layer resulted in a breakdown field strength of 459.65 MV m−1 and an energy storage density of 3.2 J cm−3 at 150 °C. Subsequently, the polyimide film coated with a 100 nm SiO2 inorganic layer was infused with small quantities of SrTiO3 nanoparticles, leading to a breakdown field strength of 504.08 MV m−1 and an energy storage density of 6.75 J cm−3 and maintained an efficiency of 90.9 %. These results surpass the performance of the majority of high-temperature polymer films reported to date, with the inorganic layer deposited via electron beam thermal evaporation matching that of the costly magnetron sputtering method. The study presents a cost-effective method suitable for large-scale industrial production, significantly enhancing the electrical performance of PI at elevated temperatures and offering an economical solution for the commercialization of poly composite-based high-temperature capacitors.

Enhanced energy density in cellulose doped polyimide-based all organic composites for high temperature capacitor applications

Abstract The growing demand for electronic devices has induced a significant requirement for high energy density capacitors. In this investigation, we introduced small groups of cyanoethyl cellulose (CEC) into a polyimide (PI) substrate to create all organic CEC/PI composite films for high energy density capacitor applications. Due to the large dipole moment in C–CN dipoles in CEC groups, the dielectric constant of the CEC/PI-5 (5% CEC) composite increased by 26.3% to 4.31. Compared to the pristine PI film at room temperature, the breakdown field of the CEC/PI-0.5 increased by 4.7% from 502.29 to 526.1 MV m−1 and the energy storage density increased by 95% to 11.70 J cm−3. Furthermore, the CEC/PI-0.5 film exhibited an energy density of 6.39 J cm−3 with the breakdown field of 400 MV m−1 at 150 °C, which is 93.05% higher in energy densities than that of the pristine PI film. Furthermore, simulation results indicate that CEC groups can introduce deep traps in the CEC/PI composite, which can inhibit charge movement in the composite and increase the breakdown field of it. In this study, it was found that by adding small amount of CEC polar group in PI film, the high temperature energy density of CEC/PI composite materials was significantly improved. This study not only makes a significant contribution to the development of high-temperature energy-density capacitors, but also pave a way by using small molecule polar polymers to improve the energy density of dielectric materials at high temperature.

Highly Thermally Conductive Super-Aligned Boron Nitride Nanotube Films for Flexible Electronics Thermal Management.

Flexible electronics toward high integration, miniaturization, and multifunctionality, leading to a dramatic increase in power density. However, the low thermal conductivity of flexible substrates impedes efficient heat dissipation and device performance improvement. In this work, we propose a template-assisted chemical conversion strategy for obtaining boron nitride nanotube (BNNT) films with high thermal conductivity and great flexibility. Aligned carbon nanotube (CNT) films have been adopted as templates; a low-temperature chemical conversion followed by a high-temperature annealing has been carried out to produce a highly ordered BNNT film. Benefiting from the high orientation order, the BNNT film exhibits an exceptional thermal conductivity of 45.5 W m-1 K-1 and presents excellent heat dissipation capability, much superior to the commonly used polyimide film. Furthermore, the BNNT film demonstrated excellent flexibility and high insulation resistance. The test of integration with film resistors demonstrated its potential as a thermally conductive substrate for electronics cooling. This work provides a solution for the effective thermal management of flexible electronics.

A novel path planning approach to minimize machining time in laser machining of irregular micro-holes using adaptive discrete grey wolf optimizer

As an essential technique in fabricating substrates for flexible printed circuit boards, laser drilling of polyimide films facilitates the production of smaller holes of superior quality, which is crucial for preserving the structural integrity and functional reliability of materials. This advanced technology is increasingly critical in sectors demanding high performance, such as high-speed communications and biomedical devices. However, challenges such as the diverse sizes of micro-holes, their irregular placement, and the inherent limitations of scanning components on speed and operational range make efficient and rapid laser drilling a complex endeavor. In this paper, we develop a processing time evaluation model and present a new adaptive discrete grey wolf optimizer (A-D-GWO). The A-D-GWO utilizes exchange, shift, and 2-opt operations to enhance search efficiency and includes an adaptive parameter mechanism, improving its adaptability to various problem sizes and ensuring faster convergence. Experimental results confirmed the algorithm’s effectiveness, reducing processing times by 38.9%, 53.6%, and 55.5% for files containing 90, 286, and 649 holes, respectively. When compared to traditional algorithms, A-D-GWO showed better stability and accuracy, suggesting its suitability for inclusion in laser processing technologies.

The effect of temperature on the roll graphite films derived from Kapton polyimide films

The effect of temperature on the roll graphite films derived from Kapton polyimide films

High-temperature semicrystalline/amorphous polymer blends exhibiting enhanced dielectric constant with high breakdown strength

High-temperature polymers with high dielectric constant (K) and breakdown strength are of great interest in many electronic and electric devices and systems. Blending different polymers is a general and highly scalable strategy to improve polymer performance. We investigate two types of semicrystalline polyimide (PI) with different chemical structures blended with amorphous polymer poly (1,4-phenylene ether sulfone) (PES). They formed immiscible polymer blends and exhibited distinctively semicrystalline/amorphous behaviors. The blends of 4,4’-biphthalic anhydride (BPDA)-typed PI with PES form semicrystalline polymer phases and the blend at 50/50 wt% composition exhibits an increased dielectric constant while maintaining the high breakdown field of the neat PI(BPDA) at Eb of 600 MV/m. In contrast, blends of pyromellitic dianhydride (PMDA)-typed PI and PES, which form amorphous phases, show a dielectric increase but a large reduction in Eb. Computational simulations indicate that PI(BPDA) assumes a preferred orientation on PES, which expedites crystallization, while overlaying PI(PMDA) on PES results in more disorder and larger voids. Our finding that the PI(BPDA)/PES blends at 50/50 wt% composition generates enhancement in K without negatively affecting Eb is the first in polymer blends. The results suggest that strategically designing high-temperature polymer blends and exploiting the crystallites within the polymer matrix can achieve an enhanced dielectric constant while maintaining a high breakdown strength. This approach is highly scalable and low cost, thus paving the way for developing practical and high-performance dielectric polymers with high energy density and broad operating temperatures.

Thermal stability prediction of copolymerized polyimides via an interpretable transfer learning model

To address the issues with molecular representation of copolymerized polyimides (PIs) and the mini dataset of PI powders. We constructed an interpretable machine learning (ML) model for PI films using the weighted-additive Morgan Fingerprints with Frequency descriptors and developed an interpretable transfer learning model for PI powders. To enhance Thermal Stability (Temperature at 5% weight loss) of PI films and powders, it is recommended to add conjugated functional groups to diamines, control phenyl ring side chains, and reduce pyridine and hydroxyl groups; select copolyimides (co-PIs); ensure that anhydride is directly connected to the benzene ring in dianhydrides, avoiding aliphatic cycles. It is noteworthy that the close alignment between experimental results and model predictions serves to confirm the model is a reliable prediction tool. It is hoped that this polymer informatics approach will provide further implementation for practical applications of other functional materials.

Frequency-Selective, Multi-Channel, Self-Powered Artificial Basilar Membrane Sensor with a Spiral Shape and 24 Critical Bands Inspired by the Human Cochlea.

A spiral-artificial basilar membrane (S-ABM) sensor is reported that mimics the basilar membrane (BM) of the human cochlea and can detect sound by separating it into 24 sensing channels based on the frequency band. For this, an analytical function is proposed to design the width of the BM so that the frequency bands are linearly located along the length of the BM. To fabricate the S-ABM sensor, a spiral-shaped polyimide film is used as a vibrating membrane, with maximum displacement at locations corresponding to specific frequency bands of sound, and attach piezoelectric sensor modules made of poly(vinylidene fluoride-trifluoroethylene) film on top of the polyimide film to measure the vibration amplitude at each channel location. As the result, the S-ABM sensor implements a characteristic frequency band of 96-12,821Hz and 24-independent critical bands. Using real-time signals from discriminate channels, it is demonstrated that the sensor can rapidly identify the operational noises from equipment processes as well as vehicle sounds from environmental noises on the road. The sensor can be used in a variety of applications, including speech recognition, dangerous situation recognition, hearing aids, and cochlear implants, and more.

Rapid photothermal reduction-derived Pt1.6Ni nanoalloys embedded in laser-induced graphene for hydrogen evolution reaction

Water electrolysis is one of the most intriguing technologies for hydrogen production because of its carbon-neutral nature, however the development of efficient electrocatalysts is required to improve the energy conversion efficiency of water splitting. In this study, we suggest a facile route for the fabrication of Pt1.6Ni nanoalloys on laser-induced graphene (Pt1.6Ni NAs/LIG) by the photothermal reduction using commercial CO2 laser which is irradiated on the surface of the LIG. The laser ablation process on the polyimide (PI) film resulted in porous and interconnected graphene sheets, while uniform nanoparticles with an average size of around 4.5 nm were decorated on their surface by the photothermal reduction effect. The overall process took only 60 s. Bonding structure investigation confirmed that PI film was successfully transformed into a graphene structure and the metal precursors were converted into bimetallic nanoalloy by using Raman spectroscopy and XPS, respectively. Electrochemical measurements for hydrogen evolution reaction discovered that the Pt1.6Ni NAs/LIG showed superior catalytic performance which required an overpotential of only 96 mV to achieve a current density of 10 mA cm−2. It exhibited superior catalytic activity compared to LIG (740 mV), Pt NPs/LIG (204 mV), and PtNi1.6 NAs/LIG (205 mV), as well as other previously reported catalysts at the same current density. Based on these results, the Pt1.6Ni NAs/LIG was employed for hydrogen gas collection and detection. The generated bubbles were collected separately from both electrodes, and their compositions with evolution rate were confirmed to be hydrogen using a commercial H2 sensor.

A study of kapton as a flexible substrate for perovskite solar cells; advantages and disadvantages

The increasing usage of perovskite solar cells is being driven by their high efficiency and cost-effective manufacture. Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) are flexible, transparent, and cost-effective. However, issues have been raised about their long-term stability, especially to the sensitivity of perovskite materials to environmental conditions like as moisture and heat, as well as the challenge of oxygen and moisture transmission across these substrates. Researchers are investigating Polyimide (PI), particularly colorless PI, for enhanced stability, but the techniques are costly. Kapton, a popular colored PI, provides excellent thermal and electrical insulation, but its reduced transparency provides optical issues. In this study, finite-difference-time-domain (FDTD) modeling and experimental analysis were utilized to investigate the optical properties and efficiency of perovskite solar cells on Kapton, PET, and glass substrates. According to the modeling, using Kapton instead of traditional substrates leads to a decrease of 16.6 % in the solar cells short circuit current (JSC). In laboratory experiments, by adding lithium (Li) as the dopant in the electron transport layer (ETL), the sheet resistance of the ETL was reduced from 214 to 2.4 kΩ/□. According to modeling, this enhancement resulted in a 3 % increase in the power conversion efficiency (PCE) of the solar cell, increasing to 17.4 % compared to 16.8 % on a PET substrate. Furthermore, using a Kapton substrate improves critical performance parameters like open circuit voltage (VOC) and fill factor (FF).

Frequency-Dependent Dielectric Permittivity and Water Permeability in Ordered Mesoporous Silica-Grafted Fluorinated Polyimides.

Polymers with a low dielectric constant (Dk) are promising materials for high-speed communication networks, which demand exceptional thermal stability, ultralow Dk and dissipation factor, and minimum moisture absorption. In this paper, we prepared a series of novel low-Dk polyimide films containing an MCM-41-type amino-functionalized mesoporous silica (AMS) via in situ polymerization and subsequent thermal imidization and investigated their morphologies, thermal properties, frequency-dependent dielectric behaviors, and water permeabilities. Incorporating 6 wt.% AMS reduced the Dk at 1 MHz from 2.91 of the pristine fluorinated polyimide (FPI) to 2.67 of the AMS-grafted FPI (FPI-g-AMS), attributed to the free volume and low polarizability of fluorine moieties in the backbone and the incorporation of air voids within the mesoporous AMS particles. The FPI-g-AMS films presented a stable dissipation factor across a wide frequency range. Introducing a silane coupling agent increased the hydrophobicity of AMS surfaces, which inhibited the approaching of the water molecules, avoiding the hydrolysis of Si-O-Si bonds of the AMS pore walls. The increased tortuosity caused by the AMS particles also reduced water permeability. All the FPI-g-AMS films displayed excellent thermooxidative/thermomechanical stability, including a high 5% weight loss temperature (>531 °C), char residue at 800 °C (>51%), and glass transition temperature (>300 °C).

EFFECT OF DIFFERENT UV EXPOSURE ENERGY ON POLYIMIDE-BASED NONVOLATILE RESISTIVE PHOTOMEMORY DEVICE

Recently, many researchers pay attractive attention to organic memory technology. Polyimide film was used as the resistive switching layer of nonvolatile photomemory in this study. In order to improve the performance of the device, different wavelengths of Ultraviolet (UV) light were used to operate the device, and its impact on the polyimide film was discussed. In this paper, three different UV light bands, UVA, UVB, and UVC, are used to switch devices between low resistance state (LRS) and high resistance state (HRS). It can be seen from the results that all three kinds of energies of UV light can transform the polyimide film from HRS to LRS successfully. According to the data, after 1s of UVB irradiation, the LRS current of polyimide-based photomemory device is the largest, and the data retention ability is also the best, the second is to irradiate UVA, and the last is to irradiate UVC. The results of the optical properties and electrical properties are coincidental. Therefore, different UV energies can affect this photomemory device.