Fabrication Of Polyimide Research Articles

Bioinspired carbon black deposited polyimide fabric for sustainable water energy harvesting

Water is the source of life and the largest energy carrier on Earth. Various excellent hydrovoltaic technologies have been proposed, but still suffer from issues such as intermittent output, material limitations, and poor flexibility. Here, we proposed a method for fabrication of a hydrovoltaic generator using the flexible polyimide fabric. Carbon black was deposited on the polyimide fabric surface using a simple method of candle flame burning. On the basis of water transport in the fabric and charge separation induced by negatively charged carbon black channels, sustainable hydrovoltaic power generation was achieved by the generator. A single carbon deposited polyimide fabric (CBP) could generate a continuous voltage output of nearly 260 mV by dripping a water drop on one side. Multiple CBP devices were connected in series and parallel to increase output power, which could be applied for the power and energy storage of small electronic devices. This work may provide a convenient strategy for fabricating sustainable flexible hydrovoltaic generators and offer insights for the development of clean power sources.

Construction of polyimide composite aerogels via multi-coordination structure of polymer-metal for improving heat-induced shrinkage, thermal insulation, mechanical and dielectric properties

The fabrication of polyimide (PI) composite aerogels can promote and optimize the characteristics and performance efficiency. But in fact, interface effect and assembly technique are the key problems in preparing PI composite aerogels. To settle this critical issue, a series of PI composite aerogels were designed via forming multi-coordination structure between PI molecular chain and Cu(II) metal ions. Multi-coordination structure connects the two-phase systems closely to obtain the improved comprehensive performances. The resulting PI composite aerogels still have high specific surface and mesoporous structure. The addition of Cu(II) improves the thermal and mechanical properties of the PI composite aerogels with an over 581 °C initial decomposition temperature, tensile strength of up to 9.48 MPa and modulus of up to 232.4 Mpa，along with compression Young’s modulus increased by 173% (up to 28.7 MPa) and stress at 10% strain improved by 150% (up to 1.70 Mpa). In the meantime, the brilliantly controllable dielectric property (with the dielectric constant down to 1.60 and the dielectric loss reaching 0.0171 at 10 MHz) and thermal insulation property (with the thermal conductivity down to 31.9 mWm−1K−1) of PI composite aerogels make them can be used as low dielectric and thermal protection materials. The small heat-induced shrinkage between 100 and 250 °C allows the PI composite aerogels to operate in persistent extreme conditions. Besides, this work can provide a new strategy for preparing PI composite aerogels.

Fabrication of controllable and reversible bidirectional shape memory fabric composites based on multiblock copolyimide and their properties

The construction of polymer-based materials with reversible bidirectional shape memory effects and good thermal properties is of paramount importance for the development of the intelligent exploration in high temperature fields. In this work, a series of multiblock shape memory copolyimides were synthesized with the introduction of soft segments containing aliphatic diamines into aromatic polyimide structures to control the mobility of the molecular chains. The number of blocks for copolyimide was finely regulated to optimize the shape memory behaviors with thermal stability and both of the shape fixity ratio and shape recovery ratio could reach higher than 97% with the triggering temperature around 260 °C. Then controllable fabric composites with high temperature and reversible bidirectional shape memory effects were firstly constructed by incorporating of deliberately designed block copolyimide with commercialized polyimide fabric. The flexible fabric composites exhibited variable fixed shapes by regulating the thickness discrepancies between upper and lower layers, which showed good two-way shape memory properties with the shape recovery ratio of 98% during the programming process, providing a new sight of the exploration for high temperature shape-memory materials.

Hierarchically porous polyimide aerogel fibers based on the confinement of Ti3C2Tx flakes for thermal insulation and fire retardancy

Thermally insulating and flame-resistant fibers/textiles have drawn enormous attention attributing to their great application prospects in personal thermal management and protective clothing. Nevertheless, conventional natural fibers and synthetic fibers are insufficient for advanced thermal regulation. Herein, an in-situ polymerization method and wet-spinning technique are employed for the continuous and scalable fabrication of polyimide (PI) aerogel fibers utilizing monolayered Ti3C2Tx flakes as the pore-generating agents. Benefiting from the intimate interfacial interaction between MXene and the macromolecular chains, hierarchical porosity is constructed in the composite aerogel fibers due to the confinement of the interconnected PAA/Ti3C2Tx networks during liquid-solid phase separation. As a result, the PI/Ti3C2Tx aerogel fibers manifest significantly enhanced mechanical properties (tensile strength of 26 MPa), large specific surface area (145 m2 g−1), excellent flame resistance, and remarkable thermal insulation performance (with a low thermal conductivity of 36 mW m−1 K−1), which can be readily weaved into flexible textiles for practical thermal regulating applications. This approach is expected to pave a new way for the fabrication and application of high-performance thermal insulating fibers and textiles.

Functional POSS based polyimide nanocomposite for enhanced structural, thermal, antifouling and antibacterial properties

Polyhedral oligomeric silsesquioxane (POSS) molecules are a combination of organic and inorganic hybrid nanocage structures (1–3 nm), which makes them ideal building blocks for the fabrication of functional nanostructured filler, and modify physico-chemical properties of polymeric nanocomposites. Herein, silver nanoparticles functionalized POSS nanofillers were incorporated in poly(pyromellitic dianhydride-co-4,4̍-oxydianiline) amic acid (PAA) matrix by in-situ chemical method followed by imidization for the fabrication of polyimide (PI) nanocomposite. Significant improvement in structural, thermal and wettability properties of functional Ag-POSS-PI nanocomposites were observed due to electrostatic, Van der Waals and hydrogen bonding interactions of functional Ag-POSS nanofiller with –NH2 and –COOH groups of PAA. The hydrophilicity of Ag-POSS-PI film increased (contact angle 79 ± 1.5°) as compared with neat PI (103 ± 1.8°). The antibacterial response using Ag-POSS-PI nanocomposite film against the E. coli bacterial colonies tended to decline with 64 × 106 CFU/mL as compared with neat PI film (1 × 108 CFU/mL) which is attributed to the antibacterial action of Ag NPs and amine groups of octaammonium POSS in PI. As-synthesized functional POSS based PI nanocomposite potentially finds their applications in aerospace, fire retardancy, microelectronics, environmental and biomedical fields.

Hyper cross‐linked polymers containing amino group functionalized polyimide mixed matrix membranes for gas separation

AbstractThe design and synthesis of porous materials with novel structures and functional groups to prepare mixed matrix membranes (MMMs) is an effective way to break through trade‐off effect of membrane technology. Here, hyper cross‐linked polymers containing amino groups (HCPs‐NH2) with philic‐CO2 frame were successfully prepared for the fabrication of polyimide (PI)/HCPs‐NH2 MMMs. The separation performance of pure gas is studied in order to explore NH2 groups facilitating CO2 diffusion and transmission and enhancing CO2 permeability. Consequently, the permeability of the PI/HCPs‐NH2 MMMs toward CO2 and O2 are 77.56 Barrer and 17.91 Barrer versus pure PI film toward CO2 and O2 (62.42 Barrer and 13.85 Barrer). The selectivity for CO2/CH4 and O2/N2 pairs is 24.44 and 4.01, and the selectivity of pure PI film toward CO2/CH4 and O2/N2 pairs is 20.76 and 3.29, respectively. The permeability and selectivity of PI/HCPs‐NH2 MMMs are higher than pure PI film breaking through the trade‐off effect. Moreover, the PI/HCPs‐NH2 MMMs show better separation performance on the CO2/CH4 pair than the O2/N2 pair, indicating HCPs‐NH2 with philic‐CO2 frame plays a very important role in promoting CO2 permeability. Thus, the PI/HCPs‐NH2 MMMs have potential applications in the field of natural gas purification.

Hierarchical FeCoNiOx-PDA-rGO/WPU layers constructed on the polyimide fabric by screen printing with high microwave absorption performance

The fabrication of flexible microwave absorbers with high-performance has become an arduous challenge for applications of anti-electromagnetic pollution and radar stealth technology. Herein, a series of FeCoNiOx-PDA-rGO absorbers were prepared and coated on the surface of pretreated polyimide (PI) fabric with PDA-rGO, and finally by screen printing FeCoNiOx-PDA-rGO/WPU for acquiring robust microwave absorption performance, in which the first layer of treated PI fabric was used as the microwave-reflection layer, the medium microwave absorbing powder and water-based polyurethane (WPU) hybrid coating served as the microwave-absorbing layer, and the outside hydrophobic polydimethylsiloxane (PDMS) layer was utilized as the microwave-transmission layer. The well-designed microwave absorption fabric exhibits excellent performance in the X-band (8.2–12.4 GHz). The minimum reflection loss (RLmin) value of the designed fabric can reach −74.70 dB with a thickness of 3.97 mm. Meantime, almost in the entire X-band, the sample can absorb more than 99% (RL < -20 dB) of incident electromagnetic waves. Besides, the performance can be adjusted by changing the load rate of each microwave absorbing layer to obtain lighter and thinner samples in practical applications. We believe this work will bring new inspiration to the design of flexible and wearable microwave absorbers.

Parametric Optimization and High Resolution Fabrication of Freeform Gas Diffusion Layers

The gas diffusion layer (GDL) is a multifunctional part of a fuel cell governing reactant and product transport in opposing directions, thermal and electrical conductivity as well as mechanical stability. Its design and production are cumbersome and, for now, obtainable architectures are random networks with uncontrollable transport pathways. According to simulations, an optimized “designer GDL” architecture may lead to immediate benefits in conductivity and permeability by several orders of magnitude.1 This could result in an increase of the achievable current density and a reduction in transport losses. To realize transport optimized architectures, a fabrication method is required that can convert architectures with computer defined properties directly into physical models.2 Here we present our latest results on the fabrication of “designer GDLs” with high-resolution stereolithography of dimensionally stable photopolymers with high aromatic content. These polymers have the potential to be converted to amorphous carbon at predictable dimensional shrinkage retaining their CAD defined geometry. Particularly, we present the high-throughput fabrication of polyimide and SU-8 formulations. We present process parameters, tolerances achievable and show initial results on the carbonization of these formulations as well as absolute dimensions and tolerances obtainable. Our research may lead to a new toolbox for studying and fabricating the next generation of porous membranes for Polymer Electrolyte Membrane Fuel Cells (PEMFCs) and likely a variety of other electrochemical devices requiring effective transport characteristics. D. Niblett, V. Niasar, and S. Holmes, J. Electrochem. Soc., 167, 013520 (2019).J. Torgersen et al., Adv. Funct. Mater., 23, 4542–4554 (2013). Figure 1

Green facile fabrication of polyimide by microwave‐assisted hydrothermal method and its decomposition dynamics

ABSTRACTA microwave‐assisted hydrothermal technique was proposed in this work to fabricate polyimide using ethanol as sole solvent, and the decomposition dynamics of the resulting polyimide was also investigated. The preparation process involved that the ammonium carboxylic ester intermediates could be able to cyclize de‐alchoholation, thus generating imide ring structures. The obtained polyimide exhibited excellent thermal properties. Specifically, the glass transition temperature of the polyimide was around 267.8 °C, and it begun to decompose gradually from about 550 °C. A novel method was employed to choose the dynamics model according to the linear correlation between g(α) and 1/β. As a result, the three‐dimensional diffusion (Jander) model was much more suitable for the thermal decomposition process of the resulting polyimide, and the thermal decomposition mechanism was explained by using the model. The apparent activation energy (E a) values calculated by Flynn–Wall–Ozawa and Kissinger methods were similar showing the same variation tendency. Furthermore, a series of fitting polynomials for E a and pre‐exponential factor (A) values were achieved to reflect the trend more accurately. The dynamics results revealed that the decomposition process was complex and could be regarded as multistep reactions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48484.

High-performance flexible electromagnetic shielding polyimide fabric prepared by nickel-tungsten-phosphorus electroless plating

In this paper, functional polyimide (PI) fabric with high electrically conductive and electromagnetic shielding effect was prepared by nickel-tungsten-phosphorus (Ni-W-P) electroless plating. Firstly, a wave-absorbing and conductive polyaniline (PANI) layer was in-situ polymerized on the surface of fabric. Secondly, the PANI reduced the palladium ions to palladium particles acting as catalytically active sites. Finally, Ni-W-P electroless plating was initiated and formed a uniform and dense layer. The features of Ni-W-P alloy layer on PI fabric were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The thermal stability of the sample was also evaluated by thermogravimetric analysis (TGA). The results showed that the electrical conductivity was 0.08 Ω/sq and the outstanding electromagnetic shielding effectiveness (SE) could reach 103 dB. Moreover, the robust SE performance after multiple ultrasonic washing and bending tests also implied the resultant material had a great potential in the textile protection fields.

Surface characteristics and dyeing properties of polyimide fabric treated with sodium hydroxide

A polyimide fabric was treated with sodium hydroxide to improve its dyeing property. The X‐ray photoelectron spectroscopy analysis showed that carboxyl groups were introduced onto the fibre surface after an alkali treatment. The mean zeta potentials were 7.19 mV for the original sample and –12.1 mv for the treated sample. The surface morphology measured using atomic force microscopy and scanning electron microscopy indicated the presence of a very rough surface structure for the alkali‐treated sample. The alkali‐treated sample showed a higher equilibrium exhaustion than the untreated sample did. The adsorption isotherms of the treated fabric followed the Langmuir sorption model.

Fabrication of polyimide and covalent organic frameworks mixed matrix membranes by in situ polymerization for preliminary exploration of CO2/CH4 separation

More and more polyimide (PI) mixed matrix membranes (MMMs) have been reported for gas separation. In this study, a novel PI MMM, named as PI/SNW-1 and composed of PI and Schiff base network (SNW) type covalent organic frameworks (COFs) SNW-1, was used for gas permeation measurements of carbon dioxide (CO2) and methane (CH4). The prepared PI/SNW-1 was investigated by the Fourier transform infrared spectroscopy, the field emission scanning electron microscopy, and the thermal gravimetric analysis. The results indicated that PI/SNW-1 had maintained a high thermal stability and uniform distribution of filler. Compared with the pure PI membrane, MMMs showed an increment of 48.7% in ideal selectivity of CO2/CH4 and an enhancement of 106.4% in CO2 permeability at 5 wt% SNW-1. The enhancement of permeability and selectivity was mainly attributed to the high porosity of SNW-1, the specific sorption affinity for CO2, and the close interface interaction with the PI matrix. It can be seen that PI/SNW-1 has a great potential for actual gas separation.

Preparation of silver-plated polyimide fabric initiated by polyaniline with electromagnetic shielding properties

A novel and efficient method for the electroless silver plating polyimide fabric was developed with electromagnetic shielding properties. Firstly, polyaniline (PANi) was in situ polymerized with ammonium persulfate used as oxidizing agent. Secondly, Ag+ was in situ reduced to Ag0 by PANi, and the electroless silver plating was initiated by Ag0 used as active center. Fourier transform infrared, scanning electron microscopy, X-ray diffraction, contact angle analysis and energy dispersive spectroscopy were used to characterize the composite fabric. It could be observed that silver layer-coated polyimide fabric was compact and uniform with surface resistance about 0.02 Ω/sq. The thermal stability was evaluated by thermogravimetric analysis. The as-prepared fabric had excellent anti-corrosion, tensile strength and fastness. The shielding effectiveness of this fabric could reach 54–90 dB, which implied it was a good candidate as electromagnetic shielding materials in many fields.

Fabrication of polyimide and functionalized multi-walled carbon nanotubes mixed matrix membranes by in-situ polymerization for CO 2 separation

Abstract Mixed matrix membranes (MMMs) consisting of acid-treated functionalized multi-walled carbon nanotubes (MWCNTs) incorporated into polyimide (PI) polymer were fabricated for gas separation. The functional groups and dispersion properties of the MWCNTs were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed that the functionalized MWCNTs were cut into short ropes and acid oxidation introduced oxygen containing functional groups such as hydroxyl (OH) and carboxylic acid (COOH) on the surface of MWCNTs. Based on the assumption of strong interfacial interactions between the functionalized MWCNTs and PI matrix, the MWCNTs were first incorporated into poly(amic acid) (PAA) to form a highly dispersed solution, then the PI/MWCNTs nanocomposites were formed after in-situ chemical imidization. Scanning electron microscopy (SEM) indicated that the functionalized MWCNTs were dispersed homogenously in the PI matrix. The gas separation performance showed that the CO2 permeability coefficient increased 292% at 3 wt.% MWCNTs incorporated into the MMMs, and there was a 145% increase in the selectivity of CO2/N2 and a 144% increase in the selectivity of CO2/CH4. This result demonstrates that the carboxylic and hydroxyl groups have a strong interaction with CO2, which increases the solubility coefficient of the polar gases. The in-situ polymerization approach of fabricated MMMs improves the interfacial interaction between the dispersed nanomaterials and the polymer matrix, which can be utilized in the practical gas separation technology.

Fabrication of polyimide based microfluidic channels for biosensor devices

The ever-increasing complexity of the fabrication process of Point-of-care (POC) devices, due to high demand of functional versatility, compact size and ease-of-use, emphasizes the need of multifunctional materials that can be used to simplify this process. Polymers, currently in use for the fabrication of the often needed microfluidic channels, have limitations in terms of their physicochemical properties. Therefore, the use of a multipurpose biocompatible material with better resistance to the chemical, thermal and electrical environment, along with capability of forming closed channel microfluidics is inevitable. This paper demonstrates a novel technique of fabricating microfluidic devices using polyimide (PI) which fulfills the aforementioned properties criteria. A fabrication process to pattern microfluidic channels, using partially cured PI, has been developed by using a dry etching method. The etching parameters are optimized and compared to those used for fully cured PI. Moreover, the formation of closed microfluidic channel on wafer level by bonding two partially cured PI layers or a partially cured PI to glass with high bond strength has been demonstrated. The reproducibility in uniformity of PI is also compared to the most commonly used SU8 polymer, which is a near UV sensitive epoxy resin. The potential applications of PI processing are POC and biosensor devices integrated with microelectronics.

A flexible, sandwiched high-performance super-insulation fabric

A flexible, sandwiched high-performance super-insulation polyimide fabric has been designed and fabricated. The sandwiched fabric possesses ultra-low thermal conductivity (16.7 mW m−1 K−1), excellent mechanical properties and a wide operating temperature range. The sandwiched fabric will have potential applications under some harsh conditions.

Influence of pulse tapping technology on surface roughness of polyimide capsule

As one of the most important ignition capsules, the polyimide capsule was prepared by depolymerizable mandrels technique combined with vapor deposition polymerization method. Instead of the plane pan and piezoelectric vibration model, the mesh pan and pulse tapping was selected to reduce microsphere collision so that surface quality was improved in polyimide fabrication. Experimentsal and theoretical results show that the capsule surface becomes more rough because of collisions between microspheres and the pan. The mesh pan could reduce microsphere collisions, which was also reduced by changing piezoelectric vibration into pulse tapping. As a result, root-mean-square value ranges from 5293 nm to 2844 nm. There are many advantages with pulse tapping model, such as better controllability,lower bounce rate and less static; however piezoelectric vibration model is slightly better than the pulse taping in wall thickness uniformity. Measurements of single microsphere show that the deviation of the former is 0.68 which is better than that of the latter (0.73 m). For the average value of microspheres in the same batch, the former has a value 0.26 which also is better than the latter (0.57 m).

Fabrication of polyimide micro/nano-structures based on contact-transfer and mask-embedded lithography

Polyimide materials are well known for their excellent mechanical and chemical stability which, as an adverse consequence, makes their fabrication processes much more difficult, especially in micro- and nano-scales. In this paper, we demonstrate an innovative and powerful method for fabricating micro/nano-structures on polyimides. The proposed method first adopts an imprinting approach to transfer a patterned metal film from a mold to a polymer layer coated on a polyimide layer. The patterned double polymer layers are then dry etched using the transferred metal pattern as an etching mask. Finally, polyimide structures are obtained by lifting off the top polymer layer and the metal film through wet etching. Experiments have been carried out and important parameters to achieve high pattern-transformation fidelity are determined. Fine structures of polyimides with a feature size of 500 nm and a total patterned area of 8 × 8 mm2 are demonstrated. Advantages of the proposed method include low-temperature, low contact pressure, small feature size, high throughput and ease of in implementation. Most importantly, it is applicable for a large number of tough polymers which are difficult to deal with by other methods in terms of micro/nano-fabrication.

Fabrication of Porous Nanoscale Polyimide Structures

Abstract In the fabrication of polyimide (PI) spherical nanoparticles by the reprecipitation method, intriguing uniquely shaped objects, including doughnut-like and/or hollow, and polymeric soccer ball-shaped PI nanoparticles are rarely obtained. Furthermore, PI fine particles, which possess a hollow core and some 100 nm-sized surface pores leading to the inner hollow, were reproducibly obtained by the improved reprecipitation method.

Humidity-dependent mechanical properties of polyimide films and their use for IC-compatible humidity sensors

Thin polyimide layers have been investigated to determine their volume expansion as a result of humidity absorption and desorption, respectively. Furthermore, we have used the experiments in order to clarify the physical and chemical processes of polyimide films in a wet environment as well as their humido-mechanical properties. It can be shown that the humidity-induced material extension is fairly linear in a wide range of humidity. The observed material behaviour strongly depends on the conditions of the polyimide fabrication process. Analogous to the well-known temperature extension coefficient, a humidity extension value of about 60 to 80 ppm/%RH is observed. This physical effect can be used to create piezoresistive humidity sensors working similarly to bimetal elements influenced by temperature.