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Polyimide (PI) films with extremely high heat‐resisting and dimensional stability are ideal substrate materials for flexible organic light‐emitting diodes. In this study, three diamines containing rigid bisbenzoxazole structures, 2,2′‐p‐phenylenebis(5‐aminobenzoxazole) (phDBOA), 2,2′‐m‐pyridylenebis(5‐aminobenzoxazole), and 2,2′‐p‐pyridylenebis(5‐aminobenzoxazole) (p‐PDBOA), were polymerized with 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride and pyromellitic dianhydride (PMDA) separately with traditional two‐step approach to prepare a set of PI films. Introduction of bisbenzoxazole improves stiffness of molecular chain, whereas that of pyridine increases in‐plane orientation and molecular chain tend to be densely stacked. Among prepared films, PI‐6 (PMDA/p‐PDBOA) shows the most excellent mechanical properties, with an ultra‐high glass transition temperature of >450°C, an ultra‐low thermal expansion coefficient of <5 ppm K−1 (50–450°C), a tensile strength of 259 MPa, and a modulus of 8.3 GPa. Given these excellent properties, PI‐6 could be applied in flexible display. [ABSTRACT FROM AUTHOR]

Herein, a kind of carbon/carbon composite electrode is prepared using polyimide (PI)/3D sphere‐like polyimide composite films as precursors, followed by carbonization. 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane and 4,4'‐(hexafluoroisopropylidene)diphthalic anhydride are polymerized and thermally imidized to form the matrix, and 3D sphere‐like PI particles synthesized by the solvothermal process are introduced via the in situ polymerization method. The electrochemical behaviors of C/C composites are examined in relation to the loading of the 3D sphere‐like PI crystals and carbonization temperatures. The C/C composite PI/5%3D‐PI‐800 demonstrates a specific capacitance maximum of 322.7 F g−1 at 0.5 A g−1 due to synergistic effects between different types of PIs. The specific capacitance decreases to 214 F g−1 with a retention rate of 66.3% as the current density increases to 10 A g−1. Moreover, the symmetrical supercapacitor (SC) assembled by PI/5%3D‐PI‐800 shows a specific capacitance of 244.4 F g−1 at 0.5 A g−1, with a high energy density of 33.94 Wh kg−1 and a power density of 500 W kg−1. In addition, after 6 months of storage, the button SC is retested and still shows fantastic capacitance retention rate of above 99.5%. Thus, this work proposes a facile method to fabricate the C/C composite electrodes with outstanding electrochemical properties. [ABSTRACT FROM AUTHOR]

To explore the feasibility of the flexible Sb2S3−ySey thin‐film solar cell fabrication using polyimide thin films as substrates, CdS thin films are prepared on SnO2:F conducting glass (FTO) substrates by decreasing the ammonia concentration of chemical bath deposition, and Sb2S3−ySey thin films are grown on the FTO/CdS substrate by changing the selenourea concentration of hydrothermal process. The influence of the ammonia and selenourea concentration on properties of CdS and Sb2S3−ySey is systematically investigated and solar cells with the architecture of FTO/CdS/Sb2S3−ySey/spiro‐OMeTAD/Au are fabricated. For CdS thin films on FTO substrate, the thickness decreases and roughness increases with the decrease of ammonia concentration in chemical bath deposition. The compact and full‐coverage CdS thin films with thickness of 50 ± 6 nm are successfully obtained using the low ammonia concentration (0.59 m). For Sb2S3−ySey thin films on FTO/CdS substrate, the Se:S:Sb atomic ratio and thickness increases with the increase of selenourea concentration in hydrothermal process. The optimal selenourea concentration is 6 mM. The solar cells with the 50 ± 6 nm thick CdS thin film and Sb2S2.10Se0.56 thin film achieve photoelectric conversion efficiency of 8.07%. The results can provide an efficient support for further applying polyimide thin films to fabricate flexible Sb2S3−ySey thin film solar cells. [ABSTRACT FROM AUTHOR]

The ever increasing demand for high‐speed communication at high frequency promotes the rapid development of low‐dielectric polymer films. Aromatic polyimide (PI) has been widely used as the main dielectrics in the flexible circuit board due to its excellent dielectric, mechanical, and thermal properties. Nevertheless, the dielectric constant of PI films at a high frequency range (several GHz) is relatively high and cannot satisfy the requirement of high‐frequency communication. On this basis, a hyper‐crosslinked polymer (HCP) and fabricated all‐organic HCP/PI composite films through a physical blending method is synthesized. The porous structure of HCP is helpful to reduce the dielectric constant of PI matrix. The effects of HCP loadings on the dielectric, mechanical, and thermal properties of HCP/PI composite films are systematically investigated. The dielectric constants of the composite films can be reduced to 1.6–1.8 in the frequency range of 8.2–9.6 GHz when the HCP content reached 10 wt.%. The proposed method in this work is simple and effective to reduce the dielectric constant of PI and can be easily extended to other organic component‐filled PI systems. [ABSTRACT FROM AUTHOR]

With the acceleration of industrialization, the removal of refractory organic dyes from water and how to promote its practical application remains a challenge. Herein, we synthesized an FeCo-LDH/LI-NDG composite electrode material by a simple laser-induced technique on polyimide films, which could electrocatalytically activate peroxymonosulfate (PMS) to completely degrade MB in about 6 min. The reaction rate constant (kobs) was 0.461 min−1. It was faster than most of the currently reported electrocatalysts. The reaction system demonstrated good interference resistance and catalytic effectiveness in the pH range of 3 to 9. According to the chemical quenching and electron paramagnetic resonance (EPR) experiments, the non-radical pathway of 1O2 and the radical pathways of SO4·−, ·OH and O2·− were involved in the reaction synergistically, with 1O2 playing the dominant role. 1O2 was produced through the dual pathway of PMS electron loss at the anode and O2·− intermediate transformation at the cathode. The two activation methods of electro-activation and catalytic activation of PMS had synergistic effects to achieve high efficiency in the whole process of production, reaction and recovery, providing new ideas to advance practical applications. [ABSTRACT FROM AUTHOR]

A microwave atmospheric pressure plasma jet (MW‐APPJ) generator based on a substrate‐integrated waveguide (SIW) resonator is proposed. A thin, straight plasma needle with a length of 9 cm could be obtained. Higher than 90% of microwave feeding efficiency is obtained under a wide range of gas flow rates without a microwave matching network. As the gas flow increased from 1 to 14 L/min, a transition from laminar to turbulent mode is observed in the plasma jet's morphology. Furthermore, a preliminary surface treatment was tested for the device. The polyimide film became super hydrophilic after a 5‐min treatment with the developed SIW‐based plasma generator. Generally, the SIW‐based MW‐APPJ is low‐cost, electrodeless, and low‐profile along the plasma jet length direction. [ABSTRACT FROM AUTHOR]

This study describes a novel colorless polyimide window film using the concept of charge‐transfer complex (CTC) intensification. The resulting film has a tensile modulus of 8.4 GPa, total transmittance of ≈90%, and yellow index below 3. This is the best‐recorded balance between mechanical strength and optical properties for a highly flexible optical film. Additionally, the film exhibits a pencil hardness grade over 2H and folding reliability over 200,000 folding/unfolding cycles. These outstanding properties are attributed to the unique supramolecular structure, which features multiple hydrogen bonding and salt complexation interactions that lead to CTC intensification. [ABSTRACT FROM AUTHOR]

This paper proposes a tunable antenna based on graphene for future wireless communication technology. The proposed antenna that is made by graphene/polyimide film able to tune the frequency using thermal that is exposed on it. The approach is investigated since it able to work as the other reconfiguration technique but cannot be adjustable likes diodes and liquid crystal. The antenna is fabricated into fifteen similar pieces and are separately cured at different temperature and exposure time; 250 °C, 300 °C, and 350 °C, for 20 minutes, 30 minutes, 1 hour, 2 hours, and 3 hours. The fabricated antennas are measured its S‐parameter as well as the characterisation of relative complex permittivity, sheet resistance, conductivity, surface morphology, and structure analysis. The measured results indicate that the frequency is tuned to lower within 4.1 GHz at 250 °C, 5.5 GHz at 300 °C, and 400 MHz at 350 °C. Looking into the future, even though this work is not using the same antenna, but it will lead to the proof of concept for tunable graphene antenna using thermal at fifth generation (5G) and next generation. [ABSTRACT FROM AUTHOR]

In this paper, we report on novel polyimide (PI) nanocomposites filled with binary mixtures of metal oxide (either TiO2 or ZrO2) nanoparticles and nanocarbon (either carbon nanofibers (CNFs) or functionalized carbon nanotubes (CNTfs)). The structure and morphology of the materials obtained were comprehensively studied. An exhaustive investigation of their thermal and mechanical properties was performed. We revealed a synergistic effect of the nanoconstituents with regard to a number of functional characteristics of the PIs compared with single-filler nanocomposites, including thermal stability, stiffness (below and above glass transition temperature), yield point, and temperature of flowing. Moreover, the possibility of manipulating the properties of the materials by choosing a proper combination of the nanofillers was demonstrated. The results obtained can become a platform in the design of PI-based engineering materials with tailored characteristics capable of operating in extreme conditions. [ABSTRACT FROM AUTHOR]

Despite its long history, synthesizing n-type polycrystalline Ge layers with high-electron mobility on insulating substrates has been difficult. Based on our recently developed solid-phase crystallization technology, here, we have demonstrated the highest recorded electron mobility (450 cm2 V−1 s−1) for Ge-based polycrystalline thin films on insulating substrates. The underlayer type and small amount of Sn addition were the key parameters controlling both the density and barrier height of the grain boundaries in the P-doped polycrystalline Ge layers. The low growth temperature (≤400 °C) allowed us to develop a GeSn layer on a heat-resistant polyimide film, which exhibited the highest electron mobility (200 cm2 V−1 s−1), as a semiconductor thin film synthesized directly on a flexible substrate. These achievements herald the development of high-performance polycrystalline Ge-based devices on inexpensive glass and flexible plastic substrates. [ABSTRACT FROM AUTHOR]

Firstly, the BaTiO3 nanoparticles were coated with a layer of paraffin, forming a core shell structure. Then, as‐prepared paraffin@BaTiO3 nanofillers were directly blended with polyimide (PI) prepolymer to fabricate paraffin@BaTiO3/PI composite films. The microstructure, thermal, and dielectric properties were investigated in detail. The surface‐modified paraffin@BaTiO3 nanoparticles exhibited a typical core shell structure with uniform and complete coverage. The char yield of the composite film with 10 wt% paraffin@BaTiO3 increased from 56.40% to 70.73%. It is obvious that the paraffin@BaTiO3 nanofillers have a positive effect on ablative performance of the composite film. Compared with pure PI, the εr of paraffin@BaTiO3/PI composites with 40% mass fraction increased from 3.41 to 9.35 (1 kHz). The tanδ of paraffin@BaTiO3/PI composites was just 0.0065 (1 kHz) when the filler loading was 40 wt%. Temperature dependency of the permittivity of the composites reveals a zero‐temperature‐coefficient from 80°C to 180°C. [ABSTRACT FROM AUTHOR]

In this study, thermal and argon (Ar) plasma/wetting treatments were combined to enhance the bonding strength of polyimide (PI) films. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to analyze the changes in the PI imidization degrees. The contact angles of the PI films were also measured. The results show that the contact angles of the fully cured PI films markedly decreased from 78.54° to 26.05° after the Ar plasma treatments. X-ray photoelectron spectroscopy (XPS) analysis was also conducted on the PI surfaces. We found that the intensities of the C-OH and C-N-H bonds increased from 0% to 13% and 29% to 57%, respectively, after Ar plasma activation. Such increases in the C-OH and C-N-H intensities could be attributed to the generation of dangling bonds and the breakage of the imide ring or polymer long chains. Shear tests were also conducted to characterize the bonding strength of the PI films, which, after being treated with the appropriate parameters of temperature, plasma power, and wetting droplets, was found to be excellent at greater than 35.3 MPa. [ABSTRACT FROM AUTHOR]

New polymeric materials formation by controlling their properties is the primary and most challenging problem in developing a methodology for synthesizing a chosen technology and its use. The combined effect of high-energy electron radiation and tensile stress will cause a decrease in crystallinity and the breakage of chemical bonds in polyimide film macromolecules and is a new approach in their production technology. The effect of uniaxial tension and electron irradiation on the modification of polyimide film at room temperature was studied. Irradiation of the films caused an increase in the intensity of the IR spectrum by ~2–6 times and an increase in the width of the bands. The intensity in the range of 1700–3500 cm−1 increased, indicating an increase in the content of radicals as a result of irradiation. The amplitudes of the electron paramagnetic resonance signal from non-irradiated films increased from 3 × 103 to 5 × 103 as a result of uniaxial tension to fracture, indicating an increase in radicals in the material. The lines of the electron paramagnetic resonance spectrum shifted from 3475.0 cm−1 to 3512.5 cm−1, with a simultaneous decrease in the signal's amplitude from 6 ×103 to 4 × 103, as a result of the electron irradiation of the films, followed by their subjection to tension. This was due to a decrease in the concentration of the radicals of the =N-H and –N-H2 groups until their disappearance and the formation of new ones. [ABSTRACT FROM AUTHOR]

High-quality and free-standing polyimide (PI) film with desirable mechanical properties and uniformity is in high demand due to its widespread applications in highly precise flexible and chip-integrated sensors. In this study, a free-standing PI film with high toughness was successfully prepared using a diamine monomer with ether linkages. The prepared PI films exhibited significantly superior mechanical properties compared to PI films of the same molecular structure, which can be attributed to the systematic exploration of the film-forming process. The exploration of the film-forming process includes the curing procedures, film-forming substrates, and annealing treatments. Additionally, the thickness uniformity and surface homogeneity of free-standing films were crucial for toughness. Increasing the crystallinity of the PI films by eliminating residual stress also contributed to their high strength. The results demonstrate that by adjusting the above-mentioned factors, the prepared PI films possess excellent mechanical properties, with tensile strength and elongation at break of 194.71 MPa and 130.13%, respectively. [ABSTRACT FROM AUTHOR]

In the present study, amine groups were first modified to diamond and silver nanoparticles using APTMS to improve their homogeneous dispersion and compatibility in polyamic acid. Flexible polyimide nanocomposite films were successfully prepared by adding modified nanodiamond and silver nanoparticles to 4,4′-(1,3-phenylenedioxy) dianiline and benzophenone-3,3′,4,4′-tetracarboxylic dianhydrides with different proportions. The effects of added amine-modified nanoparticles on dielectric constant and thermal stability were investigated. With SEM analysis, nanoparticles were homogeneously distributed on the polyimide surface and the presence of Si atom resulting from APTMS modification is clearly seen with the SEM-EDAX results. Considering the thermal resistance, the maximum decomposition temperature of the nano particle-free PI film was found to be 501 °C, while the thermal decomposition temperatures of the PI nanocomposite film that contains 1% m-Ag and the PI film that contains 5% m-ND, 502 °C and 505 °C, respectively. Also, it was seen that the dielectric constants of the prepared nanocomposite films that contain m-Ag NP decrease with increasing m-Ag NP ratio, and the dielectric constants of the films that contain m-ND increase with increasing m-ND ratio. [ABSTRACT FROM AUTHOR]

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.)

In this study, a lightweight composite polyimide film optic with antireflective coating was prepared using an ion-beam-assisted reactive sputtering method. It exhibited high transmittance in visible (87%, 0.5~0.8 μm), short (86%, 1.8~2.7 μm) and middle (78%, 3.3~5.4 μm) wavelength infrared regions. Additionally, it also showed great optical homogeneity (0.006 λ in RMS and 0.034 λ in PV, λ = 632.8 nm) with smooth surfaces (RMS = 0.786 nm). The thermal stability of the polyimide film was also effectively maintained after the antireflective coating. At the same time, by utilizing the hydrophobic properties of coating materials (Ta2O5/SiO2), the antireflective layer acted as an effective water barrier on the film surface to reduce the water absorption. [ABSTRACT FROM AUTHOR]

Boron nitride nanosheet (BNNS) is widely used in electronic thermal management due to its excellent planar thermal conductivity and insulating properties. However, it is challenging to improve the out-of-plane thermal conductivity of BNNS-doped composites due to the anisotropy of the thermal conductivity of BNNS. Therefore, the BNNS in the matrix must be oriented to obtain composites with high out-of-plane thermal conductivity. In this study, BNNS powders with directional structures were synthesized directly using sodium chloride templates. The as-obtained BNNS powders have a unique hollow cube-like structure with an ultra-low density of 2.67 × 10−2 g/cm3 and nearly 8 times the volume of the same mass of two-dimensional (2D) BNNS, making it easy to form the out-of-plane thermal conductivity paths in the polymer matrix. In addition, the high out-of-plane thermal conductivity of 4.93 W m−1 K−1 at 23.3 wt% loadings was obtained by doping it into a polyimide (PI) matrix. This value is 9.7 times higher than that of 2D BNNS-doped PI at the same loadings, 17.6 times higher than pure PI, and 6.1 times higher than the thermally conductive PI film sold by DuPont. Therefore, the prepared composite film has great potential for application in electronic thermal management. [ABSTRACT FROM AUTHOR]

Fabrication of a through hole in a polyimide film (PI) was demonstrated by holographic ultraviolet (UV) nanosecond laser processing with a computer-generated hologram displayed on a phase-only spatial light modulator (SLM). The UV laser was directly modulated into a Bessel beam by a diffractive axicon displayed on the SLM. The direct modulation contributed to improved light-utilization efficiency of the UV laser and a simplified optical setup compared to the conventional method based on a combination of an SLM and harmonic generation using a nonlinear optical crystal. The Bessel beam reduced the number of pulse shots required for through-hole fabrication to 1/5 compared to the Gaussian beam near the ablation threshold energy of the PI film. Furthermore, adaptive optics was implemented in holographic laser processing to compensate for aberrations in the optical setup. The aberration was reduced to 1/5 compared with before the compensation. The proposed method is suitable for improving the throughput and accuracy of drilling, cutting, and additive manufacturing using UV lasers with industrial requirements. [ABSTRACT FROM AUTHOR]

In the rapidly growing area of high-frequency communications, polyimide films with ultralow dielectric constant and dielectric loss, adequate insulating strength, and recyclability are in high demand. Using a synthesized soluble fluorinated polyimide, a series of recyclable porous dielectric films with varying porosities were fabricated in this study through nonsolvent-induced phase separation. By manipulating the mass ratio of the binary solvent used to dissolve the polyimide, the shape, size, and size distribution of the pores generated throughout the polyimide matrix can be accurately regulated. The porosity and average pore size of the as-prepared porous films were adjustable between 71% and 33% and between 9.31 and 1.00 μm, respectively, which resulted in a variable dielectric constant of 1.51–2.42 (100 kHz) and electrical breakdown strength of 30.3–119.7 kV/mm. The porous sPI film with a porosity rate of 48% displayed a low dielectric constant of 2.48 at 10 GHz. Coupled with their superior thermal stability, mechanical characteristics, and recyclability, these porous polyimide films are highly promising for constructing high-frequency microelectronic devices. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films are wildly used in the field of electrical equipment and electronic devices due to their excellent thermal, electrical, and mechanical properties. The various mechanisms of sample thickness on the electrical breakdown of polyimide have been proposed. The purpose of this study is to apply the state of macromolecular aggregation to analyze the breakdown strength of PI film with different thickness. In this paper, the direct current (dc) electrical breakdown properties of PI films as a function of thickness were investigated employing water absorption, mechanical properties, thermal properties, and thermally stimulated depolarization current (TSDC). These experimental results exhibit a good coincidence with the breakdown measurement. On the condition of the structure of the polymeric molecules to the same case, the congregating state of the polymer might be the fundamental reason causing the dc electrical breakdown field of PI film with different thickness. [ABSTRACT FROM AUTHOR]

The hydrolytic stability of polyimide films (PI) in a 0.9% sodium chloride solution in the temperature range of existing biological objects was studied. The kinetic parameters of hydrolysis of PI films were calculated. It was established that the hydrolysis rate constant of an adamantane-containing film was significantly lower than that of an industrial Kapton film. The dielectric constant after hydrolysis was determined. It was shown that the dielectric properties of the adamantane-containing polymer remained unchanged under the hydrolysis conditions. [ABSTRACT FROM AUTHOR]

Polyimides are widely used in the MEMS and flexible electronics fields due to their combined physicochemical properties, including high thermal stability, mechanical strength, and chemical resistance values. In the past decade, rapid progress has been made in the microfabrication of polyimides. However, enabling technologies, such as laser-induced graphene on polyimide, photosensitive polyimide micropatterning, and 3D polyimide microstructure assembly, have not been reviewed from the perspective of polyimide microfabrication. The aims of this review are to systematically discuss polyimide microfabrication techniques, which cover film formation, material conversion, micropatterning, 3D microfabrication, and their applications. With an emphasis on polyimide-based flexible MEMS devices, we discuss the remaining technological challenges in polyimide fabrication and possible technological innovations in this field. [ABSTRACT FROM AUTHOR]

As a common two-dimensional carbon material, graphene has been widely doped into polymers to prepare high-performance dielectric materials. However, the shortcomings of graphene, such as large specific surface area and poor dispersion, limit its further application. Therefore, in this work, to solve the problem regarding the uniform dispersion of graphene in the matrix, in situ polymerization was used to prepare graphene/polyimide films, in which 1,4-diiodobutane was used as a reduction agent to prevent the aggregation of graphene oxide (GO) during imidization. High dielectric constant composite films were obtained by adjusting the ratio of 1,4-diiodobutane in GO. The results show that the resulting graphene/polyimide composite film possessed a dielectric constant of up to 197.5, which was more than 58 times higher than that of the polyimide (PI) film. Furthermore, compared to the pure PI film, the composite films showed better thermal stability and mechanical properties. Thermal performance tests showed that the 1,4-diiodobutane added during the preparation of the composite film was thermally decomposed, and there was no residue. We believe our preparation method can be extended to other high dielectric composite films, which will facilitate their further development and application in high power density energy storage materials. [ABSTRACT FROM AUTHOR]

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N′-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4′-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4′-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV–Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials. [ABSTRACT FROM AUTHOR]

Copyright of Plastics Science & Technology / Suliao Ke-Ji is the property of Plastics Science & Technology 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.)

Spin valves containing a Dy layer have been formed on an elastic polyimide film by magnetron sputtering. The field dependences of the magnetoresistance of samples subjected to different tensile deformations have been measured. The character of the variations of the magnetoresistive properties of a spin valve subjected to tensile deformation is shown to depend on the thickness of the dysprosium layer. In particular, the thickness of the dysprosium layer affects the maximum relative elongation at which the magnetoresistance of spin valves remains unchanged. [ABSTRACT FROM AUTHOR]

The fatigue properties of metallizations used as electrical conductors in flexible electronic devices have been thoroughly studied over the years. Most studies use time-intensive characterization methods to evaluate mechanical damage. For their ease of access, in situ electrical resistance measurements are often performed along with other characterization methods. However, the data are mostly used as an indicator of failure and a thorough analysis is usually missing. This work presents some deeper analysis methods of such datasets, using gold films on polyimide, with and without a chromium interlayer, revealing that grain growth, through-thickness cracking, and more general fatigue behavior can be determined from electrical resistance data alone. A case is made for increased utilization of such easily obtained data, reducing the time required for the evaluation of experiments. [ABSTRACT FROM AUTHOR]

This paper focuses on the study of internal charging of four space used polymers: polyetheretherketone, fluorinated ethylene propylene, polyimide films, and epoxy based material (Epoxy FR4). Experiments were carried out for each material using the GEODUR facility (Toulouse, ONERA) that mimics the geostationary space environment behind shielding. Two different irradiation currents have been applied: 1 pA/cm2 and 10 pA/cm2. 1 pA/cm2 is used to analyze the charging behavior and the intrinsic electrical properties of each polymer. 10 pA/cm2 is used to study the influence of high electric field levels on their charging behavior. In this paper, two different numerical tools used for the study of internal charging are presented: Monte-Carlo Internal Charging Tool (MCICT) and Transport of Holes and Electrons Model under Irradiation in Space (THEMIS). MCICT has been used in the space community for several years. THEMIS has been recently developed at ONERA and is compared to MCICT. Both numerical tools showed consistent results for the 1 pA/cm2 integrated current but with deviations for the 10 pA/cm2 integrated current, supposedly due to nonlinear electric field effects on charge transport. THEMIS has a more refined physical model for the conductivity than MCICT. It studies more accurately the electron-polymer interactions and the charge transport kinetics of polymers under space radiations. Subsequently, the analysis of the underlying physical phenomena responsible for the polymers' charging behaviors will be carried out with THEMIS. In addition, studying these phenomena will permit to assess the risks of electrical discharges that may occur on a spacecraft in orbit (e.g., Geostationary (GEO) spacecraft) or during an elliptic trajectory (e.g., sub-GEO) in an Electric Orbit Raising case [E. Y. Choueiri, A. J. Kelly, and R. G. Jahn, J. Spacecr. Rockets 30(6), 749–754 (1993)]. [ABSTRACT FROM AUTHOR]

The effect of the thickness of the amorphous polymerized films of poly-4,4'-diphenylene oxide pyromellitimide on the structure after deformation by stretching at 293 K and 77 K was studied. The evolution of the macromolecular structure was concluded based on the results of the redistribution of the intensity diffraction peaks. It was established that the structure of films with a thickness of 75 μm is homogeneous and does not cardinal changes after deformation. Deformation of polymer films with a thickness of 125 μm leads to the appearance of regions with long-range order in the sample. [ABSTRACT FROM AUTHOR]

Strain is inevitable in two-dimensional (2D) materials, regardless of whether the film is suspended or supported. However, the direct measurement of strain response at the atomic scale is challenging due to the difficulties of maintaining both flexibility and mechanical stability at low temperature under UHV conditions. In this work, we have implemented a compact nanoindentation system with a size of ∼ 160 mm 2 × 5.2 mm in a scanning tunneling microscope (STM) sample holder, which enables the reversible control of strain and gate electric field. A combination of gearbox and piezoelectric actuator allowed us to modulate the depth of the indentation continuously with nanometer precision. The 2D materials were transferred onto the polyimide film. Pd clamp was used to enhance the strain transfer from the polyimide from to the 2D layers. Using this unique technique, strain response of graphene lattice were observed at atomic precision. In the relaxed graphene, strain is induced mainly by local curvature. However, in the strained graphene with tented structure, the lattice parameters become more sensitive to the indentor height change and stretching strain is increased additionally. Moreover, the gate controllability is confirmed by measuring the dependence of the STM tip height on gate voltage. [ABSTRACT FROM AUTHOR]

Polyimide (PI) composite films with hybrid fillers containing hBN (hexagonal boron nitride) sheets and rGO (reduced graphene oxide) were successfully fabricated by in‐situ polymerization. Herein, hBN sheets and rGO were obtained by ball milling and chemical reduction, respectively. In PI composite films, hBN can be tightly attached onto the surface of rGO via π‐π interaction, which can benefit the construction of heat‐conduction pathways and reduce boundary of heat resistance. The results show that the addition of rGO and hBN could enhance the thermal conductivity by synergistic effects. Specially, hBN and rGO are at the weight ratio of 1:1 and at the total loading of 33 wt%, thermal conductivity of PI composites can reach up to 1.19 Wm−1 K−1, which is 5.61 times higher than that of pure PI. Thermal property and dynamic mechanical property of composite films were also investigated. Besides, compared with pure PI, mixed fillers have obvious surface‐enhanced Raman scattering signals, indicating the synergistic effect of the mixed fillers. Overall, this study gives insights into heat dissipative and high sensitivity analysis components which may be used in the field of high‐temperature micro fabrication. [ABSTRACT FROM AUTHOR]

Simultaneous improvement in dielectric, water resistance and mechanical properties of polyimide (PI) films is critical for their practical use, but difficult to achieve. Herein, a sandwich‐type porous GO/PI film with excellent comprehensive properties was obtained through integrating a GO‐containing complex, fluorine‐containing porous structure and sandwich‐type distribution of porous structure by a simple, low‐cost and green breath figure method. With the addition of only a small amount of GO‐containing complex, a low dielectric constant of 2.21, water absorption of 0.51%, increment in dielectric constant after moisture treatment of 1.60% and high tensile strength of 113.1 MPa, tensile modulus of 1.70 GPa, with 35.39%, 79.42%, 81.81% of reduction and 17.22%, 21.43% of increase compared to PI film were shown, respectively. Moreover, these properties could be adjusted through regulating the component and porous structure by changing the parameters of breath figure method. These outstanding properties make the film a promising candidate for high‐performance low‐dielectric materials. [ABSTRACT FROM AUTHOR]

Ordered porous polyimide films were fabricated from (AB)m type of diblock copolymer polyimide-b-polystyrene (PI-b-PS). An increase in PS volume fraction (f VPS) is beneficial to decrease the relative dielectric constants and water contact angles of the obtained porous PI films: the relative dielectric constant decreases to 1.89 and water contact angle decreases to 43° when f VPS is 0.36, indicating porous PI films can be used as low-κ material and have good wettability. The solvent uptake of the porous PI films increases with increasing f VPS. A net-like morphology appears when f VPS reaches 0.36. The net-like porous PI film reaches equilibrium uptake of water within approximately 2.5 h, with a final equilibrium uptake ratio of 17.5%, and reaches equilibrium uptake of toluene within approximately 8 h, with a final equilibrium uptake ratio of 15.4%, displaying the highest and fastest solvent uptake compared with other microstructured porous PI films, which is ascribed to the specific characteristic of the interconnecting porous channels derived from the self-assembly of PI-b-PS with f VPS 0.36. Introducing thermally degradable segments to PI-based block copolymer is an effective method to prepare porous PI films and can enhance some of their properties. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA) thin films have received great importance in the research of smart (or intelligent) materials for their utilization in micro-electromechanical systems (MEMS). It is suggested that the fabrication of SMA thin films on flexible polyimide (PI) substrates paves the way for their utility as micro-actuators and sensors in many microdevices. In this review article, the development of SMA/polyimide thin-film composites using various physical vapor deposition techniques is discussed. The actuation characteristics, the influence of actuation controlling parameters, and the life cycle behavior of these composites are also concisely discussed. Furthermore, the viability of SMA/polyimide composites in various applications is also scrutinized for their shape memory properties and performance. These composites set out to be considered in soft robotic technology, an emerging domain in the field of robotics. The successful implementation of these composite actuators in bio-inspired aquatic and aerial soft robotic systems requires the generation of high actuation force and frequency to carry the payload. In the present article, the prospect of the development of SMA/polyimide sandwich-structured composite is discussed which would possibly facilitate its deployment in soft robotic applications. [ABSTRACT FROM AUTHOR]

The breakdown of the dry-type reactor induced by being exposed to moisture needs to be further explored. For this purpose, as the common insulating films in the dry-type reactor, PET and PI films were targeted to investigate the effects of atmospheric hydrothermal aging on the microstructure, thermal stability, and mechanical properties of the films. As the result of hydrothermal aging, the moisture-based thermal degradation obviously occurred on the surface of both PET and PI films, even at a low temperature. More defects and flaws can be observed on the surface of PET than that of PI film, which were responsible for decreasing the transmittance and tensile strength of films. According to the statistical analysis with a one-sample t test, the thermal stability of aged PET and PI films has no significant difference with raw films during the hydrothermal aging. Compared with thermal stress, the hydrolysis of ester linkage and the imide ring are the main factors of hydrothermal aging for PET and PI films, respectively. Improving the waterproof ability of PET and PI films can be effective to prevent deterioration of the interturn insulation performance of the dry-type reactor. [ABSTRACT FROM AUTHOR]

The development of novel polymer dielectrics with enhanced dielectric performance is a great challenge for application of film capacitors in modern electronics and electrical systems. Herein, an innovative approach of chemical vapor deposition polymerization technology is proposed to prepare the all‐organic sandwich structured parylene/polyimide/parylene (Py/PI/Py) composite films by employing poly(chloro‐para‐xylylene) (parylene C) as the outer layers and polyimide (PI) as the inner layer. The Py/PI/Py composites exhibit superior thermal resistance and outstanding mechanical properties. Moreover, thanks to the interfacial effect which contributes to reinforcing the dielectric response and the thickness effect which facilitates improving the breakdown strength, the dielectric performance of Py/PI/Py composites has been enhanced significantly. Accordingly, dielectric constant of 4.52–5.09, dissipation factor of 0.21–1.01%, and breakdown strength of 307–460 MV m−1 are achieved. Besides, notable energy storage performance is also obtained in Py/PI/Py composite dielectrics. Consequently, this novel application of chemical vapor deposition polymerization method in preparing all‐organic multilayered polymer composite films with sandwich structure shows promising potential in film capacitor applications in harsh conditions. [ABSTRACT FROM AUTHOR]

In the process of geo-energy drilling, the real-time vibration measurement of drill pipes is of significance for an understanding of the downhole conditions and the properties of rock. However, the vibration sensors used in downhole areas at present require additional power sources, such as batteries, and replacing the batteries would significantly reduce production efficiency and increase costs. In our work, a new vibration measurement method using a triboelectric nanogenerator is proposed which will synchronously achieve axial and lateral vibration, and also simultaneously be self-powered. The triboelectric nanogenerator is mainly made of nanomaterials, such as polyimide film and polytetrafluoroethylene (PTFE), and depends on the pulse signal generated by the contact of the two friction layers to measure the vibration frequency. Axial vibration tests show that the output voltage signal amplitude is approximately 3 V, the measurement range is from 0 to 9 Hz, the measurement error is less than 4%, and the maximum output power is 5.63 uW. Additionally, the lateral vibration tests show that the output voltage signal amplitude is approximately 2.5 V, the measurement range is from 0 to 6.8 Hz, the measurement error is less than 6%, and the maximum output power is 4.01 uW. The nanogenerator can typically work in an environment where the temperature is less than 145 °C and the relative humidity is less than 90%. [ABSTRACT FROM AUTHOR]

We developed a flow and pressure measurement device for detection of extravasation by intravenous injection of anticancer drugs at an early stage. Intravenous injection of a drug solution using a syringe pump enables a low‐speed and highly accurate drug‐administration rate. However, because the syringe pump forcibly delivers the drug solution, the drug solution is administrated at a constant administration rate regardless of the leakage of the drug solution to the outside of the blood vessel (extravasation) due to the indwelling needle coming out of the blood vessel. The proposed device is integrated into a flow‐channel structure consisting of a PDMS layer in which a MEMS thermal‐flow sensor formed on thin polyimide film and a pressure sensor are stacked on a plastic plate as a substrate. Therefore, it is possible to measure both the drug‐administration rate and injection pressure. Early detection of extravasation can be achieved by identifying the state of needle‐puncture based on changes in injection pressure. Then, the amount of leaked drug after leak occurs can be accurately measured with a flow sensor. We evaluated the flow and pressure detection function of the proposed device and confirmed that it is possible to detect extravasation early through an experiment involving a piece of raw chicken simulating human skin and flesh. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Heat-sealable isomeric co-polyimide (CPI) films with enhanced atomic oxygen (AO) resistance and mechanical strength were synthesized from 2,3,3′,4′-oxydiphthalic anhydride (aODPA), 4,4′-oxydianiline (ODA), and 2,5-bis [(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO). We investigated how the molecular structure and diamine ratio affected the thermal properties, solubility, mechanical properties, AO resistance and heat-sealability. The diphenylphosphine oxide (DPO) side group decreased the CPI film mechanical strength and its higher ODA reactivity increased the molecular weight. At 10 mol% ODA in the aODPA-BADPO system, the CPI film exhibited increased tensile strength with no detriment to the AO resistance. Meanwhile, the CPI films demonstrated good heat-sealability indicated by a completely merged interface after heat sealing. [ABSTRACT FROM AUTHOR]

Fluorinated polyimide materials were selected for their exceptional flexibility, high thermal stability, and minimal absorption loss. These materials were subsequently employed in the production of single-mode polymer optical waveguide devices using photolithography. In this study, a fluorinated polyimide material doped with NaYF4 nanocrystals was prepared and confirmed to exhibit low absorption loss near 1550 nm, which is within the common communication window. The refractive index of the fluorinated polyimide films was precisely adjusted by the NaYF4 doping, the adjustable ranges for the refractive index were 1.95% and 1.72% for doped and undoped, respectively. Secondly, utilizing the NaYF4 nanocrystals doped-fluorinated polyimide materials, a three-layer single-mode polymer optical waveguide device for C-band (near 1550 nm) optical interconnection was fabricated by etching the underlying cladding and employing silicon nitride as a mask. The transmission performance of the device was excellent, with a total waveguide coupling and transmission loss of 1.502 dBm. [ABSTRACT FROM AUTHOR]

Scorpions, through ruthless survival of the fittest, evolve the unique ability to quickly locate and hunt prey with slit receptors near the leg joints and a sharp sting on the multi-freedom tail. Inspired by this fantastic creature, we herein report a dual-bionic strategy to fabricate microcrack-assisted wrinkle strain sensor with both high sensitivity and stretchability. Specifically, laser-induced graphene (LIG) is transferred from polyimide film to Ecoflex and then coated with silver paste using the casting-and-peeling and prestretch-and-release methods. The shape-adaptive and long-range ordered geometry (e.g., amplitude and wavelength) of dual-bionic structure is prestrain-tuned to optimize the superfast response time (∼ 76 ms), high sensitivity (gauge factor = 223.6), broad working range (70%–100%), and good reliability (> 800 cycles) of scorpion-inspired strain sensor, outperforming many LIG-based materials and other bionic sensors. The alternate reconnect/disconnect behaviors of slit-organ-like microcracks in the mechanical weak areas initiate tremendous resistance changes, whereas the scorpion-tail-like wrinkles act as a "bridge" connecting the adjacent LIG resistor units, enabling reversible resilience and unimpeded electrical linkages over a wide strain range. Combined with the self-developed miniaturized, flexible, and all-in-one wireless transmission system, a variety of scenarios such as large body movements, tiny pulse, and heartbeat are real-time monitored via bluetooth and displayed in the client-sides, revealing a huge promise in future wearable electronics. [ABSTRACT FROM AUTHOR]

Recyclability and self‐healing are two most critical factors in developing sustainable polymers to deal with environmental pollution and resource waste. In this work, a dynamic cross‐linked polyimide insulation film with full closed‐loop recyclability is successfully prepared, which also possesses good self‐healing ability after being mechanical/electrical damaged depending on the Schiff base dynamic covalent bonds. The recycled and self‐healed polyimide film still maintain its good tensile strength (σt) >60 MPa with Young's modulus (E) >4 GPa, high thermal stability with glass transition temperature (Tg) >220 °C, and outstanding insulation property with breakdown strength (E0) >358 kV mm−1, making it a very promising low energy consumption and high temperature resistant insulation material. The strategy of using Schiff base dynamic covalent bonds for reversible repairing the structure of high Tg polyimides promotes the wider application of such sustainable and recyclable material in the field of electrical power and micro‐electronics. [ABSTRACT FROM AUTHOR]

Proper selections of microwave-transmitting thermal control materials play key roles in the orbit operations of aerospace microwave detectors. Currently, white paint and germanium-coated polyimide film are common choices for microwave-transmitting thermal control, which have been extensively studied from the perspective of material compositions, ignoring the influence of the micro-nano structure on the surface of the material. Inspired by Saharan silver ants relying on micro-nano structures of hairs for heat protection and dissipation, in this paper, based on finite element simulation, spectral characteristics (e.g., solar absorptance and infrared emissivity) of three types of biomimetic micro-nano structures (e.g., including pyramid, tetrahedron, and triangular prism) were studied and compared. Simulation results revealed that spectral characteristics of these biomimetic micro-nano structures were mainly regulated by the tip height and the air gap; the decrease of the tip height led to the decrease in the solar absorptance and the infrared emissivity; the solar absorptance was decreased, and the infrared emissivity was increased with the increase of the air gap. When these biomimetic structures were compared with flat surfaces without micro-nano topographies, a decrease of the solar absorptance to block the incidence of heat flow from the sun and an increase of the infrared emissivity to dissipate its own heat to the space were located, which may give suggestions on the adjustment of spectral characteristics of aerospace microwave-transmitting thermal control materials. [ABSTRACT FROM AUTHOR]

Polyimide is an emerging and very interesting material for substrate and passivation of neural probes. However, the standard curing temperature of polyimide (350 °C) is critical for the microelectrodes and contact pads of the neural probe, due to the thermal oxidation of the metals during the passivation process of the neural probe. Here, the fabrication process of a flexible neural probe, enhanced with a photosensitive and low-temperature cured polyimide, is presented. Annealing tests were performed with metallic films deposited on polyimide, which led to the reduction of the curing temperature to 250 °C, with no significant irregularities in the metallic sample annealed at that temperature and an effective polyimide curing. The use of a lower curing temperature reduces the thermal oxidation of the metals during the polyimide curing process to passivate the neural probe. Additionally, in this fabrication process, the microelectrodes of the neural probe were coated with electrodeposited platinum (Pt), only after the passivation process, and its electrochemical performance was accessed. At 1 kHz, the impedance of the microelectrodes before Pt electrodeposition was approximately 1.2 MΩ, and after Pt electrodeposition, it was approximately 350 kΩ. Pt electrodeposition changed the equivalent circuit of the microelectrodes and reduced their impedance, which will be crucial for future in-vivo tests to acquire the electrical activity of the neurons with the fabricated neural probe. [ABSTRACT FROM AUTHOR]

Thermoelectric materials in the form of thin films are used to create a wide variety of sensors and devices. The efficiency of these devices depends on the quality and efficiency of the thermoelectric materials obtained in the form of thin films. Earlier, we demonstrated that it is possible to obtain high-performance Bi2Te3Sb1.5 films less than 1 μm thick on polyimide substrates by using the PLD method, and determined optimal growth conditions. In the current work, the relationship between growth conditions and droplet fraction on the surface, microstructure, grain size, film thickness and chemical composition was studied. A power factor of 5.25 μW/cm×K2 was achieved with the reduction of droplet fraction on the film surface to 0.57%. The dependencies of the film thickness were studied, and the effect of the thickness on the efficiency of the material is shown. The general trend in the growth dynamics for Bi2Te3Sb1.5 films we obtained is the reduction of crystalline size with Pressure-Temperature (PT) criterion. The results of our work also show the possibility of a significant reduction of droplet phase with simultaneous management of crystalline features and thermoelectric efficiency of Bi2Te3Sb1.5 films grown on polyimide substrates by varying growth conditions. [ABSTRACT FROM AUTHOR]

Materials with outstanding mechanical properties and excellent dielectric properties are increasingly favored in the microelectronics industry. The application of polyimide (PI) in the field of microelectronics is limited because of the fact that PI with excellent mechanical properties does not have special features in the dielectric properties. In this work, PI composite films with high dielectric properties and excellent mechanical properties are fabricated by in-situ reduction of fluorinated graphene (FG) in polyamide acid (PAA) composites. The dielectric permittivity of pure PI is 3.47 and the maximum energy storage density is 0.664 J/cm3 at 100 Hz, while the dielectric permittivity of the PI composite films reaches 235.74 under the same conditions, a 68-times increase compared to the pure PI, and the maximum energy storage density is 5.651, a 9-times increase compared to the pure PI films. This method not only solves the problem of the aggregation of the filler particles in the PI matrix and maintains the intrinsic excellent mechanical properties of the PI, but also significantly improves the dielectric properties of the PI. [ABSTRACT FROM AUTHOR]

Poly(amic acid) (PAA) is prepared by the reaction of dianhydride 4,4′-biphthalic anhydride and diamine bis[4-(3-aminophenoxy)phenyl]sulfone in N,N'-dimethylacetamide. Two types of fillers were dispersed in the as-synthesized PAA via a solution intercalation method; polyimide (PI) hybrid films were synthesized under various heat treatment conditions. Octylamine (C8) was introduced into graphene sheets (C8-GS) and bentonite (C8-BTN), which were then used as nanofillers in the PI hybrid films. The synthesized nanofillers were used in varying amounts of 0.25–1.00 wt% with respect to the matrix PI. The thermal and morphological properties and optical transparency of the hybrid films were investigated and compared for both C8-GS and C8-BTN at varying nanofiller content. The C8-BTN nanocomposite showed superior thermal properties, and optical transparency, and the filler was well dispersed in the PI matrix compared to the C8-GS nanocomposite. The thermal stability of the hybrid films improved upon the addition of small amounts of the nanofiller. However, beyond a certain critical filler concentration, the thermal stability declined. These results were verified through the dispersion of fillers via transmission electron microscopy. [ABSTRACT FROM AUTHOR]