Search

Purpose Methods Results Conclusions To develop and evaluate a photovoltaic, wireless wide‐field epiretinal prosthesis for the treatment of retinitis pigmentosa.A mosaic array of thinned silicon‐based photodiodes with integrated thin‐film stimulation electrodes was fabricated with a flexible polyimide substrate film to form a film‐based miniaturized electronic system with wireless optical power and signal transmission and integrated electrostimulation. Manufactured implants were characterized with respect to their optoelectronic performance and biocompatibility following DIN EN ISO 10993.A 14 mm diameter prosthesis containing 1276 pixels with a maximum sensitivity at a near infrared wavelength of 905 nm and maximized stimulation current density 30–50 μm below the electrodes was developed for direct activation of retinal ganglion cells during epiretinal stimulation. Fabricated prostheses demonstrated mucosal tolerance and the preservation of both metabolic activity, proliferation and membrane integrity of human fibroblasts as well as the retinal functions of bovine retinas. Illumination of the prosthesis, which was placed epiretinally on an isolated perfused bovine retina, with infrared light resulted in electrophysiological recordings reminiscent of an a‐wave (hyperpolarization) and b‐wave (depolarization).A photovoltaic, wireless wide‐field epiretinal prosthesis for the treatment of retinitis pigmentosa using near infrared light for signal transmission was designed, manufactured and its biocompatibility and functionality demonstrated in vitro and ex vivo. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) is a wide-band gap semiconductor that exceeds other semiconducting materials (except diamond) in electrical, mechanical, chemical, and radiation stability. In this paper, we report a novel approach to fabrication of SiC nano films on a Si substrate, which is based on the endotaxial growth of a SiC crystalline phase in a graphite-like carbon (GLC) matrix. GLC films were formed by carbonization of rigid rod polyimide (PI) Langmuir–Blodgett (LB) films on a Si substrate at 1000 °C in vacuum. After rapid thermal annealing of GLC films at 1100 °C and 1200 °C, new types of heterostructures SiC(10 nm)/GLC(20 nm)/Si(111) and SiC(20 nm)/GLC(15 nm)/SiC(10 nm)/Si(111) were obtained. The SiC top layer was formed due to the Si-containing gas phase present above the surface of GLC film. An advantage of the proposed method of endotaxy is that the SiC crystalline phase is formed within the volume of the GLC film of a thickness predetermined by using PI LB films with different numbers of monolayers for carbonization. This approach allows growing SiC layers close to the 2D state, which is promising for optoelectronics, photovoltaics, spintronics. [ABSTRACT FROM AUTHOR]

Titanium oxide (TiO2) coated polyimide has broad application prospects under extreme conditions. In order to obtain a high-quality ultra-thin TiO2 coating on polyimide by atomic layer deposition (ALD), the polyimide was activated by in situ oxygen plasma. It was found that a large number of polar oxygen functional groups, such as carboxyl, were generated on the surface of the activated polyimide, which can significantly promote the preparation of TiO2 coating by ALD. The nucleation and growth of TiO2 were studied by x-ray photoelectron spectroscopy monitoring and scanning electron microscopy observation. On the polyimide activated by oxygen plasma, the size of TiO2 nuclei decreased and the quantity of TiO2 nuclei increased, resulting in the growth of a highly uniform and dense TiO2 coating. This coating exhibited excellent resistance to atomic oxygen. When exposed to 3.5 × 1021 atom cm−2 atomic oxygen flux, the erosion yield of the polyimide coated with 100 ALD cycles of TiO2 was as low as 3.0 × 10−25 cm3/atom, which is one order less than that of the standard POLYIMIDE-ref Kapton® film. [ABSTRACT FROM AUTHOR]

Polyethylene oxide composite electrolytes are widely used in lithium‐ion batteries because of their excellent moldability, good flexibility, and favorable chemical compatibility. However, they still suffer from low ionic conductivity and weak mechanical strength. Herein, a 3D nanofiber‐reinforced dual‐salt composite solid electrolyte (PI@PCB) is synthesized. Benefiting from the support of the porous polyimide films and the addition of lithium bis(oxalate)borate, the obtained PI@PCB electrolyte exhibits high mechanical strength, good thermal stability, excellent electrochemical stability, and a high lithium ion transference number (0.70). In addition, the assembled Li/PI@PCB/Li cell shows the lowest overpotential of 200 mV at the initial cycling stage and increases to 246 mV slightly after 1500 h. The capacity retention rate of Li/PI@PCB/LFP battery is about 88.3% after 500 cycles at 60 °C. [ABSTRACT FROM AUTHOR]

The excellent electrical properties of graphene have received widespread attention. However, the difficulty of electron transfer between layers still restricts the application of graphene composite materials to a large extent. Therefore, in this study, graphene/polyimide films were subjected to a Joule heating treatment to improve the electrical conductivity of the film by ~76.85%. After multiple Joule thermal cycle treatments, the conductivity of the graphene/polyimide film still gradually increased, but the increase in amplitude tended to slow down. Finally, after eight Joule heat treatments, the conductivity of the graphene/polyimide film was improved by ~93.94%. The Joule heating treatment caused the polyimide to undergo atomic rearrangement near the interface bonded to the graphene, forming a new crystalline phase favourable for electron transport with graphene as a template. Accordingly, a model of the bilayer capacitive microstructure of graphene/polyimide was proposed. The experiment suggests that the Joule heating treatment can effectively reduce the distance between graphene electrode plates in the bilayer capacitive micro-nanostructures of graphene/polyimide and greatly increases the number of charge carriers on the electrode plates. The TEM and WAXS characterisation results imply atomic structure changes at the graphene/polyimide bonding interface. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films equipped on the surface of spacecraft are susceptible to ultraviolet damage. Herein, the performance of two kinds of polyimide films i.e. 3,3′,4,4′-biphenyl dianhydride-p-phenylenediamine (BPDA-PDA) and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) under vacuum ultraviolet (VUV, 172 nm) irradiation was studied. The failure behavior of the PI films was studied by tensile tests, thermogravimetry (TGA), thermomechanical analysis (TMA), electric breakdown, UV–visible transmittance and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the molecular structure. The results indicated that the tensile strength of BPDA-PDA PI and PMDA-ODA PI films decreased by 10.4 and 7.4% under VUV irradiation, respectively; the breakdown strength and UV-transmittance also deteriorated. Besides, the surface morphology of the PI films showed a large number of microcracks after VUV irradiation, which we ascribe to the breakage of imide rings (C-N-C) and ether bonds (C-O-C) of the PI films. However, the thermal stability (residual weight) of both PI films remained constant compared to the initial level; this can be explained by the combined effect of bond breaking and cross-linking of the polyimide films. [ABSTRACT FROM AUTHOR]

NASA seeks to develop technologies to mitigate dust accumulation from planetary surfaces on robotic and human systems hardware during planned space exploration missions. With a return to the Lunar surface, lunar dust threatens the durability and reusability of components and vehicles due to its fine, jagged morphology and highly abrasive nature. Lunar dust consists of particles less than 60 μm in size that are chemically reactive, electrostatically and sometimes magnetically charged. Unique materials and technologies that reduce or mitigate lunar dust adhesion will be critical to support long duration missions and eventual sustained presence on the lunar surface. The goal of this work was to prepare dust resistant, space durable polymer films to satisfy dust accumulation mitigation needs for future NASA missions. In this regard, several graphene coated polyimide thin films have been developed with surface resistivity properties in the range of 103 Ω/sq to 1011 Ω/sq and evaluated for their dust adhesion performance. Raman spectroscopy was used to characterize and assess the quality of graphene ink coated sheets while surface resistivity measurements were used to assess electrical conductivity. Scratch testing and abrasion resistance measurements were used to evaluate overall abrasion performance. Water contact angle and optical microscopy were used to evaluate changes in surface topography and chemistry. Graphene coated polyimide surfaces with charge dissipative resistivity (106 Ω/sq) demonstrated a minimum in residual particle areal coverage compared to conductive and insulating surfaces. Graphene ink/polymer thin film coated polyimide sheets (15 cm X 15 cm area, 75 μm thickness) are shown in order of decreasing sheet surface resistivities ranging from 103 Ω/sq, 104 Ω/sq, 106 Ω/sq, 108 Ω/sq, 1010 Ω/sq, and 1011 Ω/sq. Uncoated Kapton®, with sheet surface resistivity 1014 Ω/sq, is shown for comparison. [Display omitted] • Graphene ink coated polyimide sheets with surface resistivities in the range of 102 Ω/sq to 1012 Ω/sq have been prepared. • A significant improvement in scratch hardness (∼2 times) was observed for the coated substrates compared to the uncoated. • A minimum in residual particle areal coverage was observed for surfaces that exhibited intermediate surface resistivity values. • Dust resistant polymer films have been demonstrated for graphene coated polyimide sheets. [ABSTRACT FROM AUTHOR]

Despite the remarkable progress of perovskite solar cells (PSCs), challenges remain in terms of finding effective and viable strategies to enhance their long‐term stability while maintaining high efficiency. In this study, a new insulating and hydrophobic fluorinated polyimide (FPI: 6FDA‐6FAPB) was used as the interface layer between the perovskite layer and the hole transport layer (HTL) in PSCs. The functional groups of FPI play a pivotal role in passivating interface defects within the device. Due to its high work function, FPI demonstrates field‐effect passivation (FEP) capabilities as an interface layer, effectively mitigating non‐radiative recombination at the interface. Notably, the FPI insulating interface layer does not impede carrier transmission at the interface, which is attributed to the presence of hole tunneling effects. The optimized PSCs achieve an outstanding power conversion efficiency (PCE) of 24.61 % and demonstrate excellent stability, showcasing the efficacy of FPI in enhancing device performance and reliability. [ABSTRACT FROM AUTHOR]

Despite the remarkable progress of perovskite solar cells (PSCs), challenges remain in terms of finding effective and viable strategies to enhance their long‐term stability while maintaining high efficiency. In this study, a new insulating and hydrophobic fluorinated polyimide (FPI: 6FDA‐6FAPB) was used as the interface layer between the perovskite layer and the hole transport layer (HTL) in PSCs. The functional groups of FPI play a pivotal role in passivating interface defects within the device. Due to its high work function, FPI demonstrates field‐effect passivation (FEP) capabilities as an interface layer, effectively mitigating non‐radiative recombination at the interface. Notably, the FPI insulating interface layer does not impede carrier transmission at the interface, which is attributed to the presence of hole tunneling effects. The optimized PSCs achieve an outstanding power conversion efficiency (PCE) of 24.61 % and demonstrate excellent stability, showcasing the efficacy of FPI in enhancing device performance and reliability. [ABSTRACT FROM AUTHOR]

Attenuated total internal reflection (ATR) spectra of polyimide PI-2610 films deposited on single-crystal silicon wafers by centrifugation were studied after irradiation with 5-MeV electrons in a linear accelerator at doses of 1∙1014–2∙1015 cm–2. The strongest bands in the spectrum of the PI-2610 polyimide films were attributed to vibrations of the imide ring C–N–Cst (1349 cm–1) and aromatic ring (1517 cm–1), stretching vibrations of the imide ring C=Ostr (1700 cm–1) and CO–Cst-group C–C bonds (1074 cm-1), and bending vibrations of C–H bonds with maxima at 734 and 828 cm–1. The spectral shape and intensities of bands with maxima at 1700 and 1349 cm–1 due to C=O and C=N–Cstr vibrations were observed to change at an initial dose of 1∙1014 cm–2. It was assumed that this was due to relaxation of metastable states of these groups. The intensities of bands corresponding to asymmetric and symmetric stretching vibrations of C–H2 bonds decreased at a dose of 2∙1015 cm–2. The intensities of ATR bands due to vibrations of C=O and C–N bonds and aromatic and imide rings practically did not change. [ABSTRACT FROM AUTHOR]

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

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect. [ABSTRACT FROM AUTHOR]

Communication with hand gestures plays a significant role in human‐computer interaction by providing an intuitive and natural way for humans to communicate with machines. Ultrasound‐based devices have shown promising results in contactless hand gesture recognition without requiring physical contact. However, it is challenging to fabricate a densely packed wearable ultrasound array. Here, a stretchable ultrasound array is demonstrated with closely packed transducer elements fabricated using surface charge engineering between pre‐charged 1–3 Lead Zirconate Titanate (PZT) composite and thin polyimide film without using a microscope. The array exhibits excellent ultrasound properties with a wide bandwidth (≈57.1%) and high electromechanical coefficient (≈0.75). The ultrasound array can decipher gestures up to 10 cm in distance by using a contactless triboelectric module and identify materials from the time constant of the exponentially decaying impedance based on their triboelectric properties by utilizing the electrostatic induction phase. The newly proposed metric of the areal‐time constant is material‐specific and decreases monotonically from a highly positive human body (1.13 m2 s) to negatively charged polydimethylsiloxane (PDMS) (0.02 m2 s) in the triboelectric series. The capability of the closely packed ultrasound array to detect material along with hand gesture interpretation provides an additional dimension in the next‐generation human‐robot interaction. [ABSTRACT FROM AUTHOR]

Flexible organic light-emitting diode display devices fabricated on polyimide (PI) substrates have more obvious residual image problems due to the abnormal threshold-voltage (Vth) shifts of a thin film transistor (TFT). In this paper, the Vth shift of TFT fabricated on a PI substrate was analyzed. We explained the worse bias stability and worse recovery of TFT with a PI substrate compared with TFT with a glass substrate, by an interlayer charging effect (Maxwell–Wagner effect) and a technology computer-aided design (Silvaco). When bias stress was applied for a long time, the interface between the PI substrate and the buffer layer will have a charging effect under the action of an electric field, and the charging charge will react on the channel and hinder the formation of the channel. We found that there are differences in the scale of charge under different voltage stress conditions, and this will result in different Vth shifts of driving TFTs for displays units. [ABSTRACT FROM AUTHOR]

Modulating the thermal emission of a material in the infrared (IR) range can be essential for various practical applications such as smart textiles, camouflage, and anti-counterfeiting. Although many different materials or structures have been proposed, the complex manufacturing processes are still hindering their widespread use. Herein, a facile femtosecond laser processing technology and a drop-coating method are introduced to form a patternable low emissivity film. Laser-treated polyimide films resulted in superhydrophilic structured surfaces that are uniformly coated with silver-nanowires (AgNWs) in aqueous solutions for low emissivity surfaces. Furthermore, the emissivity of the samples is as low as ∼0.2 without deterioration over 800 bending-releasing cycles. The as-prepared films also display good thermal camouflage properties, namely, the films reduced the thermal radiation temperature of an object by 35.8 °C when the object temperature was ∼69.1 °C. Additionally, this IR camouflage effect of the AgNWs coated samples shows excellent stability even in harsh environments such as immersion in water, acid, alkali, and salt solution and applied voltage. We also show that information encryption was possible by adjusting the amount of AgNWs. The design of this programmable patterned low emissivity film indicates an idea for the thermal camouflage and anti-counterfeiting technology, which can carry more abundant application scenario and disguise them more complex and sophisticated. [ABSTRACT FROM AUTHOR]

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

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

Polyimide films with molecular imprints of erythrosine and indigocarmine have been obtained. The structure and morphology of the film surfaces have been studied by scanning probe microscopy and IR spectroscopy. It has been found that the surface roughness of molecularly imprinted polymers (MIPs) increases, while the relief height amounts to 3–4 nm. The removal of template molecules leads to a redistribution of pores over sizes in the polymers with molecular imprints. The adsorption of dyes by MIP films has been carried out under static conditions. The degrees of extraction and the imprinting factors have been calculated for polymers with molecular imprints of the dyes. The high values of these parameters indicate the selectivity of MIPs to the target template molecules. [ABSTRACT FROM AUTHOR]

Acquiring physical and mechanical strain information of the human body with wearable strain sensors can provide essential data from personal healthcare to human‐machine interfaces and others. Recent research reveals that CO2 laser scribing can convert polyimide films into porous graphene sponges under ambient atmospheres. However, the electrically conductive laser‐induced graphene (LIG) film mismatches with the tough and rigid plastic substrates when it is employed as stretchable strain sensors. In this work, by leveraging the advantageous properties of atoms‐level configured defects within crystalline LIG and heat transfer printing techniques, a flexible LIG‐SEBS (styrene‐ethylene‐butylene‐styrene) strain sensor is made. It is able to achieve exceptional electromechanical properties including a remarkable sensitivity in terms of gauge factor (413–3118), minimal hysteresis, and a broad strain range (>100% strain). Meanwhile, the SEBS‐LIG strain sensor has a stable and fast dynamic response and good repeatability. Additionally, the sensor can be integrated with a wireless communication module for remote monitoring of physiological signals in a real‐time manner with a smartphone App. [ABSTRACT FROM AUTHOR]

A versatile strategy of preparing colored polyimide (PI) films is developed by embedding colored monomers on the backbones of colorless substrate polymers. Intrinsically colored PI films of four colors—red, yellow, blue, and purple—are prepared by introducing relative chromophores to the substrate PI that are synthesized from 2,2′‐bis(trifluoromethyl)benzidine (TFMB) and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA)—two widely used monomers for colorless and transparent PI films. In addition, a series of orange and green PI films are prepared by simple mixing of the red, yellow, or blue PIs. The properties of these colored PI films are characterized, exhibiting good mechanical, thermal, and solubility properties, as well as different color and brightness depending on the amounts and types of chromophores. The optical properties of these films are determined by UV–vis spectroscopy and Commission Internationale de I'Eclairage (CIE) Lab. It is demonstrated that the introduction of even small amounts of chromophores can afford spectrally colored films while maintaining the original benign properties of the substrate PIs. [ABSTRACT FROM AUTHOR]

The design of high-performance polyimide (PI) films and understanding the relationship of the structure–dielectric property are of great significance in the field of the microelectronics industry, but are challenging. Herein, we describe the first work to construct a series of novel tert-butyl PI films (denoted as PI-1, PI-2, PI-3, and PI-4) based on a low-temperature polymerization strategy, which employed tetracarboxylic dianhydride (pyromellitic anhydride, 3,3′,4,4′-biphenyl tetracarboxylic anhydride, 4,4′-diphenyl ether dianhydride, and 3,3′,4,4′-benzophenone tetracarboxylic anhydride) and 4,4′-diamino-3,5-ditert butyl biphenyl ether as monomers. The results indicate that introducing tert-butyl branches in the main chain of PIs can enhance the free volume of the molecular chain and reduce the interaction between molecular chains of PI, resulting in a low dielectric constant. Particularly, the optimized PI-4 exhibits an excellent comprehensive performance with a high (5) wt% loss temperature (454 °C), tensile strength (117.40 MPa), and maximum hydrophobic angle (80.16°), and a low dielectric constant (2.90), which outperforms most of the results reported to date. [ABSTRACT FROM AUTHOR]

In order to prepare polyimide (PI) films with a low dielectric constant and excellent comprehensive performance, a two-step method was employed in this study to integrate β-cyclodextrin into a semi-aromatic fluorine-containing polyimide ternary system. By introducing trifluoromethyl groups to reduce the dielectric constant, the dielectric constant was further reduced to 2.55 at 10 MHz. Simultaneously, the film exhibited noteworthy thermal stability (a glass transition temperature exceeding 300 °C) and a high coefficient of thermal expansion. The material also demonstrated outstanding mechanical properties, boasting a strength of 122 MPa and a modulus of 2.2 GPa, along with high optical transparency (transmittance reaching up to 89% at 450 nm). Moreover, the inherent high transparency of colorless polyimide (CPI) combined with good stretchability contributed to the attainment of a low dielectric constant. This strategic approach not only opens up new opportunities for novel electroactive polymers but also holds potential applications in flexible displays, circuit printing, and chip packaging. [ABSTRACT FROM AUTHOR]

The X-ray Integral Field Unit (X-IFU) is one of the two focal plane detectors of Athena, a large-class high energy astrophysics space mission approved by ESA in the Cosmic Vision 2015–2025 Science Program. The X-IFU consists of a large array of transition edge sensor micro-calorimeters that operate at ~100 mK inside a sophisticated cryostat. To prevent molecular contamination and to minimize photon shot noise on the sensitive X-IFU cryogenic detector array, a set of thermal filters (THFs) operating at different temperatures are needed. Since contamination already occurs below 300 K, the outer and more exposed THF must be kept at a higher temperature. To meet the low energy effective area requirements, the THFs are to be made of a thin polyimide film (45 nm) coated in aluminum (30 nm) and supported by a metallic mesh. Due to the small thickness and the low thermal conductance of the material, the membranes are prone to developing a radial temperature gradient due to radiative coupling with the environment. Considering the fragility of the membrane and the high reflectivity in IR energy domain, temperature measurements are difficult. In this work, a parametric numerical study is performed to retrieve the radial temperature profile of the larger and outer THF of the Athena X-IFU using a Finite Element Model approach. The effects on the radial temperature profile of different design parameters and boundary conditions are considered: (i) the mesh design and material, (ii) the plating material, (iii) the addition of a thick Y-cross applied over the mesh, (iv) an active heating heat flux injected on the center and (v) a Joule heating of the mesh. The outcomes of this study have guided the choice of the baseline strategy for the heating of the Athena X-IFU THFs, fulfilling the stringent thermal specifications of the instrument. [ABSTRACT FROM AUTHOR]

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

To analyze X-ray diffraction patterns obtained from polyimide films subjected to external influence (uniaxial tension and exposure at liquid helium temperature), radial distribution function (RDF) curves were constructed and the geometry of the 4,4′-oxydiphenylene-pyromellitimide monomer (PM) was calculated. From the RDF analysis, it follows that uniaxial tension of PM polymer films leads to a change in the geometry of the monomer, and exposure at low temperatures leads to mutual ordering of the polymer chains. [ABSTRACT FROM AUTHOR]

Although polyimide films have a low dielectric constant, with the advent of the 5G era, the dielectric properties of the material are required to be further improved. Therein, we prepared controlled hollow mesoporous SiO2 nanomicrospheres by the hard template method to make mesoporous low dielectric polyimide films. The composite membrane exhibits better thermal stability, mechanical properties, and hydrophobicity compared to the pure membrane. Hollow mesoporous SiO2 dispersed in polyimide can reduce the inhomogeneity of charge distribution between molecules and reduce the interaction between polar chemical bonds and aromatic rings, thus improving the dielectric properties of the whole film. The minimum dielectric constant of the composite films was 2.80 when the hollow mesoporous SiO2 was added at 1.0%. These results fully indicate that the addition of hollow mesoporous SiO2 is beneficial to the multifaceted performance of the polyimide films. Highlights: Preparation of hollow mesoporous SiO2 microspheres by using different polystyrene microsphere solutions and TEOS ratios.Synthesis of composite films with different contents of hollow mesoporous SiO2 as functional fillers.The effect of hollow mesoporous SiO2 content on the mechanical properties and thermal stability of PI composite films was investigated.Addition of hollow mesoporous SiO2 reduces the dielectric constant of polyimide composite films. [ABSTRACT FROM AUTHOR]

Since compact high temperature superconducting (HTS) transformer has a small size and high efficiency, it can meet the requirements of high‐voltage transformers for vehicle‐mounted mobile substation. However, due to the small internal insulation size of the compact HTS transformers, it is necessary to improve the insulation strength to ensure the insulation safety of the transformer. Reasonable main insulation structure can greatly improve the insulation level of transformer. Based on the design theory of main insulation structure, this paper designs a main insulation structure model "small liquid nitrogen gap—barrier" suitable for compact HTS transformer. The insulation withstand voltage experiment of the main insulation structure shows that when the liquid nitrogen gap distance is less than 8 mm, the insulation strength of liquid nitrogen in the structure is improved. When the liquid nitrogen gap distance is too small, the size and thickness of the barrier will affect the insulation strength of the structure. According to the insulation strength of main insulation structures with different liquid nitrogen gaps, the feasibility of "small liquid nitrogen gap—barrier" main insulation structure is verified. The small liquid nitrogen gap structure can be adopted for the main insulation of compact HTS transformer. [ABSTRACT FROM AUTHOR]

Polyimide (PI) has been widely used in cable insulation, thermal insulation, wind power protection, and other fields due to its high chemical stability and excellent electrical insulation and mechanical properties. In this research, a modified PI composite film (MoS2@PDA/PI) was obtained by using polydopamine (PDA)-coated molybdenum disulfide (MoS2) as a filler. The low interlayer friction characteristics and high elastic modulus of MoS2 provide a theoretical basis for enhancing the flexible mechanical properties of the PI matrix. The formation of a cross-linking structure between a large number of active sites on the surface of the PDA and the PI molecular chain can effectively enhance the breakdown field strength of the film. Consequently, the tensile strength of the final sample MoS2@PDA/PI film increased by 44.7% in comparison with pure PI film, and the breakdown voltage strength reached 1.23 times that of the original film. It can be seen that the strategy of utilizing two-dimensional (2D) MoS2@PDA nanosheets filled with PI provides a new modification idea to enhance the mechanical and electrical insulation properties of PI films. [ABSTRACT FROM AUTHOR]

The development of soft photoactuators with multifunctionality and improved performance is highly important for their broad applications. Herein, we report on a facile and efficient strategy for fabricating such photoactuators with UV‐NIR dual light‐responsivity, room‐temperature 3D shape reprogrammability and reprocessability, and photothermal healability by doping polydopamine (PDA) nanoparticles into a main‐chain azobenzene semi‐crystalline poly(ester‐amide) (PEA). The PEA/PDA nanoparticle composite was readily processed into free‐standing films with enhanced mechanical and photomechanical properties compared with the blank PEA films. Its physically crosslinked uniaxially oriented films showed rapid and highly reversible photochemically induced bending/unbending under the UV/visible light irradiation at room temperature in both the air atmosphere and water. When exposed to the NIR light, they (and their bilayer films formed with a polyimide film) exhibited photothermally induced bending even at a temperature much lower than their crystalline‐to‐isotropic phase transition temperature based on a unique mechanism (involving photothermally induced polymer chain relaxation due to the disruption of their hydrogen bonds). The room‐temperature 3D shape reprogrammability and reprocessability and photothermal healability of the composite polymer films were also demonstrated. Such multifunctional dual light‐responsive photoactuators with well‐balanced mechanical robustness, actuation stability, 3D shape reprogrammability/reprocessability and photothermal healability hold much promise in various photoactuating applications. [ABSTRACT FROM AUTHOR]

Polyimide (PI) film with hydrophilic greatly limits their application in the field of microelectronic device packaging. A novel hydrophobic PI film with sag structure and improved mechanical properties is prepared relying on the reaction between anhydride‐terminated isocyanate‐based polyimide (PIY) containing a seven‐membered ring structure and the amino‐terminated polyamide acid (PAA) via multi‐hybrid strategy, this work named it as hybrid PI film and marked it as PI‐PIY‐X. PI‐PIY‐30 showed excellent hydrophobic properties, and the water contact angle could reach to 102°, which is 20% and 55% higher than simply PI film and PIY film, respectively. The water absorption is only 1.02%, with a decrease of 49% and 53% compared with PI and PIY. Due to that the degradation of seven‐membered ring and generation of carbon dioxide led to the formation of sag structure, the size of sag structures is ≈16.84 and 534.55 nm for in‐plane and out‐plane direction, which are observed on surface of PI‐PIY‐30. Meanwhile, PI‐PIY‐30 possessed improved mechanical properties, and the tensile strength is 109.08 MPa, with 5% and more than 56% higher than that of pure PI and PIY film, showing greatly application prospects in the field of integrated circuit. [ABSTRACT FROM AUTHOR]

In this study, we developed a pioneering non-enzymatic electrochemical sensor utilizing a flexible porous graphene electrode modified with ZnO nanoparticles (ZnO/fPGE sensor) to assess hypoxanthine (HXA) content in pork at post-mortem time. The ZnO/fPGE sensor was synthesized via hydrothermal method and direct laser writing with a CO2 laser on a polyimide film at ambient conditions. Its characterization was analyzed by Raman, Fourier-transform infrared spectroscopy, field-emission scanning microscopy, energy-dispersive x-ray spectroscopy, and cyclic voltammetric techniques. Linear response, the limit of detection, and sensitivity to the HXA were enhanced with the values of the range from 1.5 to 150, 0.14 µM, and 6.6 µA μM−1 cm−2, respectively. Effective resistance to common physiological interferences (such as uric acid, ascorbic acid, dopamine, glucose, and xanthine) was indicated, and additionally, the determination of HXA concentration in real samples with good selectivity is attributed to the synergistic effects between ZnO nanoparticles and fPGE. Therefore, the ZnO/fPGE has provided a favorable electrical environment for developing high-performance electrochemical biosensors to determine hypoxanthine in pork meat. [ABSTRACT FROM AUTHOR]

Colorless and transparent polyimide (CPI) films with good atomic oxygen (AO) resistance and high thermal endurance are highly required in low earth orbit (LEO) space exploration. Conventional CPI films based on fluoro-containing 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) have been widely used in space applications. However, the AO erosion yields and glass transition temperatures (Tg) of the 6FDA-based CPI films have to be modified in order to meet the severe serving environments. In the current work, novel CPI films based on a multi-ring fluoro-containing 9,9-bis(trifluoromethyl)xanthene-2,3,6,7-tetracarboxylicdianhydride (6FCDA) monomer were developed. In order to enhance the AO resistance of the derived CPI film, a phosphorus-containing aromatic diamine, 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO) was used to polymerize with the dianhydride to create the organo-soluble resin. Then, two phosphorus-containing CPI films (PPI), including PPI-1 (6FDA-BADPO) and PPI-2 (6FCDA-BADPO) were prepared by thermally curing of the PPI solutions at elevated temperatures. The PPI films maintained good optical transparency with transmittance values over 80% at a wavelength of 450 nm. PPI-2 exhibited a Tg value of 311.0 °C by differential scanning calorimetry (DSC) measurement, which was 46.7 °C higher than that of the PPI-1 counterpart (Tg = 264.3 °C). In addition, the PPI-2 film showed a coefficient of linear thermal expansion (CTE) value of 41.7 × 10−6/K in the range of 50~250 °C, which was apparently lower than that of the PPI-1 sample (CTE = 49.2 × 10−6/K). Lastly, both of the two PPI films exhibited good AO resistance with the erosion yields (Ey) of 6.99 × 10−25 cm3/atom for PPI-1 and 7.23 × 10−25 cm3/atom for PPI-2 at an exposure flux of 5.0 × 1020 atoms/cm2. The Ey values of the current PPI films were obviously lower than that of the standard polyimide (PI) film based on pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) (Ey = 3.0 × 10−24 cm3/atom). [ABSTRACT FROM AUTHOR]

A series of uniaxially oriented polyimide (PI) films were fabricated via hot drawing at varying temperatures and draw ratios, and their orientation structure and thermal dimensional stability were investigated in detail. The infrared dichroism based on C = O symmetrical stretching was employed to effectively determine the orientation of chain segments. Other characteristic peaks, such as C = O asymmetric and C-N stretching, were highly sensitive to the geometric structure of chain segments, thereby providing a valuable means for comprehending their morphology. It has been observed that lower thermal expansion coefficient (CTE) can be achieved through low-temperature stretching, while high-temperature stretching is more effective in suppressing thermal shrinkage of the film. By quantitatively analyzing the orientation structure of infrared groups, the minimum structural unit highly associated with CTE was determined. These findings help to deepen our understanding of PI film performance and provide new ideas for studying thermal dimensional stability and draw processing. [ABSTRACT FROM AUTHOR]

Moisture detection plays a crucial role in physiological monitoring and wearable electronics. Nevertheless, most of the humidity sensors were restricted by the power supply, hindering their applicability in internet of things and mobile healthcare. Herein, we reported a hierarchical piezoelectric composite film for active humidity detection and wearable biomonitoring. The as-electrospun piezoelectric transducing textile consists of samarium-modified lead magnesium niobate lead titanate piezoceramic fillers and polyvinylidene fluoride matrix, while the spin coated polyimide film serves as the humidity sensitive layer. By tuning the thickness ratio between transducing layer and the humidity sensing layer as well as the porosity of the electrode, an optimal moisture-sensing performance was accomplished with a high response of ∼500% and rapid response/recovery time of 23 s/31 s. Furthermore, a theoretical modeling of active humidity sensing mechanism was established by combining thermodynamic derivation and finite element calculation. [ABSTRACT FROM AUTHOR]

Polyimide (PI) composite films with enhanced mechanical properties were prepared by incorporating modified fumed silica (FS) particles while preserving their optical and thermal characteristics. The PI matrix was synthesized using a fluorinated diamine, a fluorinated dianhydride, and a rigid biphenyl dianhydride via chemical imidization. Commercially available FS particles, including unmodified FS particles (0-FS) and particles modified with dimethyl (2-FS), trimethyl (3-FS), octyl (8-FS), octamethylcyclotetrasiloxane (D4-FS), and polydimethylsiloxane (PDMS-FS) were used. Scanning electron microscope images and nitrogen adsorption–desorption isotherms revealed well-defined porous structures in the FS particles. The water contact angles on the composite films increased compared to those of the pristine PI films, indicating improved water resistance. The PI/0-FS films exhibited a typical trade-off relationship between tensile modulus and elongation at break, as observed in conventional composites. Owing to the poor compatibility and agglomeration of the PDMS-FS particles, the PI/PDMS-FS composite films exhibited poor mechanical performance and diminished optical characteristics. Although the longer-chained FS particles (8- and D4-FS) improved the tensile modulus of the PI film by up to 12%, a reduction of more than 20% in toughness was observed. The PI composite films containing the methylated FS particles (2- and 3-FS) outperformed 8- and D4-FS in terms of mechanical properties, with PI/3-FS films showing an over 10% increased tensile modulus (from 4.07 to 4.42 GPa) and 15% improved toughness (from 6.97 to 8.04 MJ/m3) at 7 wt. % silica loading. Except for the PI/PDMS-FS composites, all composite film samples exhibited more than 86% transmittance at 550 nm. Regarding thermal properties, the glass transition temperature (Tg) and thermal stability remained stable for most composite films. In addition, PI/3-FS films demonstrated enhanced dimensional stability with lower coefficients of thermal expansion (from 47.3 to 34.5 ppm/°C). Overall, this study highlights the potential of incorporating specific modified FS particles to tailor the mechanical, optical, and thermal properties of PI composite films. [ABSTRACT FROM AUTHOR]

This study developed a novel approach to ammonia borane (AB) and silica assembly for all-solid-state thermal dehydrogenation, which can be integrated into current hydrogen generation systems. The AB/silica assembly apparatus is created by attaching pelletized AB specimens to both sides of a polyimide film heater, thus facilitating direct heat supply. The temperature, pressure, and power consumption data of the heater demonstrate that the dehydrogenation reaction is completed within 2 min from the initiation of the electric heating signal. Notably, the temperature and pressure of the generated hydrogen gas reach 39.5 °C and 1.95 barg, respectively, and the maximum hydrogen yield reached 11.46 wt% during the experiment. The infrared spectroscopy analysis indicates that all AB/silica samples inside the assembly undergoes complete reaction. This direct heating method significantly reduces the energy required for AB thermal decomposition and it increases the amount of AB that can be used at once. • All-solid-state thermal decomposition enables generation of large amounts of H 2. • Ammonia borane (AB) and silica were used for thermal dehydrogenation. • AB/silica pellets were attached to a polyimide film heater to create the assembly. • The AB/silica assembly made it possible to facilitating direct heat supply. • The direct heating reduced the energy required for thermal dehydrogenation. [ABSTRACT FROM AUTHOR]

Polyimide films of thickness 7.5 µm are irradiated by a wide range of ions (1H to 197Au) with energies between 1.05 and 48 MeV. Irradiated samples are then chemically etched in sodium hypochlorite solution to investigate nanopore formation due to ion track etching. A threshold in terms of electronic stopping power, Set, needs to be surpassed to preferentially etch the ion tracks. Close to Set, intermittent tracks are formed where only part of the track is etchable. The fraction of these etchable parts increases as we move away from Set, toward higher stopping powers, eventually yielding continuous etchable tracks. Both intermittent and continuous track formation thresholds are observed to be velocity‐dependent, yielding a decrease of the thresholds in the present work compared to previously reported thresholds for swift heavy ions. This finding leads the authors to suggest that electrostatic ion accelerators with terminal voltages of several MV are applicable for the production of ion track membranes up to ≈10–20 µm in thickness. Suitable ions for nanopores in 7.5 µm polyimide films include 42 MeV 59Co and 48 MeV 197Au. The growth mechanism for the pores during etching is discussed, relating it to the properties of the original ion track. [ABSTRACT FROM AUTHOR]

Herein, the concept of triboelectric generators using dipolar polarization energy as an electrical power source is introduced. Dipolar polarization energy is stored in dielectric films by rubbing, and is conveyed to external circuits for use during the depolarization process. Pyromellitic dianhydride‐4,4'‐oxydianiline polyimide films are used as a possible candidate for triboelectric generators, where polarization is formed by rubbing owing to the orientational alignment of polar molecular groups. The current–voltage measurements are used to evaluate the equivalent‐circuit parameters of the generator. The current source Is is 0.07 nA at 30 °C, which is enhanced to 0.13 nA at 110 °C. It is indicated in these results that the depolarization process proceeds in a short time at higher temperatures, causing an increase in the current. Consequently, the maximum power increases from 18 nW (30 °C) to 33 nW (110 °C). The enhancement of the output power at higher temperatures well supports the idea of using dipolar polarization energy as a power source of triboelectric generators. [ABSTRACT FROM AUTHOR]

Polyimide belongs to the class of high performance polymers containing imide functionalities in the backbone. Polyimide has wide ranging properties of optical transparency, heat stability, mechanical strength, dimensional stability, thermal conductivity, dielectric properties, etc. Fullerene is a zero dimensional hollow symmetrical nanocarbon, frequently employed as nanofiller in the polymers. Fullerene has been reinforced in the polyimide films to further augment the exclusive features and performance. This state-of-the-art review basically emphases the fundamentals, structure, properties, and applications of polyimide films, especially the films reinforced with fullerene nanofiller. The polyimide/fullerene nanocomposite films have been prepared using facile routes such as solution casting, spin casting, in situ method, and other film forming methods. Fullerene nanofiller has been filled in numerous designed polyimides. Number of experimental and theoretical studies have been performed on the high performance polymer/fullerene nanocomposite films. The structural diversity of the polymer/fullerene nanocomposite films and inimitable characteristics have led to significant applications in the optoelectronic devices, photodetectors, and sensors. [ABSTRACT FROM AUTHOR]

Charge injection and conduction are fundamental phenomena that occur in dielectric materials when subjected to both low and high electric fields. This paper delves into the exploration of various conduction mechanisms, including space-charge-limited current (SCLC), Schottky charge injection, Poole–Frenkel, and hopping charge conduction, to elucidate the prevailing conduction mechanism in single and multilayer polyimide (PI)/SiO2 nanocomposite films across a range of temperatures. At elevated electric field strengths, the conduction behavior transitions from ohmic to exhibiting a non-linear current–voltage dependence. The investigation highlights that PI nanocomposite films display distinct conduction behaviors contingent on both the applied electric field and temperature conditions. The insights derived from this study provide valuable empirical groundwork and explanations for conducting current measurements in PI-based insulation systems, particularly in applications such as motor insulation for electric vehicles. [ABSTRACT FROM AUTHOR]

Neat polyimide films are known to be dense and rigid. They are therefore not suitable for use in membranes, sensors and sustainable energy storage applications. In this study, a novel technique has been used to simultaneously improve the porosity, rigidity, damping ability and impact resistance of polyimide membranes. It is demonstrated that dispersion of a small amount of polyaniline copolymer-modified clay of about 0.25–0.5 wt.% into the polyimide matrix resulted in an enhanced storage modulus while maintaining high damping ability and glass transition temperature, Tg. Novel polyimide/substituted polyaniline-copolymer-clay nanocomposite membranes containing poly(N-ethyl-aniline-co-aniline-2-sulfonic-acid)-modified-clay (SPNEAC) was successfully prepared and incorporated into the polyimide matrix to form modified clay/polyimide nanocomposites. UV-Vis analysis of the nanocomposite films shows that the optical transparency of the SPNEAC-PI nanocomposite membranes decreased with increasing SPNEAC concentration due to the high UV-Vis absorption of SPNEAC. Transmittance of about 3% was observed in the nanocomposite membrane containing 5 wt.% modified clay at 500 nm wavelength, which is significantly lower than that for the neat PI membrane of about 36%. The dispersion of SPNEAC containing a high concentration of clay (≥40 wt.% clay), in polyimide matrix, resulted in the attainment of a higher degree of imidization than was possible for the organoclay/polyimide nanocomposite. This behavior is believed to be due to the synergistic interaction between PI and SPNEAC. A correlation of the morphology and elastic modulus of the SPNEAC2/PI nanocomposites shows that at low loading of SPNEAC 2 ≤ 0.5 wt.%, the cross-sectional morphology of the composite is an open, spiky, weblike structure with a storage modulus of about 1 GPa, but it progressively evolves into densely packed microspheroids with storage moduli of ≥2 GPa at 10 wt.% SPNEAC2. The impact energy of SPNEAC/PI composites, calculated from the α-transition peak area, increased with increasing SPNEAC loading and were about 4 times that of neat PI at 10 wt.% SPNEAC. [ABSTRACT FROM AUTHOR]

An ordered micron-sized honeycombed macroporous polyimide (PI) film was efficiently fabricated from polyamic acid-b-polystyrene (PAA-b-PS) copolymer. The synergistic effect of the hydrogen bonding and π–π interaction contributes to the generation of this distinct morphology of PAA-b-PS. [ABSTRACT FROM AUTHOR]

In this work, a new diamine was designed by connecting flexible structures such as ether bond and aliphatic carbon chain between benzene rings, and was synthesized and purified through simple reactions such as Suzuki reaction. Finally, a series of polyimide (PI) films were synthesized by copolymerization with 4.4'-diaminodiphenyl ether (ODA)\pyromellitic dianhydride (PMDA) in different proportions. We prepared polyimide films with new monomer copolymerization ratios of 1% (PI-1), 5% (PI-2), 10% (PI-3), and 20% (PI-4). The polyimide films showed excellent glass transition temperatures, which were attributed to their unique bent architectures. The mechanical and thermal properties of the thermosets were studied using tensile testing, static thermomechanical analysis (TMA), and thermogravimetric analysis (TGA). As the results, the films exhibited the optimal glass transition temperatures (317.56°C–381.91°C), and the component with the highest copolymerization ratio has a 15% decrease in glass transition temperature compared to the component without copolymerization. Moreover, PI-1-PI-4 showed good heat resistance in the N2 atmosphere. The temperatures corresponding to a 5% heat loss in the films (T5%) were 458.12 °C–548.75°C, respectively. [ABSTRACT FROM AUTHOR]

Atomic oxygen (AO) is the dominant constituent of the residual atmosphere in low Earth orbit (LEO). AO collides with spacecraft at a velocity of 8 km/s, causing oxidation and erosion of polymeric materials. Particularly in very low Earth orbit (VLEO) at altitudes below 300 km, the AO density is at least ten times that at 500–700 km, and the concentration of molecular nitrogen (N 2) is 10% or more. Such high-flux AO and N 2 can cause nonlinear processes and mass losses for polymers. This study aims to clarify the optical property changes for polymeric materials exposed to LEO and VLEO in the Material Degradation Monitor (MDM) mission onboard the Super-Low-Altitude Test Satellite (SLATS). The AO and N 2 fluences and the UV irradiances were estimated using the NRLMSISE-00 atmospheric and solar radiation models. The relationships were investigated between the changes in CCD images and the estimated fluences of the samples. For silsesquioxane (SQ)-coated polyimide film, the diffuse reflection of visible light increased noticeably with an AO fluence above 1 × 1021 atoms/cm2. The formation of a silica layer on the coating induces cracks. For silver-coated FEP films, the diffuse reflection increased entirely at AO fluences above 3 × 1021 atoms/cm2. The AO and N 2 collisions would erode and roughen the FEP surfaces. Visible transmission through silver-coated FEP films also increased locally with increasing AO fluence, indicating that some AO oxidized the silver layer despite the presence of an Inconel (Ni alloy) layer. The visible reflection from Beta Cloth was decreased by its reaction with UV. Further, the competitive reactions with UV and AO resulted in two-step changes in the visible reflection from the ETFE polymer (cable covering). • Density of atomic oxygen (AO) is exceptionally high in very low Earth orbit (VLEO). • Material Degradation Monitor (MDM) exposed 13 spacecraft materials to LEO and VLEO. • Cracks were seen for SQ -coated polyimide at the AO fluence above 1 × 1021 atoms/cm2. • Surfaces of FEP films were roughened by the AO fluence above 3 × 1021 atoms/cm2. • Silver coatings of the FEPs would be oxidized by AO despite Inconel coating. [ABSTRACT FROM AUTHOR]

One of the important problems of the modern rheology of polymer materials, namely, the possibility of describing the deformation of amorphous polymers within the framework of linear rheological relationships between relative deformation and deforming stress or the need to use nonlinear rheological equations is considered. The criteria for distinguishing these approaches, namely, the determination of the corresponding critical values of the macro- and microphysical characteristics of the material and the conditions for carrying out the mechanical tests are also discussed. In particular, the difference between the influence of kinetic and thermodynamic nonlinear effects on the regularities of deformation processes of amorphous polymers in warm and frozen states was noted. The influence of nonlinear effects on the general shape and characteristics of individual stages of the "relative strain - deforming stress" diagram at deformation of polymer samples with specified values of strain rate and temperature is analyzed in detail. The results of the theoretical analysis were used for the physical interpretation of the general form and features of individual stages of the tensile test diagrams of amorphous polyimide films (V. D. Natsik, H. V. Rusakova, S. V. Lubenets, V. A. Lototskaya, and L. F. Yakovenko, Fiz. Nyzk. Temp. 49, 569 (2023) [Low Temp. Phys. 49, 521 (2023)]), empirical estimates for the rheological characteristics of this polymer were obtained. [ABSTRACT FROM AUTHOR]

The influence of the exposure time in the initial state at room temperature, which is comparable to the time of operation in orbit (5, 8, and 10 years), on the mechanical properties of polyimide films of the kapton H type of different thicknesses and manufacturers under tensile conditions at room temperature was studied. A change in all studied characteristics (forced elasticity limit, fracture stress, total deformation before fracture, contributions of individual strain components to it, modules of elasticity, and forced elasticity at individual stages of deformation) was revealed. The changes were different for amorphous and partially crystalline films, as well as for amorphous films of the same thickness, but obtained by different manufacturers. [ABSTRACT FROM AUTHOR]

Stretching has been extensively applied for decades in the production of polyimide (PI) materials with improved mechanical, electrical, and thermal properties. Meanwhile, a detailed understanding of the molecular motions during stretching is still limited. Herein, the thermomechanical behaviors of uniaxially stretched PI films prepared from 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl) benzidine (TFDB) are studied, and the possible molecular motions responsible for the sub‐glass transition temperature (Tg) stretchability and retraction after stretching are systematically investigated. Based on X‐ray diffraction and dynamic mechanical analysis, it is revealed that both the sub‐Tg stretchability and retraction correlates with β2 relaxation, which originates from the highly cooperative molecular motions of conformational rotations involving segmented BPDA units. A thermodynamic model is established and applied for the analysis of the retraction behaviors of stretched BPDA‐TFDB PI films. It is found that the increase of entropy under stretching plays a significant role in most retraction cases. However, as the stretching temperature increases, the α relaxation‐correlated large‐scale molecular motions emerge. Such motions partially counterbalance the conformational rotations of BPDA segments, leading to an enhanced contribution of enthalpy decrease during the retraction of BPDA‐TFDB PI films. [ABSTRACT FROM AUTHOR]

Total reflection X‐ray fluorescence (TXRF) is widely used for trace elemental analysis, wherein a thin monochromatic X‐ray beam is typically applied at glancing angles. The actual volume of the sample measured by the instrument (analysis volume) depends on the dimensions of the X‐ray beam and glancing angle, and it is a key feature in sample preparation for TXRF analysis. Herein, the analysis volume, including the analysis region and analysis height, was experimentally evaluated. A thin Au layer approximately 5 nm thick and 1 mm in diameter was prepared at a specific position on a flat glass substrate using a vacuum evaporation device. The position of this Au layer was controlled by manipulating a mask plate with a small hole. Nine samples were prepared at different Au layer positions and analyzed at 8 azimuth angles using a tabletop TXRF instrument. Finally, the Au XRF intensity distribution was visualized on a glass substrate. It was found that the XRF emitted over a diameter of approximately 5 mm was effectively detected using the tabletop TXRF instrument. The analysis height was experimentally evaluated using a thin Au layer deposited on a polyimide film 5 mm in diameter and 5 nm thick. The Au layer height was adjusted by inserting polyimide thin films between the Au layer and the glass substrate. The Au XRF intensity drastically decreased with increasing Au layer height, suggesting that the XRF emitted from the sample is effectively detected at heights of <10 μm by using the described setup. [ABSTRACT FROM AUTHOR]

The molecular orientation of steroidal side chains at rubbed polyimide (PI) surfaces is studied by sum frequency generation (SFG) vibrational spectroscopy. The main objective is to find a correlation between the molecular structure of the PI film and the liquid crystal alignment on the polymer. Analysis of the SFG spectra shows that rubbing of the polymer film appears to cause conformational changes in the methyl group of the polymer side chain near the steroidal structure. However, rubbing does not significantly influence the orientation of the isopropyl group at the end of the polymer side chain. This shows that the liquid crystal alignment is not correlated with the orientation of the isopropyl group. [ABSTRACT FROM AUTHOR]