Search

[Display omitted] • The material is prepared on a flexible polyimide and has good bending resistance. • The material can undergo multistage phase transition, which can effectively improve the storage density. • The material has extremely low resistance drift, and the electronic structure remains essentially unchanged after aging testing. • The device can achieve reversible SET/RESET operation before and after bending without being affected. The In 2 Se 3 -doped Sb phase change material was deposited onto a polyimide substrate using magnetron sputtering technique. A comprehensive investigation was conducted on the thermal stability, bending resistance, crystal structure, and electrical properties of this material. The findings revealed its remarkable thermal stability, data retention, and bending resilience, particularly in the In 0.05 Se 0.19 Sb 0.76 film, which exhibited minimal resistance drift. The aging test confirmed the stability of the electronic structure in In 2 Se 3 -doped Sb, accompanied by reduced structural relaxation. Notably, no new crystalline phase emerged in In 0.05 Se 0.19 Sb 0.76 film, but stronger In-Sb bonds were formed. Raman spectroscopy and bending tests further indicated that deformation had minimal impact on the film's structure and surface. Utilizing the In 0.05 Se 0.19 Sb 0.76 material and polyimide substrate, a flexible phase change memory device demonstrated reliable SET/RESET operations even after bending, offering three stable resistance states for multilevel storage. This enhanced the storage density, making In 2 Se 3 -doped Sb material a promising flexible phase change material with excellent performance and vast potential for applications in phase change storage, such as electronic fabrics and flexible smart wearable electronics. [ABSTRACT FROM AUTHOR]

[Display omitted] • ToF-SIMS surface analysis of polyimide layers only revealed surface contamination. • A depth profiling approach allowed to obtain chemical information on the layers. • The use of a large cluster ion source enabled preservation of molecular information. • Multivariate analysis pointed out the characteristic mass peaks for each layer. • This approach allowed to discriminate polyimide layers with very similar structures. Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, high-power and high-temperature applications. However, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer. Thanks to their high operating temperature and dielectric strength, spin coated polyimide (PI) layers are considered ideal candidates for SiC devices passivation and insulation. In this view, a robust methodology for the physico-chemical characterization of such PI layers is required. Thanks to the use of time of flight-secondary ion mass spectrometry (ToF-SIMS), a SIMS-based surface-sensitive technique that provides specific identification of molecules, it was possible to distinguish different types of PIs employed in commercial SiC devices and postulate their molecular structure. This was obtained after careful selection of the analytical conditions used for the characterization of the specimens. The results attained in this study open the way for further improvements in one of the most key issues in the development of higher SiC power devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A mathematical model for the influence of the transition layer on metal-polymer film adhesion. • The growth of a transition layer featuring metal nanoparticles between Ni and PI has been proposed for the first time. • The film with a transition layer can withstand more than twice the maximum tensile force of untreated Ni-PI films when the resistance change reaches 10%. The shear strength between Ni and PI has increased by more than 50%. • This research provides a fine application prospect in flexible electronics, facilitating the application of these types of sensors in harsh environments. Metal-polymer films are widely used for flexible sensors and actuators, enduring various mechanical loads and facing the risk of structural damage. In this work, a method of manipulating the metal-polymer interface characteristics by metal nanoparticles in the transition layer is presented to prevent film fracture and restrain electrical failures. A transition layer with nickel (Ni) nanoparticles is grown on the surface of polyimide (PI) film through the stages of ring cleavage, ion exchange, and reduction. Further, the research investigates the influence of three parameters — the concentration of ring cleavage solution, the time of ring cleavage, and the concentration of reductant — on the thickness and particle morphology of the transition layer. After depositing ∼ 200 nm Ni film by magnetron sputtering, the film with a transition layer can withstand twice more than the maximum tensile force of untreated Ni-PI films when the resistance change reaches 10 %. The transition layer featuring metal nanoparticles increases the shear strength between Ni and PI by over 50 %. This method has been proposed for the first time, which considerably improves the adhesion properties of these two widely used materials, which provides a fine application prospect in flexible electronics. [ABSTRACT FROM AUTHOR]

Conductive polyimide/metal (PIC/Cu) composite fibers are prepared by depositing a dense and uniform conductive copper layer on the surface of carboxylated polyimide fibers, which exhibit an excellent electromagnetic interference (EMI) shielding performance. The bonding strength of heterogeneous interfaces is enhanced by the nickel nanoparticles (Ni NPs) embedded on the polyimide fiber surface by nanoscale mechanical interlocking without any adhesive layer. More importantly, the nickel layer-protected PIC/Cu fibers exhibit an excellent electrical conductivity even under a high temperature condition, ensuring their application in some harsh environments. [Display omitted] • A novel polyimide-based conductive fibers were fabricated by continuous electroless metal plating. • High interfacial bonding strength was obtained through nanoscale mechanical interlocking. • Uniform Cu layer endowed composite fibers with high conductivity and EMI shielding performance. • Further incorporation of nickel layer provides a remarkable high-temperature electrical stability. Surface metallization of high-performance polymer fibers via electroless plating represents a significant advancement in producing lightweight, flexible and durable electromagnetic interference (EMI) shielding fabrics. The conventional process for metallization of polyimide (PI) fibers faces challenges, including complex procedures and insufficient interfacial adhesion between the metal layer and fiber matrix. Herein, carboxylate-containing PI (PIC) fibers were developed to mitigate the mechanical degradation caused by traditional alkaline etching. Conductive composite fibers (PIC/Cu) were successfully produced through a continuous electroless copper plating process. The robust PIC/Cu interfacial bonding achieved based on nanoscale mechanical interlocking through Ni nanoparticles imparts excellent flexibility and durability, evidenced by only a 4 % increase in electrical resistance after 5000 bending cycles. The dense, uniform copper layer provides high conductivity (1.3 × 104 S/cm), resulting in an optimal EMI shielding efficiency of 63.4 dB for the corresponding fabric. Moreover, PIC/Cu-Ni fibers prepared by further electroless plating of nickel layer on the surface of PIC/Cu fibers demonstrate remarkable electrical stability across temperatures ranging from 50 to 350°C, with only a 1.2 % reduction in conductivity after exposure to 350°C for 1 h. These findings advance the development of high-performance conductive PI fibers for applications in aerospace vehicles and high-temperature environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • A laser-induced graphene was introduced on the surface of PI nanofiber membrane. • The TENG outputs were improved by the enhanced charge transfer efficiency. • The arrangement of the graphene patterns crucially impacts the charge transfer process. • The TENGs have a great potential in wearable self-powered display systems. In the realm of self-powered systems, the efficacy of triboelectric nanogenerators (TENGs) has garnered significant attention which hold promise for revolutionizing energy supply technologies. However, enhancing their output performance remains a challenge in the field. In this paper, a laser-induced graphene (LIG) pattern was introduced beneath a polyimide (PI) nanofiber membrane, serving as an efficient charge transfer layer (CTL) significantly amplifying the transfer of friction charges, thereby enhancing the charge storage capacity. The inclusion of the LIG pattern in the TENG design has resulted in a remarkable improvement in the outputs. Furthermore, the strategic arrangement of the LIG patterns crucially impacts the charge transfer process, aligned with electrostatic equilibrium principles, and resulting in a structurally stable and cost-effective CTL. When subjected to an external force, the enhanced TENG exhibited a power density sufficient to power small electronics like LED lights and calculators. Finally, wearable self-powered display systems were designed by combing the TENG based on PI nanofiber membranes with the electroluminescent fibers. It is possible to release the functional displays and real-time information transmission, providing an innovative and efficient design idea for the practical application of TENGs as the power supply of microelectronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • PHSN Enhancement: Novel cage-like PHSN boosts polyimide materials' AO resistance. Key for aerospace. • Molecular Dynamics: Reveals PI/PHSN's AO resistance via reaction pathways and surface analysis. • DFT Analysis: Uses density functional theory to identify AO reaction sites on PHSN, inhibiting volatilization. • Mechanism Discovery: Cage-like PHSN transforms AO to SiO 2 , offering molecular-level protection. • Aerospace Applications: Provides insights for AO erosion protection in spacecraft materials and design. Polyimide (PI) has excellent insulating properties and is widely used in aerospace electrical transmission devices and equipment. Polysilazane coatings have demonstrated excellent resistance to reactive atomic oxygen (AO). However, the understanding of the atomic oxygen erosion mechanism for polymer materials mixed with polysilazane components remains limited. In this study, a cage-like polyhydroxysilylazane (PHSN) primarily composed of silicon and nitrogen was designed. Two PI/PHSN hybrid structures were established, and their resistance to AO erosion, reaction pathways, and surface separation products were explored through reactive molecular dynamics simulations. Density functional theory (DFT) was employed to analyze the molecular orbitals of PHSN at different stages, predicting possible reaction sites for AO. The natural binding of generated small molecular fragments to PHSN side chains was studied through binding energy, revealing the volatilization inhibition mechanism of these small molecular fragments. Results indicate that the added cage-like polyhydroxysilylazane enhances the polymer's resistance to AO erosion by absorbing AO and converting it into SiO 2. This study explores the protective behavior of PHSN nano-cages at the molecular level, providing a new perspective for the design of AO erosion protection systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simple methods of impregnation and thermal treatment are used to synthesis PGPI composites. • PGPI composites modified by PG8 have a strong π-π stacked crystalline structure. • Photo-Fenton synergistic catalytic system accelerates Fe2+/Fe3+ cycling and effectively inhibits photogenerated carrier recombination. • PGPI composites possess high photo-Fenton catalyzed oxidative degradation efficiency driven by visible light. Composite material (PGPI) of polyimide (PI) modified by C.I. Pigment Green 8 (PG8) were prepared by solid-phase thermal polycondensation, impregnation and thermal treatment. The introduction of PG8 enhanced the π-π stacked crystalline structure and the visible light absorption of PI. The photo-Fenton synergistic system can effectively increase the decomposition efficiency of H 2 O 2 , accelerate Fe2+/Fe3+ cycling and reduce the recombination of photogenerated carriers. The synergistic oxidative removal of TH (Tetracycline hydrochloride, 50 ppm) by PGPI after 40 min under visible-light irradiation was 95.1 %, which was significantly better than that of the photocatalysis alone (40.7 %) and the Fenton reaction alone (55.0 %). [ABSTRACT FROM AUTHOR]

[Display omitted] • The introduction of CeO 2 could well modulate the microstructure of CMSMs. • CeO 2 specially enhances the separation performance of CMSMs for O 2 /N 2. • The separation performance could be finely controlled by altering the CeO 2 content in CMSMs. • The CMSMs can enrich the O 2 molar concentration from initial 21% of compressed air to 77.3% by one single step. In this study, CeO 2 /carbon composite molecular sieving membranes (CMSMs) were prepared on carbonaceous plate supports using polyimide as precursor and cerium oxide (CeO 2) as fillers via spin-coating method and pyrolysis. The microstructure and properties of CMSMs were analyzed by thermogravimetric analysis, infrared spectroscopy, X-ray diffraction, scanning electron microscope, particle size distribution and gas permeation test. The influence of the filler amount of CeO 2 on the microstructure and performance of CMSMs was mainly investigated. The results showed that the incorporation of CeO 2 significantly enhanced the graphitization degree and structural compactness of CMSMs. The optimal gas separation performance of CMSMs reaches to 16.3 for O 2 /N 2 selectivity and 240.3 Barrer for O 2 permeability, which is fabricated by the precursor containing CeO 2 content of 0.2 % under the permeation condition of 30 °C and 0.02 MPa. [ABSTRACT FROM AUTHOR]

The all organic PI composites with size adjustable hollow polydopamine microspheres (H-PDA) exhibited decreased the dielectric constant and dielectric loss with enhanced mechanical performance. [Display omitted] • The ultra-low dielectric polyimide composites with hollow polydopamine microspheres were successfully synthesized. • The PI/H-PDA composite achieved the ultra-low dielectric constant of 1.96 with a dielectric loss of 0.0123 at 1 MHz. • The PI/H-PDA composites possessed excellent thermal stability and mechanical properties. Polydopamine (PDA) has been extensively investigated due to its excellent adhesion ability and versatile chemical potential for secondary reactions. However, the potential application of hollow polydopamine microspheres (H-PDA) in the field of low-dielectric electronic packaging remains an unexplored area. Here, H-PDA microspheres with adjustable size were synthesized by a template-assisted approach, and the influence of size and content of H-PDA on the comprehensive performance of PI/H-PDA composites was explored in detail. The morphology observation revealed that the presence of H-PDA could be homogeneously dispersed in the PI matrix, and the PI/H-PDA composite containing 2 wt% H-PDA-800 achieved the lowest dielectric constant of 1.96 with a dielectric loss of 0.0123 at 1 MHz. It was attributed to the synergistic effects of nano-sized air bubbles from H-PDA and the dielectric confinement effect. Meanwhile, PI/H-PDA composites maintained high thermal stability (T 5 > 517 °C). In addition, the incorporation of H-PDA had a strengthening and toughening effect on PI composites, which can be explained by the sliding theory of macromolecular chains. This work offers a feasible strategy to obtain ultra-low dielectric constant of porous PI composites while maintaining good mechanical properties and thermal stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel MOFs coating with excellent flexibility, bonding property and AO resistance was prepared. • Homogeneous MOFs film formation was achieved through adjustment of binding energy and surface energy. • Porous MIL-53(Al) coatings exhibited better flexibility and AO resistance than dense aluminum-based coatings. Rapid development of coatings with atomic oxygen (AO) resistance, which benefit long-duration exploration mission in low earth orbit (LEO), poses a challenging requirement on flexible coatings with excellent bonding property. Metal organic framework (MOF) has abundant sites and organic–inorganic hybrid chemical composition, which displays potential in increasing AO resistance, flexibility and bonding property simultaneously. Here, we combined surface modification and spin-coating to prepare MIL-53(Al) (a kind of materials of Lavashir skeleton) coated polyimide (PI) thin film exhibiting excellent flexibility, bonding property and AO resistance, which had no cracks after bending 1000 times, had no peeling off and had only 12% erosion yield compared with pristine PI, verified by the bend test, cross-cut tape test and AO exposure experiment respectively. Also, the mechanism of homogeneous film formation was explained, in which MIL-53(Al) seed layer provided binding force between coating and substrate, and the microstructural transformation caused by breathing effect and negative linear compressibility (NLC) prevented the occurrence of coating cracking. This work extends the application range of MIL-53(Al), optimizes the application of MOFs film formation, and offers a new idea to protect the spacecrafts in LEO. [ABSTRACT FROM AUTHOR]

Nowadays, flexible substrates, as a part of flexible electronics, receive great attention by its wide application. Particularly, organic light emitting diodes and photovoltaics place high demands on the optical transmittance of flexible substrates. In this paper, direct fluorination is selected to treat commercial poly(ethylene terephthalate) (PET) and polyimide (PI) films. A suitable gradient distribution of fluorine atoms in the fluorinated layer were obtained in the vertical direction of the PET film by optimizing the conditions of direct fluorination. In this way, the refractive index was reduced by the introduction of the fluorine atoms, and the fluorine atoms with gradient distribution on the film's vertical direction led to the gradient decrease of the refractive index. Given this gradient-refractive index, a high broadband and omnidirectional transmittance of >93.0% was achieved by such a non-nanostructured surface over the entire optical wavelength (380–2200 nm), while the transmittance still remains relatively high (>85.0%) when the incident angle is increased from 0° to 60°. Moreover, this cost-effective and easy method presents its universality with the treatment of PI film, which also achieves high broadband and omnidirectional transmittance by direct fluorination. Unlabelled Image • High transmittance of PET and PI films can be achieved by direct fluorination, the transmittance of fluorinated PET can reach 97.5% at 850nm. • The transmittance of the fluorinated flexible substrates is broadband (380-2200nm) and omnidirectional, the transmittance still remains relatively high (> 85.0%) when the incident angle is increased from 0° to 60°. • The gradient-refractive index of fluorinated flexible substrate is non-nanostructured and achieved by fluorine diffusion. [ABSTRACT FROM AUTHOR]

Organic residues formed when using organic binders to increase the adhesive strength of Cu ink to PI substrates degrade the electrical conductivity of Cu electrodes. Binder-free Cu ink can be used to fabricate highly conductive Cu electrodes but lead to poor adhesion owing to inherently weak adhesion between the polymer substrates and metals. We therefore propose a facile method to enhance adhesion between a printed copper electrode formed by flash light sintering and a polyimide (PI) substrate without sacrificing the electrical conductivity by forming an interlocking structure at the interface between the Cu electrode made of binder-free ink and PI substrate through simple chemical treatment. The surface of the PI substrate was converted to polyamic acid (PAA) via potassium polyamate formation after sequential chemical treatment using potassium hydroxide and hydrochloric acid. During the flash light sintering process, the PAA layer, which is much softer than PI, could easily migrate into the cavities between the sintered Cu nanoparticles due to the pressure difference originating from evaporation of H 2 O released through reduction of the oxide shell of Cu nanoparticles. Thus, an interlocking structure was formed and the substrate surface quickly reverted to PI by absorbing thermal energy during sintering. The increased contact area between Cu nanoparticles and the substrate surface of the interlocking structure could explain the dramatic improvement of the adhesion strength of the Cu electrode from 0 B to 5 B, which corresponds to the highest class of adhesion strength. In addition, the resistivity of the Cu electrode fabricated in this process was measured to be 2.5 times larger (4.17 μ Ω·cm) than that of bulk Cu, which has not been achieved for printed Cu electrodes before. Our results could lead to new perspectives in the field of printed electronics. • A simple method to enhance adhesion between a Cu electrode and a polyimide substrate by forming an interlocking structure • Dramatic improvement of the adhesion strength from 0 B to 5 B through interlocking structure • Demonstration of low resistivity comparable to that of bulk, which has not been achieved for printed Cu electrodes before. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (RGO) loaded with magnetic Fe 3 O 4 nanoparticles was synthesized through coprecipitation. Then, an Fe 3 O 4 /RGO-modified polyimide aqueous sizing agent was successfully synthesized with ultrasonic dispersion technology and coated on the surface of a high modulus carbon fiber (CF) under an applied magnetic field. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results show that the Fe 3 O 4 with a cubic spinel crystal structure was successfully prepared. The morphology and particle size of the Fe 3 O 4 /RGO were characterized using transmission electron microscopy (TEM), indicating that Fe 3 O 4 was uniformly dispersed onto the RGO sheet. Fourier transform infrared spectroscopy (FTIR) and a laser particle size analyzer proved that the aqueous dispersion of polyamic acid (PAA) was obtained with an average particle diameter of 158 nm. The mechanical property testing results showed that the interlaminar shear strength (ILSS) of CF/polyimide (PI) composites consisting of CFs coated with the Fe 3 O 4 /RGO-modified PI aqueous sizing agent under a magnetic field increased by 159.0%. This is attributed to the orientation of the Fe 3 O 4 magnetic particles under a magnetic field that allowed them to be uniformly dispersed on the graphene, effectively weakening the potential for graphene agglomeration. • A Fe 3 O 4 /reduced graphene oxide (RGO) modified polyimide aqueous sizing was prepared. • A PAA-Fe 3 O 4 /RGO sizing agent was magnetically coated on the surface of the high modulus carbon fiber. • The sizing agent increased the surface energy and roughness of the carbon fibers. • The interlaminar shear strength of carbon fiber/PI was increased by 159.0% due to the magnetron coated sizing agent. • The interface adhesion mechanism of coated carbon fiber/PI was demonstrated. [ABSTRACT FROM AUTHOR]

In this study, a new type of polyimide (PI) composite material was synthesized by a two-step method using 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPDA), 4,4′-methylenedianiline (MDA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA). The PI material was then used to prepare an ultrafiltration (UF) membrane by phase inversion method. The membrane showed a dense surface layer, a porous sublayer, and fully developed finger-like macrovoids at the bottom, which had excellent hydrophilicity and antifouling property. In the recovery experiments with a protein solution, the PI membrane displayed a satisfactory water flux recovery ratio of 90.03%. The PI membrane can operate stably in 1 mol L−1 hydrochloric acid solution, and the retention rate of BSA remains at 93%. In addition, the flux of the membrane is 325.60 L m−2 h−1 and the BSA retention rate the retention rate is still higher than 95% after soaking in various solvents for 7 days. • A novel polyimide polymer was synthesized by a two-step method using TMPDA, MDA and BTDA. • The polyimide ultrafiltration membrane with fully developed finger-like macro voids were prepared by phase inversion. • The PI membrane displayed a satisfactory water flux recovery ratio of 90.03% in the recovery experiments. • The PI membrane can operate stably in 1 mol L-1 hydrochloric acid solution and the retention rate of BSA remains at 93%. • The flux of the PI membrane is 325.60 L m-2h-1 and the BSA retention rate is still higher than 95% after soaking in various solvents for 7 days. [ABSTRACT FROM AUTHOR]

Abstract The high durability of low-k value is the key parameter for the low dielectric materials especially used under humid conditions, because the k value is very sensitive to moisture. Here, to decrease the dielectric constant and improve the water resistance, a series of novel co-polyimides are successfully prepared based on cross-linkable diamine monomer by a two-step pathway combining polymerization and crosslinking reaction. It is intriguingly found that with the gradual increase content of cross-linkable group, the dielectric properties, water resistance as well as thermal and mechanical properties of those co-polyimides can be finely tuned. After cross-linking, the dielectric properties are significantly enhanced and the film surface changed from hydrophilic (78.7–89.2°) to hydrophobic (93.0–104.2°), which endow the cross-linked films with superior water resistance and high durability of low-k value. The best performance is obtained for cross-linked co-polyimide (CL-Co-PI-4) containing 30% cross-linkable group. The CL-Co-PI-4 exhibits low dielectric constant of 2.32 and dielectric loss of 0.016 at 1 MHz. Excitingly, the CL-Co-PI-4 demonstrates an extremely low water uptake of 0.051 ± 0.010%, which represents the best water resistance for the reported polyimides. After exposing to different humidity conditions for 12 h, the increasing percentage of k value is very low and below 0.84%. The CL-Co-PI-4 still keep its k value below 2.35 after equilibrating at 75% R.H. for 14 days. The excellent moisture resistance and overall performance make the CL-Co-PI-4 a good candidate for dielectric material under both dry and humid conditions. Graphical abstract A series of new fluorinated co-polyimides (CL-Co-PIs) containing hydrophobic crosslinked network were synthesized. The CL-Co-PIs exhibit significantly reduced dielectric constant, extremely low water uptake and outstanding stability of low k value at high humidity for a long time. Unlabelled Image Highlights • A series of fluorinated co-polyimides containing hydrophobic crosslinked network were prepared. • The properties of crosslinked films can be finely tuned by changing the content of cross-linkable group. • The crosslinked films have significantly reduced dielectric constant and superior water resistance. • The crosslinked films show excellent stability of low-k value under humid condition and high temperature. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Phosphotungstate/polyimide (MPWPI) photocatalyst was synthesized. • Self-assembly melamine phosphotungstate as a precursor. • The effects of electron delocalization and alternate stacking structure are critical. • 5MPWPI shows superior photocatalytic activity for imidacloprid. • Charge transfer and photocatalytic reaction mechanism of MPWPI were proposed. Abstract In previous research, phosphotungstic acid (H 3 PW 12 O 40 , PW)/polyimide (PI) composites were constructed using insoluble heptazine melem. We found that the introduction of PW can cause a slight increase in the light absorption of the composites. To further study the effects of polyoxometallate on the light absorption and photocatalytic activity of photocatalysts, a novel phosphotungstate/polyimide photocatalyst (MPWPI) was constructed via in situ solid-state thermal polymerization using melamine phosphotungstate ((C 3 N 6 H 7) x [PW 12 O 40 ], MPW) synthesized by water-soluble triazine melamine (C 3 H 6 N 6 , MA) and PW. The structural and morphological results confirm the successful construction and the alternate stacking structure of MPWPI. The alternate stacking structure is more favorable for the contact between polyoxometallate and polyimide, and it also facilitates the electron delocalization through the intermolecular phosphotungstate anions-π interactions. This will lead to the extended light absorption and enhanced visible-light photocatalytic degradation capacity. The UV–visible diffuse reflectance spectroscopy (UV–Vis DRS) results display that the light absorption of MPWPI can be obviously extended to 800 nm. Compared to the inactive polyimide and phosphotungstate, MPWPI exhibits extraordinary photocatalytic activity of imidacloprid under visible light irradiation (λ > 400 nm) for the extended light absorption and suppressed carriers recombination. For this photocatalytic system, the OH and O 2 − are the main active species. Furthermore, the encapsulated phosphotungstate anions in the specific structure of MPWPI give it excellent recyclability for the inhibited polar solvent dissolution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MP-GO was prepared by introducing 4-amino-1-methypiperidine. • The MP-GO can act as a curing catalyst for polyimide nanocomposites. • The oxygen barrier property of PI/MP-GO 1 wt% was 80% better than pristine PI. Abstract We synthesized methylpiperidine-functionalized graphene oxide (MP-GO) by introducing 4-amino-1-methylpiperidine into reactive epoxy and/or carboxylic acid groups on pristine GO. Then, we applied the MP-GO as a curing catalyst for polyimide (PI) nanocomposites. The MP-GO was found to be an effective base-catalysts for the thermal conversion of polyamic acid (PAA) precursor to PI. Interestingly, when 3 wt% of MP-GO was added to the PI matrix, the complete imidization of nanocomposites was achieved at a temperature lower than 200 °C. In addition, the PI/MP-GO nanocomposite films exhibited reinforcement of the oxygen barrier properties which were even better than those of pristine PI, due to the excellent dispersion state of MP-GO and the favorable non-covalent interaction between MP-GO and the PI matrix. Comparison to pristine PI, the oxygen permeability of nanocomposite films that contained only 1 wt% of MP-GO loading was significantly decreased, by about 80%. Furthermore, all the PI/MP-GO nanocomposites exhibited high thermal stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • High electrical conductive patterns are laser-synthetized on two flexible commercial substrates: polyetherimide and polyimide. • The laser-synthesis process is studied in detail to optimize the electrical conductivity of the resulting materials. • The two carbon-based materials obtained are structurally and morphologically characterized and identified as laser-induced graphene and glassy amorphous carbon. • The use of both materials for the fabrication of electrodes for energy storage pplications is also presented. One of the key challenges in the field of flexible electronics relies on finding conductive materials that can withstand bending and stretching stresses while maintaining their performance. In this context, this work presents a comparative study of laser-induced conductive materials from the direct laser-scribing of two commercial flexible films: the benchmark Kapton® HN polyimide (PI) precursor and the UltemTM 1000 polyetherimide (PEI) alternative contender. The synthesis process on both materials is optimized in terms of electrical conductivity using a high-performance galvanometric laser with a wavelength of 532 nm for the fabrication of multiple samples at different laser powers and speeds. The samples are structurally characterized using Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transform Infrared Spectroscopy (FTIR) aiming at understanding the chemical and physical changes of the ablated material. The results demonstrate that the proposed setup is feasible for the synthesis of uniform and reliable conductive patterns on the surface of both substrates with high reproducibility. In particular, it is proved that PEI is more suitable precursor for flexible electronics applications which demand high electrical conductivity, leading to a sheet resistance of 3.62 ± 0.35 Ω/sq at 0.8 W and 5 mm/s once the laser-synthesis process is optimized (against the 6.04 ± 0.63 Ω/sq at 0.6 W and 5 mm/s offered by the LIG on PI). The performance of both laser-induced patterns as electrodes for the fabrication of electrochemical capacitors is also studied and compared in terms of areal specific capacitance. [ABSTRACT FROM AUTHOR]

Figure. Wear mechanism of polyimide modified with binary hybrid nano-additives. [Display omitted] • Friction coefficient evolution as a function of stepwise increase in velocity or load for a neat PI and its nanocomposite. • The excellent thermodynamic behavior of nanocomposites is beneficial for the high-temperature resistance properties in tribological applications. • The physicochemical transformation of nanofillers on the frictional interface reveals the antifriction and antiwear mechanism of carbonaceous materials. • The molecular dynamics simulations and TEM morphology of the worn fragments intuitively present the synergistic lubrication mechanism of GCNT/PI composites. The internal lubrication of polyimide (PI) with added graphene oxides (GOs) and carbon nanotubes (MWCNTs), as well as their binary hybrid nano-additives (GCNTs), were contrastively investigated under dry sliding conditions. The friction coefficient of neat PI or its nanocomposites decreases as a stepwise increase of the load fitting a negative exponential equation while growing linearly as a stepwise increase of the velocity. Micromorphological and physicochemical variations occurring at friction interfaces have been analyzed using X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy results. Given the structural discrepancy between GOs and MWCNTs, the obtaining results showed that the different microcosmic tribological mechanisms for GCNTs enable to produce a synergistic lubricating effect, resulting in facilitating the complicating interface sliding between nanocomposites and steel balls. [ABSTRACT FROM AUTHOR]

Integration of nanostructures of semiconducting materials such as zinc oxide with flexible substrates represent a great opportunity to obtain unique sensing platform especially for the biomedical market. However, the attractive optical and electrical properties of ZnO are usually obtained by growing or annealing nanostructured films at relative high temperatures (>400 °C), which are not suitable to substrates made of polymeric materials. We demonstrate in this work that high quality ZnO nanostructures can be processed at relative low temperature (<100 °C) by combining low temperature deposition process and XeCl excimer laser (wavelength 308 nm), used to locally anneal and recrystallize ZnO without affecting the underlying polymeric substrate. We obtain unique post-annealed ZnO nanostructures, grown and processed both on rigid and flexible substrates, that show comparable optical and structural properties of ZnO films that are processed at high temperatures. We discuss the effect of the laser energy density on the nanostructure by analyzing the recrystallized ZnO films through photoluminescence and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

A novel approach named laser induced molten transfer (LIMT) was proposed to rapidly fabricate the metallic patterns on the insulating substrates with high bonding strength by nanosecond laser direct writing. The laser beam selectively irradiated and melted the donor foil and transferred the molten droplets on the target substrate by the induced laser shock, resulting in the formation of designed metallic pattern. The processing parameters were firstly optimized, the morphology of transferred pattern was characterized, and the pattern conductivity and bonding strength were investigated experimentally. The optimized processing parameters for the fabrication of high-quality pattern were the scanning speed of 750 mm/s, laser power of 21 W, and scanning interval of 15 μm. This transferred copper pattern was porous and composed of aggregated micro droplets. The copper pattern surface was homogeneously rough and its edges were clear. The electrical resistivity of transferred pattern was approximately 8 times of the bulk copper due to the oxidation of copper droplets and porosity of pattern. The transferred copper pattern has good bonding strength on the glass substrate due to the existence of a copper-glass recast layer. A micro-heater pattern was integrated in a microfluidic chip, which demonstrated the LIMT approach can selectively transfer pattern on 3D surface. LIMF can successfully transfer the pure metal and alloy patterns on the various target substrates, even the flexible substrate, which further exhibited its excellent versatility and flexibility. [ABSTRACT FROM AUTHOR]

A simple and effective method was adopted to fabricate microcellular polyimide (PI)/reduced graphene oxide (GO)/multi-walled carbon nanotubes (MWCNTs) nanocomposites. Firstly, microcellular poly (amic acid) (PAA)/GO/MWCNTs nanocomposites were prepared through solvent evaporation induced phase separation. In this process, PAA and dibutyl phthalate (DBP) co-dissolved in N,N-dimethylacetamide (DMAc) underwent phase separation with DMAc evaporating, and DBP microdomains were formed in continuous PAA phase. Subsequently, PAA was thermally imidized and simultaneously GO was in situ reduced. After DBP was removed, the microcellular PI/reduced GO (RGO)/MWCNTs nanocomposites were finally obtained. When the initial filler loading was 8 wt%, the electrical conductivity of microcellular PI/RGO, PI/MWCNTs and PI/RGO/MWCNTs nanocomposites were 0.05, 0.02 and 1.87 S·m −1 , respectively, and the electromagnetic interference (EMI) shielding efficiency (SE) of microcellular PI/RGO, PI/MWCNTs and PI/RGO/MWCNTs nanocomposites were 13.7–15.1, 13.0–14.3 and 16.6–18.2 dB, respectively. The synergistic effect between RGO and MWCNTs enhanced both the electrical conductivity and EMI shielding performance of the microcellular PI/RGO/MWCNTs nanocomposites. The dominating EMI shielding mechanism for these materials was microwave absorption. While the initial loading of GO and MWCNT was 8 wt%, the microcellular PI/RGO/MWCNTs nanocomposite (500 μm thickness) had extremely high specific EMI SE value of 755–823 dB·cm 2 ·g −1 . Its thermal stability was also obviously improved, the 5% weight loss temperature in nitrogen was 548 °C. In addition, it also possessed a high Young’s modulus of 789 MPa. [ABSTRACT FROM AUTHOR]

Polyimide (PI) surface was ablated by the single pulse of picosecond laser, and the effects of laser wavelength (λ= 355 nm and 1064 nm) and fluence on surface microstructure and chemistry were explored. Scanning electron microscopy (SEM) analysis found that different surface microstructures, i.e., the concave of concentric ring and the convex of porous circular disk, were generated by 355 nm and 1064 nm picosecond laser ablation, respectively. X-ray photoelectron spectroscopy (XPS) characterization indicated that due to the high peak energy density of picosecond laser, oxygen and nitrogen from the ambient were incorporated into the PI surface mainly in the form of C O and C N C groups. Thus, both of the O/C and N/C atomic content ratios increased, but the increase caused by 1064 nm wavelength laser was larger. It inferred that the differences of PI surface microstructures and chemistry resulted from different laser parameters were related to different laser-matter interaction effects. For 355 nm picosecond laser, no obvious thermal features were observed and the probable ablation process of PI was mainly governed by photochemical effect; while for 1064 nm picosecond laser, obvious thermal feature appeared and photothermal effect was thought to be dominant. [ABSTRACT FROM AUTHOR]

On the basis of the outstanding fouling resistance of zwitterionic polymers, an antifouling ultrafiltration membrane was fabricated through phase inversion induced by immersion precipitation method, directly using the novel zwitterionic polyimide (Z-PI), which was synthesized via a two-step procedure including polycondensation and quaternary amination reaction, as membrane material. The chemical structure and composition of the obtained polymer were confirmed by using FTIR, 1 H NMR and XPS analysis, and its thermal stability was thoroughly characterized by TGA measurement, respectively. The introduction of zwitterionic groups into polyimide could effectively increase membrane pore size, porosity and wettability, and convert the membrane surface from hydrophobic to highly hydrophilic. As a result, Z-PI membrane displayed significantly improved water permeability compared with that of the reference polyimide (R-PI) membrane without having an obvious compromise in protein rejection. According to the static adsorption and dynamic cycle ultrafiltration experiments of bovine serum albumin (BSA) solution, Z-PI membrane exhibited better fouling resistant ability, especially irreversible fouling resistant ability, suggesting superior antifouling property and long-term performance stability. Moreover, Z-PI membrane had a water flux recovery ratio of 93.7% after three cycle of BSA solution filtration, whereas only about 68.5% was obtained for the control R-PI membrane. These findings demonstrated the advantages of Z-PI membrane material and aimed to provide a facile and scalable method for the large-scale preparation of low fouling ultrafiltration membranes for potential applications. [ABSTRACT FROM AUTHOR]

High energy density polymer nanocomposites with high-temperature resistance are quite desirable for film capacitors and many other power electronics. In this study, polyimide-based (PI) nanocomposite films containing the core-shell structured barium titanate@silicon dioxide (BT@SiO 2 ) nanofibers have been successfully synthesized by the solution casting method. In the BT@SiO 2 /PI nanocomposite films, the dielectric permittivity as well as the breakdown strength increase significantly. The SiO 2 shell layers with moderate dielectric permittivity could effectively mitigate the local field concentration induced by the large mismatch between the dielectric permittivity of BT and PI, which contributes to the enhancement of the breakdown strength of the PI nanocomposite films. As a result, the PI nanocomposite film filled with 3 vol% BT@SiO 2 nanofibers exhibits a maximal energy density of 2.31 J cm −3 under the field of 346 kV/mm, which is 62% over the pristine PI (1.42 J cm −3 at 308 kV/mm) and about 200% greater than the best commercial polymer, i.e. biaxially oriented polypropylenes (BOPP) (≈1.2 J cm −3 ). The thermogravimetric analysis results indicate that the BT@SiO 2 /PI nanocomposite films have good thermal stability below 500 °C. [ABSTRACT FROM AUTHOR]

Nitrogen-doped 3D flower-like carbon materials (NFCs) have been fabricated using a simple and effective strategy, namely, the hierarchical assembly of polyimide (PI) and subsequent thermal treatment. The effect of pyrolysis temperature on the structural evolution process of PI is also investigated systematically. When evaluated as anode materials for lithium ion batteries (LIBs), the as-obtained NFCs, especially NFCs-550, exhibit good electrochemical performance, including a high reversible capacity (1488.1 mAh g −1 at 0.05 A g −1 ), excellent rate performance (287.6 mAh g −1 at 2 A g −1 ), and good cycling stability (645 mAh g −1 with 96% retention after 300 cycles at 0.1 A g −1 ). The good electrochemical performance is attributed to the synergistic effect between 3D flower-like nanostructure and high nitrogen content. This approach may provide some inspiration to construct a series of heteroatom doped and hierarchical structured carbon materials using polymers for LIBs. [ABSTRACT FROM AUTHOR]

The cost of effective preparation of graphene-based nanomaterials is a challenge in high-performance flexible electrodes. We demonstrated the formation of hierarchical porous graphene (HPG) films with defects from polyimide (PI) sheets using a high repetition rate nanosecond fiber laser. The honeycomb structure with mesopores and macropores can be rapidly induced on the polyimide by the localized focused laser beam in air atmosphere. Employing laser direct writing method, the one-step synthesis and patterning of conductive HPG films were achieved directly on the surface of polyimide sheets. The results show that the unique honeycomb porous structure on HPG film is composed of few-layer graphene or graphene stacks. The lattice structure of graphene nanoplatelets contains the Stone-Wales defects. Furthermore, there are a lot of small-size graphene nanoplatelets on the surface of HPG films with high content of edge defects. These two defects can not only enhance the adsorption without compromising on high diffusivity of ions, but also contribute to the infiltration and flow of electrolyte on the surface of electrode. The proposed one-step laser direct writing technique with highly valuable suitable for developing large-scale fabrication of conductive HPG based flexible electrodes at low-cost. [ABSTRACT FROM AUTHOR]

Low-cost, flexible wearable graphene-based sensors demand a high-quality and highly conductive graphene. The scalable production of graphene is challenged by complexity, cost, and energy requirements resulting in no direct facile method for volume production. Reduced graphene oxide (rGO) is a promising graphene derivative that could serve as an alternative with similar properties of graphene. Graphene oxide (GO) is an electrical insulator due to distorted sp 2 bonding and is transformed to rGO by eliminating oxygen through a reduction process. We report an extensive reduction of oxygen in GO films with producing high quality rGO on flexible polyimide (PI) and polyethylene terephthalate (PET) substrates using ultrashort laser pulses. After laser reduction, the sheet resistance of GO significantly reduces from MΩSq−1 to few hundreds ΩSq−1 where the C/O ratio enhances from 1.8 to 10.0 obtained from XPS analysis. Raman spectroscopy revealed highly conductive rGO thin film where the I D /I G ratio decreases from 0.94 to 0.27, and I 2D /I G ratio increases from 0.12 to 0.63 confirming the restoration of sp 2 carbon as a result of laser reduction. The fabrication of LrGO based multifunction sensor and pH sensor with high sensitivity is demonstrated which provide a great potential for use in healthcare and flexible sensor applications. [Display omitted] • Ultrashort laser reduction of GO on thin, flexible polymers. • Production of high quality and highly conductive LrGO at room temperature. • Selective tuning of electrical and structural properties of rGO. • Fabrication and demonstration of LrGO based flexible sensors. [ABSTRACT FROM AUTHOR]

An anisotropic aerogel hot-extrusion strategy is designed to convert polyimide aerogels into aerogel-based paper. The multilayer interconnected aerogel-based paper exhibits excellent thermal stability and mechanical properties, and the mechanical properties remain great at high temperatures. This aerogel-based paper has huge application potential in the aerospace field. [Display omitted] • Multi-layer interconnected aerogel based paper was successfully prepared by anisotropic aerogel hot extrusion strategy. • Aerogel-based papers exhibit excellent thermal stability and stable mechanical properties (PI-1: 216.28 MPa at 25 °C). • The tensile strength of PI-1 was 3 times that of commercial polyimide paper and 24 times that of aramid paper at 400 °C. • Aerogel-based paper maintain stable mechanical property after 5000 cycles. The continuous improvement of papermaking technology has attracted widespread attention. However, the prevention of high-temperature decomposition and a subsequent decline in mechanical strength is still a significant challenge with current papermaking technology. Herein, a newly developed multilayer interconnected polyimide aerogel-based paper was successfully prepared via an anisotropic aerogel hot-extrusion strategy. Precursor solutions of highly rigid benzimidazole units containing intermolecular hydrogen bonds and linear rod-like benzimide units were first prepared. Anisotropic precursor polyimide (PAAS) aerogels with a thickness of 3 mm were then manufactured by unidirectional freeze-drying. Then, aerogel-based papers with a thickness of 40 μm and microstructure multilayer interconnected properties were obtained by a hot extrusion strategy and a thermal imidization process. This polyimide structural paper exhibited excellent thermal and mechanical properties. Through the design of micro and macro structures, the tensile strength of the aerogel-based paper was much higher than that of commercial paper at both room temperature and 400 ℃. This aerogel-based paper also exhibited high-temperature cycle stability, high flexibility, and good stretchable bending properties. The successful preparation of this aerogel-based paper demonstrates the feasibility of the hot extrusion strategy. This work provides a new papermaking technology method and broadens the application field of paper. [ABSTRACT FROM AUTHOR]

[Display omitted] • Applying electroless copper plating to fabricate advanced 5G/Sub-6 GHz antennas. • A pulsed UV laser selectively activated metal–organic catalyst on PI substrate. • Copper lines showed excellent adhesion and conductance after cyclic bending tests. • Economical process due to effective reuse of unreacted metal–organic catalyst. An improved electroless copper plating method for fabricating 5G/Sub-6 GHz antennas is reported. A catalyst, palladium ion/4-vinylpyridine (Pd2+/4VP) complex, which not only initiated electroless copper plating but also promoted the adhesion of the copper layer, was dip-coated onto a polyimide (PI) substrate. Selective curing and activation of the Pd2+/4VP complex catalyst were induced by a pulsed UV laser. Wherever the laser scanned on the PI substrate, the palladium ions were reduced to palladium atoms, and the free radicals created from the decomposition of tert -butyl peroxybenzoate (TBPB) initiated the copolymerization of 4VP and PI, which enhanced the adhesion of the catalyst on the substrate. The unreacted Pd2+/4VP was removed by ethanol and collected for reuse, hence a much-reduced material cost. By adjusting the laser power, scanning speed, defocusing distance, and electroless plating time, the optimized process condition for Cu circuit fabrication without damaging the PI substrate was found. A high-quality copper circuit pattern was achieved with a laser power of 100 mW, a scanning speed of 330 mm/s, a defocusing distance of 2.0 mm, and an electroless plating time of 40 min. The copper patterns exhibited excellent adhesion and maintained good conductance after the bending fatigue tests. This laser treatment approach is simple, cost-effective, and applicable to non-planar 3D substrates, and the usefulness of this method was demonstrated by fabricating a 5G/Sub-6 GHz antenna with good device performances. [ABSTRACT FROM AUTHOR]

In this study it is demonstrated that the triboelectric charging of polyimide thin films is significantly reduced by using a femtosecond laser to nanostructure its. It is found that the contact charge transfer between laser-ablated Kapton and aluminum is almost negligible, and even much lower than the significant current occurring when non-treated Kapton touches the metal. Scanning electron microscopy demonstrates that laser ablation produces a hierarchical micro and nanostructure, and it is found that the structural anisotropy leads to spatially varying contact angles of water droplets residing on the surface. Raman spectra suggest that the centers of the laser-ablated tracks are carbonized; therefore, the loss of insulation can be responsible for the reduction of charge transfer. [ABSTRACT FROM AUTHOR]

This work explores the use of polyimide substrates for the development of flexible graphene-based devices. Single layer graphene was synthesized by chemical vapour deposition and transferred to untreated and treated polyimide substrates. Of the four different surface treatments, the tetrafluoromethane/oxygen plasma and, especially, hydrochloric acid bath treatments showed the best performance, as they reduced the resistivity of the graphene samples by as much as 46%. At the same time, resistivity was also reduced by as much as 96% due to the increase in the graphene coverage area as a result of repeating the transfer process up to four times. The combination of HCl treatment and transfer iteration led to the samples acquiring a sheet resistance of 800 Ω/sq. To the best of our knowledge, this is the lowest value ever reported in the literature for graphene samples on conventional flexible polymeric substrates and, in particular, in polyimide, the most widely used material for flexible applications. This result represents a major contribution to the development of graphene-based flexible devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conjugated polyimide with tunable polarity is synthesized by a facial solid-state reaction. • PIK 1.5 exhibits 117-folds enhanced photocatalytic H 2 O 2 production compared with PI under visible-light irradiation (λ > 420 nm). • Improved polarization in conjugated polyimide increases the separation and transport efficiency of electron-hole pair. • The photocatalytic reaction is driven by two electron pathways. Ternary carbon nitride oxygen semiconductors have been developed as metal-free catalysts for photocatalysis, but the efficiencies are still far from satisfaction. Herein, we report that polarization adjusted conjugated polyimide (PIK) can be substantially optimized the activity of visible-light induced H 2 O 2 production. The structures of catalyst have been well characterized by XRD, FTIR, BET and XPS. Compared with bulk polyimide, optimized PIK 1.5 displays 117-folds-enhanced photocatalytic H 2 O 2 production under visible light (λ ≥ 420 nm), achieving an excellent H 2 O 2 production rate of 160.5 umol·g·h−1. Fluorescence spectroscopic measurements confirm that reinforced photocatalytic H 2 O 2 production is mainly attributed to the increased polarization in conjugated polyimide, which effectively accelerates the separation and migration kinetics of electron-hole pairs. These results indicate that polarization play an important role in polymeric semiconductors for solar energy utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Successful modification of PI patches with sodium hypochlorite (NaOCl). • Chlorination of the membranes changes their hydrophobic character to hydrophilic. • Decreased zeta potential of the patches is beneficial for antimicrobial activity. • Chlorinated PI patches inhibit bacteria growth, both gram-positive and gram-negative. Atopic dermatitis (AD) is a common andcomplex disorder caused by many inherently intractable factors. One of the symptoms is an increased amount of Staphylococcus aureus on the skin surface. These bacteria trigger, accelerate, and exacerbate AD. In order to reduce inflammation, we designed antimicrobial patches, which inhibit bacterial growth. Using electrospinning, we produced polyimide (PI) nanofibers collected in the form of porous membranes. These PI membranes were modified with sodium hypochlorite (NaOCl). The active chlorine content was confirmed with scanning electron microscopy (SEM) with secondary electrons (SE) mode, backscattered electrons (BSE) mode, and energy-dispersive X-ray (EDX) spectroscopy, with Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Moreover, we evaluated the wettability and zeta potential of the patches. Finally, we performed an antimicrobial efficacy assay against the Gram-positive model organism S. aureus and the Gram-negative model, Escherichia coli. We observed that the chlorinated PI patches demonstrate effective bacterial killing, making them excellent material for antimicrobial skin patches applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A nanoscale PI/Cr 2 O 3 nanocomposite coating was fabricated by an ion-exchange method. • The coating exhibits ultralow SEE attribute to the weakly emissive Cr 2 O 3 and the introduced traps. • Significantly enhanced vacuum surface insulation was achieved. • An ad hoc SEE model revealed the relationship between the SEEY and the trap states. Polymers with high surface electric insulation capability are greatly demanded in various electrical devices operating in vacuum ambient. Low secondary electron emission (SEE) is favorable to mitigate vacuum flashover by inhibiting the SEE avalanche across the surface. Although numerous approaches, esp. the surface modifications, promote the flashover strength of the insulator, a facile yet cost-effective modification strategy of a high-quality and scalable flexible insulator remains a formidable challenge. Herein, a facile ion-exchange technique is implemented to fabricate a nanoscale polyimide/chromic oxide (PI/Cr 2 O 3) nanocomposite coating comprising hundreds of organic/inorganic interfaces securely adhered to a flexible PI substrate, which features ultralow secondary electron emission yields (SEEY). The low emissivity is achieved by introducing weakly emissive Cr 2 O 3 nanoparticles as well as interfacial traps within the nanocomposite layer, which outperforms the existing and modified polymers. The PI/Cr 2 O 3 shows a remarkable increase in flashover strength while keeping sufficient mechanical durability. The proposed surface engineering strategy is convenient and scalable, bringing up new insight into industrial applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An additive method of metallization skipping the step of preparing bridging layers. • Aldehyde groups were formed to reduce silver ammonia ion to Ag particles. • Metallic silver was in-situ generated in the substrate for electroless plating. • Customized circuit patterns were printed with the via of computer programs. • The deposited copper layer exhibits lower roughness with low resistivity of 3.83 × 10-6 Ω·cm. In this paper, a facile method of fully additive process to manufacture copper lines on flexible polyimide (PI) substrates was developed. The selective modification on film, involving silver ammonia solution and plasma treatment, was performed to produce Ag particles that catalyze electroless copper plating. It was found that reductive aldehyde groups (R-CHO) were generated at the treated PI surface to reduce silver ammonia ion to Ag particles, which is supported by the of chemical and morphological characterizations. The obtained solid copper deposition demonstrates highly reliable features including limited oxidation, lower roughness and compact crystalline grain with low resistivity of 3.83 × 10-6 Ω·cm. The practical fabricated flexible circuits with designed pattern have passed the mechanical and electrical property tests, confirming the compatibility of the developed additive method with the flexible PI substrate. [ABSTRACT FROM AUTHOR]

Flat polyimide (PI) film and silicon dioxide nanoparticle-textured PI film were prepared by means of the spin-coating technique. The adhesion and friction properties of the flat PI surface and nano-textured PI surface were investigated by a series of Atomic force microscope (AFM) colloidal probes. Experimental results revealed that the nano-textured PI surface can significantly reduce the adhesive force and friction force, compared with the flat PI surface. The main reason is that the nano-textures can reduce the contact area between the sample surface and colloidal probe. The effect of colloidal probe size on the friction behavior of the flat and nano-textured PI surfaces was evaluated. The adhesive force and friction force of nano-textured PI surface were increased with the increasing of the size of interacting pairs (AFM colloidal probe) due to the increased contact area. Moreover, the friction forces of flat and nano-textured PI surfaces were increased with applied load and sliding velocity. [ABSTRACT FROM AUTHOR]