PI Film Research Articles

Functionalization of MWNTs and its Influence on Thermal Performance of Modified Diphenyl Ether Polyimide Films

In this paper, we treated MWNTs by Fendon oxidation method and mixed acid method, finding the factors of functionalized effect affecting MWNTs. And added MWNTs treated to PI matrix for the study of the impact of MWNTs treated on thermal properties of the films. We using 3,3/,4,4/-diphenyl ether tetraacid dianhydride (ODPA) and 4,4'-diamino diphenyl ether (ODA) as raw material, mixing functional MWNTs and monomer by situ polymerization, then MWNTs / PAA hybrid glue was prepared. The molecular weight and distribution of the polyamic acid were measured by gel permeation chromatography (GPC), and the effects of different addition amounts on the product were examined. The PI/MWNTs films were prepared using an automatic film applicator, and finally the PI films were obtained by thermal imidization. The thermal behavior of the imidization process of the product was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The results showed that the PAA film has thermodynamic behavior at 150 ° C and 280 ° C approximately, which could be regarded as the kinetic interruption temperature of the imidization reaction. The dehydration cyclization reaction mainly occured in these two temperature ranges, moreover, the addition of MWNTs had no significant effect on the thermal decomposition temperature of the material which doping amount that does not affect the mechanical strength.

In-Situ self-encapsulated flexible multi-layered poly (imide siloxane) copolymer film with resistance to atomic oxygen

Silvered polyimide films, synthesized by an in-situ self-assembly method, find many applications in the fields of electronics and aerospace materials. In this work, polyimide/siloxanes were introduced into silvered PI films by an in-situ self-assembly process, which were resistant to atomic oxygen. Their atomic oxygen (AO) resistance behaviors were studied, wherein the mass loss of 20% Si-poly(amide acid salt) PAAS film was 30 ug cm−2 after exposure to AO fluence of 1.33 × 1020 O (10.5 h) and 190 ug cm−2 even after 42 h. Additionally, the volume resistivity value of the flexible PI/Ag composite film was 9.9 Ω cm−1 after 260 cycles of bending. The peel strength of PI/Ag/PI composite film was seven times more than that of the coated one (0.7 N cm-1 to 0.1 N cm-1). Moreover, (Dynamic Mechanical Analysis) DMA and (Thermogravimetric Analysis) TGA data also show that the introduction of self-encapsulating PAAS can not only increase the interlayer strength but maintain the performance of PI film. X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy were also employed to test the relative AO resistance behaviors. Thus, the silvered poly(siloxane amic acid) Si-PI composite films have AO resistance, high peel strength and alternating conductivity/ insulative effect, and hence can serve as a flexible printed circuit board for potential applications in low earth orbit.

Thermal conductivity of polyimide/AlN and polyimide/(AlN + BN) composite films prepared by in-situ polymerization

A series of polyimide/AlN composite films and polyimide/AlN/BN composite films with different contents were prepared by using polyimide as organic matrix, AlN and BN as inorganic fillers. The filling of the ALN + BN particles increases the dielectric constant, the breakdown strength, and the thermal conductivity of the film. After filling in 9 vol% AlN content, the thermal conductivity of the polyimide/AlN composite film was 0.675 W/(m·K), which was three times that of the pure PI film. The PI/AlN/BN composite film had a thermal conductivity of 0.711 W/(m·K) when the content of AlN and BN was 3 vol% and 6 vol%, When the inorganic packing particles are 3%, the tensile strength loss is small and the breakdown strength is increased to 180 kV/mm. The SEM image of PI film showed that when different contents of AlN particles were added to the matrix, whitening phenomenon may occur due to poor interface bonding ability, and the problem was improved after KH560 modification. The result showed that two fillers with different particle sizes formed a close-packing, which was beneficial to increase the number of thermal conduction paths, thereby improving the thermal conductivity. Overall, this paper prepared a series of PI thin films with high thermal conductivity and high insulation.

High-performance FBAR humidity sensor based on the PI film as the multifunctional layer

For achieving the high-performance film bulk acoustic resonator (FBAR) humidity sensor with MEMS process reliability, we proposed a novel FBAR design based on the polyimide film (PI-FBAR). The PI film was employed to provide multifunction for the structural supporting and humidity sensing simultaneously, which was first used in the back-trench FBAR. Due to its flexible and low acoustic impedance characters, it can provide adequate structural robustness and high quality factor (Q=210). According to its hygroscopic property, it would be greatly optimized the humidity sensor’s sensitivity. The feasibility of this design was verified by theoretical analysis, finite element method (FEM) simulation, and combined with the indentation and various humidity response experiments. It is proved that the sensitivity reaches to +67.3 kHz/% RH (about 64 ppm/%) between 15 % RH and 85 % RH, which is 39 times higher than the sample without PI film. The fabrication processes are more simple and controllable at the same time, so that the sensor has shown good properties of repeatability and reproducibility. The temperature coefficient of frequency (TCF) is 126 ppm/°C from -50 °C to +50 °C and the hysteresis error is no more than 1.77 % RH at 50 % RH. Owing to the strong stability and higher sensitivity of the PI-FBAR sensor, it is promising to achieve high accurate humidity monitoring in practical applications.

Mechanical properties and thermal stability of porous polyimide/hollow mesoporous silica nanoparticles composite films prepared by using polystyrene microspheres as the pore‐forming template

ABSTRACTThe porous polyimide/hollow mesoporous silica nanoparticles (PI/HMSNs) composite films were fabricated via blending polymerization by using polystyrene (PS) microspheres as the pore‐forming template. The morphologies, microstructures, thermal stability, thermal expansion coefficient (TEC), and mechanical performances of the porous PI/HMSNs films were characterized in detail. Results showed that the uniform dispersion of HMSNs benefits from the strong hydrogen‐bonding interaction between the hydroxyl groups of HMSNs and poly(amic acid) chains. Both weight loss and TEC of the porous PI/HMSNs films are lower than those of the pure porous PI film. When 0.8 wt % HMSNs and 7.0 wt % PS were added into the PI matrix, the Young's modulus and tensile strength of composite film increased by about 32.4% and 68.1% compared with those of the pure porous PI film. Conclusively, the introduction of HMSNs in the porous PI matrix is an important strategy to enrich the diversity of porous structure, improve the thermal and mechanical properties of the porous PI material simultaneously. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48792.

Preparation and distinguish dielectric properties of multi-layer nanoparticles-based polyimide films

Insulation structure of inverter fed motors, mainly used in high-speed railways undergo continuous stresses of short pulses, making it difficult to maintain the insulation strength. Core–shell type of dielectric material and deposition of multilayer nanocomposite structures are being utilized in modern research to enhance the mechanical and dielectric strength of motor insulation. There is a high demand to explore electrical properties of such multilayer structure possessing thin dielectric layers of nanometric dimensions particles. The electrical performance of single-layer (polyimide/nano) and three-layer structure (nano-polyimide-nano) consisting of two different types of nano particles (Al2O3 and SiO2) are investigated, and results are compared with each other as well as with single layer structure. The structural interface and physical properties of dispersion of nano additive layers on polyimide are studied by microscopic analysis and other features such as weight loss, dielectric spectroscopy, and electrical and mechanical breakdown strength are also analyzed. Results showed that the three-layer structure with SiO2 additive have higher electrical breakdown strength compared with other types, 40% increase compared with single-layer nanofilms, 30% enhancement compared with three-layer Al2O3-PI-Al2O3 films. Besides, notable variations in results are observed at higher temperatures. The current research study on the basis of type, size and structure of sample will help manufacturers especially in the field of motor industry to select nano reinforced PI film according to industrial application.

Synthesis and properties of cardo-type polyimides containing hydroxyl groups for application in specific detection of fluoride ion

Here, four cardo-type polyimides containing hydroxyl groups have been successfully synthesized by one-step solution polymerization of a hydroxyl-containing fluorene diamine monomer and various commercial dianhydride monomers. The obtained PIs with high molecular weights were readily soluble in many polar solvents. Simultaneously, they still maintain the excellent thermal stability (the 5% and 10% weight loss temperatures over 480 °C and 510 °C in nitrogen, respectively) and the high glass transition temperatures (Tgs, 342–442 °C). Furthermore, PI films show high tensile strength (>78 MPa) and relatively high optical transparency (over 82% at 500 nm), except PI-4. Utilizing that hydroxyl group in PI chain is able to form H-bond interaction with F−, these hydroxyl-containing PIs in DMSO solution are successfully applied as colorimetric chemosensors for detection of F− with high selectivity and sensitivity. Finally, the PI film chemosensors is also used for visual and reversible sensing of F−, which enables them to be a fast and portable test kit for visible detection of F−.

High-quality flexible antenna fabricated by ion-exchange technique

In this work, low-cost ion exchange technique coupled with printed-mask method has successfully been applied on the fabrication of high-quality flexible antennas. Nano-silver particles are chosen as conductive material of the CPW-fed antenna. The structure of the antennas is well-defined by the inkjet printing method. The experimental results indicate that a compact, smooth and highly-defined silver pattern is formed on the PI film with thickness of 800 nm, particle size of 50 nm and sheet resistance of 2.34 Ω/sq. A peak gain of 42.68 dB at resonant frequency 2.4 GHz nicely accords with the simulated result by ANSYS Electronics, demonstrating that the desired impedance matching can be realized. Moreover, the PI-based antenna shows excellent flexibility with a low sensibility to the bending tests. Therefore, the flexible patterned antenna by ion exchange technique and printed mask is suitable for flexible wireless electronics devices such as wearable devices, RFID labels and wireless mobile communication.

Functionalized Multiwalled Carbon Nanotube-Reinforced Polyimide Composite Films with Enhanced Mechanical and Thermal Properties

Polyimide- (PI-) based nanocomposites containing the 4,4′-diaminodiphenyl ether- (ODA-) modified multiwalled carbon nanotube (MWCNT) filler were successfully prepared. The PI/MWCNTs-ODA composite films exhibit high thermal conductivity and excellent mechanical property. The optimal value of thermal conductivity of the PI/MWCNTs-ODA composite film is 0.4397 W/mK with 3 wt.% filler loading, increased by 221.89% in comparison with that of the pure PI film. In addition, the tensile strength of the PI/MWCNTs-ODA composite film is 141.48 MPa with 3 wt.% filler loading, increased by 20.74% in comparison with that of the pure PI film. This work develops a new strategy to achieve a good balance between the high thermal conductivity and excellent mechanical properties of polyimide composite films by using functionalized carbon nanotubes as an effective thermal conductive filler.

Sustainable production of reduced graphene oxide using elemental sulfur for multifunctional composites

We herein report on a green, facile, and sustainable production of sulfur-doped reduced graphene oxide (S-RGO) and their use in mechanically strong gas barrier polymers. S-RGO was successfully obtained by directly utilizing elemental sulfur in the absence of any organic solvent or catalyst. This method suggests that the sulfur treatment of GO causes the insertion of a variety of sulfur forms such as thiol, thioether, sulfoxide, sulfone, and sulfonic acid at the platelet edges or surfaces. It also restores graphitic networks on the basal planes, enabling easy exfoliation in liquid phases. The resultant S-RGO is highly dispersible in organic solvents and exhibits a high C/O ratio (13.2), excellent electrical conductivity (179 S cm−1), and a high Hg removal capacity. The molecular dynamics (MD) simulation supports the discussion on the interfacial mechanics for the solvent-exfoliation of S-RGO. The S-RGO can significantly improve the tensile strength (255 MPa) and Young's modulus (6.2 GPa) of the host polyimide, (PI) even with a 0.5 wt% filler loading. Furthermore, loading S-RGO as a filler in PI films can lead to an exceptional oxygen gas barrier performance, resulting in an approximately 95% reduction (at 3 wt%) compared with that of a pristine PI film. This strategy provides a new, environmentally friendly, and cost-effective reduction methodology for synthesizing high-quality and multifunctional RGOs and their nanocomposites.

Preparation of polyimide composites reinforced with oxygen doped boron nitride nano-sheet as multifunctional materials

In this article, oxygen doped boron nitride (OBNNS) was selected and introduced into PI to form OBNNS/PI composite films. The thermal, electrical, optical and mechanical properties of the OBNNS/PI composite films were all improved compared to pure PI. Our experimental results shown that the synthesized OBNNS/PI composite with a low OBNNS content (0.25wt%) have thermal conductivity of 0.291W·m−1·K−1, tensile strength of 127.1MPa, elongation at break of 13.3%, and corona resistant life of 9.50h, all were significantly enhanced compared with that of a pure PI film. This can be attributed the homogeneous and ordered dispersion of OBNNS in PI matrix. The successful preparation of the OBNNS/PI composites will pave a way for the development of multifunctional polyimide-based composites for applications.

Characterization on the operation stability of mechanically flexible memory thin-film transistors using engineered ZnO charge-trap layers

The charge-trap memory thin-film transistors (CTM-TFTs) using ZnO charge-trap layer (CTL) were fabricated and characterized, in which ZnO CTL was deposited by atomic layer deposition (ALD) and the deposition temperatures were controlled to be 75, 100, and 125 °C to improve both specifications of device characteristics and stability for the flexible memory devices. The CTM-TFT using ZnO CTL deposited at 100 °C obtained a wide memory window (MW) of 14.7 V, large memory margin between ON- and OFF-states (ION/IOFF, 7.3 × 106) at 1 µs voltage pulses. The ION/IOFF larger than 107 was also obtained with a progress of retention time. It was noteworthy that the deposition temperature for the ZnO CTL was worked as one of the most important control parameters affecting the memory device characteristics of the fabricated flexible CTM-TFTs. Alternatively, the fast program operation and long retention time were suggested to result from a suitable number of trap sites and their appropriate positions within the ZnO CTL prepared at 100 °C. The improved device stabilities were guaranteed even under bending condition at a radius of curvature of 10 mm after the delamination process of PI film substrate from carrier glass.

Polyimide/mica hybrid films with low coefficient of thermal expansion and low dielectric constant

AbstractPolyimide (PI)/mica hybrid films were successfully prepared by in situ condensation polymerization method, in which the mica particles were modified by coupling agent γ-aminopropyltriethoxy silane (APTS) to strengthen the interaction between the mica particles and PI matrix. The morphology, structure, thermal and mechanical properties as well as dielectric properties of PI films were systematically studied via Scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR spectrometer), Thermal gravimetric analysis (TGA), tensile experiments, Thermal mechanical analyzer (TMA), impedance analyzer, etc. The results indicated that the mica particles were dispersed homogeneously in PI matrix, leading to an improvement of the mechanical property, thermal stability and hydrophobicity. It was novel to notice that hybrid films exhibited low coefficient of thermal expansion (CTE) and low dielectric constant simultaneously. The CTE and dielectric constant of hybrid film dropped to 25.36 ppm/k and 2.42 respectively, in the presence of 10 wt% mica into polyimide matrix.

Effect of Physical Aging on the Bending Recovery of PEEK and PI Films

The relationship between the viscoelasticity and bending recovery responses of PI and PEEK films were studied as well as the effect of physical aging treatment on these properties. The residual elastic modulus (Er) and degree of aging of the films were measured from the stress relaxation-recovery experiment using DMA and the enthalpy relaxation endotherms near glass transition temperature using DSC, respectively. The instantaneous bending recovery ratio (BR+) of the films was measured from the change in radius of curvature before and after the bending under the condition of 85 °C/85%RH/24 hr. The DMA test was also performed at 85 °C in order to evaluate the progression of the stress relaxation during bending. The Er and BR+ values showed good correlation, and higher contributions of elastic response or longer delay of the stress relaxation led to improved bending recovery. Films with BR+ values close to zero can be obtained if the conditions of Er <0.05 are satisfied. A physical aging method was proven to be effective for controlling the viscoelastic response of the films; it contributes to the retardation of stress relaxation. The optimum physical aging temperatures were 200 °C for PI and 130 °C for PEEK, respectively. Both films achieved a sufficient aging effect with the treatment time of 24 hours.

Laser‐induced Graphene‐based Non‐enzymatic Sensor for Detection of Hydrogen Peroxide

AbstractIn this study, a laser‐induced graphene (LIG) loaded platinum nanoparticles (PtNPs) was prepared for precise, rapid and non‐enzymatic electrochemical detection of hydrogen peroxide (H2O2). The commercial PI films were used as the substrate of LIG. In order to improve the electrochemical performance of LIG, a layer of PtNPs catalyst was fabricated through a magnetron sputtering process on the surface of LIG (PtLIG). Under optimized conditions, a linear relationship between H2O2 reduction current and H2O2 concentration was recorded, the correlation coefficient R2 is 0.9919 with the detection limit of 0.1 μM (S/N=3) and the sensitivity of 248.4 μA mM−1cm−2. Moreover, the PtLIG exhibits excellent selectivity, reproducibility and repeatability. Because of these remarkable advantages, we believe that PtLIG will provide a wider range of applications in biosensors and bioelectronic devices.

Electromechanical efficiency improvement of the surface DBD by composite dielectric

The induced airflow velocity level and the mechanical efficiency are the significant issues for the surface DBD flow control application. In this paper, the effects of optical characteristics, electrical performances and mechanical properties of surface DBD with composite dielectric glass/PI film are investigated. The current, discharge plasma morphology, electrical power consumption, and induced airflow velocity are analyzed at applied voltage 17-23 kV with working frequency 9.15 kHz. The experiment results indicate that with the addition of PI film, the discharge just occurs near the exposed electrode and is suppressed obviously in the negative half cycle of current. Though the induced airflow velocity decreases slightly about 0.1-0.2 m/s at each voltage level, the mechanical efficiency substantially improves. The maximum mechanical efficiency increases by 25.12% under the 23 kV.

Photo-deposition of cobalt-phosphate group modified hematite for efficient water splitting

In this work, Cobalt Phosphate Group (Co−Pi) Modified nanostructured hematite (α-Fe2O3) photoanodes films were deposited on fluorine-doped tin oxide (FTO) coated glass by means of the hydrothermal process. The α-Fe2O3 film morphology can be tuned from nanoparticle – based patterns to high-density cabbage-like structures as Co−Pi deposition time is increased.Systematic studies were performed to clarify the mechanisms that enhance water-splitting performance of α-Fe2O3 electrodes as Co−Pi deposition time increases. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Co-Pi/α-Fe2O3 photoanode exhibited higher photoelectrochemical activity than the α-Fe2O3 films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 30 s Co-Pi/α-Fe2O3 photoanode. All samples reached their best IPCE at 400 nm. IPCE values for 30 s Co-Pi hematite films were 5 times higher than that of α-Fe2O3 sample. For the α-Fe2O3 photoanode, the H2 evolution rate was ∼5.14 μmol cm−2 h−1. After decoration by Co-Pi, the rate increases to ∼7.31 μmol cm−2 h−1, showing an enhancement of about ∼ 42.2%. It was found that under illumination, the Co−Pi catalyst can efficiently collect and store photogenerated holes from the α-Fe2O3 electrode. This charge separation reduces surface state recombination, leading to the enhancement of the efficiency of water oxidation. Thicker catalytic Co−Pi films were found to increase charge separation and surface area, which in turn increase water oxidation efficiency. These results provide important new understanding of the catalytic enhancement and limitations of the Co−Pi catalyst once coupled to semiconductor electrodes for water-splitting applications.

Preparation and Properties of Poly(imide-siloxane) Copolymer Composite Films with Micro-Al2O3 Particles

In the current study, poly(imide-siloxane) copolymers (PIs) with different siloxane contents were synthesized and used as a matrix material for PI/Al2O3 composites. The PIs were characterized via their molecular weight, film quality, and thermal stability. Among the PI films, free-standing and flexible PI films were selected and used to prepare PI/Al2O3 composite films, with different Al2O3 loadings. The thermal conductivity, thermal stability, mechanical property, film flexibility, and morphology of the PI/Al2O3 composite films were investigated for their application as heat-dissipating material.

Tunable dielectric and other properties in high-performance sandwich-type polyimide films achieved by adjusting the porous structure

Excellent dielectric and other properties of PI films were realized and tuned through the introduction of a sandwich-type porous structure.

Impact of the phenyl thioether contents on the high frequency dielectric loss characteristics of the modified polyimide films

With the combination of the phenyl thioether group into the molecular chain of polyimide, the high frequency dielectric loss of the modified polyimide film can be effectively reduced, which will avail this insulating material of application in high frequency electrical equipment. In the proposed study, polyimide films containing different proportions of phenyl thioether were prepared via alternating thermal imidization method and the impact of phenyl thioether contents on the high frequency dielectric loss characteristics investigated. Frequency-domain dielectric spectrum analysis indicated that the dielectric loss of the modified films decreased in the first instance and then roared again with increased phenyl thioether content, among which cases the lowest dielectric loss factor (tanδ = 0.000929 at 1 kHz) occurred in the film with phenyl thioether content of 40%. Both X-ray diffraction (XRD) and Ultraviolet-visible spectroscopy (UV–Vis) measurements, with reactive force field-based molecular dynamics simulation, were utilized to further elucidate the influencing mechanism of phenyl thioether content on dielectric loss characteristics. When the content of phenyl thioether was <40%, the charge transfer effect decreased with the increased phenyl thioether content, gradually reducing the degree of micro-crystallinity in the modified polyimide, and thereby increasing the dispersion of dipole moment that directly led to the reduced dielectric loss. When the phenyl thioether content is higher than 40%, the charge transfer effect reversed, which results in the PI film with increased crystalline region caused by the tighten molecular stacking and has the increased dielectric loss. Synthesis of the low-dielectric-loss polyimide films can be then optimized for high frequency applications.