Colorless Polyimide Film Research Articles

Mechanically Robust and Colorless Polyimide Films Cross-Linked with a Cycloaliphatic Amide Linkage

Mechanically Robust and Colorless Polyimide Films Cross-Linked with a Cycloaliphatic Amide Linkage

Research of aging test on high Tg colorless polyimide

AbstractFor the past few years, colorless polyimide (CPI) has been drawn much attention for its application in transparent electronics. The high temperature (even to 450°C) process of the preparation of organic light‐emitting diode display (OLED) device may have huge challenges on the properties of CPI, so we designed a series of aging test experiments to study the influence of test temperature and atmosphere on the high transparency percentages (Tr%) of CPI films with structure of Glass/SiO2/CPI/SiO2. As the aging temperature increased from 430 to 450°C and then to 470°C, the Tr% of the film decreased significantly. Comparing with the sample without aging, the transmission losses were 0.22%, 1.42%, and 4.82% for the films aging with 430, 450, and 470°C in N2 atmosphere, respectively. Additionally, aging in nitrogen resulted in less Tr% loss (1.22%) compared with air (1.42%). This research offers insights into how to maintain the high Tr% of CPI films during high‐temperature processing. Furthermore, it supports the development of more durable and reliable CPI‐based components for OLED displays and other transparent electronic devices. This can lead to advancements in the performance of these devices, potentially extending their lifespan and broadening their range of applications.

Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma.

Mesoporous metal oxides exhibit excellent physicochemical properties and are widely used in various fields, including energy storage/conversion, catalysis, and sensors. Although several soft-template approaches are reported, high-temperature calcination for both metal oxide formation and template removal is necessary, which limits direct synthesis on a plastic substrate for flexible devices. Here, a universal synthetic approach that combines thermal activation and oxygen plasma to synthesize diverse mesoporous metal oxides (V2O5, V6O13, TiO2, Nb2O5, WO3, and MoO3) at low temperatures (150-200°C), which can be applicable to a flexible polymeric substrate is introduced. As a demonstration, a flexible micro-supercapacitor is fabricated by directly synthesizing mesoporous V2O5 on an indium-tin oxide-coated colorless polyimide film. The energy storage performance is well maintained under severe bending conditions.

Synthesis of UV-resistant and colorless polyimide films for optoelectrical applications

Due to their excellent mechanical properties and intrinsic flexibility, polyimides (PIs) are promising candidates for optoelectrical applications under harsh conditions such as flexible organic solar cells as well as flexible smart windows, etc. Much progress has been made on their optical transmittance; however, there remain significant concerns about their environmental stability, particularly their UV resistance. Herein, 4 types of colorless polyimides (CPIs) with different molecular structures containing trifluoromethyl, ethers, or fluorenes are carefully designed, and the dependence of their UV resistance on structures is explored systematically. It is found that the introduction of isopropylidene, ethers and fluorenes effectively enhances the UV resistance of CPI and its initial performance (optical transparency, thermal stability, and toughness) simultaneously as a result of the subtle manipulation of the conjugation structures. Specifically, the optimized polyimide film shows decent optical properties (T550 nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{550{\\rm{nm}}}$$\\end{document} ~ 88%, yellowness index ~3.26), and thermal stability (T5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{5 \\% }$$\\end{document} ~ 503 °C in N2 atmosphere, Tg\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{{\\rm{g}}}$$\\end{document} ~ 312 °C). Moreover, after high-intensity UV irradiation, CPI not only maintains over 90% of mechanical properties but also retains excellent optical properties (T550 nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{550{\\rm{nm}}}$$\\end{document} ~ 88%) and thermal stability (T5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${T}_{5 \\% }$$\\end{document} ~ 506 °C). The design strategy paves the way for enhancing the durability of PIs for energy conversion and electronic applications resisting harsh conditions.

Enhancing optical properties and wettability of colorless polyimide films by direct fluorination

Colorless polyimide (CPI) films were modified by direct fluorination. The effects of fluorination duration on the chemical structure and surface physical morphology of CPI films were investigated in detail. The results show that direct fluorination induces significant changes in the surface composition and structure, leading to an enhancement in the F/C and O/C ratios. Fluoridation also resulted in increased surface microcracking. In comparison to the original CPI films, the fluorinated CPI films showed good thermal stability and higher glass transition temperatures ([Formula: see text]), and higher optical transmittance (about 93.0%) in the ultraviolet–visible light region. Moreover, the fluorinated surfaces exhibit a high hydrophily and lipophilicity, and consequently a very high surface energy, according to contact angle measurements.

Transparent semi-aliphatic polyimide films with excellent thermal stabilities for applications in the display technology

A set of colorless polyimide (CPI) films with norbornene-aliphatic ring structures has here been prepared through polycondensation reactions by using cyclopentanone bis-spironorbornane tetracarboxylic dianhydride (CpODA), 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 4,4′-diaminodiphenyl ether (ODA) monomers as raw materials. The transmissivities, dielectric properties and thermal stabilities of CPI films are optimized by adjusting the CpODA-to-6FDA molar ratios. Compared with the aromatic and aliphatic PI films, the thermal stabilities and transmissivities of CPI films are well balanced. Moreover, the CPI films possessed low dielectric constants and low dielectric losses. The thermal expansion coefficients, temperatures at a 5% weight loss and glass-transition temperatures are maintained at 31–41 ppm K−1, 461–484 °C and 348–362 °C, respectively. In addition, the transmittances (86–89%), dielectric constants (2.15–2.47) and dielectric losses (<0.023) are all prominent. In short, the CPI films have been shown to have a high potential for use in the display technology.

Unveiling the Potential of Colorless Polyimide‐Derived Laser‐Induced Graphene: A Novel Pathway for Advanced Sensor and Energy Harvester Performance

AbstractThe potential of laser‐induced graphene (LIG), recognized for its distinct attributes in diverse fields, has significantly grown. However, the creation of LIG using colorless polyimide (CPI) films remains unexplored. This research sheds light on the graphitization technique for generating LIG from CPI films via laser techniques, a process validated through ReaxFF simulations. It is also illustrated that CPI integrated with fluorine atoms possesses an elevated porous configuration, rendering it apt for high‐sensitivity, low‐detection limit pressure sensors. The pressure sensor, constructed with LIG derived from CPI, showcases superior performance metrics such as an exceptional sensitivity rate of 60.340 kPa−1 in low‐pressure ranges (1.0–1.5 kPa), prompt response and recovery intervals (27/36 ms), and commendable durability. The sensor's ability is further validated to precisely track human movements. Moreover, the study employs the LIG sourced from CPI as a dielectric‐to‐dielectric triboelectric nanogenerator (TENG), yielding a peak power output of 411.4 mW m−2 under a 40 MΩ load resistance. The CPI‐based LIG offers increased porosity in comparison to traditional LIG, which aids in superior functioning in pressure sensors and TENG devices. This research offers a fresh perspective on the application possibilities of CPI‐sourced LIG, notably in pressure sensors and energy harvesting devices.

Colorless polyimide films with low birefringence and retardation: Synthesis and characterization

In this study, two series of polyimides (PI) were synthesized from one step solution polycondensation of two diamines containing sulphonyl group with aromatic and aliphatic dianhydrides. These PIs showed good organosolubility and were casted into films with high transparency of T500>86%, and cutoff wavelength in the range of 295–370 nm. Optical birefringence (0.0020–0.0127) of these PIs was lower than that of traditional aromatic PI. PI films demonstrated out-of-plane retardation (Rth) in the range of 42–279 nm, indicating low optical anisotropy of these films. All PIs also exhibited high thermal stability with glass transition temperatures ranging from 200 to 339 °C. PI-1c derived from bis[4-(3-aminophenoxy)phenyl] sulfone (m-BAPS) and 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) showed the lowest birefringence and good transparency.

High-Transparency and Colorless Polyimide Film Prepared by Inhibiting the Formation of Chromophores.

Colorless polyimides (CPIs) with outstanding mechanical properties are essential materials in the production of flexible display panels, foldable windows, and even spacecraft cockpits. This paper specifically elaborates that the Morkit unit, and azo and nitro chromophores are important factors contributing to yellow PI, together with the well-known charge transfer complex (CTC) theory. Three diamine monomers, two anhydrides monomers, and three blockers were used to inhibit chromophores formation and, thus, obtain CPI films. The cut-off wavelength was blue-shifts to 334 nm and the transmittance is improved to 98.9% in the UV–vis range. Mechanical and thermal properties of the CPI films are not reduced through coupling effects of the blockers. Therefore, the inhibition method of the Morkit units and chromophore groups is a promising process for preparing CPIs to be used as flexible display materials.

Synthetic strategies for highly transparent and colorless polyimide film

AbstractPolyimide (PI) is one of the best engineering plastics with excellent thermal, mechanical, dielectric performance and chemical stability. Among various PI products, film is one of the most dominant types. If PI films are to be applied to optical devices and display equipment, it is necessary to improve their optical transparency in the ultraviolet–visible region. However, improving the optical transparency of PI films would affect their thermal performance including thermal and dimensional stability. Therefore, how to balance optical and thermal performance to obtain highly transparent PI films with the best overall performance becomes a focus of current research field. In this review, we categorize transparent PI films into highly transparent PI, transparent PI with high glass transition temperature (Tg) and transparent PI with low coefficient of thermal expansion (CTE) based on their optical and thermal properties. Then, we review research progress in the field of polymer molecular design including synthesis strategies and properties in recent 5 years, to inspire research ideas and elaborate on the possible ways to develop high‐performance, colorless and transparent PI materials.

Laser-Induced Hydrothermal Growth of Iron Oxide Nanoparticles on Diverse Substrates for Flexible Micro-Supercapacitors

State-of-the-art microdevice fabrication requires patterned growth of functional nanomaterials on the desired position of the desired substrate. However, it is challenging, particularly in conventional hydrothermal synthesis, due to difficulties generating a local high-temperature field at the desired place. We introduce a laser-induced hydrothermal growth (LIHG) process for the rapid and selective synthesis of iron oxide nanoparticles (NPs). The substrates absorb the laser energy to generate a local high-temperature field necessary for the growth of iron oxide NPs. On various substrates, a dome-like structure comprising many iron oxide NPs is selectively synthesized within a localized temperature field. The LIHG process has several advantages for iron oxide NP growth, including rapidity, seedless growth, substrate compatibility, position selectivity, and patterning availability. Using its advantages, the LIHG process is used to fabricate flexible micro-supercapacitors based on laser-carbonized colorless polyimide films with iron oxide NPs.

Characteristics of the Colorless Polyimide-Based Flexible X-ray Detector with Non-Fullerene Acceptor Polymer.

In this paper, we investigate the characteristics of the colorless polyimide (CPI) film-based flexible organic X-ray detector. The CPI film can be applied to various applications, because it shows excellent visible light transmittance by removing the yellow color of polyimide (PI) film, which has the advantage of physical and chemical stability. In addition, the deformation curvature of the CPI substrate according to temperature showed similar characteristics to that of the glass substrate. For the organic active layer of the proposed detector, PBDB-T was fixed as a donor, and PC71BM and ITIC were used as acceptors. To evaluate the mechanical stability of the flexible detector, the degradation sensitivity was measured as bending curvature and bending cycle. The sensitivity of the detector with ITIC acceptor showed a 46.82% higher result than PC71BM acceptor on bending curvature (R = 10); and at the same curvature, when the bending cycle was 500 times, a 135.85% higher result than PC71BM acceptor.

Invisible and Flexible Printed Sensors Based on ITO Nanoparticle Ink for Security Applications

Here, we propose a method to create a transparent security system based on printed conductive indium tin oxide (ITO)—the most widely used transparent conducting oxide material integrated into the devices with high transparency. Commonly used solution-processed ITO annealing methods are utilizing temperatures which are limiting the use of flexible polymeric substrates. Our method combines inkjet printing on flexible temperature-stable colorless polyimide (CPI) substrate with fast flash lamp annealing (FLA). In this study, millisecond pulses of visible light from a xenon lamp induce rapid heating of the ITO films up to 650°C through the light-absorbing additional layer of a colored organic dye onto printed ITO, whereas the CPI bulk never exceeds the melting point. Fabricated flexible ITO patterns on CPI film processed with the flash lamp annealing through the dye layer exhibit a transmittance of up to 85% at the wavelength of 550 nm and sheet resistance of 520 Ω/sq for a 70 nm layer thickness. With the proposed technology of our demonstrator realization—transparent glass/window or any other object such as a curved door lock can be used for integrating a touch-enabled transparent security access system, which would be completely invisible.

Comparison of Properties of Colorless and Transparent Polyimide Nanocomposites Containing Different Diamine Monomers.

To improve the optical properties of polyimide (PI) films, we prepared two series of colorless transparent PIs from the dianhydride 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and a diamine, either 2,2-bis(3-aminophenyl)hexafluoropropane (FDN) or 2,2-bis(3-amino-4-hydroxy-phenyl)hexafluoropropane (FDN-OH). Next, colorless PI (CPI) composite films were prepared by dispersing 0–1.00 wt % of organically modified clay (Cloisite 30B) in the intermediate poly(amic acid) (PAA) solution via solution intercalation, followed by imidization. The resultant CPI films had excellent optical transparency, which was achieved by reducing the charge-transfer effects by using a highly electronegative trifluoromethyl group and a kinked monomer structure. The thermal and mechanical properties, morphologies, and optical transparencies of the two as-synthesized CPI hybrid film series were investigated and compared. Electron microscopy observation of the two hybrid series revealed that the clay was well-dispersed with a nanoscale dispersion at all clay contents. However, agglomeration occurred at nanoclay loadings of 1.0 wt %. In addition, the effect of the presence of hydroxyl groups in the PI chain on various physical properties of the two CPI hybrids was also compared.

Synthesis and characterization of amide-bridged colorless polyimide films with low CTE and high optical performance for flexible OLED displays

Starting from three novel amide-incorporating dianhydride monomers, we synthesized a series of amide-bridged cPI films that have ultra-low CTE and high Tg due to the formation of hydrogen bonds as well as great optical performance.

Preparation and properties of semi-alicyclic colorless polyimide films and light-colored sheets with low dielectric features for potential applications in optoelectronic integrated circuits

Preparation and properties of semi-alicyclic colorless polyimide films and light-colored sheets with low dielectric features for potential applications in optoelectronic integrated circuits

Highly Transparent and Colorless Polyimide Film with Low Dielectric Constant by Introducing Meta-substituted Structure and Trifluoromethyl Groups

An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented. The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains. By using this design strategy, a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride (m-TFPDA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) through a two-step method. The obtained m-TFPDA/6FDA (CPI) film (∼30 µm) possesses high optical transparency (λcutoff=334 nm, T450nm=85.26%, Haze=0.31) and is close to colorless (L*=96.03, a*=−0.34, b*=2.12, yellow index=3.96). The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz, respectively. More importantly, such low dielectric performance could remain stable up to 280 °C, and the film shows a low moisture rate (∼0.51%), which helps to maintain the low-k property stability in different humid environments. Meanwhile, the film also shows good thermal stability and mechanical properties, with a glass transition temperature (Tg) of 296 °C and the 5 wt% decomposition temperature (Td,5%) of 522 °C under N2. The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa, respectively. In addition, the film is soluble in common solvents, which allows simple solution processing and low-cost, continuous roll-to-roll processes. This design strategy is beneficial to improving the transparency, lightening yellow color, lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films, which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex (CTC) effects and increasing the free volume of film. This design strategy could also be extended to other high-performance polymer systems.

Study of indium tin oxide films deposited on colorless polyimide film by magnetron sputtering

Polyimide attracted most interest for its high performance as a flexible substrate of touch panels. Experimental models were built to evaluate production feasibility. The solution with monomer was coated on a glass substrate, cured at 250 °C to form a solid colorless polyimide (CPI) film. Then, a supporting layer with silicon oxide and a conducting layer with indium tin oxide (ITO) were deposited on the CPI film by magnetron sputtering. Composite with a CPI substrate and ITO patterns were prepared via a series of procedures. Test results indicated ITO film thickness and sheet resistance could be controlled by adjusting sputtering power, and the film showed smooth curves on the contour line chart. The transmittance of CPI/ITO film composite was up to 80%. The bending durability of the film was evaluated by two-point bending method, and it could be significantly improved by shielding the ITO pattern with ultraviolet cured resin as an external buffer layer. Samples with buffer layers passed 64,000 cycles bend test, and the minimum fracture radius reached 4 mm. The increase of ITO film thickness had no significant negative impact on the performance of flexible devices.

Synthesis of highly transparent and thermally stable copolyimide with fluorine‐containing dianhydride and alicyclic dianhydride

ABSTRACTThe development of optical films is highly desirable for applications in flexible displayers. In this work, a copolyimide (co‐PI) film with high thermal stability and high transparency was prepared by the copolymerization of 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminodiphenyl ether, cyclobutanetetracarboxylic dianhydride, and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). The effects of aliphatic dianhydride and fluorine dianhydride monomers on the optical, thermal, and mechanical properties of the co‐PIs were discussed in detail based on the experimental results and theoretical simulations. We found that the preparation of polyimide (PI) based on the combination of two dianhydrides could obtain the PI film with excellent comprehensive performance due to nonconjugated structure and strong electron‐withdrawing effect. Through the structure and composition optimization, a PI film of PI‐6FDA‐70 with Tg of 300 °C, Td10% more than 500 °C, the average transparency of 90% and the elongation at the breakage more than 8% was prepared. Such molecular design provides a practical approach to develop high‐performance colorless PI films. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48603.

Charge-trap-assisted flexible nonvolatile memory applications using oxide-semiconductor thin-film transistors

We introduce mechanically flexible nonvolatile memory thin-film transistors (MTFTs) for future highly functional flexible and stretchable electronic devices and systems. The proposed memory devices are uniquely composed of oxide-semiconductor thin films and operated with charge-trap and detrap mechanisms for nonvolatile memory operations. Charge-trap-assisted MTFTs (CT-MTFTs) using In–Ga–Zn–O active and ZnO charge-trap layers are designed and fabricated on flexible poly(ethylene naphthalate) and colorless polyimide films prepared on carrier glass substrates. We describe the fabrication processes and evaluation methodologies for realizing flexible CT-MTFTs in a detailed way and discuss related technical issues. The device characteristics and memory performance of the fabricated flexible CT-MTFTs, including when the devices are mechanically strained, are extensively discussed. We also propose further improvements for remaining issues on device performance from the viewpoints of memory operations and mechanical flexibility.