Polyimide Kapton Research Articles

The effect of temperature on the roll graphite films derived from Kapton polyimide films

The effect of temperature on the roll graphite films derived from Kapton polyimide films

POLYIMIDE FILMS IMPLANTED BY MANGANESE IONS

The optical and strength properties of Kapton polyimide films implanted with manganese ions with an energy of 40 keV and a dose of 5·1016 – 1·1017 cm–2 at a current density in the ion beam of 4 μA/cm2 have been studied. It has been experimentally established that during the process of ion implantation, modification of a thin nearsurface layer of polyimide occurs not only on the implanted side, but also on the reverse side of the film. Radiationstimulated modification of the back surface of the polyimide film leads to the formation of a surface layer up to 5 μm thick with increased microhardness. This may be due to the restructuring of metastable defects formed during the film manufacturing process and the simultaneous relaxation of elastic stresses in the surface layer. During the implantation process, a decrease in the intensity of absorption bands with maxima at ~ 2870 and ~ 2750 nm is observed, due to the evaporation of residual water under high vacuum conditions and reactions of residual solvent molecules, as well as radiation-induced processes on by-products of polyimide synthesis.

A study for gamma attenuation behavior of polyimide (PI) film by MPPC

Although lead is a very good radiation shielding material, its toxicity has led researchers to find alternative materials instead of it. Moreover, as the use of Kapton polyimide (PI) film in nuclear power plants and space exploration increases, the need to reveal the radiation degradation properties of this material has come along. In this regard, in the present study, it is aimed to determine the mass and linear attenuation coefficients, half value layer, tenth value layer, mean free path and radiation protection efficiency attenuation parameters for this material, experimentally and theoretically, by using the gammas of the 133Ba radioisotope. Experimental gamma attenuation measurements were made by a spectrometer using a Hamamatsu multi pixel photon counter device with a silicon photomultiplier sensor. The constant fraction discrimination timing method was used to reduce the electronic noise of the spectrometer. The attenuation parameters determined experimentally by following two ways were compared with the theoretical ones obtained from the XCOM program.

Characterization of a flexible a-Si:H detector for in vivo dosimetry in therapeutic x-ray beams.

The increasing use of complex and high dose-rate treatments in radiation therapy necessitates advanced detectors to provide accurate dosimetry. Rather than relying on pre-treatment quality assurance (QA) measurements alone, many countries are now mandating the use of in vivo dosimetry, whereby a dosimeter is placed on the surface of the patient during treatment. Ideally, in vivo detectors should be flexible to conform to a patient's irregular surfaces. This study aims to characterize a novel hydrogenated amorphous silicon (a-Si:H) radiation detector for the dosimetry of therapeutic x-ray beams. The detectors are flexible as they are fabricated directly on a flexible polyimide (Kapton) substrate. The potential of this technology for application as a real-time flexible detector is investigated through a combined dosimetric and flexibility study. Measurements of fundamental dosimetric quantities were obtained including output factor (OF), dose rate dependence (DPP), energy dependence, percentage depth dose (PDD), and angular dependence. The response of the a-Si:H detectors investigated in this study are benchmarked directly against commercially available ionization chambers and solid-state diodes currently employed for QA practices. The a-Si:H detectors exhibit remarkable dose linearities in the direct detection of kV and MV therapeutic x-rays, with calibrated sensitivities ranging from (0.580±0.002) pC/cGy to (19.36±0.10) pC/cGy as a function of detector thickness, area, and applied bias. Regarding dosimetry, the a-Si:H detectors accurately obtained OF measurements that parallel commercially available detector solutions. The PDD response closely matched the expected profile as predicted via Geant4 simulations, a PTW Farmer ionization chamber and a PTW ROOS chamber. The most significant variation in the PDD performance was 5.67%, observed at a depth of 3mm for detectors operated unbiased. With an external bias, the discrepancy in PDD response from reference data was confined to±2.92% for all depths (surface to 250mm) in water-equivalent plastic. Very little angular dependence is displayed between irradiations at angles of 0° and 180°, with the most significant variation being a 7.71% decrease in collected charge at a 110° relative angle of incidence. Energy dependence and dose per pulse dependence are also reported, with results in agreement with the literature. Most notably, the flexibility of a-Si:H detectors was quantified for sample bending up to a radius of curvature of 7.98mm, where the recorded photosensitivity degraded by (-4.9±0.6)% of the initial device response when flat. It is essential to mention that this small bending radius is unlikely during in vivo patient dosimetry. In a more realistic scenario, with a bending radius of 15-20mm, the variation in detector response remained within±4%. After substantial bending, the detector's photosensitivity when returned to a flat condition was (99.1±0.5)% of the original response. This work successfully characterizes a flexible detector based on thin-film a-Si:H deposited on a Kapton substrate for applications in therapeutic x-ray dosimetry. The detectors exhibit dosimetric performances that parallel commercially available dosimeters, while also demonstrating excellent flexibility results.

ZnSb Films on Flexible Substrates: Stability, Optical Bandgap, Electrical Properties, and Indium Doping

AbstractUndoped and In‐doped ZnSb thin films are deposited on rigid glass and flexible polyimide (Kapton) by physical vapor deposition. Detailed structural and chemical characterization is performed along with measurement of electrical and optical properties. These properties are very similar for films on glass and Kapton. Flexible ZnSb films show remarkable stability of electrical and optical properties, which are unchanged after 104 cycles of linear bending with surface strain 0.18%. Only severe flexing after this treatment (torsional bending with surface strain 1.7%) causes progressive degradation of conductivity over tens to hundreds of cycles. The ZnSb optical direct gap is determined to be 0.89 ± 0.05 eV. The optical direct gap of β Zn4Sb3 was 1.07 ± 0.05 eV. Other absorption features in the films, including smaller indirect gaps, are discussed.

Ultrafast laser texturing to improve wettability of polyimide (Kapton) films

Aim of this study is investigating the possibility of increasing the wettability of polyimide Kapton thin films by laser texturing. The laser textured surfaces were characterized through the water contact angle measurement and the surface tension evaluation; morphological and topological analyses were performed by scanning electron microscopy and atomic force microscope, respectively. As main outcome, it was found that laser texturing increases the wettability with respect to the untreated material with a decrease of contact angle of more than 20 %. In addition, the ultrashort pulse laser induced, on the material, LIPSS structures oriented in the direction of the polarization plane.

Unraveling spatial variations of graphenization of Kapton polyimide via CO2 laser interaction: a comprehensive theoretical simulation and Raman spectroscopy mapping study

Unraveling spatial variations of graphenization of Kapton polyimide via CO2 laser interaction: a comprehensive theoretical simulation and Raman spectroscopy mapping study

Improving lithium-ion cells by replacing polyethylene terephthalate jellyroll tape.

Polyethylene terephthalate (PET) tape is widely used by well-known lithium-ion battery manufacturers to prevent electrode stacks from unwinding during assembly. PET tape is selected since it has suitable mechanical and electrical properties, but its chemical stability has been largely overlooked. In the absence of effective electrolyte additives, PET can depolymerize into its monomer dimethyl terephthalate, which is an unwanted redox shuttle that induces substantial self-discharge in a lithium-ion cell. This study presents a chemical screening experiment to probe the PET decomposition mechanism involving in situ generated methanol and lithium methoxide from dimethyl carbonate, one of the most common electrolyte solvents in lithium-ion cells. By screening other polymers, it is found that polypropylene and polyimide (Kapton) are stable in the electrolyte. Finally, it is demonstrated that reversible self-discharge of LiFePO4-graphite cells can be virtually eliminated by replacing PET jellyroll tape with chemically stable polypropylene tape.

Investigations on the Effect of Laser Texturing of Kapton Polyimide on the Piezoelectric Response of ZnO‐Based Nanogenerators

In this work, zinc oxide–based piezoelectric nanogenerator (PENG) over the flexible Kapton polyimide (PI) substrate is developed. The device performance is improved by laser texturing of PI substrate, which increases the effective surface area of PI and adhesivity of ZnO thin film with PI substrate to improve the reliability and life span of the device. The untextured PI‐based PENG generates a peak‐to‐peak output voltage, current, and power of 6 V, 420 nA, 2.42 μW, respectively, which increases to 15.8 V, 790 nA, and 12.51 μW, respectively, on using textured PI obtained by 60% laser spot overlap. On further increasing the laser spot overlap to 80%, the peak‐to‐peak output voltage, current, and power improve to 22.2 V, 1210 nA, and 26.88 μW, respectively. Therefore, as compared to the untextured‐PI‐based PENG, laser‐textured‐PI‐based PENG is a promising candidate for energy‐harvesting applications.

Reactive molecular dynamics simulation on the disintegration of Kapton and Upilex-S during atomic oxygen impact

Polyimides are polymeric materials that are widely used in spacecraft applications owing to their unique properties. However, exposure to a low-Earth-orbit environment containing atomic oxygen (AO) results in the disintegration of polymeric materials on the surface of spacecraft, thereby affecting the lifespan. Along with the development of theoretical research, the reactive force-field (ReaxFF) interatomic potential has become a robust computational method for exploring, developing and optimizing the material properties. This study employs the ReaxFF reactive-force-field molecular dynamics simulation (ReaxFF MD) program to investigate and compare the performance of two typical polyimide materials, Kapton and Upilex-S, under the impact of AO. Various aspects such as variations in the temperature, mass loss, decomposition products, and damage propagation depth were examined. Although these materials have similar elemental composition (C/H/O/N), they have different structures. Our results indicate that AO is initially adsorbed on the surfaces of both Kapton and Upilex-S. The continuous impact of AO leads to chemical reactions between AO and Kapton/Upilex-S. Erosion proceeds from the surface toward the interior of the materials. Similar to the findings of Experiment 2 conducted by the Materials International Space Station, our results also reveal that Upilex-S exhibits a lower mass loss and erosion yield than Kapton under the same AO conditions. This difference is primarily attributed to the distinct molecular structures of both Kapton and Upilex-S. Our study could provide valuable technical support for the extensive application of Upilex-S in spacecraft.

Structural characterization and electrochemical performance of laser-induced graphene: Insights into electron transfer kinetics and 4-aminophenol sensing

Laser-induced graphene (LIG) is increasingly gaining importance as a 3D porous graphene material with outstanding properties. Here, LIG structures are realized for electrochemical sensors by patterning polyimide Kapton using a visible 405 nm laser under ambient conditions. The LIG electrodes for flexible electrochemical sensors show a large surface area with a hierarchical porosity distribution along the cross-section.To optimize the laser parameters, we investigated the electron transfer (ET) kinetics and the electrochemical performance of LIG surfaces produced with an exposure time varied from 10 ms to 50 ms. Characterization of the resulting LIG was performed to understand the correlation between the resulting electrochemical properties and the LIG surface properties by optical microscopy and Raman spectroscopy. The electrochemical properties were evaluated in ferri-ferrocyanide [Fe(CN)6]3−/4− by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The highest electron transfer rate constant was registered at an exposure time of 10 ms. However, for an exposure time of 20 ms, the electrochemical behavior is better due to both high surface area and high electron transfer rate constant.A voltammetric 4-Aminophenol sensor is developed as a proof-of-concept device. It exhibits a good analytical performance realizing a low limit of detection at a level of 9.23 nM in the concentration range from 10 nM to 400 nM. The results demonstrate the suitability of LIG for the development of efficient, disposable, and flexible electrochemical sensors. The developed technological approach supports sustainability while simplifying production and reducing costs.

Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors

The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport. However, it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors, especially vacuum-deposited small molecules. Here, interfacial molecular screening of polyimide (Kapton) dielectric in organic field-effect transistors (OFETs) is comprehensively studied. It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide (PI) dielectrics compared with the molecules without alkyl side chains. On this basis, the fabricated transistors could reach the mobility of 1.2 cm2 V−1 s−1 the molecule with alkyl side chains on bare PI dielectric. What is more, the compatible semiconductor and dielectric would further produce a low activation energy (EA) of 3.01 meV towards efficient charge transport even at low temperature (e.g., 100 K, 0.9 cm2 V−1 s−1). Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.

Piezoresistive and thermoresistive responses of carbon nanotube-based strain gauges with different grid geometric parameters

Arrays of carbon nanostructures have gained relevance in current strain sensor technology, pursuing high sensitivity, enhanced stretchability and tunability in the temperature coefficient of resistance. The design and fabrication parameters such as the grid geometry and polymer coating of a strain gauge based on a dense array of carbon nanotubes (CNTs) comprising the grid, deposited over a polyimide (Kapton®) substrate, are investigated herein. It is found that varying the geometrical parameters of the CNT grid led to a 13% increase in the gauge factor. Polysulfone coating lowers the sensitivity compared to polyurethane coating, but increases the repeatability and linearity of the response. The fabricated gauges were characterized regarding their piezoresistive response at room and higher temperatures. A small negative temperature coefficient of resistance (−5.63 ×10−2 %/°C) was found. The fabricated gauges show repeatability and linearity when using as a strain sensor bonded to a 4-point bending coupon during 50 loading-unloading cycles.

In situ formation of POSS layer on the surface of polyimide film and anti-atomic oxygen of SiO2/POSS coatings

Polyhedral oligomeric silsesquioxane (POSS) nanoparticles have attracted wide attention due to their unique capability to reinforce polymers. However, if POSS cannot be uniformly dispersed in the polymer matrix, the desired properties of composites will be reduced. To solve this problem, a method of in situ formation of POSS layer on the surface of polyimide (Kapton) was explored, which not only kept the original properties of polymer unaffected, but also endowed the composites with new properties. The Kapton film completely wetted by γ-aminopropyltriethoxysilane (APTES) was placed in a solution containing tetraethylammonium hydroxide (TEAOH) catalyst, and a POSS layer was gradually grown on the Kapton surface. Subsequently, SiO2 coating was deposited on the surface of POSS layer by magnetron sputtering to prepare SiO2/POSS/Kapton (SPK) samples. FTIR and XPS analyses showed that a layer with POSS structure was formed on the surface of Kapton after 6 h self-growth. Atomic oxygen irradiation test shows that the erosion rate of 6 h SPK sample is 0.19 × 10−24 cm3/atom, only equivalent to 6.0 % of original Kapton, which improves the corrosion resistance of polymer materials.

Resonance Analysis and Gain Estimation Using CMA-Based Even Mode Combination Method for Flexible Wideband Antennas.

This work presents an efficient design and optimization method based on characteristic mode analysis (CMA) to predict the resonance and gain of wideband antennas made from flexible materials. Known as the even mode combination (EMC) method based on CMA, the forward gain is estimated based on the principle of summing the electric field magnitudes of the first even dominant modes of the antenna. To demonstrate its effectiveness, two compact, flexible planar monopole antennas designed on different materials and two different feeding methods are presented and analyzed. The first planar monopole is designed on Kapton polyimide substrate and fed using a coplanar waveguide to operate from 2 to 5.27 GHz (measured). On the other hand, the second antenna is designed on felt textile and fed using a microstrip line to operate from about 2.99 to 5.57 GHz (measured). Their frequencies are selected to ensure their relevance in operating across several important wireless frequency bands, such as 2.45 GHz, 3.6 GHz, 5.5 GHz, and 5.8 GHz. On the other hand, these antennas are also designed to enable competitive bandwidth and compactness relative to the recent literature. Comparison of the optimized gains and other performance parameters of both structures are in agreement with the optimized results from full wave simulations, which process is less resource-efficient and more iterative.

Constructing Novel High-Performance Dipolar Glass Polymer Dielectrics by Polar Rigid/Flexible Side Chains.

Developing new polymer dielectrics with superior dielectric and energy storage properties is urgent to meet the demand for electronic devices in the field of microminiaturization or harsh environments. In this paper, two dipolar glass polymers based on polynorbornene main chain and flexible/rigid cyano side chain were synthesized by ring opening metathesis polymerization method: polymer PCEMT with flexible side chains and polymer PCPMT with rigid side chains. The backbone is built from two rigid five-membered rings, which not only avoids the narrow band gap caused by π-π conjugation of traditional aromatic main chains, but also maintains high thermal stability and high glass transition temperature (Tg). The introduced polar cyano groups on the side chain gave high dielectric constants (εr) for both polymers, where the εr of PCEMT and PCPMT reached 7.9 and 4.6 at room temperature and 1 kHz, respectively. Due to high polarization and high breakdown strength, the PCPMT obtains a maximum discharge energy density (Ud) of 4.47 J/cm3 at room temperature, which is 1.61 and 1.57 times of biaxially oriented polypropylene and polyimide (Kapton). The supernal Tg of 229 °C makes the energy storage performance of PCPMT almost unaffected at 100 °C. The charge-discharge efficiency (η) always keeps over 90% and an Ud of 5.2 J/cm3 at 480 MV/m is achieved, which is much better than Kapton (Ud = 1.77 J/cm3, η = 42.5%) under the same conditions. This work provides a new idea for preparing the high-performance polymer dielectrics via introducing rigid polar side chains.

Inkjet-Printed Soft Intelligent Medical Bracelet for Simultaneous Real-Time Sweat Potassium (K+), Sodium (Na+), and Skin Temperature Analysis

Truly wearable, fully flexible, multi-parametric sweat analysis with soft and socially discrete packaging offers tremendous potential to enable the next generation of non-invasive digital biomarkers analysis. Several examples of miniaturized potentiometric ion selective electrodes (ISE) have been proposed. However, several challenges remain unsolved concerning their long-term stability due to variations in physical sweat parameters. We hypothesize that the simultaneous monitoring of such parameters (e.g., skin-surface temperature, sweat rate, and pH) may pave the way for accurate and robust sweat biomarker analysis. Therefore, we propose a flexible multiparameter sensory interface fabricated on Kapton polyimide (PI) foil with high-resolution inkjet printing using silver nanoparticles (AgNPs). A facile controlled drop-casting of a custom synthesized ion-selective membrane ensures the selectivity of the biosensing. Next, we interfaced the fabricated sensory array with a custom-designed compact flexible biosignals conditioning embedded system, which enables system calibration, data processing, and wireless data transmission to a smartphone device. Later, we validate the proposed system in simultaneous sweat multi-ion (K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and Na <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ) and skin-surface temperature recording. After that, we characterize the system by embedding the smart medical bracelet in a soft microfluidic platform to mimic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> analysis on the body. Overall, the reported results represent the fundamental evidence proof for the development of the wearable multimodal sweat parameter analyzer.

Deformation diagrams of amorphous polyimide (kapton H) in the state of moderate and deep cooling: Experiment and theory

A comprehensive experimental and theoretical study of the regularities of active deformation at a constant rate of an amorphous polymer at room temperature and the influence of moderate and deep cooling on them was performed. The samples of amorphous aromatic polyimide (an analogue of kapton H) that are randomly cut fragments of the industrially produced thermoplastic film with a thickness of 25 μm were the object of the experimental study. The σ–ε diagrams of the tensile test, where σ and ε=ε˙t are the tensile stress and the relative strain, respectively, were recorded for 32 samples at three rates ε˙ = 7⋅10–5, 7⋅10–4, 6⋅10–3 s–1 under three temperatures T = 293, 77, and 4.2 K. In the state of deep cooling at T = 4.2 K, several samples were deformed as brittle glassy bodies – rupture after short elastic deformation. But the majority of the samples at all values of the experimental parameters (T,ε˙) had the rheological properties of rubber-like highly elastic materials (elastomers) with traditional tensile test diagrams: initial stage I of linear elastic deformation σI=Meε with Young’s modulus Me=Me(T); stage III of linear highly elastic deformation σIII=σfe+Mheε with modulus Mhe=Mhe(T) and conditional limit of elasticity σfe=σfe(T,ε˙); intermediate stage II of the relaxation type σII(ε;T,ε˙) with a nonlinear stress-strain dependence. The σ–ɛ diagrams of the individual samples with sufficiently high accuracy coincide with the graph of the function σ(ε;T,ε˙) which is the solution of the previously derived nonlinear rheological equation (V. D. Natsik and H. V. Rusakova, Fiz. Nizk. Temp.48, 281 (2022) [Low Temp. Phys.48, 253 (2022)]; Fiz. Nyzk. Temp.49, 246 (2023) [Low Temp. Phys.49, 228 (2023)]). In its derivation, a molecular-kinetic model was used: an amorphous polymer is considered as a set of statistically independent kinetic units, namely, molecular segments, and the elementary act of deformation is caused by thermomechanical activation of nonlinear excitations of these segments called elastons. The elaston mechanism of transformation of the deformation diagrams of amorphous polyimide samples under their moderate and deep cooling is discussed in detail: the transition between deformation states of warm and frozen elastomer, low-temperature effects of structural-deformation glass transition and deformation melting. Comparing the results of experiments and theory made it possible to obtain the empirical estimates for the macromechanical characteristics of the studied samples and the microparameters of elaston excitations. A significant and unsystematic (random) scatter of the macro- and micromechanical characteristics of the samples was revealed, which indicates a significant and random heterogeneity of the macro- and microstructure of the polyimide film from which they were made.

A Simulation Study of Triband Low SAR Wearable Antenna

The proposed paper presents a flexible antenna that is capable of operating in several frequency bands, namely 2.45 GHz, 5.8 GHz, and 8 GHz. The first two frequency bands are frequently utilized in industrial, scientific, and medical (ISM) as well as wireless local area network (WLAN) applications, whereas the third frequency band is associated with X-band applications. The antenna, with dimensions of 52 mm × 40 mm (0.79 λ × 0.61 λ), was designed using a 1.8 mm thick flexible kapton polyimide substrate with a permittivity of 3.5. Using CST Studio Suite, full-wave electromagnetic simulations were conducted, and the proposed design achieved a reflection coefficient below −10 dB for the intended frequency bands. Additionally, the proposed antenna achieves an efficiency value of up to 83% and appropriate values of gain in the desired frequency bands. In order to quantify the specific absorption rate (SAR), simulations were conducted by mounting the proposed antenna on a three-layered phantom. The SAR1g values recorded for the frequency bands of 2.45 GHz, 5.8 GHz, and 8 GHz were 0.34, 1.45, and 1.57 W/Kg respectively. These SAR values were observed to be significantly lower than the 1.6 W/Kg threshold set by the Federal Communication Commission (FCC). Moreover, the performance of the antenna was evaluated by simulating various deformation tests.

The Effects of PWM With High dv/dt on Partial Discharge and Lifetime of Medium-Frequency Transformer for Medium-Voltage (MV) Solid State Transformer Applications

Medium-frequency (MF) transformer in a phase-shift modulated dc solid state transformer (SST) is prone to partial discharge (PD) that impacts the system reliability and lifetime. Tightly packed MF transformer windings carrying PWM voltages create favorable conditions for PD inception. A peak potential condition is created between adjacent posterior windings as a result of phase-shifted modulation. This along with fast alternating electric fields incepts PD at lower than expected operating voltages. Early inception of PD lead to premature transformer failure leading to unanticipated DC SST down-time. The effects of PWM voltages containing high dv/dt switching transients on PD and lifetime characteristics of MF transformer in a dc SST is not yet understood, which is investigated in this paper. A non-intrusive PD detection strategy for MF PWM ac voltage is presented using high speed optical sensors. PD characterization is performed on Kapton polyimide insulated copper foil windings for a foil-type MF transformer. Winding samples are stress tested with steady state PWM voltages upto 2 kV and frequencies upto 50 kHz with high dv/dt upto 60 V/ns while maintaining the transformers geometric profile. Accelerated dielectric lifetime characterization is performed and novel lifetime prediction models are derived containing both frequency and dv/dt dependent variables.