Polyimide Thin Films Research Articles

Effects of Alkyl Side Chain Length on the Structural Organization and Proton Conductivity of Sulfonated Polyimide Thin Films

Effects of Alkyl Side Chain Length on the Structural Organization and Proton Conductivity of Sulfonated Polyimide Thin Films

A Micro Capacitive Humidity Sensor Based on Al-Mo Electrodes and Polyimide Film.

Quickly sensing humidity changes is required in some fields, such as in fuel cell vehicles. The micro humidity sensor used for the relative humidity (RH) measurement with fast response characteristics, and its numerical model and method are rare. This paper firstly presents a numerical model and method for a parallel plate capacitor and a numerical analysis of its dynamic characteristics. The fabrication of this sensor was carried out based on the numerical results, and, the main characteristics of its moisture-sensitive element are shown. This parallel plate capacitor is made using complementary metal-oxide semiconductor (CMOS)-compatible technology, with a P-type monocrystalline silicon wafer used as the substrate, a thin polyimide film (PI) between the upper grid electrode and the lower parallel plate electrode, and electrodes with a molybdenum-aluminum bilayer structure. The shape of the micro sensor is square with 3 mm on the side of the source field. The humidity sensor has a linearity of 0.9965, hysteresis at 7.408% RH, and a sensitivity of 0.4264 pF/%RH. The sensor displays an average adsorption time of 1 s and a minimum adsorption time of 850 ms when the relative humidity increases from 33.2% RH to 75.8% RH. The sensor demonstrates very good stability during a 240 h test in a 25 °C environment. The numerical model and method provided by this study are very useful for predicting the performance of a parallel plate capacitor.

Development and experimental testing of an innovative nondestructive thermal sensor utilizing the thermal interrogation method for detecting leakage in water plastic pipes

Leak detection in water pipelines is still an important issue in real-world industrial systems. Thus, a new nondestructive thermal sensor design based on the thermal interrogation method has been developed to detect and estimate the real-time leaks in water plastic pipes without environmental interference. The proposed thermal interrogation method utilizes a combination of heat flux and temperature measurements on the upstream and downstream outside plastic pipe surfaces. These measurements are obtained by using heat flux sensors and thermocouples that are covered by thin-film polyimide electric heaters. The interrogation method approach delivers that at constant input heat flux, the difference in sensor temperature values is dependent on the leakage volume flow rates. The sensor was tested over a range of water leakage volume flow rate from 0.1 m3/h to 1.3 m3/h and a range of water temperature from 21 °C to 25 °C. The water leakage volume flow rates were correlated to the difference in temperature values between the upstream and downstream sensors. The measurement results reveal that this sensor can be used to detect and estimate the real-time water leakage volume flow rate with high accuracy and repeatability for plastic pipes.

SIMULATING MOLECULAR OPTICAL PROPERTIES OF POLYIMIDE FOR NONVOLATILE RESISTIVE PHOTOMEMORY DEVICES

In this study, the focus was on utilizing the polyimide (PI) thin film as a resistive conversion layer for organic polyimide-based resistive random-access memory (ReRAM) applications. We utilized the 3D molecular editor WebMO to manipulate and analyze the structures of Aromatic-PI and Quinoid-PI molecules. The molecular chain length, molecular weight, and HOMO/LUMO molecular orbitals were investigated to gain insights into the fundamental properties of PI molecular structures. The analysis revealed that the Quinoid-PI molecule exhibited a shorter molecular chain compared to Aromatic-PI, attributed to the inability of the cyclic structure in Quinoid-PI to maintain a planar conjugated structure, resulting in an uneven overall structure and reduced molecular chain length (Norcorss, 1988). The research results demonstrate that the optical energy gap of Aromatic-PI remains constant regardless of the number of molecular bonds, with a value of approximately 3.2661 eV. In contrast, for Quinoid-PI, the optical energy gap undergoes a significant decrease as the number of molecular bonds ranges from 1 to 5. As the bond count increases to 20~23, the change in the optical energy gap gradually diminishes, ultimately resulting in an optical energy gap of 0.6932 eV. This observation indicates that longer molecular chains composed of Aromatic-PI act as insulators, while Quinoid-PI transforms into a low-energy gap conductor.

Laser-induced graphene decorated with Ni[sbnd]Pt alloy nanoparticles for non-enzymatic electrochemical quantification of glucose

Enzyme-free electrochemical glucose (Glu) sensors, adopting electrochemically active catalysts, are of vital significance to effectively monitoring and analyzing the blood Glu level in diabetes diagnosis. Meanwhile, developing novel electrode substrates have been the hot research pot to meet the demand for constructing flexible sensors. In this work, porous laser-induced graphene (LIG) was prepared through a facile one-step laser-engraving technique on a polyimide thin film, and then used directly as the electrode. Furthermore, NiPt alloyed nanoparticles (NPs) were electrodeposited on the LIG electrode surface to gain the NiPt/LIG composite electrode, which was applied to construct the nonenzymatic electrochemical Glu sensor. The morphology, element and electrochemical performance of NiPt/LIG composite was characterized through various techniques. NiPt alloyed NPs were homogeneously distributed on the LIG scaffolds, which possess plenty of porous structure, high surface area and many active sites. The cooperative effect between the outstanding electrocatalytic capacity of NiPt alloyed NPs, the extraordinary electroconductibility of LIG and the numerous exposed active sites endow the NiPt/LIG sensor outstanding electrocatalytic performance for electrochemical oxidation of Glu. Under the most appropriate conditions, the obtained NiPt/LIG sensor was adopted to detect Glu, showing a broad detection concentration range of 0.5 μM to 2.1 mM and 2.1 mM to 5.6 mM, good sensitivities of 1.824 and 0.467 μA μM−1 cm−2, a low detection limit of 0.03 μM. The as-fabricated nonenzymatic Glu sensor also displays high selectivity, stability considering ageing effects under different environment conditions and prominent reproducibility. Additionally, this novel NiPt/LIG nonenzymatic Glu sensor was applied to quantify Glu successfully in blood serum and food samples and the results were in good agreement with that by UV–vis spectrophotometer, demonstrating high precision and accuracy as well as excellent recovery, showing good application prospects in Glu monitoring. This research confirmed the potential of exploiting NiPt/LIG as a highly sensitive Glu nonenzymatic electrochemical sensor and provided a practicable and suitable approach for construction of novel electrochemical sensors.

Research and development of double layer P-doped laser induced graphene thin film electrode for flexible micro-supercapacitor applications

Laser-induced graphene (LIG) has garnered significant attention for its cost-effectiveness and high efficiency in fabricating flexible micro-energy storage devices. In this study, we devised a simple method to fabricate double layer P-doped LIG electrodes through repetitive laser induction technology for high-performance flexible energy storage applications. Instead of utilizing commercial polyimide (PI) thin film, we optimized the formation process of P-doped PI thin film and achieved a highly flexible double layer P-doped LIG thin film electrode with a uniformly porous structure and the high porosity through repeated laser induction processes. Experimental results demonstrated that the developed double layer P-doped LIG thin film electrode exhibits high porosity, high specific areal capacitance of 180 mF cm−2, and high energy density of 0.025 mWh cm−2. Furthermore, an all-solid-state micro-supercapacitor utilizing hydrogel electrolyte was assembled, demonstrating a high areal capacitance of 62 mF cm−2 and excellent cycling stability with 95% capacitance retention after 6000 charging/discharging cycles. Moreover, the developed all-solid-state micro-supercapacitor successfully powered a light-emitting diode, showcasing its significant potential for practical energy storage applications.

Compact Monoenergetic Proton Generator in MeV Region Using NANOGAN

For simple applications, such as the calibration of a charged particle detector, a multi-MeV proton generator may be preferable to cyclotrons or electrostatic accelerators such as Van de Graaff. Thus, a compact proton generating system, consisting of 10Ghz ECR ion source NANOGAN and a deuteron target, was developed at the Research Center for Nuclear Physics at Osaka University. A 3He2+ beam was generated by the NANOGAN with the acceleration voltage of 20∼45 kV in an experiment that utilized the fusion reaction 3He + deuteron (d) → proton(p) + 4He. The monochromatic protons with energies of 14.67 MeV were successfully obtained at the atmosphere side of the target in the experimental setup, when a novel target base with a thin metal foil and Polyimide film window are used.

Smart Hydrogel Swelling State Detection Based on a Power-Transfer Transduction Principle.

Stimulus-responsive (smart) hydrogels are a promising sensing material for biomedical contexts due to their reversible swelling change in response to target analytes. The design of application-specific sensors that utilize this behavior requires the development of suitable transduction concepts. The presented study investigates a power-transfer-based readout approach that is sensitive to small volumetric changes of the smart hydrogel. The concept employs two thin film polyimide substrates with embedded conductive strip lines, which are shielded from each other except at the tip region, where the smart hydrogel is sandwiched in between. The hydrogel's volume change in response to a target analyte alters the distance and orientation of the thin films, affecting the amount of transferred power between the two transducer parts and, consequently, the measured sensor output voltage. With proper calibration, the output signal can be used to determine the swelling change of the hydrogel and, consequently, to quantify the stimulus. In proof-of-principle experiments with glucose- and pH-sensitive smart hydrogels, high sensitivity to small analyte concentration changes was found along with very good reproducibility and stability. The concept was tested with two exemplary hydrogels, but the transduction principle in general is independent of the specific hydrogel material, as long as it exhibits a stimulus-dependent volume change. The application vision of the presented research is to integrate in situ blood analyte monitoring capabilities into standard (micro)catheters. The developed sensor is designed to fit into a catheter without obstructing its normal use and, therefore, offers great potential for providing a universally applicable transducer platform for smart catheter-based sensing.

Evaluation of the thin film polyimide‐based holographic metasurface inspired leaky‐wave antenna

AbstractThe proposed paper presents the design of a leaky‐wave antenna inspired by holographic metasurfaces employing thin film. Leveraging the holographic principle, this metasurface showcases its transformative capacity by converting an omnidirectionally radiating monopole into a highly directional antenna emitting leaky waves. The holographic metasurface is constructed using a thin film of polyimide (PI) (Df = 0.008; Dk = 3.5), measuring 50 μm in thickness. The antenna structure comprises multiple layers, commencing with the top PI layer, succeeded by a 40 μm thick adhesive layer (Df = 0.004; Dk = 6). Subsequent layer includes the Rogers RT/duroid 5880 substrate (Df = 0.0009; Dk = 2.20), grounded at the bottom and has a thickness of 1.6 mm. The meticulously tailored design of the proposed antenna ensures optimal performance at 15 GHz, facilitating directional radiation and precise beam steering at 10 degrees (ϴ = 10°). This innovative design, incorporating the holographic metasurface on thin film, significantly enhances the antenna's performance, increasing gain from 1.5 dBi to 13.8 dBi.

Excellent Stable Cycle Performance of Polyethylene Oxide‐Based 3D Solid Dual‐Salt Composite Electrolyte with Porous Polyimide Thin Films Host

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

Thermalization of Mesh Reinforced Ultra-Thin Al-Coated Plastic Films: A Parametric Study Applied to the Athena X-IFU Instrument.

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

Spray-deposition of graphene/polymer thin coatings on polyimide sheets for lunar dust adhesion mitigation

NASA seeks to develop technologies to mitigate dust accumulation from planetary surfaces on robotic and human systems hardware during planned space exploration missions. With a return to the Lunar surface, lunar dust threatens the durability and reusability of components and vehicles due to its fine, jagged morphology and highly abrasive nature. Lunar dust consists of particles less than 60 μm in size that are chemically reactive, electrostatically and sometimes magnetically charged. Unique materials and technologies that reduce or mitigate lunar dust adhesion will be critical to support long duration missions and eventual sustained presence on the lunar surface. The goal of this work was to prepare dust resistant, space durable polymer films to satisfy dust accumulation mitigation needs for future NASA missions. In this regard, several graphene coated polyimide thin films have been developed with surface resistivity properties in the range of 103 Ω/sq to 1011 Ω/sq and evaluated for their dust adhesion performance. Raman spectroscopy was used to characterize and assess the quality of graphene ink coated sheets while surface resistivity measurements were used to assess electrical conductivity. Scratch testing and abrasion resistance measurements were used to evaluate overall abrasion performance. Water contact angle and optical microscopy were used to evaluate changes in surface topography and chemistry. Graphene coated polyimide surfaces with charge dissipative resistivity (106 Ω/sq) demonstrated a minimum in residual particle areal coverage compared to conductive and insulating surfaces.

Implantation accuracy of novel polyimide stereotactic electroencephalographic depth electrodes-a human cadaveric study.

Stereoelectroencephalography (sEEG) is a minimally invasive procedure that uses depth electrodes stereotactically implanted into brain structures to map the origin and propagation of seizures in epileptic patients. Implantation accuracy of sEEG electrodes plays a critical role in the safety and efficacy of the procedure. This study used human cadaver heads, simulating clinical practice, to evaluate (1) neurosurgeon's ability to implant a new thin-film polyimide sEEG electrode according to the instructions for use (IFU), and (2) implantation accuracy. Four neurosurgeons (users) implanted 24 sEEG electrodes into two cadaver heads with the aid of the ROSA robotic system. Usability was evaluated using a questionnaire that assessed completion of all procedure steps per IFU and user errors. For implantation accuracy evaluation, planned electrode trajectories were compared with post-implantation trajectories after fusion of pre- and postoperative computer tomography (CT) images. Implantation accuracy was quantified using the Euclidean distance for entry point error (EPE) and target point error (TPE). All sEEG electrodes were successfully placed following the IFU without user errors, and post-implant survey of users showed favorable handling characteristics. The EPE was 1.28 ± 0.86 mm and TPE was 1.61 ± 0.89 mm. Long trajectories (>50 mm) had significantly larger EPEs and TPEs than short trajectories (<50 mm), and no differences were found between orthogonal and oblique trajectories. Accuracies were similar or superior to those reported in the literature when using similar experimental conditions, and in the same range as those reported in patients. The results demonstrate that newly developed polyimide sEEG electrodes can be implanted as accurately as similar devices in the marker without user errors when following the IFU in a simulated clinical environment. The human cadaver ex-vivo test system provided a realistic test system, owing to the size, anatomy and similarity of tissue composition to that of the live human brain.

Closely Packed Stretchable Ultrasound Array Fabricated with Surface Charge Engineering for Contactless Gesture and Materials Detection.

Communication with hand gestures plays a significant role in human-computer interaction by providing an intuitive and natural way for humans to communicate with machines. Ultrasound-based devices have shown promising results in contactless hand gesture recognition without requiring physical contact. However, it is challenging to fabricate a densely packed wearable ultrasound array. Here, a stretchable ultrasound array is demonstrated with closely packed transducer elements fabricated using surface charge engineering between pre-charged 1-3 Lead Zirconate Titanate (PZT) composite and thin polyimide film without using a microscope. The array exhibits excellent ultrasound properties with a wide bandwidth (≈57.1%) and high electromechanical coefficient (≈0.75). The ultrasound array can decipher gestures up to 10cm in distance by using a contactless triboelectric module and identify materials from the time constant of the exponentially decaying impedance based on their triboelectric properties by utilizing the electrostatic induction phase. The newly proposed metric of the areal-time constant is material-specific and decreases monotonically from a highly positive human body (1.13 m2s) to negatively charged polydimethylsiloxane (PDMS) (0.02 m2s) in the triboelectric series. The capability of the closely packed ultrasound array to detect material along with hand gesture interpretation provides an additional dimension in the next-generation human-robot interaction.

Mechanical enhancement and high linearity health monitoring of composite materials based on CNTs/PSF/PI film sensor with ultra-low SWCNTs doping content.

A new type of embedded composite material health monitoring nano-sensor is designed to ensure that the unique material advantages of nanofillers can be maximized. The carbon nanotubes (CNTs)/polysulfone (PSF)/polyimide (PI) thin film sensor in this paper is obtained by the self-assembly of a PSF/PI asymmetric porous membrane which is prepared by a phase inversion method through vacuum filtration of SWCNTs. It is a new structure for a practical CNT sensor that can take into account both 'composite health monitoring and damage warning' and 'composite mechanical enhancement'. The new structure of the CNTs/PSF/PI film sensor is divided into two parts. The upper part consists of small-aperture finger-like holes filled with SWCNTs (the SWCNT content is 0.0127 mg cm-2). The lower part consists of large-aperture cavities conducive to resin infiltration, which enhance the interface bonding force between the sensor and the composite material. This unique structure allows the CNTs/PSF/PI film sensor to change the influence of the embedded sensor from 'introducing defects' to 'local enhancement', and the mechanical strength of the enhanced specimen can reach up to 1.68 times that of the original specimen, and the service interval can reach 2.01 times that of the original specimen. In addition, the CNTs/PSF/PI film sensor also has good sensitivity (GF = 2.54) and extremely high linearity (R2 = 0.9995), and has excellent follow-up and interface bonding ability. It can also maintain excellent fatigue resistance and stability over 46 500 vibration cycles, which provides new research ideas and research methods for the field of composite-life monitoring sensors.

Tension-Induced Localized Wrinkling in a Patched Thin Film Supported by an Elastomer.

The wrinkling behavior of thin films has received great attention for their applications in developing various wrinkle-based novel technologies. Herein, a new wrinkling system: tension-induced wrinkling in an elastomer-supported patched thin film (TW-P&SF) is investigated by using PDMS-supported patched polyimide thin films with different thicknesses and varied length/width ratios. Different from the well-studied compression-induced wrinkling in an elastomer-supported thin film (CW-SF) and tension-induced wrinkling in an edge-clamped free-standing thin film (TW-FF), in the system of TW-P&SF, the wrinkles are localized near the edge of the film with a finite length that follows a center-symmetric distribution. It was found that the wrinkle length lmax and the wrinkle period λ scale with the film thickness h as λ ∼ h0.86 and lmax ∼ h-0.79. With the assistance of the two-dimensional shear lag model and scaling analysis, the underlying mechanism for wrinkle localization is clarified. Furthermore, the promise of the TW-P&SF-enabled wrinkle-based method as a new method for thin film mechanical characterization is demonstrated.

Mesoporous Polyimide Thin Films as Dendrite-Suppressing Separators for Lithium-Metal Batteries.

Lithium-metal batteries require the effective suppression of lithium dendrites to guarantee both high performance and safety. Today's separators have macropores allowing lithium dendrites to traverse, leading to internal short circuits and other catastrophic results. Herein, we report a mesoporous polyimide separator for dendrite suppression. The polyimide separator exhibits mesopores of 21 nm width and a high storage modulus of 1.80 GPa. This mesoporous polyimide separator assists in the electrodeposition to form flat-top protrusions instead of sharp dendrites, therefore, allowing the safe cycling of lithium-metal batteries. This work is expected to advance the development of dendrite-suppressing strategies and contribute to the revival of lithium-metal batteries.

Analysis of deformation of thin polyimide film by pre-strained silicone elastomer

In this study, we analyze the deformation of the thin polyimide (PI) film on the pre-strained elastomer. When pre-strained elastomer bonded with pressure-sensitive adhesive (50 µm) and the thin PI film (under 1 μm thickness) containing rigid islands array and released mildly, the elastomer film is restored to its near initial state by the amount of pre-strain. At this time, if the compressive stiffness of the PI film is relatively small compared to the elastomeric film, the deformation occurs as much as the elastomer. In such a case, the PI film generates a wrinkle phenomenon, a special form of the compression behavior of the thin PI film. To prevent pixel area deformation, the PI panel uses rigid material placed in the vicinity of the light-emitting pixels and a metal bus-line matrix placed in the rigid pixel and soft area. However, in this case, when the deformation of the wrinkle-producing area is excessive, it can develop into folds and creases. Hence, PSA and elastomer films are placed on both sides of the thin PI panel containing rigid islands array bridged with a metal bus-line matrix for buckling analysis with the protection of the pixel area.

Suppression of Secondary Electron Emissions on the Graphene-Coated Polyimide Materials Prepared by Chemical Vapor Deposition

Polyimide thin-film materials are widely used in aerospace and particle gas pedals, etc., but the phenomenon of secondary electron emission occurred under vacuum conditions. The graphene-coated polyimide materials were prepared for this phenomenon to suppress secondary electron emissions. The graphene coating was prepared on the polyimide surface through chemical vapor deposition (CVD). Scanning electron microscope images (SEM), X-ray photoelectron spectrometer images (XPS), Raman spectroscopy, atomic force microscopy (AFM), and other analytical methods were used to characterize the properties of the prepared materials. The C1s XPS fine spectra and Raman curve analyses showed that the material has an abundant sp2 hybridized structure, and the sp2 structure can reduce secondary electron emissions. The C, O, and N contents in the tested samples were 65.85, 20.47, and 13.68 at.%, respectively. It was examined that the graphene coating had an inhibitory effect on the secondary electron emissions of polyimide materials, and the secondary electron emission yield (SEY) was significantly reduced. The results of secondary electron tests showed that the maximum SEY (δmax) of the polyimide material decreased from 1.72 to 1.52 after the preparation of the graphene coating. The mechanism of using a graphene coating to reduce the SEY of polyimide was analyzed from experimental and theoretical perspectives. The results of this study can provide research ideas for polyimide thin film materials in aerospace, particle gas pedals, and other applications.

Flexible and gradually bonded metal organic framework coatings for atomic oxygen protection of polyimide films

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.