Bending Cycle Test Research Articles

Programmable broadband ultrathin micropolarizer based on photoalignment technology

A method for creating broadband ultrathin azo dye micropolarizers is introduced, utilizing photoalignment technology and liquid crystal polymers to organize azo dyes into a long-range ordered structure. Achievements include a 3.63 μm thick polarizer with an extinction ratio over 140 and polarization efficiency over 99.3% across 400–650 nm, 5 μm × 5 μm pixel pitch flexible ultrathin checkerboard arrays and 6 μm pixel pitch flexible ultrathin one-dimensional grating with a 0.45 duty ratio through mask exposure technology. After a substrate-transfer technique, the bending cycle test demonstrates the mechanical stability and durability of the broadband ultrathin flexible polarizers, highlighting their potential for widespread use in integrated flexible optoelectronic systems.

High-performance flexible p-type Ce-filled Fe3CoSb12 skutterudite thin film for medium-to-high-temperature applications

P-type Fe3CoSb12-based skutterudite thin films are successfully fabricated, exhibiting high thermoelectric performance, stability, and flexibility at medium-to-high temperatures, based on preparing custom target materials and employing advanced pulsed laser deposition techniques to address the bonding challenge between the thin films and high-temperature flexible polyimide substrates. Through the optimization of fabrication processing and nominal doping concentration of Ce, the thin films show a power factor of >100 μW m−1 K−2 and a ZT close to 0.6 at 653 K. After >2000 bending cycle tests at a radius of 4 mm, only a 6 % change in resistivity can be observed. Additionally, the assembled p-type Fe3CoSb12-based flexible device exhibits a power density of 135.7 µW cm−2 under a temperature difference of 100 K with the hot side at 623 K. This work fills a gap in the realization of flexible thermoelectric devices in the medium-to-high-temperature range and holds significant practical application value.

Study on the Effect of Solid Solution Treatment on the Bending Fatigue Property of Fe-Mn-Si Shape Memory Alloys

Fe-Mn-Si shape memory alloys have excellent low-cycle fatigue performance and broad application prospects in the field of civil engineering and construction. It is necessary to conduct comprehensive and in-depth research on the mechanical properties of Fe-Mn-Si shape memory alloys. This study takes the Fe17Mn5Si10Cr5Ni shape memory alloy as the research object. After solid solution treatment at different temperatures and times, the effect of solid solution treatment on the bending fatigue performance of Fe-Mn-Si shape memory alloys was studied using bending cycle tests. The phase composition and fracture morphology of the sample were analyzed. The results showed that solid solution treatment can significantly improve the bending fatigue performance of Fe-Mn-Si shape memory alloys, reaching the optimal value at 850 °C for 1 h. The number of bending cycles until fracture increased by 131% compared to untreated specimens. Stress induction γ → ε martensitic transformation occurred in Fe-Mn-Si shape memory alloy specimens during bending cyclic testing, which is reversible. The fracture area of Fe-Mn-Si shape memory alloy specimens is mainly characterized by ductile fracture, with some areas exhibiting quasi-quasi-cleavage fracture characteristics.

A Freestanding, Dissolution- and Diffusion-Limiting, Flexible Sulfur Electrode Enables High Specific Capacity at High Mass Loading.

The acquisition of stable and high-areal-capacity S cathodes over 10mA h cm-2 is a critical and indispensable step to realize the high energy density configuration. However, increasing the areal capacity of S cathodes often deteriorates the specific capacity and stability due to the aggravated dissolution of S and diffusion of solvable polysulfides in the thick electrode. Herein, the design of a freestanding composite cathode that leverages 3D covalent binding sites and chemical adsorption environment to offer dissolution-limiting and diffusion-blocking functions of S species is reported. By employing this architecture, the coin cell exhibits excellent cycling stability and an exceptional specific capacity of 1444.3mA h g-1 (13mA h cm-2), and the pouch cell configuration manifests a noteworthy areal capacity exceeding 11mA h cm-2. This performance is coupled with excellent flexibility, demonstrated through consecutive bending cycle tests, even at a sulfur loading of 9.00mg cm-2. This study lays the foundation for the development of flexible Li-S batteries with increased loading capacities and exceptional performance.

Assessing the Role of Yarn Placement in Plated Knit Strain Sensors: A Detailed Study of Their Electromechanical Properties and Applicability in Bending Cycle Monitoring.

In this study, we explore how the strategic positioning of conductive yarns influences the performance of plated knit strain sensors fabricated using commercial knitting machines with both conductive and non-conductive yarns. Our study reveals that sensors with conductive yarns located at the rear, referred to as 'purl plated sensors', exhibit superior performance in comparison to those with conductive yarns at the front, or 'knit plated sensors'. Specifically, purl plated sensors demonstrate a higher sensitivity, evidenced by a gauge factor ranging from 3 to 18, and a minimized strain delay, indicated by a 1% strain in their electromechanical response. To elucidate the mechanisms behind these observations, we developed an equivalent circuit model. This model examines the role of contact resistance within varying yarn configurations on the sensors' sensitivity, highlighting the critical influence of contact resistance in conductive yarns subjected to wale-wise stretching on sensor responsiveness. Furthermore, our findings illustrate that the purl plated sensors benefit from the vertical movement of non-conductive yarns, which promotes enhanced contact between adjacent conductive yarns, thereby improving both the stability and sensitivity of the sensors. The practicality of these sensors is confirmed through bending cycle tests with an in situ monitoring system, showcasing the purl plated sensors' exceptional reproducibility, with a standard deviation of 0.015 across 1000 cycles, and their superior sensitivity, making them ideal for wearable devices designed for real-time joint movement monitoring. This research highlights the critical importance of conductive yarn placement in sensor efficacy, providing valuable guidance for crafting advanced textile-based strain sensors.

A Simple and Fast Compression‐Based Method to Fabricate Responsive Gold‐pNIPAM Hybrid Materials: From Thin Films to Anisotropic Microgels

AbstractIn recent years, hydrogel‐based soft materials with hybrid properties have found widespread use in various technological fields, including tissue engineering, soft actuators, and flexible electronics. The proper implementation of these smart multifunctional materials into real‐world applications requires the development of simple, cost‐effective, and large‐scale fabrication methods. Herein, a simple compression‐ and colloid‐based method is presented to fabricate responsive Au‐poly(N‐isopropylacrylamide) (pNIPAM) hybrid films using photopolymerizable resin containing Au‐pNIPAM core–shell microgels as building blocks. Uniform Au‐pNIPAM hybrid films of 25 × 25 mm with adjustable thickness in the micron‐size range (2.3–1.2 µm) w ere successfully fabricated on glass substrates and flexible commercial acetate sheets. The resulting flexible Au‐pNIPAM films exhibit robust optical and mechanical properties, even after repeated edge‐to‐edge bending cycle tests. Additionally, using patterned light to polymerize the Au‐pNIPAM films allows synthesizing of anisotropic Au‐pNIPAM microgels with high width‐to‐height aspect ratios, such as square, circular, and rectangular microgels, adding a new dimension to the proposed fabrication method.

Metal Work Function Effects on the Performance of UV–Visible–NIR Cs2SnI6 Photodetectors for Flexible Broadband Application

Herein, the role of top metal electrode work functions on the performance of flexible broadband ultraviolet (UV)–visible–near‐infrared (NIR) flexible Cs2SnI6 (CSI) photodetectors (PDs) are reported in the present study. The change in crystal plane orientation, surface morphology, and chemical composition of prepared films compared to hydrothermally synthesized CSI particles is confirmed by physical characteristics tools. The optical bandgap of CSI films is estimated to be 1.36 eV. The flexible CSI PDs are fabricated with three top metal electrodes (Mo, Ti, and Ni). The current–voltage (I–V) characteristics under the illumination of light sources with different wavelengths reveal the broadband UV–visible–NIR photodetection properties of flexible CSI PDs. The device with top Ti electrodes demonstrates maximum photoresponsivity (Rph = 1.65 ± 0.45 A W−1) and specific detectivity (Dph = 4.53 ± 0.36) × 1010 Jones for 455 nm compared to other wavelengths at Vb = 5 V. The fast photoresponse/decay time is 18 ms/24 ms for 455 nm at Vb = 1 V. The 85% and 90%–95% retentions of Rph of devices after 12 days keeping in a desiccator and after 500 bending cycle tests suggest the device's good environmental stability and mechanical flexibility, respectively. Thus, it is indicated in the results that CSI materials can be a potential candidate for flexible UV–visible–NIR photodetector for wearable electronic device applications.

Microscopic Analysis of Degraded Living Hinges of Polypropylene Aerial Cable Closure

Living hinges of polypropylene aerial cable closures that had been field-aged for eight years were analyzed in detail. Severe degradation including deep cracking was observed in the hinge central section, which had been subjected to UV light in the outdoor environment and repetitive sharp bending cycles during maintenance. On the other hand, the degradation of the other section was limited to within 10μm from the top surface. A repetitive bending cycle test alone did not reproduce the severe degradation. It was concluded that synergistic effects of solar UV irradiation and repetitive bending stress generated the severe degradation at the hinge section. Micro-cracks initially generated on the UV-degraded brittle top surface were the initial points of major cracks leading to breakage. Microscopic observations revealed craze structures around the major cracks. The crazes, caused by repetitive shear stress during the hinge-bending operations, were considered to be major routes for crack propagation. A test combining UV irradiation and repetitive sharp bending cycles on unused hinge specimens supported the crack generation and propagation mechanism.

Flexible high-resolution thin micropolarizers for imaging polarimetry

More durable (with high impact force), lighter, and more compact flexible azo dye micropolarizers are attractive candidates for low-cost, simple polarization imaging systems. The liquid crystal polymer (LCP), as an emerging material developed by photo-alignment technology, is a potential material for organizing the long-range ordered structure of azo dyes. However, little research has been done on LCP aligned azo dyes. This paper points out and solves a key problem that restricts the fabrication of high-precision arrays in guest (azo dye)-host (LCP) systems: the doping of dyes leads to disorder of the LCP during curing. After solving the problem, the relationship between the thickness of the LCP and the extinction ratio of the polarizing film was investigated, which effectively improved the extinction ratio. Alignment of azo dye molecules in the range of 2 µm (0°–180°) and arrays of micropolarizers (0°, 45°, 90°, -45°) with 8 µm × 8 µm pixel pitch was achieved by laser direct writing technology. The bending cycle test demonstrates the mechanical stability of the ultrathin flexible polarizer. The flexible patterned polarizer with robust chemical and mechanical stabilities provides a flexible way to capture the polarization of the light and highly integrated advanced flexible optoelectronic devices.

A crack templated copper network film as a transparent conductive film and its application in organic light-emitting diode

In this paper, a highly transparent, low sheet resistance copper network film fabricated by a crack template, which made by drying an acrylic based colloidal dispersion. The fabricated copper network film shows excellent optoelectronic performances with low sheet resistance of 13.4 Ω/sq and high optical transmittance of 93% [excluding Polyethylene terephthalate (PET) substrate] at 550 nm. What’s more, the surface root mean square of the copper network film is about 4 nm, and the figure of merit is about 380. It’s comparable to that of conventional indium tin oxide thin film. The repeated bending cycle test and adhesive test results confirm the reliability of the copper network film. As a transparent conductive film, the copper network film was used as an anode to prepare organic light-emitting diode (OLED). The experiment results show that the threshold voltage of the OLED is less than 5 V and the maximum luminance is 1587 cd/m2.

Room Temperature Fabrication of SnO2 Electrodes Enabling Barrier‐Free Electron Extraction for Efficient Flexible Perovskite Photovoltaics

AbstractRoom temperature‐processed electron transport layers (RT‐ETLs) demonstrate vast potential to be used in fabricating high‐performance flexible perovskite solar cells (PSCs) in an energy‐saving manner. However, the RT‐ETL normally suffers from inferior crystallinity, mismatched energy level, and high surface trap‐state density, which would result in under‐optimized interfacial electron extraction and undesirable interfacial charge recombination at ETL/perovskite interface, thus limiting the device performance. Herein, a novel strategy is demonstrated to prepare annealing‐free RT‐ETL based on precrystalline metal ion‐modified SnO2 nanocrystals, which perfectly optimizes the interfacial energy level alignment between ETL and perovskite layer, achieving nearly zero‐barrier charge transfer at the interface. As a result, the charge extraction has been remarkably accelerated and the interfacial charge recombination has been largely suppressed, leading to a ≈26% enhancement in device efficiency. The best‐performing flexible PSCs achieve efficiencies up to 19.3%, accompanied by outstanding mechanical strength under repeated bending cycle tests, which, to the best of the knowledge, is one of the highest reported values for the flexible perovskite photovoltaics fabricated with RT‐ETLs.

Mo Contact via High-Power Impulse Magnetron Sputtering on Polyimide Substrate

It has always been a huge challenge to prepare the Mo back contact of inorganic compound thin film solar cells (e.g., CIGS, CZTS, Sb2Se3) with good conductivity and adhesion at the same time. High-power impulse magnetron sputtering (HiPIMS) has been proposed as one solution to improve the properties of the thin film. In this study, the HiPIMS technology replaced the traditional DC power sputtering technology to deposit Mo back contact on polyimide (PI) substrates by adjusting the experimental parameters of HiPIMS, including working pressure and pulse DC bias. When the Mo back contact is prepared under a working pressure of 5 mTorr and bias voltage of −20 V, the conductivity of the Mo back contact is 9.9 × 10−6 Ω·cm, the residual stress of 720 MPa, and the film still has good adhesion. Under the minimum radius of curvature of 10 mm, the resistivity change rate of Mo back contact does not increase by more than 15% regardless of the 1680 h or 1500 bending cycle tests, and the Mo film still has good adhesion in appearance. Experimental results show that, compared with traditional DC sputtering, HiPIMS coating technology has better conductivity and adhesion at the same time, and is especially suitable for PI substrates.

One‐step anchored polymers via phenolamine bionic design on textile‐based heater for application in personal heat management

AbstractFlexible electronic fabrics urgently need to solve the problem of adhesion between the conductive layer and the fabric substrates. Inspired by phenamine bionics, we designed and fabricated copper nanoparticle conductive network/nylon 6 woven fabric (CNNs/NWF) wearable heaters through rapid co‐deposited of tannic acid and polyethyleneimine (PEI) by using CuSO4/H2O2 as a trigger. The grafted TA/PEI interface is capable of anchoring on the fabric surface via covalent and non‐covalent bonds on the one hand and providing an ideal platform to absorb and reduce catalyst Ag+ to facilitate subsequent electroless deposition on the other. Furthermore, the electrical heater could rise temperature from 14.6 to 152.6°C within 90 s under 1.5 V voltage, better than that of recently reported literature. The heater had a splendid conductivity (sheet resistance R0 ≈ 0.0086 Ω sq−1) and remain stable after 1000 bending cycle tests (normalized resistance R/R0 ≈ 2.5). Furthermore, the heater could meet 50 standard washing tests, satisfying the essential needs of the wearable devices. The deviation between the simulated data and the measured data was no more than 10% by the simulation of the finite elemental analysis. This study might provide a viable source for wearable heating devices.

Performance improvement of flexible ultraviolet photodetectors based on ZnO nanorod arrays by hydrothermal method with assistance of polyethyleneimine

Investigations on the high-performance flexible ultraviolet photodetectors have been becoming one of the interesting research focuses in recent years. ZnO is considered as suitable material for ultraviolet photodetection due to its wide bandgap (~3.37 eV). In this work, ZnO nanorod arrays were prepared using the hydrothermal method at the temperature of 70 ℃ on flexible substrates. Polyethyleneimine (PEI) was added into hydrothermal solution as the growth additive to achieve the performance improvement of the ZnO nanorod arrays ultraviolet photodetector. SEM, XRD, absorption spectroscopy, Raman spectroscopy and XPS were employed to characterize the morphology, crystallinity, optical properties and chemical composition. The introduction of PEI adjusts the growth process of ZnO nanorod arrays and affects the distribution of defect states, which brings out the improvement of the optoelectronic performance of ZnO nanorod arrays ultraviolet photodetectors. Compared with pure ZnO, the higher photo to dark current ratio and responsivity, and quicker time response speed are demonstrated in the PEI-assisted ZnO nanorod arrays photodetectors. And more photoresponse parameters are also discussed and compared. Furthermore, the photodetectors also display outstanding mechanical flexibility and robustness under multiple bending cycle tests. Our work presents a potential approach for improving the optoelectronic performance of simple-operated flexible ultraviolet photodetectors.

2.1: Invited Paper: 16.9‐Inch Flexible AMOLED Display with High Performance Top Gate Oxide TFT

We have fabricated top‐gate IGZO TFTs on PI substrate, which exhibit excellent electrical properties and high mechanical reliabilities to meet the demand for large area flexible display. The ΔVth under PBTS and NBTIS for 10 hours are only +0.26 V and −0.34 V, respectively. The mechanical bending properties of the TFT backplane is investigated. There are almost no change after 200,000 bending cycle test at a curvature radius of 20mm. To improve flexible capability and reduce cost of flexible OLED display, integrated gate driver on array (GOA) circuits with spilt channel structure has been investigated. Finally, we successfully realize 16.9‐inch rollable OLED display with high performance top gate IGZO TFT and GOA circuits

Conductive and antibacterial cellulose nanofibers decorated with copper nanoparticles for potential application in wearable devices

AbstractOne of the contributions of nanotechnology to our daily life is the preparation of a large variety of polymer‐based nanofibers, which could be the basis of future wearable devices. Wearable electronics are a great part of smart textiles research. Herein, we have reported an easy method to fabricate electrically conductive cellulose nanofibers (CNFs). To fabricate CNFs, we first prepared cellulose acetate (CA) nanofibers by using the electrospinning technique and later, the deacetylation process was done to obtain the CNFs. The electroless deposition (ELD) technique was then used to create the conductive nanofibers. Copper (Cu) was used to coat the CNFs because of their high conductivity and low cost. The ELD process parameters including time, temperature, volume, and pH were optimized to obtain a nanofiber with higher conductivity. The optimized condition was temperature: 40 °C, time: 10 min, volume: 600 ml, and pH: 13 to obtain a nanofiber web with 983.5 S/cm conductivity. Cu‐coated CNFs were characterized by scanning electron microscope, energy‐dispersive X‐ray spectroscopy, Fourier‐transform infrared spectroscopy, water contact angle, antibacterial activity, tensile, and electrical conductivity. The bending cycle test was performed to quantitatively demonstrate the durability and flexibility of the Cu‐coated nanofibers. Cu‐coated CNFs exhibited great performance to be used as a conductive layer with antibacterial activity.

Tannic acid modified graphene/CNT three-dimensional conductive network for preparing high-performance transparent flexible heaters

In this paper, the eco-friendly plant polyphenol, tannic acid (TA) was demonstrated as a non-covalent modifier for carbon nanotubes (CNTs), as well as a stripping medium to achieve exfoliated graphite to graphene by microfluidization. High-performance transparent flexible heater (TFH) with an embedded structure had been successfully fabricated by integrating conductive nanocomposites (TA-functionalized grapheme/TA-functionalized CNT/PEDOT:PSS; TG/TCNT/PEDOT) into waterborne polyurethane (WPU) film. Such a film exhibited favorable optical transmittance and sheet resistance (T = ca. 80% at 550 nm, Rs = 62.5 Ω/sq.), low root mean square (rms) roughness (approximately 0.37 nm), excellent adhesion and mechanical stability (the sheet resistance remained almost constant after 1000 bending cycle test for the bending radius of 10 mm), which are ideal as transparent heaters with high thermal efficiency. For TG/TCNT/PEDOT-WPU TFHs, the temperature increased rapidly and reached a steady state within 20 s with the maximum temperature reached to 116 °C, when the applied voltage was 20 V. Moreover, no variation in temperature was observed after the repeated heating–cooling tests and long-time stability test, indicating that TG/TCNT/PEDOT-WPU TCFs can be used as high performance TFHs. These TFH’s are expected to be suitable for vehicle defrosting, smart windows, portable heating, smart wearable devices, etc.

A practical approach for generation of WO3-based flexible electrochromic devices

We managed to provide one-step facile electrochromic device (ECD) preparation to incorporate two cathodic coloring components into lithium ion (Li+)-doped UV-curable electrolyte. The hybrid-based flexible ECDs were fabricated by using tungsten trioxide (WO3) and poly(3,4-ethylenedioxythiophene) (PEDOT) as electrochromic components without the need for deposition procedures. The influences of lithium salts (lithium perchlorate (LiClO4) and lithium trifluoromethanesulfonate (LiTRIF)) on the electrochromic performance of flexible ECDs were evaluated. The electrochromic and the intrinsic kinetic features of all ECDs were investigated via transmittance and electrochemical impedance measurements. The ECD fabricated from LiClO4 electrolyte exhibited the highest optical transmittance modulation of 38.7% under an applied potential of ± 2 V. To evaluate the mechanical robustness of the flexible ECDs, a bending cycle test was also conducted. After performing repetitive bending cycle tests, the optical modulation of ECD fabricated from LiTRIF electrolyte was remained stable for applied potentials of ± 2 V. Especially, the flexible ECDs prepared from LiTRIF showed high mechanical bendability.

Reliability Improvement of Printed Circuit Boards by Designing Methods for Solder Joint Technical Diagnostics with Application of Acoustic Emission Method

The paper represents technical diagnostics of printed circuit boards in particular their solder joints performed by commonly used through-hole and surface mount technologies. Operation and technology cause mechanical interactions and forces between substrate of printed circuit board and electronic components. Such tensile, shear, bending or torque forces transmit through the contact joints, which appear to be the weakest links in the assembly. The experimental research was conducted by mechanical tensile and pure bending tests followed by using method of acoustic emission. Conducted tests demonstrated considerable sensitivity and applicability for the method of acoustic emission to detect defects and possibly to assess the ultimate strength of solder joints in nondestructive diagnostics performed under forces long before the final failure. In order to minimize errors while measuring small loads in tensile tests of ceramic capacitors the special appliance was designed. The experiment was conducted to verify the overheating effect to ultimate load of the solder joints. Surface mount technology for ceramic capacitors has been optimized by introducing high temperature preheating mode that improves adherence to the contact pads and increases tensile strength, what was also confirmed by acoustic emission analysis. The pure bending appliance was designed to provide instant monitoring of all solder joints by equal testing stress. By conducted pulsing test cycles the total count was identified as the most informative parameter of acoustic emission that correlates with types of defects and ultimate strength of the solder joints. The planar location model has been developed by the idea of remote detection of acoustic emission through the volume of homogeneous medium such as water, unlike detecting acoustic emission on the surface of printed circuit board where acoustic emission signal is likely to be distorted or even lost. Using method of acoustic emission and pure bending cycling test the method for technical diagnostics of solder joints has been designed. The results represented in the paper contribute to design and technology improvement in radio-electronics.

Self-supported flexible supercapacitor based on carbon fibers covalently combined with monoaminophthalocyanine

Flexible energy-storage technologies that can be conformal with deformation as well as maintain their electrochemical functions is consistently and significantly considered. Therefore, reinforcing the connection between active materials and supports is particularly pivotal. In this work, as a flexible support, Ar plasma treated carbon cloth (CC) combines with monoaminophthalocyanine (Pc-NH2) through covalent bond (amido bond) to make a flexible electrode, which hopes to achieve high stability. The synthesis of CC grafted with monoaminophthalocyanine was characterized using FTIR, Raman spectroscopy, energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It shows a high areal specific capacitance (CA) and energy density, up to 2.425 F cm−2 and 0.165 mWh cm−1 at 1 mA cm−2, that retains over 90.46% after 10,000 charge-discharge cycles, and exhibits the extra low charge transport resistance (Rct) possessed only 0.782 Ω. Moreover, superior flexibility could be reflected by bending material for 180°, which maintained areal capacitance with 95%. The fabricated symmetrical supercapacitor shows high stability holding 94.8% CA for 1000 bending cycle test and supplies power for a LED nearly 1 h with 0.003 m2. All these results illustrate the high performance of the active materials connected with the supports by powerful covalent bond.