Journal of Composite Materials

AbstractMicrovalves are essential in microfluidic systems, as they regulate fluid flow direction and enable critical operational functions. This study focuses on designing and fabricating a phase change polymeric microvalve utilizing polyethylene glycol (PEG) combined with multiwall carbon nanotubes (MWCNT) to improve the response time. A microchip made from polydimethylsiloxane (PDMS) features a microchannel with a cross‐sectional area of 100 × 200 µm2 where water is injected at flow rates between 10 and 100 mL min−1. In addition, effective thermal regulation is attained by implementing a nickel–chromium wire plate heater, which is meticulously controlled by a sensor to guarantee precise temperature management. The results indicate that the fabricated microvalve exhibits remarkable operational limits, withstanding a maximum tolerable pressure of 182 mmHg in the closed state. It consistently achieves an average response time of ≈170 s under various temperature conditions, underscoring its efficiency and reliability for demanding applications. Notably, the incorporation of 0.1 wt.% MWCNTs in PEG successfully reduce the response time from 180 to 130 s at an operating temperature of 60 °C, demonstrating significant potential for developing faster actuators.

AbstractThe challenges of operating robots in natural, highly variable, and diverse physical environments demand equally variable solutions. Following a flexible design approach from soft robotics, a variable stiffness structure with shape morphing and shape memory capabilities made from layered textiles and 3D printing material is developed. The stiffness change of the central conductive PLA (cPLA) is achieved electrically via Joule heating. Fabrication of multiple segment surfaces from the textile materials allows for direct printing of cPLA, which maximizes the electrodes' contact area. The material's variable stiffness is then used to modulate the structure's bending behavior and actively change its shape (shape morphing) while preserving shape memory behavior. To achieve this, models for stiffness change, heat transfer, and shape morphing are introduced and tested experimentally. The design presents a new method for achieving variable stiffness of 2794 Nmm2 in small segments of soft, deformable structures, using widely available materials and simple manufacturing methods. Furthermore, the structure's design enables shape morphing and shape memory.

AbstractTo meet the growing demand for flexible wearable devices in the information era, the development of cost‐effective, easy‐processable, and mechanically sound flexible luminescent materials is pivotal but remains challenging. Here, a facile one‐step melt mixing strategy is reported to prepare the reprocessable polyethylene with high stable fluorescence (f‐PE) using low‐density polyethylene (LDPE) and high‐dosages of benzoyl peroxide (BPO) as raw materials. Typically, after 30 min mixing 50 g LDPE with 1 g BPO in a 110‐rpm mixer, the resulting f‐PE exhibited high fluorescent brightness and remarkable fluorescent stability. In addition to good fluorescent and mechanical properties, f‐PE also demonstrated excellent processability and can be processed using conventional melt processing methods for normal PE. Based on the results, the extended through‐space n‐π*/π‐π* interactions resulting from the high‐content BPO‐induced extensive grafting of oxygen‐containing functional groups on the main chain is proposed, as well as the chain scissions and rearrangement under strong melt shearing, may be main factors to contribute f‐PE with luminescent and processable properties. Thanks to advantages such as cost‐effective raw materials, and scalable and solvent‐free production, the f‐PE and its preparation technique show great potential for flexible wearable applications, bringing new opportunities for functionalizing traditional versatile PE.

AbstractPolymer gels are versatile materials in biomedical applications, sensors, and actuators. However, designing gels with diverse functionalities, such as high toughness, self‐healing capability, and 3D printability, is often challenging. In this work, it is found that random copolymerization of N‐isopropyl acrylamide (NIPAm) with a small amount of acrylic acid (AAc) in a hydrophobic eutectic solvent consisting of menthol and decanoic acid leads to eutectogels toughened by polymer‐solvent hydrogen bonding. Interestingly, further increasing AAc content induced phase separation of glassy AAc‐riched domain that significantly increased the stiffness of the eutectogels. The stiffness and stretchability of the poly(NIPAm‐co‐AAc) eutectogels can also be easily modulated by adjusting the AAc content and monomer concentration, leading to highly transparent gels with high toughness. Furthermore, the eutectogels demonstrate efficient dissipation, reasonable recovery, and moderate self‐healing capability. The resin is also compatible with digital light processing 3D printing to prepare dielectric layers with different geometric designs for capacitive sensors. By integrating the functions of eutectogels and 3D printing, the approach provides a new avenue for soft materials with a broad palette of mechanical properties and geometrical designs.

AbstractCopper‐based halide perovskites have gained considerable interest in optoelectronic applications owing to their outstanding stability and luminescence properties. Herein, 3D structure of Cs3Cu3Cl9 single crystals is developed from the known phase of 0D Cs3Cu2I5 via addition of HCl. The transformed 3D Cs3Cu3Cl9 single crystals exhibit superior material properties such as an optical bandgap of 2.39 eV, and distinct violet emission at 425 nm, making them a potential candidate for ultraviolet (UV) photodetection. The hierarchical FTO/Cs3Cu3Cl9/C heterostructure UV photodetector showed a remarkable responsivity of 0.13 mA W−1 and specific detectivity of 2.20 × 109 Jones under 372 nm UV illumination at zero bias, possessing a better performance than the 0D Cs3Cu2I5 structure. This work brings insight into the transformation from 0D to 3D halide perovskite structure for self‐powered photodetectors via a simple solvent engineering strategy, thereby paving the way for further investigations in various optoelectronic applications.

AbstractFlexible hybrid electronics (FHEs) combine flexible substrates with conventional electronic components, offering increased mechanical stability and reduced size and weight. Laser‐Induced Graphene (LIG) presents a novel approach for patterning flexible devices, characterized by reduced weight, flexibility, and ease of synthesis. This study demonstrates a new process utilizing copper‐plated LIG to create direct‐write, on‐demand flexible electronics. The method incorporates catalytically active Pd nanoparticles into the LIG structure, enabling selective copper‐plating to form circuits. This simplifies the process by eliminating sensitization steps and avoiding challenges of homogeneous deposition found in electroplating. The impact of laser fluence on LIG structure and plating behavior is systematically studied, identifying an optimal fluence of 168 J cm−2 using a 7 W, 450 nm laser. Samples with this fluence achieve complete copper plating within 20 min, a sheet resistance of 149.9 mΩ □−1, good adhesion, and durability across 10 000 bend cycles. An operational amplifier is produced on a flexible polyimide substrate, demonstrating the feasibility of this process for creating low‐cost FHEs. This research expands LIG applications and establishes the relationship between laser fluence and copper‐plating behavior, opening new opportunities for integrating LIG into flexible electronics.

AbstractTouch is key to perception, feeling, and interaction within the social environment. Emulating these sensory capabilities toward intelligent human‐like robots and prosthetics can be achieved by integrating sensor arrays, including pressure, temperature, strain, and humidity, spatially distributed in the human skin, mimicking somatosensory functions. However, existing sensor technologies are not environmentally sustainable due to their non‐biodegradable constituent materials, generally requiring bulky power sources incompatible with wearables. To address these challenges, this study presents a lightweight, flexible, and self‐powered dynamic pressure sensor platform, emulating the functionality of type‐II mechanoreceptors inside the skin, using chitosan biopolymer. A biodegradable pressure sensor is fabricated using a thin composite film of chitosan doped with different compositions of Zinc Oxide (ZnO) nanoparticles (NPs) as the active piezoelectric layer embedded between copper electrodes. The 15 wt.% chitosan‐ZnO composite‐based sensor demonstrates superior pressure and frequency sensitivities of 70.71 mV/kPa and 471.43 mV Hz−1 with excellent cyclic stability and device‐to‐device repeatability compared with pure chitosan‐based pressure sensors. The accelerated biodegradability studies demonstrate that ultra‐thin composite films can completely degrade in slightly acidic deionized water (pH 6.5) in less than 2 h, exhibiting environmental sustainability. Applications include object classification and identification, the detection of hand and finger movements, gesture recognition, and wireless data transmission.

AbstractThe urgency for a sustainable mitigation of the environmental impacts caused by climate change highlights the importance of renewable energy technologies to fight this challenge. Perovskite solar cells (PSCs) emerge as a promising alternative to traditional photovoltaic (PV) technologies due to their unprecedented increase in efficiency (currently peaking at 26.95%) and long‐term stability proven by the successful completion of industry relevant International Electrotechnical Commission (IEC) testing standards. Flexible PSCs (f‐PSCs) offer significant advantages such as lightweight and high power‐per‐weight ratio, mechanical flexibility, and a high throughput roll‐to‐roll (R2R) manufacturing. These make f‐PSCs ideal for implementation in various applications areas, such as wearable electronics, portable devices, space PV, building‐ or automotive‐integrated PVs, and more. Notably, efficiencies over 23% now mark a significant milestone for f‐PSCs, demonstrating their competitiveness with traditional rigid solar panels. This review explores breakthroughs in f‐PSCs, focusing on flexible substrates, electrode materials, perovskite inks, and encapsulation strategies. It also covers recent advancements and studies of f‐PSCs fabricated by scalable deposition methods and emphasizes the importance of interfacial engineering and encapsulation in enhancing stability and durability. The review concludes with a summary of key findings, remaining challenges, and perspectives for the successful market uptake of f‐PSCs.

AbstractConventional processors often underutilize their computational resources because of the fixed functionality of logic gates; numerous logic gates should be embedded to support all necessary operations, even if many of them are rarely used. Reconfigurable logic gates (RLGs) offer a promising solution as they dynamically switch their logical functionality according to the demands of specific operations. Here, a novel RLG architecture based on the dual‐gate silicon nanomembrane (SiNM) field‐effect transistors (FETs) is proposed. By reconfiguring the electrostatic doping profiles of the SiNM channel, the dual‐gate SiNM FET can operate as three distinct electronic components; a forward‐biased diode, a backward‐biased diode, and a variable resistor. Furthermore, the three dual‐gate SiNM FETs are integrated to implement a single RLG, whose Boolean logic functions can be reconfigured between AND and OR operations. In addition, an array of three RLGs can be used to perform 32‐bit masking operations, thereby validating their effectiveness in digital data processing.

AbstractA significant class of semiconductor nanostructures, colloidal quantum dots (CQDs), which exhibit narrow emission spectrum and tunable emission frequency, are utilized for numerous flexible and wearable applications including state‐of‐the‐art display, biological sensing, showcasing great prospects in physiological measurement, health monitoring, and rehabilitation. Interestingly, synthesizing these semiconductor particles using methods such as hot injection as colloids can directly tune their optical properties and emission wavelengths by controlling their sizes, which greatly contributes to materials production simplicity and scalability. Importantly, from a device perspective, due to the advantages of solution‐processed synthesis, and patterning methods such as inkjet printing, CQDs can be combined with soft polymeric substrates, or hierarchical structures in a facile manner, offering extraordinary device flexibility and portability. As optoelectronic devices, CQD can function as photoresistors, phototransistors, or through other mechanisms which convert light between other forms of energy, enabling highly sensitive detection applications. In this Review, synthetic approaches are summarized for CQDs, flexible device fabrication techniques, detection mechanisms, and application scenarios. Furthermore, the challenges associated with these technologies, such as device stability and cost‐efficiency are discussed, and present this outlook on the future trends of CQD devices including multi‐functional integration, as a constituent component of flexible and wearable devices.

AbstractTemperature acts as a control lever for the electronic band structure in black phosphorus (BP), significantly influencing its device performance. While the effects of electron‐phonon coupling and lattice thermal expansion on the temperature‐dependent band gap are well understood, there have been no reports on the electronic band as a function of temperature. Additionally, although black phosphorus is well‐known for its significant anisotropic optoelectronic properties, there is comparatively less understanding regarding how various lattice constants affect the electronic band in response to temperature changes. Herein, temperature dependence of the valence band of BP has been measured by angle‐resolved photoelectron spectroscopy (ARPES) and the band shifts are quantitatively characterized. The band shift along the kx direction is larger than that along the ky direction upon heating from 10 to 200 K even if changing the photon energy. It is certified that the band shifts are primarily attributed to the lattice expansion across different crystal orientations, as determined by density functional theory (DFT) calculations. This study investigates the anisotropic temperature dependence of the electronic band shift in black phosphorus, revealing the underlying mechanisms. These findings will be instrumental in guiding the rational design of BP‐based devices tailored for operation across a range of temperatures.