High Mechanical Durability Research Articles

Brush drawing multifunctional electronic textiles for human-machine interfaces

Electronic textiles are a promising candidate for futuristic multifunctional clothes. However, the fabrication of robust and reproducible printed electrodes with high mechanical durability, high biocompatibility, and stable electrical performance under various mechanical deformations continues to pose a challenge. In this study, a silk fabric with printed carbon nanotube (CNT) patterns is used to produce a smart electronic textile (E-textile) for multifunctional applications. The printed CNT electrodes are used in triboelectric devices, electrically activated heaters, real-time electrophysiological sensors, and tactile sensors. The E-textile can be used as an electrically activated thermal patch to generate heat on cloth for providing warmth to the human skin and for therapy. Owing to the micro hierarchical pores of the fabric, skin contact generates a power density of about 0.7 mW cm−2 via effective contact electrification.

Barriers to the Effective Adhesion of High-Density Hardwood Timbers for Glue-Laminated Beams in Australia

A number of international timbers of high commercial importance are extremely difficult to glue, which is significantly hindering access to global market opportunities for engineered wood products, especially for heavily demanded structural products. Some particularly problematic timbers in Australia are the dominant commercial hardwood species, including spotted gum (Corymbia spp.) and Darwin stringybark (Eucalyptus tetrodonta). These species are renowned for their very high mechanical properties, natural durability and attractive aesthetic appeal. However, they are notoriously difficult to glue, especially for sawn laminate-based engineered wood products, such as structural glue-laminated beams. Despite considerable effort and testing of diverse internationally established best-practice approaches to improve adhesion, glue-laminated beam samples of these timbers still frequently fail to meet the requirements of the relevant standard, mainly due to excessive glue line delamination. This paper discusses the key barriers to effective adhesion of these high-density timbers and particularly emphasises the necessity of achieving greater adhesive penetration. Greater adhesive penetration is required to enhance mechanical interlocking, entanglement and molecular interactions between the adhesive and the wood to achieve stronger and more durable bonds. Potential solutions to enhance adhesive penetration, as well as to improve gluability in general, are discussed in terms of their likelihood to satisfactorily prevent delamination and the potential to be applied at an industrial scale. This new fundamental understanding will assist the development of solutions, allowing industry to commercialise newly engineered wood products made from high-density timbers.

Experimental Study on UHPC-Based Grouting Materials and Mechanical Performance of Grouted Splice Sleeve Joints

The prefabricated concrete structure is regarded as the main body of the green construction technology, while the joint connection of the prefabricated components is the weak link of force. In addition, the grouting sleeve connection is a widely used connection method in the prefabricated component joints. The effective anchorage of reinforcement is realized by the implementation of a mechanical bite force, friction force and bonding force between reinforcement, grouting material and sleeve inner wall, respectively. Along these lines, in this work, a UHPC-based grouting material was prepared, and its main technical performance was tested. The influence of the grouting mix proportion and anchorage length on the stress performance was thoroughly investigated by carrying out a unidirectional tension test of eight grout-filled splice sleeves. The acquired results show that UHPC grouting containing micro and particles possess high mechanical strength and durability. The incorporation of UHPC grouting containing steel fibers can further improve the compressive and flexural strength. However, its fluidity will be reduced and grouting difficulties will be induced. For that reason, the utilization of UHPC-based grouting material without steel fibers is recommended. The grout-filled splice sleeve joints with UHPC meet also the strength requirements, and the sleeve can be found in the elastic stage in the test, indicating that sleeve joints possess a higher safety margin.

Splitting capacity of Eucalyptus globulus beams loaded perpendicular to the grain by connections

In timber structures, knowledge of the splitting capacity of beams loaded perpendicular to the grain by dowel-type connections is of primordial importance since brittle failure can occur. In the present work, single- and double-dowel-type connections following different loaded edged distance arrangements are experimentally investigated to derive the splitting behaviour of Eucalyptus globulus L., which is a hardwood species of increasing interest for structural use due to its high mechanical performance, fast growth, and good natural durability. The correlation of experimental failure loads with those theoretically predicted by the expression included in Eurocode 5 and by eight analytical models based on an energetic approach is discussed. Most of the analytical models studied overpredict the splitting capacity. However, the code splitting expression, derived from softwoods, proves to be very conservative in predicting the eucalyptus splitting failure load.

Neutral Mechanical Plane Shifting in Bending Elastomer Film Revealed by Quantification of Internal Strain

Neutral mechanical plane (NMP) position of a bending elastomer film is experimentally identified by internal strain analysis utilizing reflection of a cholesteric liquid crystal elastomer sensor as described in article number 2101041 by Atsushi Shishido, Norihisa Akamatsu and co-workers. The internal strain analysis revealed NMP shifting during elastic bending. Quantification of the NMP shifting in the bending elastomer film enables us to design a flexible electronic device that exhibits high mechanical durability.

Ultrasensitive and wide-range reduced graphene oxide/natural rubber foam sensors for multifunctional self-powered wireless wearable applications

Flexible wearable electronics is an emerging research field in recent years, showing the great potential in human health monitoring and motion capture, electronic skin and intelligent robots. However, it is still challenging to develop all-in-one sensors with high sensitivity, wide range, fast response, excellent reliability and mechanical durability for multiple wearable purposes. Here a hierarchical conductive structure based on reduced graphene oxide (RGO) segregated network and porous natural rubber (NR) is rationally designed via industrially-applicable synchronous foaming-reduction-vulcanization (SFRV) method. The resultant all-in-one RGO/NR foam sensors have wide detection range (0.87–223 kPa), high sensitivity (7.00 kPa−1), fast response (70 ms) and excellent durability (1000 cycles), and simultaneously exhibit differentiated responsiveness to various external stimuli such as pressure, acoustic vibration, temperature, humidity and gaseous chemicals. Besides, a smart insole consisting of 24 foam blocks as sensor array is fabricated to identify plantar pressure distribution for gait recognition, abnormal posture correcting and diseases diagnosis applications. Surprisingly, the RGO/NR foam can also harvest mechanical energy during compression cycles and deliver an open-circuit voltage of 20–30 V and current of 10 nA. This provides an opportunity to develop wireless self-powered multifunctional wearable system based on the RGO/NR foam for human health and sport monitoring.

Anti-Freezing, Non-Drying, Localized Stiffening, and Shape-Morphing Organohydrogels.

Artificial shape-morphing hydrogels are emerging toward various applications, spanning from electronic skins to healthcare. However, the low freezing and drying tolerance of hydrogels hinder their practical applications in challenging environments, such as subzero temperatures and arid conditions. Herein, we report on a shape-morphing system of tough organohydrogels enabled by the spatially encoded rigid structures and its applications in conformal packaging of “island–bridge” stretchable electronics. To validate this method, programmable shape morphing of Fe (III) ion-stiffened Ca-alginate/polyacrylamide (PAAm) tough organohydrogels down to −50 °C, with long-term preservation of their 3D shapes at arid or even vacuum conditions, was successfully demonstrated, respectively. To further illustrate the potency of this approach, the as-made organohydrogels were employed as a material for the conformal packaging of non-stretchable rigid electronic components and highly stretchable liquid metal (galinstan) conductors, forming a so-called “island–bridge” stretchable circuit. The conformal packaging well addresses the mechanical mismatch between components with different elastic moduli. As such, the as-made stretchable shape-morphing device exhibits a remarkably high mechanical durability that can withstand strains as high as 1000% and possesses long-term stability required for applications under challenging conditions.

Spherical Micro/Nano Hierarchical Structures for Energy and Water Harvesting Devices.

Three-dimensional (3D) hierarchical structures have been explored for various applications owing to the synergistic effects of micro- and nanostructures. However, the development of spherical micro/nano hierarchical structures (S-HSs), which can be used as energy/water harvesting systems and sensing devices, remains challenging owing to the trade-off between structural complexity and fabrication difficulty. This paper presents a new strategy for facile, scalable S-HS fabrication using a thermal expansion of microspheres and nanopatterned structures. When a specific temperature is applied to a composite film of microspheres and elastomers with nanopatterned surfaces, microspheres are expanded and 3D spherical microstructures are generated. Various nanopatterns and densities of spherical microstructures can thereby be quantitatively controlled. The fabricated S-HSs have been used in renewable electrical energy harvesting and sustainable water management applications. Compared to a triboelectric nanogenerator (TENG) with bare film, the S-HS-based TENG exhibited 4.48 times higher triboelectric performance with high mechanical durability. Furthermore, an S-HS is used as a water harvesting device to capture water in a fog environment. The water collection rate is dramatically enhanced by the increased surface area and locally concentrated vapor diffusion flux due to the spherical microstructures.

Advancements in Ionomers for Fuel Cell Ion Exchange Membranes, Lithium Ion Battery Electrolyte Membranes and Supercapacitors

Scientists are being pushed to find more sustainable energy conversion and storage solutions as pollution levels rise, oil costs rise, and climate change becomes more problematic. Devices such as fuel cells, redox flow batteries, and electrolyzers are examples of devices that may significantly cut greenhouse gas emissions. These devices rely on ionic conductive polymers or ionomers (protonic, anionic, and amphoteric). For a variety of applications ranging from mobile to automotive and cogeneration systems, such ionomers must have high chemical and mechanical stability, performance and durability, low reagent permeability, and weight, volume, and current density. Unfortunately, the expensive cost of perfluorinated ionomers, as well as anionic polymers' low stability in alkaline settings, limit their usage.

Robust Superamphiphobic Fabrics with Excellent Hot Liquid Repellency and Hot Water Vapor Resistance.

Superamphiphobic surfaces progress rapidly but suffer from the issues of low repellency to hot liquids, complicated and nonaqueous preparation methods, and low durability. Here, a simple waterborne approach is developed to fabricate robust superamphiphobic fabrics with excellent hot liquid repellency and hot water vapor resistance. First, a perfluorodecyl polysiloxane (FD-POS) aqueous suspension was prepared by hydrolytic cocondensation of (3-glycidyloxy propyl)trimethoxysilane and 1H,1H,2H,2H-perfluorodecyltriethoxysilane with SiO2 particles. Then, the superamphiphobic fabrics were fabricated by dipping polyester fabrics in the suspension, which were then cured. The fabrics show excellent superamphiphobicity owing to the combination of the hierarchical micro-/nanostructure and FD-POS with very low surface energy. The superamphiphobic fabrics feature excellent hot liquid repellency even for a large volume of 130.0 °C soybean oil and condensed small droplets from ∼90.0 °C water vapor. This is attributed to its high superamphiphobicity, excellent hot water vapor resistance, and outstanding thermal durability. In addition, the superamphiphobic fabrics exhibit high mechanical and chemical durability against washing, abrasion, and immersion in corrosive or organic liquids. Thus, hot liquid repellent superamphiphobic fabrics may find applications in various fields such as antiadhesion of various hot liquids and in efficiently preventing scalding.

Green Synthesis of Laser-Induced Graphene with Copper Oxide Nanoparticles for Deicing Based on Photo-Electrothermal Effect.

Homogenously dispersed Cu oxide nanoparticles on laser-induced graphene (LIG) were fabricated using a simple two-step laser irradiation. This work emphasized the synergetic photo-electrothermal effect in Cu oxide particles embedded in LIG. Our flexible hybrid composites exhibited high mechanical durability and excellent thermal properties. Moreover, the Cu oxide nanoparticles in the carbon matrix of LIG enhanced the light trapping and multiple electron internal scattering for the electrothermal effect. The best conditions for deicing devices were also studied by controlling the amount of Cu solution. The deicing performance of the sample was demonstrated, and the results indicate that the developed method could be a promising strategy for maintaining lightness, efficiency, excellent thermal performance, and eco-friendly 3D processing capabilities.

Corrosion Resistance and Electrical Conductivity of Hybrid Coatings Obtained from Polysiloxane and Carbon Nanotubes by Electrophoretic Co-Deposition.

Nanocomposites developed based on siloxanes modified with carbon nanoforms are materials with great application potential in the electronics industry, medicine and environmental protection. This follows from the fact that such nanocomposites can be endowed with biocompatibility characteristics, electric conductivity and a high mechanical durability. Moreover, their surface, depending on the type and the amount of carbon nanoparticles, may exhibit antifouling properties, as well as those that limit bacterial adhesion. The paper reports on the properties of polysiloxane (PS) and carbon nanotubes (CNT) nanocomposite coatings on metal surfaces produced by the electrophoretic deposition (EPD). A comparison with coatings made of pure PS or pure CNT on the same substrates using the same deposition method (EPD) is provided. The coatings were examined for morphology and elemental composition (SEM, EDS), structural characteristics (confocal Raman spectroscopy), electrical conductivity and were tested for corrosion (electrochemical impedance spectroscopy-EIS, potentiodynamic polarization-PDP). The results obtained in this study clearly evidenced that such hybrid coatings conduct electricity and protect the metal from corrosion. However, their corrosion resistance differs slightly from that of a pure polymeric coating.

Microporous expanded polytetrafluoroethylene layer functionalized hydrophilic groups for excellent mechanical durability and superior performance in proton exchange membrane fuel cell

Introducing hydrophilic groups and increasing the compatibility of the ionomer and reinforcement layer can have a significant impact on the proton conductivity and cell performance of a proton exchange membrane (PEM) under lower relative humidity (RH). In this work, a novel PEM containing expanded polytetrafluoroethylene (ePTFE) functionalized with amino and hydroxyl groups is designed and fabricated to enhance the PEM's proton conductivity and electrochemical performance at low RH, and to improve its mechanical stability. The introduction of the hydrophilic groups and the generation of stable acid–base pairs yield a PFSA ionomer that has better compatibility with and adhesion to the hydrophilic functionalized ePTFE membrane, thereby significantly improving the prepared membrane's proton conductivity, H2 crossover current density, and single-cell performance. In addition, generated water is retained inside the PEM, keeping its cell performance high at low RH. The PEM's mechanical durability is also improved by the increased dimensional stability and compatibility of the ionomer and reinforcement layer. This work provides a promising way to improve the proton conductivity and cell performance of PEMs at low RH and has great application potential for creating PEM fuel cells with high mechanical durability.

Manganese-doped transparent conductive magnetic indium oxide films integrated on flexible mica substrates with high mechanical durability

Recent advances in flexible electronic devices have stimulated demands for the fabrication of multifunctional materials on highly flexible substrates. However, flexible diluted magnetic semiconductor films have been inadequately reported thus far. In this study, I grew polycrystalline manganese (Mn)-doped indium oxide (In2O3) films on flexible mica substrates at three deposition temperatures (Td) using the pulsed laser deposition method. All the investigated Mn-doped In2O3 films exhibited high optical transparency, high electrical conductivity, room-temperature ferromagnetism, and excellent mechanical durability. The present experimental results demonstrate that Td considerably influences the optical, electrical, and magnetic properties as well as the mechanical durability of the flexible Mn-doped In2O3 films. Based on the robustness of inorganic mica at high deposition temperatures, this detailed investigation provides a strategy for fabricating flexible diluted magnetic semiconductor films, the properties of which could be carefully optimized by widely varying the Td.

Durable self-polishing antifouling coating based on fluorine-containing pyrrolidone amphiphilic copolymer-functionalized nanosilica

Marine biofouling is detrimental to ships and has been a significant issue in the marine industry for several decades. The development of effective, long-term, and environment-friendly antifouling coating is important but remains a challenge in oceanographic engineering. A series of novel amphiphilic block copolymers (PVP-co-PTFEMA), containing hydrophilic segments (N-vinylpyrrolidone, or NVP) and hydrophobic segments (trifluoromethyl methacrylate, or TFEMA), are grafted on the nanosilica surface via surface-initiated atom transfer radical polymerization (SI-ATRP). The as-prepared amphiphilic copolymers-functionalized silica, SiO2-g-(PVP-co-PTFEMA), can be blended well with self-polishing resin, which could obtain a new type of self-polishing nanocomposite coating. The SiO2-g-(PVP-co-PTFEMA) based composite coating exhibits satisfactory antibacterial and antifouling properties due to the synergistic effect of a strong hydration layer of hydrophilic NVP fragments and low adhesion of hydrophobic TFEMA unit. The slow hydrolysis of the as-prepared self-polishing nanocomposite coating results in the formation of micro/nano structures due to the exposure of SiO2-g-(PVP-co-PTFEMA) in seawater. Moreover, the SiO2-g-(PVP-co-PTFEMA) based nanocomposite coating exhibits high mechanical durability. The as-prepared self-polishing nanocomposite coating combines outstanding antifouling performance and high mechanical durability, which could be an ideal choice in marine antifouling applications.

Numerical and experimental analyses of the crack propagation in nanocomposite thin-films by using dynamic particle difference methods

Nanocomposites composed of an organic semiconductor and an elastomer exhibit a stable electrical performance and high mechanical durability, and can thus facilitate the development of stretchable electronic devices. However, the inadequate extent of research on the mechanical behaviors of these nanocomposites limits the application scope of such materials. Identifying and clarifying the crack propagation mechanisms is essential to improve the performance and durability of electronic devices. Therefore, this study examined the crack propagation behaviors of homogeneous nanocomposite materials through numerical simulations and experimental analyses. Nanocomposite thin-film samples for the tensile strength test were manufactured by mixing an organic semiconductor poly(3-hexylthiophene) and a styrene–butadiene–styrene (SBS) elastomer in a nanocomposite format. The samples with initial cracks were subjected to pseudo-free-standing tensile tests to observe the crack propagation and stress-strain behaviors under given experimental conditions. Furthermore, the dynamic particle difference method (PDM) was used to numerically analyze the crack propagation properties of the nanocomposites in two-dimension. The PDM is more effective than the finite element method in analyzing the crack propagation, considering that nodes can be freely created and eliminated in every time step. As a result, the initial crack angle for the set problem was changed to 21, 14, and 19° with respect to the mixing concentration of SBS (0.0, 0.15, and 0.3 wt%). The numerical simulation by the PDM and experimental results was almost the same. This demonstrates that the proposed numerical technique can predict the experimentally measured fracture behavior of nanocomposites.

Fracture-controlled surfaces as extremely durable ice-shedding materials.

Icing imposes a significant burden on those living in cold climates, with negative impacts on infrastructure, transportation, and energy systems. Over the past few decades, a wide range of materials with ice-shedding characteristics have been developed, including surfaces that are non-wetting/hydrophobic, liquid-infused, stress-localized, and those with low interfacial toughness. Although many of these materials have demonstrated low ice adhesion in a laboratory setting, none have achieved widespread practical adoption. This is primarily a result of the fact that they tend to have very low durability, limiting their applicability. Thus, the primary challenge in developing ice-shedding materials is finding materials with both low ice adhesion AND good durability. Here, we introduce the concept of a so-called "fracture-controlled surface." Through coordinated mechanical and chemical heterogeneity in the material structure, we affect the interfacial crack nucleation and growth on these surfaces. Through this controlled process, fracture-controlled surfaces exhibit both low ice adhesion and very high mechanical durability. Measurements of the durability of these surfaces indicate performance that is three orders of magnitude greater than other state-of-the-art ice-shedding materials. Physically, via mechanical heterogeneity of the material, we pre-specified the crack nucleation coordinates at the interface and guided the crack growth in an interfacial plane, with no kinking in other directions. This helps to maximize the energy that goes towards crack nucleation and growth. A detailed mathematical model is developed to predict adhesion of external solid objects on these materials. The model suggests that an elastic matching criterion is required to achieve minimal adhesion of solid objects on these materials. Fracture-controlled surfaces provide a rich material platform to guide future innovation of materials with minimal adhesion while having very high durability.

Mechanical properties and self-sensing ability of amorphous metallic fiber-reinforced concrete

The aim of this research work is to develop a corrosion resistant fiber-reinforced concrete for radioactive waste disposal structures. In the case of precast concrete, the use of fibers is a solution to reduce the amount of steel reinforcement while maintaining high mechanical performance and durability. Concrete has a low strain capacity and a limited tensile strength. Generally, reinforcing bars are used to ensure tensile strength. A fiber reinforcement can also help to overcome such a mechanical weakness. For this purpose, an amorphous metallic fiber (AMF), corrosion-resistant and suitable for application in severe environment conditions are used. The fresh and hardened properties of the self-compacting fiber reinforced concrete (SCFRC) are studied with volume fractions of AMF of 0% and 0.28% and with three different aspect ratios (82, 114 and 123). Flexural tensile tests according to European standard EN 14651 are conducted to quantify the contribution of the fiber reinforcement on the residual flexural tensile strength. Since these fibers are electrically conductive, they are also tested to design a smart concrete. For this purpose, electrical resistance of specimens submitted to cyclic flexural loadings are monitored using a Wheatstone bridge.

Neutral Mechanical Plane Shifting in Bending Elastomer Film Revealed by Quantification of Internal Strain

Flexible electronic devices composed of soft materials, such as polymers and elastomers, require high mechanical durability to maintain their performance during cyclic bending, where large bending can lead to fracture. To design the appropriate structure for such devices, it is essential to utilize a neutral mechanical plane (NMP) in which the strain becomes zero inside bending materials. Despite the importance of identifying the NMP position for this utilization, the NMP position in soft materials has rarely been studied experimentally because of the difficulty in measuring internal strain in largely bending materials. Herein, the NMP position of bending polydimethylsiloxane (PDMS) film, which is a common soft material used in flexible electronic devices, is experimentally quantified via internal strain measurement with a cholesteric liquid crystal sensor. This is the first reported identification of the NMP position, revealing that bending of the PDMS film reversibly shifts the NMP position within ≈11% of the film thickness toward the inner bending surface. Considering this large NMP shift, a flexible electronic device with high mechanical durability is fabricated. The direct identification of the NMP position, which is enabled by the internal strain measurement, facilitates the development of device designs for flexible electronic devices.

A durable superhydrophobic porous polymer coated sponge for efficient separation of immiscible oil/water mixtures and oil-in-water emulsions

Oil spills and organic solvents leakages have led to serious environmental problems, which calls for the emerging materials for the separation of oil/organic solvents from water effectively. Herein, a superhydrophobic/superoleophilic, SHMP-1@Sponge, with water contact angle (WCA) of 156° and oil contact angle of 0°, was fabricated by dip coating polymer SHMP-1 powder onto the skeleton of 3D melamine sponge. The SHMP-1@Sponge featured large specific surface area (556 m2/g) as well as high chemical and mechanical durability. SHMP-1@Sponge can absorb up to 40–105 times of its own weight of light and heavy oils/organic solvents in seconds, and it can be recycled for 25 times by squeezing. Moreover, the separation efficiency of immiscible oil/water mixtures and oil-in-water emulsions by SHMP-1@Sponge are > 99.5％. SHMP-1@Sponge shows tremendous absorption capacity for chloroform-in-water emulsions (1460 mg/g) compared with nitrobenzene-in-water (1290 mg/g) and diesel-in-water emulsions (980 mg/g), which is the strongest superhydrophobic absorbent for surfactant-stabilized oil-in-water emulsions reported to date. The durable SHMP-1@Sponge fabricated by loading superhydrophobic polymer with large surface area onto 3D sponge makes it a promising material for oil/water separation in realistic aquatic environments.