Excellent Mechanical Robustness Research Articles

Dioxybenzene-bridged hydrophobic silica aerogels with enhanced textural and mechanical properties

Abstract Designing aerogel materials with excellent mechanical robustness while maintaining their basic characteristics, is of great importance for applications in energy saving management systems. Organic modification is required to strengthen silica aerogel, but the modified aerogels show decreased textural properties due to phase separation between organic-inorganic components. We report, the fabrication of organically modified aerogels without minimizing their basic properties, based on tetraethoxysilane (TEOS) and a bifunctional precursor prepared from dihydroxybenzene and TEOS via acid catalyst. Three types of dihydroxybenzene isomers were used to study the effect of the position of the hydroxyl groups on textural properties of aerogels and compatibility of the precursors. A simple, efficient, and cost effective sol-gel method was employed to develop porous aerogels with no additives and surfactants. Hydroquinone-TEOS (HT) bridged silica aerogels exhibited improved mechanical strength, low dipole moment, high specific surface area (1154 m2/g), high porosity (96%), low density (0.061 g/cm3), and ultra-low thermal conductivity of 0.0334 W/m·K. In addition, precursor was cheaper than the other isomers. The prepared aerogels show hydrophobic nature without the use of harmful silylating reagents.

Printable magnesium\xa0ion quasi-solid-state asymmetric supercapacitors for flexible solar-charging integrated units

Wearable and portable self-powered units have stimulated considerable attention in both the scientific and technological realms. However, their innovative development is still limited by inefficient bulky connections between functional modules, incompatible energy storage systems with poor cycling stability, and real safety concerns. Herein, we demonstrate a flexible solar-charging integrated unit based on the design of printed magnesium ion aqueous asymmetric supercapacitors. This power unit exhibits excellent mechanical robustness, high photo-charging cycling stability (98.7% capacitance retention after 100 cycles), excellent overall energy conversion and storage efficiency (ηoverall = 17.57%), and outstanding input current tolerance. In addition, the Mg ion quasi-solid-state asymmetric supercapacitors show high energy density up to 13.1 mWh cm−3 via pseudocapacitive ion storage as investigated by an operando X-ray diffraction technique. The findings pave a practical route toward the design of future self-powered systems affording favorable safety, long life, and high energy.

Template‐Electrodeposited and Imprint‐Transferred Microscale Metal‐Mesh Transparent Electrodes for Flexible and Stretchable Electronics

A scalable fabrication strategy is reported for the solution‐based electrochemical fabrication of microscale metal meshes from reusable, non‐sacrificial templates. This approach enables the reproducible fabrication of meshes, potentially made of any electrochemically depositable metal and transferable to a variety of polymeric substrates. Unlike other existing approaches, this benchtop method repetitively mass‐produces metal meshes whose geometric features are predefined by a template, without requiring lithography or any vacuum processes in each production cycle. Using this technique, a number of prototype‐flexible and stretchable transparent electrodes with an embedded metal mesh with micro‐sized linewidths are demonstrated with transmittance as high as 90% and sheet resistance as low as 0.036 Ω□−1, corresponding to a high figure of merit of 3.4 × 104 at 4 μm mesh linewidth, and the electrodeposition template showed no degradation after at least 20 production cycles. In addition to outstanding optical and electrical performances, the resulting electrodes show excellent mechanical robustness and stability against chemicals and harsh environment. The electrodes are further tested in flexible bifacial dye‐sensitized solar cells and stretchable transparent thin‐film heaters, confirming their suitability and reliability for practical applications.

Heavy-Metal-Free Flexible Hybrid Polymer-Nanocrystal Photodetectors Sensitive to 1.5 μm Wavelength.

Photodetection in the short-wave infrared (SWIR) wavelength window represents one of the core technologies allowing for many applications. Most current photodetectors suffer from high cost due to the epitaxial growth requirements and the ecological issue due to the use of highly toxic heavy-metal elements. Toward alternative SWIR photodetection strategies, in this work, high-performance heavy-metal-free flexible photodetectors sensitive to λ = 1.5 μm photons are presented based on the formation of a solution-processed hybrid composed of a conjugated diketopyrrolopyrrole-base polymer/PC70BM bulk heterojunction organic host together with inorganic guest NaYF4:15%Er3+ upconversion nanoparticles (UCNPs). Under the illumination of λ = 1.5 μm SWIR photons, optimized hybrid bulk-heterojunction (BHJ)/UCNP photodetectors exhibit a photoresponsivity of 0.73 and 0.44 mA/W, respectively, for devices built on rigid indium tin oxide (ITO)/glass and flexible ITO/polyethylene terephthalate substrates. These hybrid photodetectors are capable of performing SWIR photodetection with a fast operation speed, characterized by a short photocurrent rise time down to 80 μs, together with an excellent mechanical robustness for flexible applications. Exhibiting simultaneously multiple advantages including solution-processability, flexibility, and the absence of toxic heavy metal elements together with a fast operation speed and good photoresponsivity, these hybrid BHJ(DPPTT-T/PC70BM)/UCNP photodetectors are promising candidates for next-generation low-cost and high-performance SWIR photodetectors.

Influence of Acceptor Type and Polymer Molecular Weight on the Mechanical Properties of Polymer Solar Cells

Nonfullerene acceptors (NFAs), that are small-molecule acceptors (SMA) and polymer acceptors (PAs), have been extensively explored, which has yielded significant enhancements in the photovoltaic performance of polymer solar cells (PSCs). The mechanical robustness of the PSCs is of vital and equal importance to ensure long-term stability and enable their use as power-generators in flexible and stretchable electronics. Here, we report a comparative study of the mechanical properties of SMA-based, PA-based, and fullerene-based PSCs. We chose ITIC (SMA), P(NDI2OD-T2) (PA), and PCBM (fullerene) as three representative acceptor materials and blended them with the same polymer donor PTB7-Th. To understand the difference between the mechanical properties of SMA-based and PA-based PSCs, we control the number-average molecular weight (Mn) of P(NDI2OD-T2) from 15 to 163 kg mol–1 in all-PSCs. The all-PSCs-based high-Mn PAs exhibit significantly higher cohesion energy (4.03 J m–2) than SMA-PSCs (1.19 J m–2) and PCBM-PSCs (0.29 J m–2). Notably, the all-PSCs exhibit a high strain at fracture of 31.1%, which is 9- and 28-fold higher than those of SMA-PSCs and PCBM-PSCs, respectively. The superior mechanical robustness of all-PSCs is attributed to using a PA above the critical molecular weight (Mc), which produces tie molecules and polymer entanglements that dissipate substantial mechanical strain energy with large plastic deformation. This work provides useful design guidelines for photovoltaic active materials in terms of the mechanical properties and highlights the importance of incorporating high-Mn PAs above the Mc for producing PSCs with excellent mechanical robustness and device performance.

Effect of the silsesquioxane structure on the mechanical properties of the silsesquioxane-reinforced polymer composite films

As additives for reinforcing the physical properties of polymer coating materials, silicone-based silsesquioxanes (SQs) have received considerable attention owing to their excellent mechanical and thermal robustness. To understand the effect of the SQ structure on the mechanical properties of SQ-reinforced polymer composite films, a series of SQs with different siloxane structures, i.e., randomly branched SQ (RSQ), cage-like SQ (POSS) and ladder-like SQs (LPSQs), were incorporated into the poly(urethane acrylate) (PUA) polymer. Regardless of the SQ structure and loading, all the SQ-reinforced PUA (SQ-PUA) composite films exhibited excellent optical transparency and high colorlessness. Moreover, the incorporation of the SQs increased the hardness and scratch resistance, but decreased the elastic modulus of the PUA film for all the SQs due to the strong and compliant nature of the SQ network. Importantly, at the same SQ loading, the SQ-PUA films exhibited the increasing hardness, scratch resistance and modulus in the order of RSQ < POSS < LPSQ (4 K) < LPSQ (7 K). The results suggested that the highly ordered and one-dimensional LPSQ with a higher aspect ratio is desirable for effectively reinforcing the mechanical properties of polymers with guaranteeing their excellent optical transparency.

Analysis and Optimization of Transport Losses in Hydroxide Exchange Membrane Fuel Cells

As an emerging alternative to proton exchange membrane fuel cells (PEMFCs), hydroxide exchange membrane fuel cells (HEMFCs) are more cost-effective due to PGM-free catalysts options, more affordable bipolar plate production, and other potential savings.1 However, unlike PEMFCs, the HEMFC technology is in its early phases and there is a continuous effort to improve the performance and durability through the advancement of materials and optimization of operating conditions. The polarization curve is one of the most common methods of testing a fuel cell. A typical polarization curve for a fuel cell consists of open circuit potential (crossover losses), low-current behavior (kinetics losses), moderate-current behavior (ohmic losses), and high-current behavior (transport losses). Crossover and ohmic losses are determined by electrolytes, kinetics losses depend on catalysts and transport losses involve gas diffusion and water management. In addition, a triple phase boundary comprised of an electrolyte, an electrode and a gaseous reactant is crucial for the electrochemical reactions. Thus, the optimization of all these aspects is critical for HEMFC performance improvement. Here, we focus our work on transport phenomena in a fuel cell. The materials we used are hydroxide exchange membranes (HEMs) and ionomers (HEIs) based on poly(aryl piperidinium) (PAP).2 The specific chemical structure (shown in Figure 1) endows PAP HEMs with excellent chemical stability, high conductivity and mechanical robustness, making PAP HEMs/HEIs one of the best choices for HEMFC electrolyte. Furthermore, the use of PAP HEMs/HEIs enables operating HEMFCs at 95 °C, which accelerates reaction rates and decreases heat rejection. Optimization of fuel cell operating conditions is vital for water management. Water production by hydrogen oxidation reaction (HOR) tends to cause flooding in the anode, while water consumption from oxygen reduction reaction causes cathode to dry-out. In addition, the electro-osmotic drag pulls water from the cathode to the anode (in the reverse direction of PEMFCs), thus worsening the water management problem further. In this work, observable characteristics in the polarization curve for a flooded HEMFC were found, and a model was developed to describe this issue. Then we demonstrate that balanced water management can be obtained by adjusting the anode relative humidity and back pressure. Limiting current technology is widely employed for PEMFCs to characterize the transport resistance in order to reduce mass-transport losses; however, no one has done this systematically to HEMFCs, although there is a difference between limiting current behavior of PEMFCs and HEMFCs. We have found this technique useful to screen catalysts, optimize catalyst loading and adjust ionomer loading to improve the efficiency of gas diffusion, which is very helpful when switching from oxygen to air on cathode. Our optimized HEMFC can achieve a peak power density of 2.02 W cm-2 in H2/O2 and 1.33 W cm-2 in H2/air with platinum group metal (PGM) based catalysts (shown in Figure 2). The current density at 0.663 V for cell voltage is about 1.70 A cm-2, which is suitable for hydrogen fuel cell vehicles. References B. P. Setzler, Z. Zhuang, J. A. Wittkopf, and Y. Yan, Nat Nanotechnol, 11 (12), 1020-1025 (2016).J. Wang, Y. Zhao, B. P. Setzler, S. Rojas-Carbonell, C. Ben Yehuda, A. Amel, M. Page, L. Wang, K. Hu, L. Shi, S. Gottesfeld, B. Xu, and Y. Yan, Nature Energy, (2019) doi:10.1038/s41560-019-0372-8. Figure 1

(Invited) Effective Strategies to Improve Powerfactor of Flexible Thermoelectric Composites

Recent developments in wearable electronics and Internet of Things (IoT) have stimulated the research interests in light-weight, flexible, renewable and sustainable energy-harvesting sources. Considering these needs, flexible thermoelectric devices have been getting attention because of simplicity of the device and abundance of available heat energy sources. In addition, from the manufacturing point of view, various cost-effective printing techniques, such as screen printing, spraying and direct-writing, can be employed to create flexible thermoelectric devices while most commercially available thermoelectric devices are fabricated by costly and inefficient inorganic material processing methods. On the other hand, many of the advances in improving thermoelectric properties over a couple of last decades were achieved by utilizing unique phenomena in nanoscale materials. Thermoelectric nano-scaled materials allow us to manipulate heat and carrier transport to decouple interdependent parameters, thus to enhance the thermoelectric performance. Based on these backgrounds, a combination of nano-engineering of thermoelectric materials and printing manufacturing processes are expected to enable the development of highly-performing and low-cost flexible thermoelectric devices. In this research, n-type thermoelectric printing inks which are one of critical required components of the printed thermoelectric flexible devices were investigated in terms of synthesis methods, post-treatments, thermoelectric properties and mechanical flexibility. The n-type thermoelectric inks consisting of Bi2Te3 nanowires (NWs) and carbon nanotubes (CNTs) were synthesized by two different methods, ex-situ and in-situ syntheses, to understand the influences of interface between NWs and CNTs on the thermoelectric power factor. Different post-treatment processes (i.e., thermal treatment and mechanical pressing) were employed to improve the thermoelectric power factor of the vacuum-filtered Bi2Te3 NWs - CNTs thermoelectric films. First of all, the composition of CNTs in the composites was varied in the range 10 – 20 vol% and the corresponding electrical conductivity and Seebeck coefficient were measured to identify the correlation between the composition and two parameters. Then, in the same manner, the thermoelectric power factor of the composites was assessed after the annealing process in an inert environment, and the subsequent mechanical pressing, in order to to see how those processes affect the ex-situ and in-situ synthesized films and consequently their thermoelectric properties. The composites films prepared with different conditions including CNTs composition and different post-treatments were characterized using X-ray Diffraction Spectroscopy (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and X-ray Photoelectron Spectroscopy (XPS) to reveal the relationship among the post treatment processes, the microstructure of materials, and the thermoelectric properties. We found that the thermal treatment process is significantly effective to improve stoichiometry and crystallinity of Bi2Te3 NWs, leading to enhance Seebeck coefficient and electrical conductivity, simultaneously. As a result, the thermoelectric power factor of the ex-situ composites and the in-situ films after the post-treatments was drastically increased to be 225.9 μW m−1K−2 and 0.74 mW m−1K−2, respectively. In particular, the considerable enhancement observed in the in-situ synthesized sample is attributed to the phase homogenization of Bi2Te3 inorganic nanowires as well as the enhanced interfaces between NWs and CNTs both qualitatively and quantitatively, through a combination of three approaches, (i) in-situ synthesis (ii) annealing and (iii) mechanical pressing. The flexibility and the conductivity change over the repeated bending cycle were examined to show the excellent mechanical robustness and flexibility of the films. We expect that the findings from this study can be applied to other flexible thermoelectric materials systems to enhance thermoelectric properties.

Laser Fabrication of Graphene-Based Flexible Electronics.

Recent years have witnessed the rise of graphene and its applications in various electronic devices. Specifically, featuring excellent flexibility, transparency, conductivity, and mechanical robustness, graphene has emerged as a versatile material for flexible electronics. In the past decade, facilitated by various laser processing technologies, including the laser-treatment-induced photoreduction of graphene oxides, flexible patterning, hierarchical structuring, heteroatom doping, controllable thinning, etching, and shock of graphene, along with laser-induced graphene on polyimide, graphene has found broad applications in a wide range of electronic devices, such as power generators, supercapacitors, optoelectronic devices, sensors, and actuators. Here, the recent advancements in the laser fabrication of graphene-based flexible electronic devices are comprehensively summarized. The various laser fabrication technologies that have been employed for the preparation, processing, and modification of graphene and its derivatives are reviewed. A thorough overview of typical laser-enabled flexible electronic devices that are based on various graphene sources is presented. With the rapid progress that has been made in the research on graphene preparation methodologies and laser micronanofabrication technologies, graphene-based electronics may soon undergo fast development.

Flexible oxide neuromorphic transistors with synaptic learning functions

Realization of brain-inspired hardware devices is deemed to be a significant step for constructing a neuromorphic system. Moreover, flexible bioinspired neuromorphic devices have broad applications in bioinspired intelligent electronics. Here, we propose flexible IWO neuromorphic transistors gated with proton-conducting chitosan-based electrolytes. The transistor exhibits a low subthreshold swing of ~112 mV/dec and a high mobility of ~17 cm2 V−1 s−1. Moreover, the transistor exhibits excellent mechanical robustness against mechanical stress. Some crucial synaptic functions in biological synapses are mimicked on the proposed flexible transistor, including excitatory post-synaptic currents, paired-pulse facilitation, post-tetanic potentiation, etc. Most importantly, ‘learning-experience’ behaviors are implemented in the device. The proposed flexible neuromorphic devices have applications in artificial perception learning systems, including electronic skin and personal health monitoring.

Toward durable and robust superhydrophobic cotton fabric through hydrothermal growth of ZnO for oil/water separation

In this study, an eco-friendly superhydrophobic cotton fabric (CF) with water contact angle of 155° was fabricated via a facile two-step approach: imparting surface roughness through hydrothermal growth of ZnO particles, and using stearic acid to create a low-energy surface. ZnO prepared by hydrothermal reaction was in a rod-like shape and had nano- or micro-scale sizes. It was located on the surface in loose aggregates. After modification with stearic acid, the aggregate structure of ZnO particles was changed from loose packing to compact packing. The superhydrophobic CF could be wetted by oil but could not be wetted by water, showing excellent oil/water separation performance. The superhydrophobic CF was able to absorb oils selectively from their mixtures with water and could be used as a filtering membrane to separate oil/water mixtures directly with separation efficiency and oil flux of 96–99% and 2000–9000 L m−2 h−1, respectively, depending on the intrinsic property of the oils. In addition, the superhydrophobic CF showed excellent mechanical robustness and environmental durability with water contact angle almost remaining unchanged after exposure to sandpaper abrasion, ultrasonication, boiling water treatment and organic solvents erosion. With excellent robustness and durability, the superhydrophobic CF exhibits great potential in oil/water separation even under some harsh conditions.

A Simple Strategy towards Highly Conductive Silver‐Nanowire Inks for Screen‐Printed Flexible Transparent Conductive Films and Wearable Energy‐Storage Devices

AbstractPrintable silver‐nanowire (Ag NW) inks with simple formulation, low cost, and high conductivity are developed and screen printed on flexible poly(ethylene terephthalate) substrates. By using ultralong Ag NWs (≈75 µm in length) as the conductor, the screen‐printed Ag NW patterns exhibit exceptional conductivity (up to 8.32 × 103 S cm−1) and excellent mechanical robustness. Rheological behavior suitable for screen printing is achieved by adjusting the formulation of the inks, which assures neat and smooth screen‐printed lines with resolution as high as 100 µm. Uniform and honeycomb‐structured Ag NW transparent conductive films with superior flexibility and optical transmittance ≈80% are obtained by screen printing the Ag NW inks. Flexible all‐solid‐state supercapacitors based on Ag NW/PEDOT:PSS electrodes reach areal specific capacitance as high as 8.58 mF cm−2, a value threefold higher than that of pristine PEDOT:PSS electrodes. Moreover, a high flexibility with a bending angle of 180° and long‐term stability with ≈90% capacitance retention over 2500 cycles, is also obtained, manifesting this material's great potential applications for flexible and wearable energy‐storage devices.

Robust hydrophobic surface driven by Al2O3/glass composite coatings

Fabrication of hydrophobic surface with exceptional mechanical robustness has been of considerable interest for its urgent practical application. Herein, we demonstrate a facile approach to fabricate mechanically robust, hydrophobic surface by combining Al2O3, glass frits, and hydrophobic solution. Al2O3-based composite coatings with different roughness were prepared by controlling the ratio of Al2O3 particles and glass frits. Surface properties of Al2O3-based composite coatings were carefully modified by hydrophobic fluorine-containing sol-gel solution. Hydrophobic sol-gel solution-coated Al2O3-based coatings (H-Al2O3) show strong hydrophobicity, and water contact angle of 132.38° was achieved at an optimal Al2O3/glass frits ratio of 50. To demonstrate the mechanical robustness of our H-Al2O3, the hydrophobicity was evaluated after performing sandpaper (400 mesh) abrasion and ultrasonication. The H-Al2O3 still retained great water repellency even after sandpaper abrasion for 100 cm and ultrasonication for 60 min, exhibiting excellent mechanical robustness. We believed that the presented method could provide a straightforward and effective route to fabricate mechanically robust and hydrophobic surface on various substrate materials for a great number of potential applications.

Stretchable and Bioadhesive Supramolecular Hydrogels Activated by a One-Stone-Two-Bird Postgelation Functionalization Method.

Resembling soft tissues, stretchable hydrogels are promising biomaterials for many biomedical applications due to their excellent mechanical robustness. However, conventional stretchable hydrogels with a synthetic polymer matrix are usually bioinert. The lack of cell and tissue adhesiveness of such hydrogels limits their applications. An easy but reliable postgelation functionalization method is desirable. Herein, we report the fabrication of stretchable supramolecular hydrogels cross-linked by multivalent host-guest interactions. Such hydrogels containing thiourea ( TU) functionalities can be bioactivated with a catechol-modified peptide (Cat-RGD) via thiourea-catechol ( TU-Cat) coupling reaction. This postgelation bioactivation of the otherwise bioinert hydrogels not only conjugates bioactive ligands for cell attachment but also introduces and preserves the catechol structures for tissue adhesion. This straightforward fabrication and one-stone-two-bird bioactivation of the stretchable hydrogels may find broad applications in developing advanced soft biomaterials for tissue repair, wound dressing, and lesion sealing.

Room-temperature fabrication of TiO2-PHEA nanocomposite coating with high transmittance and durable superhydrophilicity

Coatings with high transmittance and superhydrophilicity play an outstanding role in many practical applications such as antifogging, antifouling, self-cleaning, etc. The durability greatly affects their applications. In the current work, TiO2 organic nanocomposite coating with high transmittance and durable superhydrophilicity was prepared via the homogeneous compositing of modified anatase TiO2 nanoparticles (NPs) and hydroxyethyl acrylate (HEA) without any solvent. The curing process of coating and the formation of nanometer rough structure were carried out simultaneously under ultraviolet (UV) irradiation at room temperature. The composite coating exhibited an excellent intrinsic superhydrophilicity (water contact angle less than 3° in 0.45 s), high transmittance (above 90% in the visible wavelength), mechanical robustness, photocatalytic activity, anti-fogging and anti-fouling properties. The superhydrophilicity of the as-prepared nanocomposite coating could last for 330 days in the laboratory environment, which was quite a long time for maintaining the superhydrophilicity of TiO2 coatings in the literature reports. The durable superhydrophilicity is attributed to the enhancement of intrinsic hydrophilicity and the increase of surface roughness. The superhydrophilic TiO2-PHEA nanocomposite coating has a wide application prospect in solar cells, building and automobile antifogging glass, antifogging lens and other fields. The methodology proposed in this work can be applied to the fabrication of new superhydrophilic TiO2-polymeric composite materials using a low-cost, efficient and simple methodology.

New bio-inspired design for high-performance and highly robust La0.6Sr0.4Co0.2Fe0.8O3-δ membranes for oxygen permeation

Ceramic-based oxygen permeation membranes (OPM) are considered to be promising for the separation of oxygen from air. However, state-of-art membrane designs are unable to deliver satisfactory performances in terms of permeation flux, mechanical/chemical stability and membrane surface area. In this study, a new bio-inspired design has been successfully introduced in the micro-monolithic membranes made of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) for oxygen separation. By carefully controlling the process parameters of the fabrication and utilizing the hydraulic pressure of internal coagulant, the geometry of channels in the micro-monolith has been converted from a circular shape to a triangle shape with rounded corners. This new bio-inspired, ‘orange-like’ architecture not only reduces the effective oxygen diffusional length down to approximately 50 μm, but also significantly increases the ratio of active region among the overall circumference up to 90%. This new bio-inspired micro-monolithic design displays an excellent oxygen permeation flux of 1.87 ml min−1cm−2 at 950 °C, which is superior to the most reported values from LSCF material systems. In addition, such a design illustrates an excellent mechanical robustness that has long been a bottleneck for LSCF membranes. This work demonstrates a promising solution to tackle the long-existing trade-off between oxygen permeation performance and mechanical reliability.

Extraordinary thermoelectric performance in MgAgSb alloy with ultralow thermal conductivity

MgAgSb-based materials are ideal candidates for thermoelectric applications due to several advantages, such as rich elements, low cost and excellent mechanical robustness. Recently, the all-scale hierarchical architecture and strong anharmonicity in bonding are realized as effective strategies to reduce the lattice thermal conductivity greatly. Here, a design of the all-scale hierarchical architectures, in which the phonon is scattered by the high density of grain boundaries, dislocation, stacking faults, twin boundaries and nanopores, and enhancement of Grüneisen parameter have been demonstrated in reducing the lattice thermal conductivity of MgAgSb materials in the whole temperature range, resulting in an ultralow lattice thermal conductivity ∼ 0.45 W m−1 K−1 at 473 K. Furthermore, the carrier concentration and mobility are also optimized by Zn-doping and heat-treating. The simultaneous optimization of electrical and thermal transport properties contributes to a tremendous enhancement of average ZT to about 1.3 in the range from 323 K to 548 K (the maximum ZT is about 1.4 at 423 K) in the sample Mg0.97Zn0.03Ag0.9Sb0.95 with heat-treating for 10 days. The method we designed not only boosts the thermoelectric application of MgAgSb-based materials but also enables a synergetic strategy for designing thermoelectric materials with high thermoelectric performance.

“Stiff–Soft” Binary Synergistic Aerogels with Superflexibility and High Thermal Insulation Performance

AbstractDesigning aerogel materials featuring both high thermal insulation property and excellent mechanical robustness is of great interest for applications in superior integrated energy management systems. To meet the above requirements, composite aerogels based on hierarchical “stiff–soft” binary networks are reported, in which secondary mesoporous polymethylsilsesquioxane domains intertwined by bacterial cellulose nanofibrillar networks are connected in tandem. The resulting composite aerogels are characterized by highly porous (93.6%) and nanosized structure with a surface area of 660 m2 g−1, leading to the excellent thermal insulation performance with a low thermal conductivity of 15.3 mW m−1 K−1. The integrated “stiff–soft” binary nature also endows the composite aerogels with high flexibility that can conform to various substrates as well as large tensile strength that can withstand more than 2.70 × 104 times its own weight. These composite aerogels show multifunctionality in terms of efficient wearable protection, controllable thermal management, and ultrafast oil/water separation. These favorable multifeatures present composite aerogels ideal for aerospace, industrial, and commercial applications.

Robust and durable superhydrophobic cotton fabrics via a one-step solvothermal method for efficient oil/water separation

Traditional superhydrophobic cotton fabrics (CF) demonstrate various advantages such as self-cleaning, water repelling and efficient oil/water separation capacity but limited practical applications due to their poor mechanical robustness and environmental durability. In this work, robust and durable superhydrophobic polydivinylbenzene (PDVB) coated CF (PDVB@CF) are fabricated via a simple one-step, fluorine-free, and inorganic nanoparticle-free solvothermal method. The PDVB@CF displays excellent chemical resistance without losing superhydrophobicity after immersing in various organic solvents, strong acid and alkali solutions for a long time. The PDVB@CF shows excellent mechanical robustness to resist sandpaper abrasion and ultrasonication treatment. Furthermore, the PDVB@CF exhibits outstanding high and low temperature resistances since the contact angle of either acidic or alkali droplets is greater than 150° after isothermal treatment at 200 °C or immersion in liquid nitrogen for 3 h. The PDVB@CF is very efficient in separating water mixtures with various oily compounds with separation efficiency of higher than 98% and flux up to 56 k L m−2 h−1 depending on characteristics of the oils. In addition, the PDVB@CF shows excellent recyclability with superhydrophobicity and separation efficiency that remained after 10 separation cycles. The PDVB@CF with excellent robustness and durability exhibits potential utility in oil/water separation even under some harsh conditions.

Evaluation of mechanical strength and bone regeneration ability of 3D printed kagome-structure scaffold using rabbit calvarial defect model

In clinical conditions, the reconstructions performed in the complex and three-dimensional bone defects in the craniomaxillofacial (CMF) area are often limited in facial esthetics and jaw function. Furthermore, to regenerate a bone defect in the CMF area, the used scaffold should have unique features such as different mechanical strength or physical property suitable for complex shape and function of the CMF bones. Therefore, a three-dimensional synthetic scaffold with a patient-customized structure and mechanical properties is more suitable for the regeneration. In this study, the customized kagome-structure scaffold with complex morphology was assessed in vivo. The customized 3D kagome-structure model for the defect region was designed according to data using 3D computed tomography. The kagome-structure scaffold and the conventional grid-structure scaffold (as a control group) were fabricated using a 3D printer with a precision extruding deposition head using poly(ε-caprolactone) (PCL). The two types of 3D printed scaffolds were implanted in the 8-shaped defect model on the rabbit calvarium. To evaluate the osteoconductivity of the implanted scaffolds, new bone formation, hematoxylin and eosin staining, immunohistochemistry, and Masson's trichrome staining were evaluated for 16 weeks after implantation of the scaffolds. To assess the mechanical robustness and stability of the kagome-structure scaffold, numerical analysis considering the ‘elastic-perfectly plastic’ material properties and deformation under self-contact condition was performed by finite element analysis. As a result, the kagome-structure scaffold fabricated using 3D printing technology showed excellent mechanical robustness and enhanced osteoconductivity than the control group. Therefore, the 3D printed kagome-structure scaffold can be a better option for bone regeneration in complex and large defects than the conventional grid-type 3D printed scaffold.