Excellent Fatigue Resistance Research Articles

Ferroelectric and piezoelectric properties of lead-free Li0.06(K0.5Na0.5)0.94NbO3 thin films

Lead-free ([Formula: see text][Formula: see text])NbO3 (KNN) and [Formula: see text]([Formula: see text][Formula: see text])[Formula: see text]NbO3 (LKNN) thin films were fabricated by a sol-gel method. The effects of Li substitution on crystal structure, microstructure and electrical properties of KNN film were systematically studied. Li doping can enhance the ferroelectric and piezoelectric properties of KNN film. Compared with pure KNN film, the LKNN film possesses larger remanent polarization ([Formula: see text] [Formula: see text] 9.3 [Formula: see text]C/[Formula: see text]) and saturated polarization ([Formula: see text] [Formula: see text] 41.2 [Formula: see text]C/[Formula: see text]) and lower leakage current density ([Formula: see text]A/[Formula: see text] at 200 kV/cm). Meanwhile, a typical butterfly shaped piezoelectric response curve is obtained in the LKNN film with a high piezoelectric coefficient ([Formula: see text] [Formula: see text] 105 pm/V). Excellent fatigue resistance ([Formula: see text][Formula: see text] switching cycles) and aging resistance ([Formula: see text] 180 days) demonstrate the long-term working stability of LKNN film. These findings indicate that KNN-based lead-free piezoelectric films have a broad application prospect in microelectromechanical systems (MEMS).

Natural microfibrils/regenerated cellulose-based carbon aerogel for highly efficient oil/water separation

Cellulose-based carbon aerogels as biodegradable and renewable biomass materials have presented potential applications in oil/water separation. Herein, a novel carbon aerogel composed of natural microfibrils/regenerated cellulose (NM/RCA) was directly prepared by economical hardwood pulp as raw material using a novel co-solvent composed of deep eutectic solvent (DES) and N-methyl morpholine-N-oxide monohydrate (NMMO·H2O). In addition, the morphology and structure of the filiform natural microfibers could be remained after carbonized at 400 ℃, which resulted in a low density (8–10 mg cm−3), high specific surface area (768.89 m2 g−1) and high sorption capability. In addition, the aerogel exhibited high compressibility, outstanding elasticity, excellent fatigue resistance, and recyclability (80.5% height recovery after repeating 100 cycles at the strain of 80%). Due to the morphology and composition of the carbonized microfiber surface, the superhydrophobic materials with a water contact angle of 151.5°, could sorb various oils and organic solvents with 65–133 times its own weight and maintain 91.9% sorption capacity after 25 cycles. In addition, the aerogels could achieve the continuous separation of carbon tetrachloride (CCl4) from water with a high flux rate of 11,718.8 L m−2 h−1. Therefore, our prepared NM/RCA aerogels are anticipated to have broad potential applications in oil purification and contaminant remediation.

Theoretical and Experimental Analysis of a Winding Rope Fluid Viscous Damper

This paper investigated a winding rope fluid viscous damper (WRFVD) that uses the frictional amplification mechanism of a winding rope to obtain the operating characteristics of a viscous damper-like device. The WRFVD combined the advantages of fluid viscous dampers and friction dampers. It not only retained the mechanical characteristics of the fluid viscous damper but also reduced manufacturing costs. First, the construction and working principles of the WRFVD were introduced. A theoretical model that could accurately simulate the hysteretic characteristics of the damper was derived. Then, a series of dynamic tests were performed on six prototypes of the WRFVD. The dynamic performance under different displacement amplitudes and device parameters was analyzed based on the test results. In addition, the theoretical model was validated by experimental results. Finally, a series of parametric analyses of the WRFVD were performed. The experimental results showed that the WRFVD is a type of velocity-dependent damper with smooth and plump hysteretic curves under sinusoidal displacement excitation. Fatigue loading tests showed that the WRFVD had excellent fatigue resistance capacity and stable operational performance. The established theoretical model was reasonable and satisfactorily reproduced the hysteretic properties of the WRFVD. The parametric analyses showed that it was not recommended to improve the performance of the WRFVD by the method of adjusting the damping coefficient and pretightening load. It was reasonable to adjust the performance of the WRFVD by setting a smaller velocity exponent, an appropriate winding turn of winding ropes, and a suitable friction coefficient.

Large-scale manufacturing of soluble hemostatic spacer dressing with excellent mechanical and comfortable properties

Death from acute hemorrhage is a major life-threatening. Spacer fabrics-based composite dressings have been widely concerned because of their good hemostasis and protection in wound healing, but the poor liquid absorption and compression recovery properties hinder their utilization. Herein, we report a soluble hemostatic spacer dressing based on a braided yarn of PTFE (core yarn)/carboxymethylated viscose (shell yarn) as the skin contact layer, a wrapped yarn of nylon monofilament (core yarn)/Coolmax (shell yarn) as the spacer layer, and UHMWPE yarn as the waterproof layer for wound healing. Among these, carboxymethylated viscose can stop bleeding, while PTFE has low adhesion and ensures the structural integrity of the spacer fabric. Moreover, the nylon monofilament can endow the dressing with excellent comfortability, resilience, and fatigue resistance. Coolmax can absorb blood. The as-prepared spacer dressing shows excellent mechanical, comfortable, and hemostasis properties. F2 had a hemostasis time of 5.15 min, a low coagulation index of 7.96%, a hemolysis rate of 0.98%, and a blood absorption rate of 159.09%. This work presents an integrated molding method to achieve large-scale manufacturing of spacer dressing, which is expected to guide materials design for future innovations in biomedical applications.

Optimization of Mechanical Performance for 3D Printed Kevlar and Carbon Fiber Composites

Kevlar is commercial brand of fibers supporting para-aramids of light weight for major part of composite. It is applicable in robotics and automobile sectors where parts need to possess high tensile strength and excellent fatigue resistance. Carbon fibers are processed by thermal conversion of organic fiber with low Carbon content such as polyacrylonitrile (PAN) which contain around thousands of filaments. In the current work, samples are produced through Mark Two 3D printer and subjected under investigation for improving mechanical performance in evaluating tensile, flexural and impact behavior as per ASTM Standards. The differentiation is presented by finding the error between experiment and simulation results.

Euryale ferox stem-inspired anisotropic quaternized cellulose/xanthan-based antibacterial sponge with high absorbency and compressibility for noncompressible hemorrhage

Uncontrollable hemorrhage from deep noncompressible wounds remains an intractable challenge. Herein, inspired by the euryale ferox stem which is capable of transporting water and nutrient substances efficiently along longitudinally aligned channels, an anisotropic sponge with rapidly liquid absorption capacity, excellent mechanical compressibility and antibacterial property based on quaternized cellulose (QC), xanthan gum (XG) and reduced graphene oxide (rGO), was constructed. The euryale ferox stem-like structure and multiple interactions, involving hydrogen bonding, electrostatic interaction and chemical crosslinking, endowed the sponge with excellent fatigue resistance, elasticity and efficient liquid absorption capacity. In vivo rat liver injury, tail amputation and liver noncompressible hemorrhage model experiments confirmed that the sponge exhibited superior hemostatic performance than commercial gelatin sponge, attributing to the positive charge, efficient absorption capacity and rough surface of the sponge, which synergistically promoting the aggregation and activation of red blood cells and platelets as well as formation of fibrin network, leading to accelerated blood coagulation process. Besides, the sponge showed favorable cytocompatibility, hemocompatibility and antibacterial property. Overall, the bioinspired sponge had fantastic potential for controlling deep noncompressible hemorrhage and providing a new idea for designing hemostatic materials.

Bioinspired Multiscale Micro-/Nanofiber Network Design Enabling Extremely Compressible, Fatigue-Resistant, and Rapidly Shape-Recoverable Cryogels.

Cryogels with extreme mechanical properties such as ultrahigh compressibility, fatigue resistance, and rapid recovery are attractive in biomedical, environmental remediation, and energy storage applications, which, however, are difficult to achieve in man-made materials. Here, inspired by the multiscale macro-/microfiber network structure of spider web, we construct an ultraelastic chitosan cryogel with interconnected hybrid micro-/nanofibers (CMNF cryogels) via freeze-induced physicochemical cross-linking. Chitosan chains are directionally assembled into high-aspect-ratio microfibers and nanofibers under shear-flow induction, which are further assembled into an interconnected three-dimensional (3D) network structure with staggered microfibers and nanofibers. In this multiscale network, nanofibers connecting the microfibers improve the stability, while microfibers improve the elasticity of the CMNF cryogels through long-range interaction. The synergy of the two-scale fibers endows the CMNF cryogel with extraordinary mechanical properties in comparison to those assembled with single-scale fibers, including its ultrahigh ultimate strain (97% strain with 50 cycles), excellent fatigue resistance (3200 compressing-releasing cycles at 60% compression strain), and rapid water-triggered shape recovery (recovering in ∼1 s). Moreover, the fibrous CMNF cryogel shows excellent functionalization capability via the rapid assembly of nanoscale building blocks for flexible electronics and environmental remediation. Our work thereby demonstrates the potential of this bioinspired strategy for designing gel materials with extreme mechanical properties.

Highly Flexible, Freezing-Resistant, Anisotropically Conductive Sandwich-Shaped Composite Hydrogels for Strain Sensors

Anisotropically conductive hydrogels have promising applications in artificial intelligence and wearable flexible electronics. However, for conductive hydrogels, the integration of comprehensive properties, such as high electrical conductivity, strong moisture retention, and high mechanical properties, is very important. In this article, sandwich-shaped anisotropically conductive hydrogels were constructed with a conductivity of up to 1.5 S/m. The difference in conductivity along the different directions is about a factor of 6. The formation of dynamic coordination bonding enhances the cross-linked network between poly(acrylic acid) and Nd3+, which causes the hydrogels to have excellent self-healing properties and fatigue resistance, with a self-healing efficiency of up to 90%. The middle layer of the hydrogels is compounded with nanographene, which cuases the hydrogels to have good mechanical properties, such as ultrastretchability (∼1930%) and high strength (∼0.7 MPa). The binary solvent consisting of glycerin and water gives the hydrogels an excellent moisturizing and antifreezing function. It maintains good flexibility and conductivity even at −18 °C. Based on the rapid response and high sensitivity, the sandwich-shaped hydrogel strain sensors can detect human motion (such as knuckle motion, wrist movement, etc.), showing great application potential in flexible sensors.

Gas-permeable and stretchable on-skin electronics based on a gradient porous elastomer and self-assembled silver nanowires

On-skin electronics offers a noninvasive method for continuous and stable signal monitoring, which has played a significant role in healthcare and rehabilitation engineering. However, most present on-skin electronicses are highly restricted by their gas permeability and stretchability due to the materials, fabrication process, and cost. This study develops gas-permeable and stretchable on-skin electronics fabricated via a gradient porous elastomer and self-assembled silver nanowires. The introduction of a gradient porous structure offers the elastomer substrate a good water vapor permeability of 3073.3 g day−1 m−2, which is much higher than the average evaporation rate of water vapor on human skin (432 g day−1m−2). Additionally, the examined electronic device has no adverse effects on the skin and possesses good stretchability and flexibility (110%, 0.07778 MPa). In addition, it offers excellent fatigue resistance (0.70% electrical resistance change within 1000 stretch cycles). The electronic device achieves conformal and comfortable contact with human skin for a long period of wearing and accomplishes high-quality biopotential measurement with a high signal-to-noise ratio (SNR) during electromyography (EMG) signal detection. The proposed simple fabrication process may supply inspiration for new on-skin electronics used in biological signal detection and rehabilitation engineering.

Low Hysteresis Hydrogel Induced by Spatial Confinement

AbstractStress concentration and hysteresis often occur in polymer hydrogels under large deformation, affecting their mechanical properties, and durability. Here, a new spatial confinement gelation strategy is proposed for fabrication of hysteresis‐free polymer hydrogels, and stress concentration is avoided. Experimental results and theoretical calculations confirm that the hydratability difference between salts and polymer chains leads to spatial confinement of the polymer chains by control over the ratio of bound to free water. Spatial confinement acts in place of physical cross‐linking of polymer chains, which slide to dissipate energy and effectively avoid stress concentration and hysteresis, resulting in ultra‐tough hydrogels with fatigue resistance. This is also a universal strategy for preparing polymer hydrogels with different monomers and salts. Taking the prepared PAM‐CaCl2hydrogel, it displays a hysteresis of only 0.13% during load‐unload cycles, even under 1000% strain. This is the lowest value among hydrogels reported to date. Along with excellent fatigue resistance, water retention, antifreeze, and water‐assisted healing ability, this hydrogel shows good performance in fatigue resistant capacitive strain sensors. Moreover, a fishtail‐shaped PAM‐CaCl2hydrogel operates as a bionic muscle to drive a bionic fish at a forward speed of 16.3 cm s−1, when a voltage of 0.1 V is applied.

High stretchable and self-healing nanocellulose-poly(acrylic acid) composite hydrogels for sustainable CO2 shutoff

The injection of CO2 into oil reservoirs to enhance oil recovery (EOR) has become a widely accepted and effective technical method, which, however, remains subject to the gas channeling caused by the reservoir fractures. Herein, this work developed a novel plugging gel combining excellent mechanical properties, fatigue resistance, elastic and self-healing properties for the CO2 shutoff purpose. This gel consisting of grafted nanocellulose and polymer network was synthesized via a free-radical polymerization, and reinforced by using Fe3+ to cross-link the two networks. The as-prepared PAA-TOCNF-Fe3+ gel has a stress of 1.03 MPa and a high strain of 1491 %, and self-heals to its original 98 % in stress and 96 % in strain after rupture, respectively. The introduce of TOCNF/Fe3+ improves the excellent energy dissipation and self-healing via the synergy effect of dynamical coordination bonds and hydrogen bonds. Further, the PAA-TOCNF-Fe3+ gel is both flexible and high-strength in plugging the multi-round CO2 injection, during which the CO2 breakthrough pressure is above 9.9 MPa/m, the plugging efficiency exceeds 96 %, and the self-healing rate is larger than 90 %. Given that above, this gel shows a great potential to plug the high-pressure CO2 flow, which could offer a new method for CO2-EOR and carbon storage.

Ultrahigh electrostrain with excellent fatigue resistance in textured Nb 5+-doped (Bi 0.5Na 0.5)TiO 3-based piezoceramics

(Bi_0.5Na_0.5)TiO₃ (BNT)-based lead-free piezoceramics exhibit excellent electric field-induced strain (electrostrain) properties, but often suffer from large hysteresis and poor fatigue resistance, which strongly limit their applications. Here, &lt;00<i>l</i>&gt; textured Nb⁵⁺-doped 0.8(Bi_0.5Na_0.5)TiO₃–0.2(Bi_0.5K_0.5)TiO₃ (0.8BNT–0.2BKT) ceramics with a high degree of texturing (~80%) were prepared by the reactive template grain growth (RTGG) method using Bi₄Ti₃O₁₂ as a template. By the combination of donor doping in the B-site and the RTGG method, the electrostrain performance achieves a significant enhancement. A high electrostrain of 0.65% and a piezoelectric coefficient (<inline-formula> <math display="inline" id="MA1"><mrow><msubsup><mi>d</mi><mrow><mn>33</mn></mrow><mo>*</mo></msubsup></mrow></math></inline-formula>) of 1083 pm/V with reduced hysteresis at an electric field of 6 kV/mm are obtained. No electrostrain performance degradation is observed after unipolar electric field loading of 10⁵ cycles, showing excellent fatigue endurance. These results indicate that the texturing BNT-based lead-free piezoceramics by the RTGG method is a useful approach to developing eco-friendly actuators.

Analysis of Influencing Factors on Water Stability and Stripping Resistance of Paving Polyurethane Mixture

Polyurethane mixtures (PUMs) have excellent deformation resistance and fatigue resistance. However, their inferior water stability and stripping resistance have been hindering their wider application. To better understand the critical factors to PUMs’ stripping resistance and water stability, we investigated the statistical relationships among the stripping resistance, splitting strength, water stability, binder-to-aggregate ratio (BAR), gradation type, and fine aggregate content (FAC). A series of tests, including direct tensile test, binder bond strength test, and water boiling test, were used to study the flexibility and adhesion strength of polyurethane (PU) binder. Three gradation types with different FACs were designed. Three types of tests, namely the Cantabro test, the splitting test, and the water stability test, were employed to study the effects of gradation type, FAC, and BAR on the performances of PUM. The significant factors to water stability and stripping resistance of PUM were identified using a mixed-effects regression model (MERM). The results showed that the unsolidified PU binder has high fluidity and low adhesion strength, and the solidified PU binder has excellent adhesion strength and low flexibility. Increasing the BAR and FAC improved the risk of the PUM specimen’s volume bulge. Dewatering of raw materials of PU binder and aggregates was beneficial to solve the bulging problem. The fine aggregate can prevent the PU binder from flowing away under the gravity action, resulting in the film thickness of the PU binder increasing and the enhancement of stripping resistance and water stability of PUM. The gradation type and FAC affected the failure mechanisms of the PUM specimen in the splitting test. The MERM results indicated that the BAR and FAC significantly affect the stripping resistance, splitting strength, and water stability.

Self-heating ultra-high performance concrete with stainless steel wires for active deicing and snow-melting of transportation infrastructures

The development of self-heating concrete composites with stable electrical conductivity and strong heating capability as well as high mechanical properties is the key for achieving active deicing and snow-melting of transportation infrastructures. Due to their microscale diameter and high aspect ratio, stainless steel wires (SSWs) can form an extensive electrically and thermally conductive as well as reinforcing network inside concrete at a low content. Together with the stainless feature of SSWs as well as high structural compactness and durability of ultra-high performance concrete (UHPC), SSWs reinforced UHPC is expected to be developed into self-heating composites with strong and stable heating capability as well as ultra-high mechanical performance and durability. Therefore, this study evaluated the self-heating capability as well as active deicing and snow-melting performances of such composites. The developed SSWs reinforced UHPC slab demonstrates stable electrical conductivity and strong self-heating capability in cycle uses as well as efficient active deicing and snow-melting properties under different environmental conditions. The electrical resistivity of SSWs reinforced UHPC is only 2.58 Ω cm and it is hardly affected by the change in temperatures, numbers of cyclic self-heating, and numbers of deicing and snow-melting. The SSWs reinforced UHPC slab can be heated from 21.4 °C to 82.4 °C in 16.18 min under the voltages of 30 V in an indoor environment at a temperature of 21.2 °C. The slab only needs 28.98 min, 15.20 min, and 27.31 min to completely melt 9 mm of ice in a freezer at a temperature of −25.6 °C, 5 cm of naturally accumulated snow and 2 cm of artificially compacted snow in an outdoor environment at a temperature of about −5 °C with the wind speed up to 5.36 m s−1. Furthermore, thanks to their characteristics of no adverse effect on vehicle tires and excellent fatigue resistance, self-heating SSWs reinforced UHPC shows promising application prospects in active deicing and snow-melting of transportation infrastructures (e.g., airport runway, pavement and bridge deck) suffering from frigid weather.

MOF-regulated flexible wood carbon aerogel for pressure sensing

Three-dimensional and lightweight carbon aerogels are promising for next-generation wearable devices. As the most abundant renewable resource on the planet, wood provides a green and sustainable raw material for the manufacture of lightweight and elastic carbon materials. Here, a simple and sustainable design is proposed to directly prepare elastic carbon aerogel with a layered structure from the wood. Zeolitic imidazolate framework (ZIF-L) was deposited on a wood aerogel matrix without lignin and hemicellulose by in situ growth. The presence of ZIF-L significantly reduced the volume shrinkage of aerogel during carbonization, and the carbonized ZIF-L improves the contact area and provides electron transport path. The prepared aerogel has a stress of 42 kPa under 80% strain, and the elastic strength and volume remain both above 98% after 200 times of compression, indicating that the aerogel has excellent compressibility and fatigue resistance. Based on this particular structural design, as-obtained aerogel shows excellent sensitivity as pressure sensors to detect subtle signals. In addition, the carbon aerogel can be directly assembled into a all-solid-state symmetric supercapacitor that show promising electrochemical performance and could be potential candidates for high-performance supercapacitors in wearable devices.

Mechanoresponsive ionic elastomers with Ultra-Stretchability, high toughness, fatigue resistance, and extreme temperature resistance

In the development of elastic materials, the non-synergy between stretchability and toughness is a challenge. Herein, we propose a rational design of a composite hydrogel by introducing strongly polarized hydrated Li-ion clusters, electron-withdrawing carboxyl groups, and Sn(II) complexation into hydrogen-bonded poly(acrylamide) (PAM) network. Weak interaction between Li-ions and amide groups facilitates the rapid flipping and slipping of the PAM chains during stretching, optimizing the stretchability of the hydrogel. This composite also provides an energy-dispersing mechanism based on strong ionic complexation between Sn(II) and amide groups, which improves its toughness. As-prepared composite hydrogel simultaneously exhibits high stretchability (>7000% elongation), ultra toughness of 580 kPa, excellent fatigue resistance and extreme temperature resistance (elastic at − 60 and 70 °C). Due to its excellent comprehensive performances, the present soft material has broad application prospects in agriculture, medicine, construction, and machinery.

Dual-Mechanism-Driven Environmental-Friendly Fast Self-Healing Ionic Hydrogels with Excellent Sensitivity to Strain Responsiveness

Ionic hydrogels have important value for applications in bionic skin and flexible sensor fields. However, general ionic hydrogels suffer from inevitable damage and reduction of service life after long-term use. Here, we propose a dual-mechanism-driven strategy with a reversible metal coordination bond and dynamic hydrogen bond to construct a novel fast self-healing ionic hydrogel via a facile “two-step” approach based on environmental-friendly natural resources as raw materials. The dual-mechanism-driven mode endows the hydrogel with excellent self-healing properties (3 h, 95.31%), tensile strength (479.8 kPa), compression strength (5.235 MPa), and fatigue resistance. The hydrogel also showed excellent self-adhesion performance, even underwater, as well as high and stable conductivity (σ = 17.54 mS·cm–1). In addition, it has an ion-responsive deformation feature so that the hydrogel can be shaped and restored in different ion solutions. As a sensor on human skin, the high sensitivity (GF = 2.363) enables it to detect and distinguish various human movements and even different letter pronunciations and pulses. These excellent performances lay a solid foundation for its application in bionic skin and flexible sensor fields.

Peptide-Crosslinked, Highly Entangled Hydrogels with Excellent Mechanical Properties but Ultra-Low Solid Content.

Lowsolidcontentistheultimatereasonforthebrittlenessandweakness of ordinary hydrogels. Here, hydrogels with ultra-low solid content but good mechanical properties are successfully synthesized using high monomer concentrations and low cross-linker/monomer ratios to obtain highly entangled structureand poly(l-lysine)-based cross-linkertointroducepeptidechains. Compared with hydrogel cross-linked with N,N'-methylenebisacrylamide (BIS), the peptide-crosslinked one has a larger swelling degree in water, leading to fully swollen gel with ultra-low solid content (5.8%). However, it still exhibits excellent mechanical properties, including high stretchability (440%), high tensile strength (220 KPa), superb resilience (99%), high fracture toughness (2100 Jm-2 ), excellent fatigue resistance (720 Jm-2 ), low friction (0.0059), and high wear resistance. These properties are comparable to or even better than the BIS-crosslinked hydrogel, althoughthe former has much lower solid content. The excellent mechanical properties of the peptide-crosslinked gel are attributed to its highly entangled structure and also to the introduction of a novel mechanism for energy dissipation, that is, energy dissipation via breakage of intramolecular hydrogen bonds stabilizing the helical structure of thepeptide.

Nanocellulose-reinforced polyurethane as flexible coating for cork floor

Cork materials have the property of elastic deformation under pressure due to their unique closed, porous, cell structure with thin cell wall; and they accordingly need a surface coating that matches their deformation during there being used as floor materials. However, traditional wood coatings are hard, brittle, and mostly suitable for stiff wood surfaces, which are difficult to be directly adapted to the requirements of flexible cork. Although waterborne polyurethane (WPU) has the advantage of property tailorability, its fully applicable to cork materials are still a challenge. Herein, this study utilized a simple physical blending of waterborne polyurethane and nanocellulose with high aspect ratio, to develop a high-strength coating that matches the elastic deformation requirements of cork materials. When both two kinds of nanocellulose, poplar wood nanocellulose (WCNF) with an aspect ratio of 800 and bacterial nanocellulose (BCNF) with an aspect ratio of 2000, was individually added into the WPU emulsion at 0.5 wt%, the tensile strength and elastic modulus of the nanocellulose-modified polyurethane coating increased by 48.58 % and 118.88 %, 54.50 % and 120.48 %, respectively, compared to those of the pure WPU coating (14.09 MPa and 312.74 MPa). It is notable that both the nanocellulose-modified coatings showed no signs of damage on the cork surface even they underwent continuous bending over 2000 cycles, which indicates their excellent flexural fatigue resistance. Interestingly, such nanocellulose-modified coatings maintain comparable transparency, gloss, adhesion, solvent resistance and even present slightly improved hardness and wear resistance than their pure WPU coatings. Overall, the two nanocelluloses are comparative to the modification of the coatings, both of which could match the elastic deformation requirements of cork materials. Therefore, the nanocellulose physically blended polyurethane technology provides a simple and effective solution for the design and property tailoring of flexible coatings for cork floor.

Tunable Photochromism of Spirooxazine in the Solid State: A New Design Strategy Based on the Hypochromic Effect.

As an important organic photofunctional material, spirooxazine (SO) usually does not exhibit photochromism in the solid state since the intermolecular π-π stacking impedes photoisomerization. Developing photochromic SO in the solid state is crucial for practical applications but is still full of challenges. Here, a series of spirooxazine derivatives (SO1-SO4) with bulky aromatic substituents at the 4- and 7-positions of the skeleton, which provide them with a large volume with which to undergo solid-state photochromism under mild conditions, is designed and synthesized. All the compounds SO1-SO4 exhibit tunable solid photochromism without ground colors, excellent fatigue resistance, and high thermal stability. Notably, it takes only 15s for SO4 to reach the saturation of absorption intensity, thought to represent the fastest solid-state photoresponse of spirooxazines. X-ray crystal structures of the intermediate compound SO0 and the products SO1-SO2 as well as computational studies suggest that the bulky aromatic groups can lead to a hypochromic effect, allowing for the photochromism of SO in the solid state. The ideal photochromic properties of these spirooxazines open a new avenue for their applications in UV printing, quick response code, and related fields.