Double Network Structure Research Articles

Thermal-insulation and temperature-resistant foamed gel for thermal management of heavy oil steam flooding

Foamed clayey hydrogel Bent-5/PAM-2, with hierarchically double-network structure and abundant CO 2 air chambers inside, maintains low thermal conductivity and good plugging performance at high temperature, effectively reducing heat loss of heavy oil thermal recovery. • Clayey foamed hydrogel, with hierarchically double networks, was synthesized by one-pot method. • Foamed gel shows low thermal conductivity, high strength and good mobility at 300 °C. • Thermal effectiveness of steam flooding is obviously improved after foamed gel injection. Due to the serious gravity overriding and large heat loss, thermally insulated and temperature-resistant plugging agents are highly desired in steam flooding. In this work, a physically-crosslinked clayey foamed hydrogel Bent/PAM, with low thermal conductance, high thermal stability and good mobility, was synthesized by one-pot process, using bentonite as matrix and polyacrylamide as cross-linking agent. Bent/PAM has hierarchically 3D porous structure and double network. Specifically, abundant meso-sized air chambers in gel endows it with low thermal conductivity. And, its outer clay percolated network with micro-sized meshes provides a temperature-resistant coating, while the inner polymer-clay composite network with nano-sized meshes affords a high strength. On the other hand, the easily slidable clay platelets make its outer percolated network turn into a lubricating film, offering the foamed gel with low friction and viscosity. From the core flooding experiments, the Bent-5/PAM-2 gel (the optimal sample) possesses large plugging rate, plugging intensity and oil recovery (EOR), up to 83.7%, 321 KPa and 63.5%, respectively.

Recent Advances of Natural Polysaccharide-based Double-network Hydrogels for Tissue Repair.

Natural polysaccharide hydrogels have been extensively explored for many years due to their outstanding biocompatibility and biodegradability, which are very promising candidates as artificial soft materials for biomedical applications. However, their inferior mechanical performances greatly limited their applications. Introduction of double-network (DN) structure has been well documented to be an efficient strategy for significant improvement of the mechanical property of hydrogels. Here, recent progress of natural polysaccharide-based DN hydrogels is reviewed from the perspective of fundamental concepts on both design rationale and preparation strategies to biomedical application in tissue repair. Retrospect of the DN-strengthened polysaccharide hydrogels can give a deep insight into the fundamental relationship of such bio-based hydrogels among structural design, mechanical properties and practical demands, thereby prompting their translation to clinical application prospects.

Bioinspired Ultra Tear-Resistant Elastomer with a Slidable Double-Network Structure.

Tear resistance is of vital importance in the fabrication and application of synthetic soft materials. However, the paradox of simultaneously improving the tearing energy and elasticity remains a huge challenge for conventional approaches. Here, inspired by the skin, we successfully constructed an extraordinary tear-resistant, superelastic elastomer by the introduction of nanosized polycyclodextrin into the elastomer network to form a slidable interpenetrate double network structure. The tearing energy of the SDEP elastomer is up to 274 KJ/m2, which is comparable to metals and alloys and increased more than 100 times compared with the chemically cross-linked elastomer. The fracture strain exceeded 3300%, which is hardly achieved by other materials with high tearing energy. This comprehensive improvement of antitearing and super elasticity property was achieved by (i) a slide ring effect to dissipate energy and blunt a crack tip; (ii) straightening and reorientation of the slidable double network to deflect the advancing of a crack tip; (iii) a double network sharing the load. These results provide a novel strategy to fabricate elastic, tear-resistant soft material, which may contribute to the practical application as tear-resistant flexible electronics and irregular-shaped stretchable devices.

Fast Self-Healing and Self-Cleaning Anticorrosion Coating Based on Dynamic Reversible Imine and Multiple Hydrogen Bonds

Anticorrosive coatings are extensively investigated as a potential solution to prevent or at least retard metal corrosion occurrence. However, the actual breakthrough is still hampered by the risk of barrier properties loss because of the local failure of the coating. Self-healing coatings can effectively repair microcracks, but outstanding self-healing behavior is always accompanied by poor self-cleaning ability. Herein, we report a series of poly(dimethylsiloxane) (PDMS) modified with a terephthalic aldehyde (TA)-polyurea (PDMS-TA-PUa) copolymer with a double reversible dynamic bond crosslinking network structure. The PDMS-TA-PUa coating exhibits fast and re-recycled self-healing behavior that heals cracks within 40–50 min at room temperature. The fast self-healing property is attributed to the dynamic nature of the imine bonds and hydrogen bonds in polymer networks. The PDMS-TA-PUa coating also shows great self-cleaning and anticorrosive ability, due to high hydrophobic, low surface energy, and high corrosion potential. Our work gives an insight into the design and preparation of multifunctional coating material with excellent anticorrosion performance, fast self-healing, and self-cleaning properties.

A high-conductive, anti-freezing, antibacterial and anti-swelling starch-based physical hydrogel for multifunctional flexible wearable sensors

Flexible wearable sensors based on conductive hydrogels are attracting increasing interest. To meet the urgent demands of sustainability and eco-friendliness, biopolymer-based physically crosslinked hydrogels have drawn great attention. Starch has a great potential due to its renewability, biocompatibility, nontoxicity and low cost. However, poor mechanical property, low conductivity and lack of versatility are seriously limiting the applications of starch-based hydrogels in wearable sensors. Moreover, the development of starch hydrogel-based wearable sensors in harsh conditions remains a challenge. Herein, multifunctional and physical crosslinking hydrogels were developed by introducing ionic liquid (1-ethyl-3-methyl imidazolium acetate) and metal salt (AlCl3) into starch/polyvinyl alcohol double-network structure. The hydrogel exhibited excellent stretchability (567%), tensile strength (0.53 MPa), high conductivity (2.75 S·m−1), good anti-freezing, antibacterial and anti-swelling properties. A wearable sensor assembled from the starch-based hydrogel exhibited a wide working range, high sensitivity (gauge factor: 5.93) and excellent reversibility. Due to the versatility, the sensor effectively detected human motion in normal and underwater environment, and possessed a sensitive pressure and thermal response. Overall, the present work provided a promising route to develop multifunctional and “green” biopolymer-based hydrogels for wearable sensors in human health and sporting applications.

Enhanced dimensional stability of lightweight SBR/EVA foam by an inorganic scaffold structure constructed in the cell wall

The poor dimensional stability of lightweight rubber-based foam directly restricts its application. The realization of its higher dimensional stability contributes to being widely applied in the automobile industry, military equipment, aerospace, national defense engineering, medical and health care. However, this remains a huge challenge because the crystallization of rubber is too low to counterbalance the internal stresses and strains created by the rubber chains during the foaming process. Hence, An inorganic scaffold structure, containing the organically-modified lamellar montmorillonite (KDMMT) and rod-like attapulgite (KHATP) with a carbon-carbon double bond (>C C<), has been successfully constructed in the cell wall of styrene butadiene rubber/ethylene vinyl acetate (SBR/EVA) foam, which can improve the dimensional stability of SBR/EVA foam and reduce its density. The construction of the inorganic scaffold structure ascribed to a double cross-linking network structure (-C-C- and -C-S x -C-), which is based on the cellular heterogeneous nucleation while taking line tension effects at the melt-nucleator interface into account. The results indicate that when the density of SBR/EVA/KDMMT/KHATP composites foam with the inorganic scaffold structure was 0.24 g/cm 3 , the shrinkage and post shrinkage was reduced by 56.6% and 50.6%, respectively, compared with that of SBR/EVA foam (0.28 g/cm 3 ). Meanwhile, shoe soles constructed from this material have exceptional folding resistance compared to EVA foam. The inorganic scaffold structure was constructed in the cell wall of SBR/EVA/KDMMT/KHATP foam reduced its post shrinkage by 50.6%. • An inorganic scaffold structure was constructed by two shaped inorganic particles. • This structure was constructed in the cell wall based on cell heterogeneous nucleation. • The construction was ascribed to a double cross-linking network structure. • The post shrinkage of SBR/EVA composite foam reduced by 50.6%. • The foam with the inorganic scaffold structure has excellent folding resistance.

A soy protein-based film by mixed covalent cross-linking and flexibilizing networks

In order to develop a strong, tough, water-resistant, and mildew-resistant soy protein film replacing petroleum-based films, in this study, a covalent and hydrogen bond double network structure was constructed in soy protein film using self-synthesized crosslinker triglycidylamine (TGA), soy protein (SPI), and poly(vinyl alcohol) (PVA). The covalent bond network from the crosslinking reaction between TGA and SPI as the skeleton structure improved the tensile strength and water resistance of the film. The hydrogen bond network from interaction between PVA and SPI as a sacrificial bond network to improve the toughness of the film. Compared with the SPI film, the tensile strength and the insoluble matter content of the resultant film increased by 261.2% and 22.1%, respectively. The elongation at break of film increased by 106 times and the fracture toughness improved 183 times. Notably, the resultant film has anti-fungal property, which extends the anti-mold time of film to more than two weeks. This double network construction strategy effectively enhanced the soy protein film and can be applied to reinforce other composite materials and bio adhesives.

Double-network strategy for a cost-effective soybean meal-based adhesive with required and stable water resistance for structural use

Although soybean meal (SM)-based adhesives, modified by polyamidoamine-epichlorohydrin (PAE) resin exhibit satisfactory characteristics to replace formaldehyde-based adhesives, their broad commercialization is still limited due to poor water resistance and high cost. This study employed a novel double-network strategy to effectively crosslink SM and fabricated an SM-based adhesive with required and stable water resistance using a co-crosslinker (PM) composed of PAE and melamine-urea-glyoxal (MUG) resins. Analyses including 1 H NMR, 13 C NMR, FTIR, TGA, and XPS revealed that the robust double-network structures were constructed from MUG-SM and PAE-SM networks, which were further reinforced by the co-crosslinking between PAE and MUG resins. Thus, up to 40% of the expensive PAE could be substituted by low-cost MUG resin, resulting in a novel SM/PM adhesive with the required water resistance for structural use at a 16% reduced cost. Furthermore, PM exhibited much better storage stability than PAE and MUG resins. The presented double-network strategy sufficiently promotes the cost-effective application of SM-based adhesives in wood composites and extends it from indoor to outdoor products. • PAE resin blended with MUG resin to produce a PM resin via co-crosslinking. • Double-network structure constructed from PM-soybean meal crosslinking. • Enhanced adhesion properties produced by a double-network structure revealed. • Storage stability of PM resin in 60 days traced and characterized. • SM/PM adhesive reduced cost by 16% with comparable water resistance.

Highly flexible and compressible polyimide/silica aerogels with integrated double network for thermal insulation and fire-retardancy

• Polyimide/silica (PSi) aerogel with integrated double network and anisotropic structure was fabricated. • The PSi aerogel could withstand 500 cyclic compression test in the radial direction with a high silica content of 60 wt%. • The PSi aerogel exhibited ultra-low thermal conductivity of 21.2 mW m −1 K −1 in the radial direction. • The PSi aerogel exhibited structure integrity when subjected to a flame of a propane/butane blowlamp (∼1200 °C). The materials with thermal insulating and fire-retardant properties are highly demanded for architectures to improve the energy efficiency. The applications of conventional inorganic insulating materials such as silica aerogels are restricted by their mechanical fragility and organic insulating materials are either easily ignitable or exhibit unsatisfactory thermal insulation performance. Here, we report an organic/inorganic composite aerogel with integrated double network structure, in which silica constituent homogeneously distribute in the anisotropic polyimide nanofiber aerogel matrix and strong interfacial effect is formed between two components. The integrated binary network endows the polyimide/silica composite aerogels with outstanding compressibility and flexibility even with a high inorganic content of 60%, which can withstand 500 cyclic fatigue tests at a compressive strain of 50% in the radial direction. The resulting composite aerogel exhibits a combination of outstanding insulating performance with a low thermal conductivity (21.2 mW m −1 K −1 ) and excellent resistance to a 1200 °C flame without disintegration. The high-performance polyimide/silica aerogels can decrease the risk brought by the collapse of reinforced concrete structures in a fire, demonstrating great potential as efficient building materials.

Construction and Research of Multiple Stimuli-Responsive 2D Photonic Crystal DNA Hydrogel Sensing Platform with Double-Network Structure and Signal Self-Expression.

The stimuli-responsive DNA hydrogel has attracted wide attention in the fields of chemical and biological sensing. However, it is still a challenge to integrate characteristics with low-cost, high mechanical strength, and signal self-expression into a DNA hydrogel simultaneously. Herein, a stimuli-responsive 2D photonic crystal double network DNA hydrogel (2D PhC DN-DNA hydrogel) sensing platform is developed via combining the signal self-expression of 2D PhC array with the selective recognition of polyacrylamide (PAM)/DNA DN hydrogel. The change of DNA configuration induced by specific target triggers the change of 2D PhC DN-DNA hydrogel volume, leading to a shift of the Debye diffraction ring diameter. In order to verify the feasibility of this strategy, the 2D PhC DN-DNA hydrogel with C-rich sequences is chosen as a proof-of-concept. The results indicate that the hydrogel has good detection performance for pH and Ag+/Cys. And the Debye diffraction ring diameter of the hydrogel is correlated with the concentration of the Ag+/Cys in the range of 0.5-20 μM. Compared with previously pure DNA hydrogel sensing platform, the 2D PhC DN-DNA hydrogel features low-cost preparation process and label-free determination. Meanwhile, only a laser pointer and a ruler are needed for the determination of targets, which shows that the hydrogel has application prospect in the development of portable response equipment.

Superior stable, hydrophobic and multifunctional nanocellulose hybrid aerogel via rapid UV induced in-situ polymerization

Nanocellulose-based aerogels are potential candidates for the various advanced fields, but the poor structural stability and hydrophily restrains the practical applications. Herein, we report a facile strategy to in-situ polymerizes the polydimethylsiloxane on the anisotropic nanocellulose/chitosan aerogel matrix via UV-induced thiol-ene click reaction in 30 s. A superhydrophobic and elastic nanocellulose-based aerogel with a “stiff-soft” double network structure was fabricated. The inherited porous anisotropic structure and chemical-bonded interlocking interface render the hybrid aerogels with ultralight (9.42 mg/cm3), high porosity (99.29%), and hydrophobicity (contact angle of ~168.0°). Moreover, the hybrid aerogel demonstrated robustness (321 kPa), brilliant elasticity (full recovery from 80% compression), outstanding structure stability (>1000 cycles of compression). The reported strategy paves a new way for fabricating high-performance nanocellulose-based aerogel used for thermal insulation and oil absorption in harsh conditions.

Preparation of CNTs/PP@Gr composites with a segregated structure and enhanced electrical and thermal conductive properties by the Pickering emulsion method

Conductive and thermal conductive polymer composites have significant advantages in corrosion resistance and mechanical and processing properties. To improve the integrity of the network structure of the conductive filler in a polypropylene (PP) matrix, PP@Graphite (Gr) with segregated single-network structure, PP@(carbon nanotubes (CNTs)/Gr) with segregated double-network structure, and (x wt%-CNTs/PP)@Gr with segregated hybrid double-network structure were prepared by the Pickering emulsion method. The original irregular powder was converted into spherical shape by the Pickering emulsion method. Among these composites, the (2 wt%-CNTs/PP)@Gr composite had the highest conductivity and thermal conductivity. The electrical and thermal conductivity of the (2 wt%-CNTs/PP)@Gr composite reached 1.45 S/m and 0.82 W/m·K, respectively, at a Gr loading of 13.01 wt%, and the electrical conductivity was 3 and 0.5 times higher than that of PP@Gr and PP@(CNTs/Gr) composites, respectively. The CNTs acted as "bridges" to form a denser conductive network, and significantly improved the conductivity. The interfacial thermal resistance of the (2 wt%-CNTs/PP)@Gr composite was between 1.5×10-7 and 1×10-6 m2K/W according to the effective medium theory (EMT) fitting results. Additionally, the crystalline peaks of the PP@Gr and PP@(CNTs/Gr) composites showed a significant left shift, while the (2%-CNT/PP)@Gr composite showed a significant right shift, which indicated that the hybridization of CNTs with Gr caused a "bridge effect" and increased the thermal conductivity. This method provides a convenient and time-saving new approach for the study of segregated structural thermally conductive composites by encapsulating the filler on the matrix through a one-step process while meeting the requirements of green environment.

An antifreezing and thermally stable hydrogel electrolyte for high-performance all-in-one flexible supercapacitor

Hydrogel electrolyte have multifunctional properties in the flexible supercapacitors, which can have excellent mechanical behavior and wide temperature tolerance. However, the hydrogel electrolytes with poor mechanical properties, unsatisfactory ionic conductivity and narrow temperature range are still a huge challenge to limit their widely use in the flexible supercapacitors. Herein, a novel ethylene glycol-containing polyacrylamide/montmorillonite/ionic liquid (EG-PAM/MMT/EMIMBF4, EG-PME) hydrogel with significant stretchability, high ionic conductivity and wide temperature tolerant was synthesized by a cross-linking polymerization process. The double-network structure can improve the mechanical properties of hydrogel. Moreover, the introduction of EG and EMIMBF4 into the hydrogel can improve the temperature range. Furthermore, an integrated flexible supercapacitor with wide temperature range was fabricated by in-situ polymerization polypyrrole electrodes onto hydrogel. The integrated flexible supercapacitors have superior toughness under different mechanical deformation (e.g., stretch, compression and twisting ). The EG-PME-PPy composite film possesses high single electrode areal capacitance of 212 mF cm−2 at 0.8 mA cm−2, high energy density of 9.4 μWh cm−2 at power density of 319.5 μW cm−2, and good ionic conductivity of 5.18 mS cm−1 at -30 °C, as well as high ionic conductivity of 33.3 mS cm−1 at 40 °C. The integrated flexible supercapacitors have the satisfying electrochemical properties due to the rapid ion diffusivity and low charge transfer resistance of the integrated all-in-one hydrogel. Therefore, the developed all-in-one flexible supercapacitor based on multifunctional hydrogel can be a next-generation promising power sources.

Mechanical property and dielectric spectra analysis of solvent-free poly(ionic liquid)/poly(ethyl acrylate) double network elastomers under tensile deformation

Solvent-free double network elastomers have excellent mechanical properties and stability. However, there are few studies on ion transport in solvent-free double network elastomers. In this paper, we prepared a kind of poly(ionic liquid) (PIL)-based solvent-free elastomer with double network structure by using crosslinked poly[2-(methacryloyloxy)ethyl] trimethyl ammonium bis(trifluoromethanesulfonyl) imine (P[VBTMA][TFSI]) network as brittle network and crosslinked poly(ethyl acrylate) (PEA) as stretchable network. The mechanical properties and the ion transport of samples as a function of elongation strain were investigated by stress-strain curves and broadband dielectric spectroscopy, respectively. The results show the double network elastomer has medium elastic modulus of 0.4–0.9 MPa, high elongation strain of 1700–2300% and ionic conductivity of 1.04 × 10−7 S·m−1 at room temperature. When the sample does not yield, stretching almost does not affect the ion transport in the network. As the strain exceeds the yield point, the conductivity relaxation time of the samples with low crosslinking degree of PIL network increases little, while the conductivity relaxation time of the samples with high crosslinking degree increases significantly. This is because the former network breaks uniformly, while the latter appears phase separation when yielding. The result improves the understanding of ion transport in double network polyelectrolyte elastomers.

Highly Transparent, Self-Healing, and Self-Adhesive Double Network Hydrogel for Wearable Sensors.

Hydrogel-based flexible electronic devices are essential in future healthcare and biomedical applications, such as human motion monitoring, advanced diagnostics, physiotherapy, etc. As a satisfactory flexible electronic material, the hydrogel should be conductive, ductile, self-healing, and adhesive. Herein, we demonstrated a unique design of mechanically resilient and conductive hydrogel with double network structure. The Ca2+ crosslinked alginate as the first dense network and the ionic pair crosslinked polyzwitterion as the second loose network. With the synthetic effect of these two networks, this hydrogel showed excellent mechanical properties, such as superior stretchability (1,375%) and high toughness (0.57 MJ/m3). At the same time, the abundant ionic groups of the polyzwitterion network endowed our hydrogel with excellent conductivity (0.25 S/m). Moreover, due to the dynamic property of these two networks, our hydrogel also performed good self-healing performance. Besides, our experimental results indicated that this hydrogel also had high optical transmittance (92.2%) and adhesive characteristics. Based on these outstanding properties, we further explored the utilization of this hydrogel as a flexible wearable strain sensor. The data strongly proved its enduring accuracy and sensitivity to detect human motions, including large joint flexion (such as finger, elbow, and knee), foot planter pressure measurement, and local muscle movement (such as eyebrow and mouth). Therefore, we believed that this hydrogel had great potential applications in wearable health monitoring, intelligent robot, human-machine interface, and other related fields.

3D bioprintable methacrylated carrageenan/sodium alginate dual network hydrogel for vascular tissue engineering scaffolding

3D printing technology has significant advantages in the processing field of vascular tissue engineering. We have developed KCMA/SA hydrogels based on methacrylated carrageenan (KCMA) and sodium alginate (SA), which have low viscosity and shear thinning properties and can be used for 3D printing. The physicochemical double cross-linked network structure leads to good mechanical properties. The composite hydrogels maintain the liquid crystallinity of KC, which causes the HUVECs to align. The KCMA/SA gel filaments printed by the 3D extrusion printing system formed a connected microstructure. These characteristics all indicate the potential of KCMA/SAs in the field of tubular tissue regeneration.

Dynamically United Double Network Structure Based on Polydopamine to Enhance pH‐Sensitive Seaweed‐Based Film for Medicine

AbstractThe drug‐loaded and seaweed‐based composite film with high mechanical properties was prepared based on the dynamically united calcium alginate/carboxymethyl chitosan (CA/CMCS) double network structure with the help of polydopamine (PDA). The enhancement mechanism could be attributed to three aspects. Firstly, a dynamic cross‐linking network formed by Schiff base reaction between CMCS and oxidized starch (OXS). Secondly, sodium alginate (SA) and CaCl2 formed an ion cross‐linking network. Finally, PDA and CMCS underwent the Michael addition reaction to form dynamic covalent bonds that dynamically combined the two networks. The effect of CMCS content on wettability and mechanical properties of the composite film was explored in order to improve the comprehensive properties used in the medical field. The drug‐loaded film containing ciprofloxacin inclusion compound had excellent slow‐release performance and pH sensitivity. It had obvious antibacterial properties against Escherichia coli and Staphylococcus aureus, and the excellent cell growth rate. It has broad prospects as a wound dressing to treat bacterial infections and smart drug delivery, and is expected to be applied in the field of biomedicine.

Construction of polydopamine reduced graphene oxide/sodium carboxymethyl cellulose/polyacrylamide double network conductive hydrogel with high stretchable, pH-sensitive and strain-sensing properties

In recent years, electrically conductive hydrogels (ECHs) have attracted extensive attention for their potential applications in flexible wearable sensors and human motion monitoring. However, many ECHs are prone to damage during use, limiting their application. In this study, a quick and simple one-pot in situ copolymerization method was used to introduce the double network (DN) structure with good mechanical properties into the conductive hydrogel, providing a new method for preparing the multi-function DN hydrogel. A novel conductive hydrogel was prepared by introducing sodium carboxymethyl cellulose (CMCNa) and polydopamine (PDA) reduced graphene oxide (D-rGO) into polyacrylamide (PAM) hydrogel. Among them, the well-dispersed D-rGO nanofillers provided a good electron conduction pathway. CMCNa/PAM matrix was physically and chemically crosslinked with Fe3+ and N, N′-methylene-bis-acrylamide (MBA), which made the hydrogel had better mechanical properties and pH sensitivity than pure PAM hydrogel. The conductive hydrogel designed by us had better sensitivity (gauge factor (GF) value was 6.44), wider strain detection range (0–500%), better cycle stability and durability compared with other conductive hydrogels by using a composite conductive mechanism of electron and ion conductivity. More notably, D-rGO/CMCNa/PAM hydrogel could detect large-scale changes in human movement (such as bending of fingers and wrists) and sensitive signals without obvious allergic reactions to human skin, which offered great possibilities for practical applications as flexible strain sensors.

Nacre‐inspired construction of soft–hard double network structure to prepare strong, tough, and water‐resistant soy protein adhesive

AbstractSoy protein (SPI) adhesives are non‐toxic and eco‐friendly that can potentially replace traditional formaldehyde‐based adhesives to ease toxic gas emissions. The development of strong and toughness SPI adhesive benefits its bonding stability but is challenging. In this study, inspired by nacre structure, a soft–hard double network structure was constructed in SPI adhesive. The triglycidylamine (TGA) cross‐linked protein served as the hard phase to provide cohesion. In addition, the self‐synthesizing epoxidized rubber (ER) as soft phase cross‐linked protein and enhanced the interfacial force between hard and soft phase to dissipate energy during fracture, which improved the toughness of adhesive. The results showed that: compared with original SPI adhesive, the residue rate of SPI/4%TGA/3%ER adhesive increased by 7.9%, and the moisture absorption rate decreased by 16.7%. The dry and wet shear strength of the plywood prepared by SPI/4%TGA/3%ER adhesive increased by 58.9% and 160.4% to 1.86 and 1.38 MPa, which was higher than commercial polyamide‐epichlorohydrin modified SPI adhesive. The elongation at break increased by 55.2%–45%, the fracture energy increased by 233% to 2.96 MJ/m2, and the cracks on the adhesive surface disappeared, indicating that the strength, toughness, and water resistance of the adhesive were significantly improved. In this research, a soft–hard double network structure is constructed in a bio‐based adhesive to obtain excellent performance, this eco‐friendly adhesive opens up a new way to replace harmful formaldehyde‐based adhesives.

High-Strength, Large-Deformation, Dual Cross-Linking Network Liquid Crystal Elastomers Based on Quadruple Hydrogen Bonds.

Liquid crystal elastomers (LCEs) with large deformation under external stimuli have attracted extensive attention in various applications such as soft robotics, 4D printing, and biomedical devices. However, it is still a great challenge to reduce the damage to collimation and enhance the mechanical and actuation properties of LCEs simultaneously. Here, we construct a new method of a double cross-linking network structure to improve the mechanical properties of LCEs. The ureidopyrimidinone (UPy) group with quadruple hydrogen bonds was used as the physical cross-linking unit, and pentaerythritol tetra(3-mercaptopropionate) was used as the chemical cross-link. The LCEs showed a strong mechanical tensile strength of 8.5 MPa and excellent thermally induced deformation (50%). In addition, the introduction of quadruple hydrogen bonds endows self-healing ability to extend the service life of LCEs. This provides a generic strategy for the fabrication of high-strength LCEs, inspiring the development of actuators and artificial muscles.