高强度聚苯胺-聚丙烯酸/聚丙烯酰胺导电水凝胶的制备与性能

将导电聚合物引入到水凝胶网络中的导电高分子基导电水凝胶,因结合了水凝胶的三维网络结构、良好的生物相容性、优异的力学性能等和导电高分子良好电学性能等优点而被广泛研究,特别是以聚苯胺(PANI)为导电高分子的导电水凝胶。但PANI不溶于水,因此很难制备PANI基导电水凝胶。本文以制备高强度PANI基导电水凝胶为目的,尝试将PANI接枝在亲水性聚合物聚丙烯酸(PAA)上,获得能在水中均匀分散的PANI-PAA导电复合物,再使其与丙烯酰胺(AM)聚合得到高强度的PANI-PAA/PAM导电水凝胶。通过力学性能及电化学性能测试,发现该导电水凝胶具有良好的力学性能和电化学性能。当以十二烷基硫酸钠(SDS)为分散剂时,其电导率可达4.63 S·m?1,可承受压缩应力1.33 MPa (压缩耗散能为85.50 kJ·m?3),拉伸断裂伸长率达964%,相应的断裂强度为0.25 MPa;而以NaOH为分散剂时,凝胶的电导率可达4.19 S·m?1,可承受压缩应力1.13 MPa (压缩耗散能为73.45 kJ·m?3),拉伸断裂伸长率达896%;相应的断裂强度为 0.14 MPa。该研究为高强度聚苯胺基导电水凝胶的制备提供了思路。      

Strong,Tough, and Anti-Swelling Supramolecular Conductive Hydrogels for Amphibious Motion Sensors

Conductive polymer hydrogels (CPHs) are widely employed in emerging flexible electronic devices because they possess both the electrical conductivity of conductors and the mechanical properties of hydrogels. However, the poor compatibility between conductive polymers and the hydrogel matrix, as well as the swelling behavior in humid environments, greatly compromises the mechanical and electrical properties of CPHs, limiting their applications in wearable electronic devices. Herein, a supramolecular strategy to develop a strong and tough CPH with excellent anti-swelling properties by incorporating hydrogen, coordination bonds, and cation-π interactions between a rigid conducting polymer and a soft hydrogel matrix is reported. Benefiting from the effective interactions between the polymer networks, the obtained supramolecular hydrogel has homogeneous structural integrity, exhibiting remarkable tensile strength (1.63 MPa), superior elongation at break (453%), and remarkable toughness (5.5 MJ m⁻³). As a strain sensor, the hydrogel possesses high electrical conductivity (2.16 S m⁻¹), a wide strain linear detection range (0–400%), and excellent sensitivity (gauge factor = 4.1), sufficient to monitor human activities with different strain windows. Furthermore, this hydrogel with high swelling resistance has been successfully applied to underwater sensors for monitoring frog swimming and underwater communication. These results reveal new possibilities for amphibious applications of wearable sensors.     

A Hydrogel‐Film Casting to Fabricate Platelet‐Reinforced Polymer Composite Films Exhibiting Superior Mechanical Properties

The fabrication of mechanically superior polymer composite films with controllable shapes on various scales is difficult. Despite recent research on polymer composites consisting of organic matrices and inorganic materials with layered structures, these films suffer from complex preparations and limited mechanical properties that do not have even integration of high strength, stiffness, and toughness. Herein, a hydrogel‐film casting approach to achieve fabrication of simultaneously strong, stiff, and tough polymer composite films with well‐defined microstructure, inspired from a layer‐by‐layer structure of nacre is reported. Ca²⁺‐crosslinked alginate hydrogels incorporated with platelet‐like alumina particles are dried to form composite films composed of horizontally aligned alumina platelets and alginate matrix with uniformly layered microstructure. Alumina platelets are evenly distributed parallel without precipitations and contribute to synergistic enhancements of strength, stiffness and toughness in the resultant film. Consequentially, Ca²⁺‐crosslinked alginate/alumina (Ca²⁺‐Alg/Alu) films show exceptional tensile strength (267 MPa), modulus (17.9 GPa), and toughness (3.60 MJ m⁻³). Furthermore, the hydrogel‐film casting allows facile preparation of polymer composite films with controllable shapes and various scales. The results suggest an alternative approach to design and prepare polymer composites with the layer‐by‐layer structure for superior mechanical properties.     

A Novel Design of Multi‐Mechanoresponsive and Mechanically Strong Hydrogels

A newly developed polyacrylamide‐co ‐methyl acrylate/spiropyran (SP) hydrogel crosslinked by SP mechanophore demonstrates multi‐stimuli‐responsive and mechanically strong properties. The hydrogels not only exhibit thermo‐, photo‐, and mechano‐induced color changes, but also achieve super‐strong mechanical properties (tensile stress of 1.45 MPa, tensile strain of ≈600%, and fracture energy of 7300 J m^?2). Due to a reversible structural transformation between spiropyran (a ring‐close) and merocyanine (a ring‐open) states, simple exposure of the hydrogels to white light can reverse color changes and restore mechanical properties. The new design approach for a new mechanoresponsive hydrogel is easily transformative to the development of other mechanophore‐based hydrogels for sensing, imaging, and display applications.     

Freezing Molecular Orientation under Stretch for High Mechanical Strength but Anisotropic Hydrogels

The poor mechanical strength of hydrogels has largely limited their wide applications, and improving hydrogels' mechanical strength is a hot and important topic in the hydrogel research field. Although many successful strategies have been proposed to improve hydrogels' mechanical strength during the past decades, a hydrogel with a tensile stress surpassing dozens of mega Pascal is desirable, yet still a big challenge. To address this issue, the Fe³⁺‐mediated physical crosslinking formed under stretch conditions was employed in a chemically crosslinked poly (acrylamide‐co‐acrylic acid) network to achieve a dual‐crosslinked hydrogel. The expected molecular orientation occurs under stretch and allows the maximumu chelating interaction between pendant carboxylic anions and Fe³⁺ and molecules conformation being frozen, leading to the mechanical strength improving dramatically. As a result, an unprecedentedly high mechanical strength, but anisotropic dual‐crosslinked hydrogel was obtained. By optimizing the experimental parameters, the nominal tensile stress along pre‐stretching direction can reach as high as ≈40 MPa with elastic modulus of ≈40 MPa at large strain (>200%). In addition, the molecular orientation also leads to big difference of mechanical performance between parallel and perpendicular direction.     

Anisotropic,Transparent Films with Aligned Cellulose Nanofibers

Transparent films or substrates are ubiquitously used in photonics and optoelectronics, with glass and plastics as traditional choice of materials. Transparent films made of cellulose nanofibers are reported recently. However, all these films are isotropic in nature. This work, for the first time, reports a remarkably facile and effective approach to fabricating anisotropic transparent films directly from wood. The resulting films exhibit an array of exceptional optical and mechanical properties. The well‐aligned cellulose nanofibers in natural wood are maintained during delignification, leading to an anisotropic film with high transparency (≈90% transmittance) and huge intensity ratio of transmitted light up to 350%. The anisotropic film with well‐aligned cellulose nanofibers has a mechanical tensile strength of up to 350 MPa, nearly three times of that of a film with randomly distributed cellulose nanofibers. Atomistic mechanics modeling further reveals the dependence of the film mechanical properties on the alignment of cellulose nanofibers through the film thickness direction. This study also demonstrates guided liquid transport in a mesoporous, anisotropic wood film and its possible application in enabling new nanoelectronic devices. These unique and highly desirable properties of the anisotropic transparent film can potentially open up a range of green electronics and nanofluidics.     

Super‐Strong,Super‐Stiff Macrofibers with Aligned,Long Bacterial Cellulose Nanofibers

With their impressive properties such as remarkable unit tensile strength, modulus, and resistance to heat, flame, and chemical agents that normally degrade conventional macrofibers, high‐performance macrofibers are now widely used in various fields including aerospace, biomedical, civil engineering, construction, protective apparel, geotextile, and electronic areas. Those macrofibers with a diameter of tens to hundreds of micrometers are typically derived from polymers, gel spun fibers, modified carbon fibers, carbon‐nanotube fibers, ceramic fibers, and synthetic vitreous fibers. Cellulose nanofibers are promising building blocks for future high‐performance biomaterials and textiles due to their high ultimate strength and stiffness resulting from a highly ordered orientation along the fiber axis. For the first time, an effective fabrication method is successfully applied for high‐performance macrofibers involving a wet‐drawing and wet‐twisting process of ultralong bacterial cellulose nanofibers. The resulting bacterial cellulose macrofibers yield record high tensile strength (826 MPa) and Young's modulus (65.7 GPa) owing to the large length and the alignment of nanofibers along fiber axis. When normalized by weight, the specific tensile strength of the macrofiber is as high as 598 MPa g^?1 cm³, which is even substantially stronger than the novel lightweight steel (227 MPa g^?1 cm³).     

Ultrastretchable and Wireless Bioelectronics Based on All‐Hydrogel Microfluidics

Hydrogel bioelectronics that can interface biological tissues and flexible electronics is at the core of the growing field of healthcare monitoring, smart drug systems, and wearable and implantable devices. Here, a simple strategy is demonstrated to prototype all‐hydrogel bioelectronics with embedded arbitrary conductive networks using tough hydrogels and liquid metal. Due to their excellent stretchability, the resultant all‐hydrogel bioelectronics exhibits stable electrochemical properties at large tensile stretch and various modes of deformation. The potential of fabricated all‐hydrogel bioelectronics is demonstrated as wearable strain sensors, cardiac patches, and near‐field communication (NFC) devices for monitoring various physiological conditions wirelessly. The presented simple platform paves the way of implantable hydrogel electronics for Internet‐of‐Things and tissue–machine interfacing applications.     

Strong and Tough Cellulose Hydrogels via Solution Annealing and Dual Cross-Linking

Strong and tough hydrogels are promising candidates for flexible electronics, biomedical devices, and so on. However, the conflict between improving the mechanical strength and toughness properties of polysaccharide-based hydrogels remains unsolved. Herein, a strategy is proposed to produce a hierarchically structured cellulose hydrogel that combines solution annealing and dual cross-linking treatment approaches. The solution annealing considerably increases the hydrophobic stacking and chemical cross-linking of the cellulose chains, thereby facilitating their subsequent self-assembly and recrystallization during the chemical and physical cross-linking processes. The cellulose hydrogels exhibit superposed chemically and physically cross-linked domains comprising homogeneous nanoporous network structures, which in turn are composed of interconnected cellulose nanofibers and cellulose II crystallite hydrates. These cellulose hydrogels exhibit a high water content of 76–84% and excellent mechanical properties that compare favorably to those of biomacromolecule-based hydrogels. The prepared hydrogels exhibit a mechanical strength and work of fracture of 21 ± 3 MPa and 2.6 ± 0.4 MJ m⁻³ under compression, and 7.2 ± 0.7 MPa and 5.9 ± 0.6 MJ m⁻³ under tension, respectively. It is anticipated that this strategy will be applicable to other biomacromolecules and crystalline polymers, and that it will enable the construction of other hydrogels exhibiting high mechanical performances.     

聚丙烯酰胺/改性纳米纤维素晶体纳米复合水凝胶的光聚合制备与表征

先用马来酸酐对纳米纤维素晶体(NCC)进行表面改性得表面含碳-碳双键的改性NCC(mNCC),然后将丙烯酰胺(AM)和mNCC一起光聚合得PAM/mNCC纳米复合水凝胶;通过红外光谱、扫描电镜、热重分析、差热分析、溶胀实验和拉伸实验研究了水凝胶的结构和性能。结果表明,PAM/mNCC纳米复合水凝胶是一种物理/化学共交联水凝胶;与用质量分数0.25%N,N-亚甲基双丙烯酰胺交联的PAM水凝胶相比,PAM/mNCC纳米复合水凝胶中的微孔尺寸分布更宽,PAM分子链的起始分解温度和玻璃化转变温度升高;当mNCC的用量占AM质量的5%~10%时,PAM/mNCC纳米复合水凝胶的饱和溶胀率、拉伸强度、断裂伸长率分别为PAM水凝胶的2.1~2.7倍、0.45~1.1倍、3.8~7.1倍。     

Stretchable All‐Gel‐State Fiber‐Shaped Supercapacitors Enabled by Macromolecularly Interconnected 3D Graphene/Nanostructured Conductive Polymer Hydrogels

Nanostructured conductive polymer hydrogels (CPHs) have been extensively applied in energy storage owing to their advantageous features, such as excellent electrochemical activity and relatively high electrical conductivity, yet the fabrication of self‐standing and flexible electrode‐based CPHs is still hampered by their limited mechanical properties. Herein, macromolecularly interconnected 3D graphene/nanostructured CPH is synthesized via self‐assembly of CPHs and graphene oxide macrostructures. The 3D hybrid hydrogel shows uniform interconnectivity and enhanced mechanical properties due to the strong macromolecular interaction between the CPHs and graphene, thus greatly reducing aggregation in the fiber‐shaping process. A proof‐of‐concept all‐gel‐state fibrous supercapacitor based on the 3D polyaniline/graphene hydrogel is fabricated to demonstrate the outstanding flexibility and mouldability, as well as superior electrochemical properties enabled by this 3D hybrid hydrogel design. The proposed device can achieve a large strain (up to ≈40%), and deliver a remarkable volumetric energy density of 8.80 mWh cm^?3 (at power density of 30.77 mW cm^?3), outperforming many fiber‐shaped supercapacitors reported previously. The all‐hydrogel design opens up opportunities in the fabrication of next‐generation wearable and portable electronics.     

From Wood to Textiles: Top‐Down Assembly of Aligned Cellulose Nanofibers

Advanced textiles made of macroscopic fibers are usually prepared from synthetic fibers, which have changed lives over the past century. The shortage of petrochemical resources, however, greatly limits the development of the textile industry. Here, a facile top‐down approach for fabricating macroscopic wood fibers for textile applications (wood‐textile fibers) comprising aligned cellulose nanofibers directly from natural wood via delignification and subsequent twisting is demonstrated. Inherently aligned cellulose nanofibers are well retained, while the microchannels in the delignified wood are squeezed and totally removed by twisting, resulting in a dense structure with approximately two times higher mechanical strength (106.5 vs 54.9 MPa) and ≈20 times higher toughness (7.70 vs 0.36 MJ m^?3) than natural wood. Dramatically different from natural wood, which is brittle in nature, the resultant wood‐textile fibers are highly flexible and bendable, likely due to the twisted structures. The wood‐textile fibers also exhibit excellent knitting properties and dyeability, which are critical for textile applications. Furthermore, functional wood‐textile fibers can be achieved by preinfiltrating functional materials in the delignified wood film before twisting. This top‐down approach of fabricating aligned macrofibers is simple, scalable, and cost‐effective, representing a promising direction for the development of smart textiles and wearable electronics.     

Ultralight,Heat-Insulated,and Tough PVA Hydrogel Hybridized with SiO2@cellulose Nanoclaws Aerogel via the Synergy of Hydrophilic and Hydrophobic Interfacial Interactions

Lightweight porous hydrogels provide a worldwide scope for functional soft mateirals. However, most porous hydrogels have weak mechanical strength, high density (>1 g cm⁻³), and high heat absorption due to weak interfacial interactions and high solvent fill rates, which severely limit their application in wearable soft-electronic devices. Herein, an effective hybrid hydrogel-aerogel strategy to assemble ultralight, heat-insulated, and tough polyvinyl alcohol (PVA)/SiO₂@cellulose nanoclaws (CNCWs) hydrogels (PSCG) via strong interfacial interactions with hydrogen bonding and hydrophobic interaction is demonstrated. The resultant PSCG has an interesting hierarchical porous structure from bubble template (≈100 µm), PVA hydrogels networks introduced by ice crystals (≈10 µm), and hybrid SiO₂ aerogels (<50 nm), respectively. PSCG shows unprecedented low density (0.27 g cm⁻³), high tensile strength (1.6 MPa) & compressive strength (1.5 MPa), excellent heat-insulated ability, and strain-sensitive conductivity. This lightweight porous and tough hydrogel with an ingenious design provides a new way for wearable soft-electronic devices.     

Self-Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film

In the native wood cell wall, cellulose microfibrils are highly aligned and organized in the secondary cell wall. A new preparation strategy is developed to achieve individualization of cellulose microfibrils within the wood cell wall structure without introducing mechanical disintegration. The resulting mesoporous wood structure has a high specific surface area of 197 m² g⁻¹ when prepared by freeze-drying using liquid nitrogen, and 249 m² g⁻¹ by supercritical drying. These values are 5 to 7 times higher than conventional delignified wood (36 m² g⁻¹) dried by supercritical drying. Such highly mesoporous structure with individualized cellulose microfibrils maintaining their natural alignment and organization can be processed into aerogels with high porosity and high compressive strength. In addition, a strong film with a tensile strength of 449.1 ± 21.8 MPa and a Young's modulus of 51.1 ± 5.2 GPa along the fiber direction is obtained simply by air drying owing to the self-densification of cellulose microfibrils driven by the elastocapillary forces upon water evaporation. The self-densified film also shows high optical transmittance (80%) and high optical haze (70%) with interesting biaxial light scattering behavior owing to the natural alignment of cellulose microfibrils.     

A Highly Efficient Self‐Healing Elastomer with Unprecedented Mechanical Properties

It is highly desirable, although very challenging, to develop self‐healable materials exhibiting both high efficiency in self‐healing and excellent mechanical properties at ambient conditions. Herein, a novel Cu(II)–dimethylglyoxime–urethane‐complex‐based polyurethane elastomer (Cu–DOU–CPU) with synergetic triple dynamic bonds is developed. Cu–DOU–CPU demonstrates the highest reported mechanical performance for self‐healing elastomers at room temperature, with a tensile strength and toughness up to 14.8 MPa and 87.0 MJ m^?3, respectively. Meanwhile, the Cu–DOU–CPU spontaneously self‐heals at room temperature with an instant recovered tensile strength of 1.84 MPa and a continuously increased strength up to 13.8 MPa, surpassing the original strength of all other counterparts. Density functional theory calculations reveal that the coordination of Cu(II) plays a critical role in accelerating the reversible dissociation of dimethylglyoxime–urethane, which is important to the excellent performance of the self‐healing elastomer. Application of this technology is demonstrated by a self‐healable and stretchable circuit constructed from Cu–DOU–CPU.     

Highly Efficient and Environmentally Friendly Fabrication of Robust,Programmable, and Biocompatible Anisotropic,All‐Cellulose,Wrinkle‐Patterned Hydrogels for Cell Alignment

Wrinkled hydrogels from biomass sources are potential structural biomaterials. However, for biorelated applications, engineering scalable, structure‐customized, robust, and biocompatible wrinkled hydrogels with highly oriented nanostructures and controllable intervals is still a challenge. A scalable biomass material, namely cellulose, is reported for customizing anisotropic, all‐cellulose, wrinkle‐patterned hydrogels (AWHs) through an ultrafast, auxiliary force, acid‐induced gradient dual‐crosslinking strategy. Direct immersion of a prestretched cellulose alkaline gel in acid and relaxation within seconds allow quick buildup of a consecutive through‐thickness modulus gradient with acid‐penetration‐directed dual‐crosslinking, confirmed by visual 3D Raman microscopy imaging, which drives the formation of self‐wrinkling structures. Moreover, guided by quantitative mechanics simulations, the structure of AWHs is found to exhibit programmable intervals and aligned nanostructures that differ between ridge and valley regions and can be controlled by tuning the prestretching strain and acid treatment time, and these AWHs successfully induce cell alignment. Thus, a new avenue is opened to fabricate polysaccharide‐derived, programmable, anisotropic, wrinkled hydrogels for use as biomedical materials via a bottom‐up method.     

Highly Tough Bioinspired Ternary Hydrogels Synergistically Reinforced by Graphene/Xonotlite Network

The application fields of hydrogels are often severely limited by their weak mechanical performance. It is therefore highly demanded to develop an effective strategy to fabricate mechanically strong hydrogels. Herein, a kind of bioinspired ternary hydrogel consisting of graphene oxide (GO) nanosheets, xonotlite nanowires, and polyacrylamide (PAM) is constructed under the synergy of hydrogen bonding–induced GO/xonotlite network and the penetrated PAM chain network. Benefiting from the effective energy dissipation mechanism caused by double–network structural design and the strong hydrogen bonding interaction between two nanobuilding blocks, the gel exhibits a high toughness of 22 MJ m⁻³ at an elongation of 2750%. Even notched with 1/4 size, it still holds a large extensibility of 2180% its initial length. These high‐performance hydrogels could be of great interest in the fields of tissue engineering and biomedical areas.     

Healable and Mechanically Super‐Strong Polymeric Composites Derived from Hydrogen‐Bonded Polymeric Complexes

It is challenging to fabricate mechanically super‐strong polymer composites with excellent healing capacity because of the significantly limited mobility of polymer chains. The fabrication of mechanically super‐strong polymer composites with excellent healing capacity by complexing polyacrylic acid (PAA) with polyvinylpyrrolidone (PVPON) in aqueous solution followed by molding into desired shapes is presented. The coiled PVPON can complex with PAA in water via hydrogen‐bonding interactions to produce transparent PAA–PVPON composites homogenously dispersed with nanoparticles of PAA–PVPON complexes. As healable materials, the PAA–PVPON composite materials with a glass transition temperature of ≈107.9 °C exhibit a super‐high mechanical strength, with a tensile strength of ≈81 MPa and a Young's modulus of ≈4.5 GPa. The PAA–PVPON composites are stable in water because of the hydrophobic interactions among pyrrolidone groups. The super‐high mechanical strength of the PAA–PVPON composite materials originates from the highly dense hydrogen bonds between PAA and PVPON and the reinforcement of in situ formed PAA–PVPON nanoparticles. The reversibility of the relatively weak but dense hydrogen bonds enables convenient healing of the mechanically strong PAA–PVPON composite materials from physical damage to restore their original mechanical strength.     

Water‐Rich Biomimetic Composites with Abiotic Self‐Organizing Nanofiber Network

Load‐bearing soft tissues, e.g., cartilage, ligaments, and blood vessels, are made predominantly from water (65–90%) which is essential for nutrient transport to cells. Yet, they display amazing stiffness, toughness, strength, and deformability attributed to the reconfigurable 3D network from stiff collagen nanofibers and flexible proteoglycans. Existing hydrogels and composites partially achieve some of the mechanical properties of natural soft tissues, but at the expense of water content. Concurrently, water‐rich biomedical polymers are elastic but weak. Here, biomimetic composites from aramid nanofibers interlaced with poly(vinyl alcohol), with water contents of as high as 70–92%, are reported. With tensile moduli of ≈9.1 MPa, ultimate tensile strains of ≈325%, compressive strengths of ≈26 MPa, and fracture toughness of as high as ≈9200 J m^?2, their mechanical properties match or exceed those of prototype tissues, e.g., cartilage. Furthermore, with reconfigurable, noncovalent interactions at nanomaterial interfaces, the composite nanofiber network can adapt itself under stress, enabling abiotic soft tissue with multiscale self‐organization for effective load bearing and energy dissipation.     

A Facile Method to Fabricate Anisotropic Hydrogels with Perfectly Aligned Hierarchical Fibrous Structures

Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano‐ to macroscale, which are difficult to mimic synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano‐ to submicro‐ to microscale) are spontaneously formed in the bulk material, which are well‐retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications.