Layered Rare‐Earth Hydroxide/Polyacrylamide Nanocomposite Hydrogels with Highly Tunable Photoluminescence

Polymer nanocomposite (NC) hydrogels, with 3D networks composed of delaminated inorganic nanoparticles and a polymer matrix, usually display super mechanical toughness. However, the few types of inorganic materials and relatively scarce research for NC hydrogel functions seriously limit their applications. For the first time layered rare‐earth hydroxide (LRH)/polyacrylamide NC hydrogels with highly tunable photoluminescence (PL) function are reported, prepared via a convenient and green in situ polymerization process. Interestingly, the NC hydrogels reveal exciting multicolored PL phenomenon (green, yellow, orange, reddish‐orange to bluish violet), long luminescence lifetime, and relatively high quantum efficiency. Furthermore, the fascinating PL function is highly tunable by adjusting LRH constituent or its concentration, and excitation wavelength. The results highlight the fabrication and applications of functional polymer NC hydrogels with highly tunable PL function.     

Molecule–Graphene Hybrid Materials with Tunable Mechanoresponse: Highly Sensitive Pressure Sensors for Health Monitoring

The development of pressure sensors is crucial for the implementation of electronic skins and for health monitoring integrated into novel wearable devices. Tremendous effort is devoted toward improving their sensitivity, e.g., by employing microstructured electrodes or active materials through cumbersome processes. Here, a radically new type of piezoresistive pressure sensor based on a millefeuille‐like architecture of reduced graphene oxide (rGO) intercalated by covalently tethered molecular pillars holding on‐demand mechanical properties are fabricated. By applying a tiny pressure to the multilayer structure, the electron tunnelling ruling the charge transport between successive rGO sheets yields a colossal decrease in the material's electrical resistance. Significantly, the intrinsic rigidity of the molecular pillars employed enables the fine‐tuning of the sensor's sensitivity, reaching sensitivities as high as 0.82 kPa^?1 in the low pressure region (0–0.6 kPa), with short response times (≈24 ms) and detection limit (7 Pa). The pressure sensors enable efficient heartbeat monitoring and can be easily transformed into a matrix capable of providing a 3D map of the pressure exerted by different objects.     

Bioinspired Ultratough Hydrogel with Fast Recovery,Self‐Healing,Injectability and Cytocompatibility

Inspired by the mussel byssus adhesiveness, a highly hydrated polymeric structure is designed to combine, for the first time, a set of interesting features for load‐bearing purposes. These characteristics include: i) a compressive strength and stiffness in the MPa range, ii) toughness and the ability to recover it upon successive cyclic loading, iii) the ability to quickly self‐heal upon rupture, iv) the possibility of administration through minimally invasive techniques, such as by injection, v) the swelling ratio being adjusted to space‐filling applications, and vi) cytocompatibility. Owing to these characteristics and the mild conditions employed, the encapsulation of very unstable and sensitive cargoes is possible, highlighting their potential to researchers in the biomedical field for the repair of load‐bearing soft tissues, or to be used as an encapsulation platform for a variety of biological applications such as disease models for drug screening and therapies in a more realistic mechanical environment. Moreover, given the simplicity of this methodology and the enhanced mechanical performance, this strategy can be expanded to applications in other fields, such as agriculture and electronics. As such, it is anticipated that the proposed strategy will constitute a new, versatile, and cost‐effective tool to produce engineered polymeric structures for both science and technology.     

Fast and Highly Sensitive Ionic‐Polymer‐Gated WS2–Graphene Photodetectors

The combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer‐scale electronic devices. Presently, long‐lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gate‐voltage pulses, have been employed to achieve bandwidths suitable for applications such as video‐frame‐rate imaging. Here, atomically thin graphene–WS₂ heterostructure photodetectors encapsulated in an ionic polymer are reported, which are uniquely able to operate at bandwidths up to 1.5 kHz whilst maintaining internal gain as large as 10⁶. Highly mobile ions and the nanometer‐scale Debye length of the ionic polymer are used to screen charge traps and tune the Fermi level of the graphene over an unprecedented range at the interface with WS₂. Responsivity R = 10⁶ A W^?1 and detectivity D* = 3.8 × 10¹¹ Jones are observed, approaching that of single‐photon counters. The combination of both high responsivity and fast response times makes these photodetectors suitable for video‐frame‐rate imaging applications.     

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 Water‐Stable Lanthanide–Oxalate MOFs with Remarkable Proton Conductivity and Tunable Luminescence

Although proton conductors derived from metal–organic frameworks (MOFs) are highly anticipated for various applications including solid‐state electrolytes, H₂ sensors, and ammonia synthesis, they are facing serious challenges such as poor water stability, fastidious working conditions, and low proton conductivity. Herein, we report two lanthanide–oxalate MOFs that are highly water stable, with so far the highest room‐temperature proton conductivity (3.42 × 10^?3 S cm^?1) under 100% relative humidity (RH) among lanthanide‐based MOFs and, most importantly, luminescent. Moreover, the simultaneous response of both the proton conductivity and luminescence intensity to RH allows the linkage of proton conductivity with luminescence intensity. This way, the electric signal of proton conductivity variation versus RH will be readily translated to optical signal of luminescence intensity, which can be directly visualized by the naked eye. If proper lanthanide ions or even transition‐metal ions are used, the working wavelengths of luminescence emissions can be further extended from visible to near infrared light for even wider‐range applications.     

Skin‐Inspired Multifunctional Autonomic‐Intrinsic Conductive Self‐Healing Hydrogels with Pressure Sensitivity,Stretchability, and 3D Printability

The advent of conductive self‐healing (CSH) hydrogels, a class of novel materials mimicking human skin, may change the trajectory of the industrial process because of their potential applications in soft robots, biomimetic prostheses, and health‐monitoring systems. Here, the development of a mechanically and electrically self‐healing hydrogel based on physically and chemically cross‐linked networks is reported. The autonomous intrinsic self‐healing of the hydrogel is attained through dynamic ionic interactions between carboxylic groups of poly(acrylic acid) and ferric ions. A covalent cross‐linking is used to support the mechanical structure of the hydrogel. Establishing a fair balance between the chemical and physical cross‐linking networks together with the conductive nanostructure of polypyrrole networks leads to a double network hydrogel with bulk conductivity, mechanical and electrical self‐healing properties (100% mechanical recovery in 2 min), ultrastretchability (1500%), and pressure sensitivity. The practical potential of CSH hydrogels is further revealed by their application in human motion detection and their 3D‐printing performance.     

Architected Lattices with High Stiffness and Toughness via Multicore–Shell 3D Printing

The ability to create architected materials that possess both high stiffness and toughness remains an elusive goal, since these properties are often mutually exclusive. Natural materials, such as bone, overcome such limitations by combining different toughening mechanisms across multiple length scales. Here, a new method for creating architected lattices composed of core–shell struts that are both stiff and tough is reported. Specifically, these lattices contain orthotropic struts with flexible epoxy core–brittle epoxy shell motifs in the absence and presence of an elastomeric silicone interfacial layer, which are fabricated by a multicore–shell, 3D printing technique. It is found that architected lattices produced with a flexible core‐elastomeric interface‐brittle shell motif exhibit both high stiffness and toughness.     

Strawberry‐like Core–Shell Ag@Polydopamine@BaTiO3 Hybrid Nanoparticles for High‐k Polymer Nanocomposites with High Energy Density and Low Dielectric Loss

Flexible nanocomposites comprising of polymer and high‐dielectric‐constant (high‐k) ceramic nanoparticles are becoming increasingly attractive for dielectric and energy storage applications in modern electronic and electric industry. However, a huge challenge still remains. Namely, the increase of dielectric constant usually at the cost of significant decrease of breakdown strength of the nanocomposites because of the electric field distortion and concentration induced by the high‐k filler. To address this long‐standing problem, by using nano‐Ag decorated core–shell polydopamine (PDA) coated BaTiO₃ (BT) hybrid nanoparticles, a new strategy is developed to prepare high‐k polymer nanocomposites with high breakdown strength. The strawberry‐like BT‐PDA‐Ag based ferroelectric polymer [i.e., poly(vinylideneflyoride‐co‐hexafluroro propylene), P(VDF‐HFP)] nanocomposites exhibit greatly enhanced energy density and significantly suppressed dielectric loss as well as leakage current density in comparison with the nanocomposites with the core–shell structured BT‐PDA. Coulomb‐blockade effect of super‐small nano‐Ag is used to explain the observed performance enhancement of the nanocomposites. The simplicity and scalability of the described approach provide a promising route to polymer nanocomposites for dielectric and energy storage applications.     

Generic Strategy to Synthesize High‐Tap Density Anode and Cathode Structures with Stratified Graphene Pliable Pockets via Monomeric Polymerization and Evaporation,and Their Utilization to Enable Ultrahigh Performance in Hybrid Energy Storages

Hybrid energy storage systems have shown great promise for many applications; however, achieving high energy and power densities with long cycle stability remains a major challenge. Here, a strategy to synthesize high‐tap density anode and cathode structures that yield ultrahigh performance in hybrid energy storage is reported. First, vinyl acetate monomers are polymerized into molecular sizes via chain reactions controlled by the surface free radicals of graphene and metals. Subsequently, molecular‐size polymers are thermally evaporated to construct battery‐type anode structures with encapsulated tin metals for high‐capacity and stratified graphene pliable pockets (GPPs) for fast charge transfer. Similarly, sulfur particles are attached to GPPs via monomeric polymerization, and capacitor‐type hollow GPP (H@GPP) cathode structures are produced by evaporating sulfur, where sublimated S particles yield mesopores for rapid anion movement and micropores for high capacity. Moreover, hybrid full‐cell devices with high‐tap density anodes and cathodes show high gravimetric energy densities of up to 206.9 Wh kg^?1, exceeding those of capacitors by ≈16‐fold, and excellent volumetric energy densities of up to 92.7 Wh L^?1. Additionally, they attain high power densities of up to 23 678 W kg^?1, outperforming conventional devices by a factor of ≈100, and long cycle stability over 10 000 cycles.