Luminescent Perovskite-Cross-Linked Polymer with Low Shrinkage and Excellent Stability.

When organic cross-linked polymers are combined with metal halide perovskite nanocrystals (PNCs) for realizing luminescent perovskite-polymer display materials, the stability of PNCs is enhanced and their shrinkage is suppressed. This work presents a feasible strategy for preparing CsPbBr3 nanocrystals (NCs) within a polydicyclopentadiene (PDCPD) thermosetting cross-linked resin matrix simultaneously via a one-step reaction. The obtained PDCPD@PNCs composite exhibits narrow peak half-widths (15-20 nm), high light transmittance (80%), low curing volume shrinkage (1.4%), tunable tensile properties, excellent stability, and a photoluminescence quantum yield (PLQY) of 44.3%. The composite material exhibits long-term stability in water, acid, and base solutions for over 90 days, with the PL intensity being maintained at over 90%. Furthermore, the composite is highly resistant to polar organic solvents owing to the insolubility imparted by cross-linking. White LEDs (WLED) fabricated using the as-prepared composite demonstrate excellent potential as light sources in optical devices.

An Intrinsic Photothermal Supramolecular Hydrogel with Robust Mechanical Strength and NIR-Responsive Shape Memory.

Near-infrared (NIR)-triggered shape memory hydrogels with promising mechanical strength hold immense potential in the field of biomedical applications and soft actuators. However, the optical and mechanical properties of currently reported hydrogels usually suffer from limited solubility and dispersion of commonly used photothermal additives in hydrogels, thus restricting their practical implementations. Here,, a set of NIR-responsive shape memory hydrogels synthesized by polyaddition of diisocyanate-terminated poly(ethylene glycol), imidazolidinyl urea (IU), and p-benzoquinone dioxime (BQDO) is reported. The introduction of IU, a hydrogen bond reinforcing factor, significantly enhances the mechanical properties of the hydrogels, allowing for their tunable ranges of the ultimate tensile strength (0.4-2.5 MPa), elongation at break (210-450%), and Young's modulus (190-850 kPa). The unique hydrogels exhibit an intrinsic photothermal effect because of the covalently incorporated photothermal moiety (BQDO), and the photothermal supramolecular hydrogel shows controllable shape memory capabilities characterized by rapid recovery speed and high recovery ratio (>90%). This design provides new possibilities for applying shape memory hydrogels in the field of soft actuators.

Hydrogen Bonds Reinforced Ionogels with High Sensitivity and Stable Autonomous Adhesion as Versatile Ionic Skins.

Flexible wearable sensors have demonstrated enormous potential in various fields such as human health monitoring, soft robotics, and motion detection. Among them, sensors based on ionogels have garnered significant attention due to their wide range of applications. However, the fabrication of ionogels with high sensitivity and stable autonomous adhesion remains a challenge, thereby limiting their potential applications. Herein, we present an advanced ionogel (PACG-MBAA) with exceptional performances based on multiple hydrogen bonds, which is fabricated through one-step radical polymerization of N-acryloylglycine (ACG) in 1-ethyl-3-methylimidazolium ethyl sulfate (EMIES) in the presence of N,N'-methylenebis(acrylamide) (MBAA). Compared with the ionogel (PAA-MBAA) formed by polymerization of acrylic acid (AA) in EMIES, the resulting ionogel exhibits tunable mechanical strength (35-130 kPa) and Young's modulus comparable to human skin (60-70 kPa) owing to the multiple hydrogen bonds formation. Importantly, they demonstrate stable autonomous adhesion to various substrates and good self-healing capabilities. Furthermore, the ionogel-based sensor shows high sensitivity (with a gauge factor up to 6.16 in the tensile range of 300-700%), enabling the detection of both gross and subtle movements in daily human activities. By integration of the International Morse code, the ionogel-based sensor enables the encryption, decryption, and transmission of information, thus expanding its application prospects.

Autonomous underwater adhesion driven by water-induced interfacial rearrangement.

Underwater adhesives receive extensive attention due to their wide applications in marine explorations and various related industries. However, current adhesives still suffer from excessive water absorption and lack of spontaneity. Herein, we report an autonomous underwater adhesive based on poly(2-hydroxyethyl methacrylate-co-benzyl methacrylate) amphiphilic polymeric matrix swollen by hydrophobic imidazolium ionic liquid. The as-prepared adhesive is tough and flexible, showing little to none instantaneous underwater adhesion onto the PET substrate, whereas its adhesion energy on the substrate can grow more than 5 times to 458 J·m-2 after 24 hours. More importantly, this process is entirely spontaneous, without any external pressing force. Our comprehensive studies based on experimental characterizations and molecular dynamic simulations confirm that such autonomous adhesion process is driven by water-induced rearrangement of the functional groups. It is believed that such material can provide insights into the development of next-generation smart adhesives.

Ionic Switches with Positive Temperature Coefficient Enabled by Phase Separation within Hydrogel Electrolytes.

Ionic switches with a positive temperature coefficient (PTC) effect are highly desirable in the fabrication of smart electrolytes for the safety protection of electrochemical energy devices. However, most of them encounter liquid leaking or volume shrinking problems, limiting their long-term and stable operations. Herein, a PTC-type ionic switch is introduced based on a poly(acrylic acid) (PAA) hydrogel soaked by calcium acetate (CaAc), with a resistance change of six times in maximum between the homogeneous and phase separated state. The PTC effect is owing to the strong phase separation upon heating where the ion transport is restricted. Such a hydrogel-based PTC-type ionic switch is in the solid state and isochoric during phase separation without leaking or shrinking issues. The influence of different CaAc soaking concentrations is investigated. A simplified model consisting of interconnected ion channels is proposed based on microstructure analysis. A smart supercapacitor is successfully demonstrated by this PTC ionic switch with a safety protection ability. The research here would provide a new pathway for the design and development of PTC-type ionic switches in the safety protection of electrochemical energy storage devices.

Bioinspired Semicrystalline Dynamic Ionogels with Adaptive Mechanics and Tactile Sensing.

A biological system shows dynamical shapes and tunable mechanical states while working as an actuator and/or sensor. To simulate this, we prepared semicrystalline dynamic ionogels (SDIGs) via a facile process by introducing crystallized polymer domains for phase change and amorphous domains for ionic liquid loading into ionogels. The obtained SDIGs offered tunable mechanical properties upon temperature switching with a change in modulus up to 2 orders of magnitude. It also showed an excellent shape memory effect, shape programmability, and melting accelerated conductivity increase. Enabled by ionic Joule heating technique, the ionogel provided an electrical triggered actuating process to mimic flower blossoming. Moreover, it was demonstrated as a touch sensor with various working shape states, indicating cyclic and green utilization. This work provides insights into the design of semicrystalline electronics and is believed to promote the development of biomimetic actuators and sensors.

All-Solid-State Self-Healing Ionic Conductors Enabled by Ion-Dipole Interactions within Fluorinated Poly(Ionic Liquid) Copolymers.

Self-healing ionic conductors in all solid state without evaporation or leakage offers great potential for the next-generation soft ionotronics. However, it remains challenging to endow ionic conductors with all solid state while keeping their essential features. In this study, an intrinsically conducting polymer is developed as all-solid-state self-healing ionic conductors based on ion-dipole interactions within a fluorinated poly(ionic liquid) copolymer. This unique material possesses good self-healing ability at room temperature (96% of healing efficiency in 24 h), large strain (1800%), optical transparency (96%), and ionic conductivity (1.62 × 10-6 S/cm). The self-healing polymer itself is intrinsically conductive without any additives or fillers, thus it is almost free of evaporation or leaking issues of traditional conducting gels. An alternating-current electroluminescent device with self-healing performance is demonstrated. It is anticipated that this strategy would provide new opportunities for the development of novel self-healing ionotronics.

Adhering Low Surface Energy Materials without Surface Pretreatment via Ion-Dipole Interactions.

Low surface energy materials resist adhesion due to their chemical inertness and non-wetting properties. Herein, we report the creation of a transparent ionogel adhesive that uses ion-dipole interactions to achieve a higher bonding performance to polytetrafluoroethylene (PTFE) relative to most commercial glues. The ionogel adhesive is composed of a poly(hexafluorobutyl acrylate-co-methyl methacrylate) random copolymer and a hydrophobic ionic liquid. The prepared ionogel can adhere to various hydrophobic substrates, such as PTFE, polypropylene, and polyethylene, as well as hydrophilic glass, ceramics, and steel. The design strategy and adhesion behavior are well interpreted using the density functional theory calculations and molecular dynamics simulations. The straightforward ultraviolet-curing method, high optical clarity, versatile adhesion ability, and reversible adhesion capabilities make this high-performance adhesive a promising product for commercialization.

Highly Transparent, Stretchable, and Conducting Ionoelastomers Based on Poly(ionic liquid)s.

The rapid development of soft electronics has revitalized the research of conducting elastomers. However, the design of conducting elastomers having high stretchability and good transparency still remains a considerable challenge. In this study, we develop a highly transparent, stretchable, and conducting ionoelastomer based on a poly(ionic liquid) in which cations are fixed to a stretchable elastomeric network and counter anions are mobile. The ionoelastomer solves the dilemma of simultaneous transparency and stretchability in the design of traditional conducting elastomers, possessing good transparency (96%) with an extraordinarily high stretchability, up to a limiting strain of 1460%. Moreover, this novel material is completely nonvolatile and nonhygroscopic, endowing the ionoelastomer with highly stable thermal, environmental, electrochemical, and mechanoelectrical properties. An underwater sensor based on the ionoelastomer is developed with good performance in an aqueous environment. Also, a transparent dielectric elastomer actuator (DEA) is demonstrated using the ionoelastomer. It is believed that the ionoelastomer would pave the way to develop exceptional conducting elastomers toward next-generation soft electronics.