A supramolecular gel-elastomer system for soft iontronic adhesives.

Electroadhesion provides a promising route to augment robotic functionalities with continuous, astrictive, and reversible adhesion force. However, the lack of suitable conductive/dielectric materials and processing capabilities have impeded the integration of electroadhesive modules into soft robots requiring both mechanical compliance and robustness. We present herein an iontronic adhesive based on a dynamically crosslinked gel-elastomer system, including an ionic organohydrogel as adhesive electrodes and a resilient polyurethane with high electrostatic energy density as dielectric layers. Through supramolecular design and synthesis, the dual-material system exhibits cohesive heterolayer bonding and autonomous self-healing from damages. Iontronic soft grippers that seamlessly integrate actuation, adhesive prehension, and exteroceptive sensation are devised via additive manufacturing. The grippers can capture soft and deformable items, bear high payload under reduced voltage input, and rapidly release foreign objects in contrast to electroadhesives. Our materials and iontronic mechanisms pave the way for future advancement in adhesive-enhanced multifunctional soft devices.

Molecular-Level Methylcellulose/MXene Hybrids with Greatly Enhanced Electrochemical Actuation.

Ti3 C2 Tx MXene film is promising for electrochemical actuators due to its high electrical conductivity and volumetric capacitance. However, its actuation performance is limited by the slow ion diffusion through the film and poor mechanical property in aqueous electrolytes. Here, molecular-level methylcellulose (MC)/MXene hybrid films are assembled with obviously enlarged layer distance, improved wet strength, and ambient stability. The hybrid films show significantly higher in-plane actuation strain in a liquid electrolyte. Based on direct strain measurements, in situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) analyses, the actuation enhancement can be ascribed to the enlarged layer distance allowing more water and ions to be intercalated/de-intercalated and MC-induced sliding of MXene sheets. The assembled soft actuator has a high Young's modulus of 1.93 GPa and can be operated in air, generating a peak-to-peak strain difference up to 0.541% under a triangular wave voltage of ±1 V and a blocking force of 4.7 times its own weight.

Ionic covalent organic framework based electrolyte for fast-response ultra-low voltage electrochemical actuators.

Electrically activated soft actuators with large deformability are important for soft robotics but enhancing durability and efficiency of electrochemical actuators is challenging. Herein, we demonstrate that the actuation performance of an ionic two-dimensional covalent-organic framework based electrochemical actuator is improved through the ordered pore structure of opening up efficient ion transport routes. Specifically, the actuator shows a large peak to peak displacement (9.3 mm, ±0.5 V, 1 Hz), a fast-response time to reach equilibrium-bending (~1 s), a correspondingly high bending strain difference (0.38%), a broad response frequency (0.1-20 Hz) and excellent durability (>99%) after 23,000 cycles. The present study ascertains the functionality of soft electrolyte as bionic artificial actuators while providing ideas for expanding the limits in applications for robots.

Magnetically Directed Co-nanoinitiators for Cross-Linking Adhesives and Enhancing Mechanical Properties.

Magnetically directed localized polymerization is of immense interest for its extensive impacts and applications in numerous fields. The use of means untethered from an external magnetic field to localize initiation of polymerization to develop a curing system is a novel concept, with a sustainable, efficient, and eco-friendly approach and a wide range of potential in both science and engineering. However, the conventional means for the initiation of polymerization cannot define the desirable location of polymerization, which is often exacerbated by the poor temporal control in the curing system. Herein, the copper-immobilized dendrimer-based magnetic iron oxide silica (MNPs-G2@Cu2+) co-nanoinitiators are rationally designed as initiators for redox radical polymerization. The nanoinitiators are magnetically responsive and therefore enable localized polymerization using an external magnetic field. In this work, anaerobic polymerization of an adhesive composed of triethylene glycol dimethacrylate, tert-butyl peroxybenzoate, and MNPs-G2@Cu2+ as the magnetic co-nanoinitiators has been investigated. The use of a magnet locates and promotes redox free radical polymerization through the synergistic functions between peroxide and MNPs-G2@Cu2+ co-nanoinitiators. The mechanical properties of the resulting polymer are considerably reinforced because the MNPs-G2@Cu2+ co-nanoinitiators concurrently play another crucial role as nanofillers. This strategy provides a novel approach for magnetically tunable localized polymerization, which allows new opportunities to govern the formulation of advanced adhesives through polymerization under hazard-free conditions for various promising applications.

Printable elastomeric electrodes with sweat-enhanced conductivity for wearables.

We rationally synthesized the thermoplastic and hydrophilic poly(urethane-acrylate) (HPUA) binder for a type of printable and stretchable Ag flakes-HPUA (Ag-HPUA) electrodes in which the conductivity can be enhanced by human sweat. In the presence of human sweat, the synergistic effect of Cl- and lactic acid enables the partial removal of insulating surfactant on silver flakes and facilitates sintering of the exposed silver flakes, thus the resistance of Ag-HPUA electrodes can be notably reduced in both relaxed and stretched state. The on-body data show that the resistance of one electrode has been decreased from 3.02 to 0.62 ohm during the subject's 27-min sweating activity. A stretchable textile sweat-activated battery using Ag-HPUA electrodes as current collectors and human sweat as the electrolyte was constructed for wearable electronics. The enhanced conductivity of the wearable wiring electrode from the reaction with sweat would provide meritorious insight into the design of wearable devices.

One-Dimensional π-d Conjugated Coordination Polymer for Electrochromic Energy Storage Device with Exceptionally High Performance.

The rational design of previously unidentified materials that could realize excellent electrochemical-controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D π-d conjugated coordination polymer (Ni-BTA) is reported, consisting of metal (Ni)-containing nodes and organic linkers (1,2,4,5-benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni-BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm2 C-1), and high gravimetric capacity (168.1 mAh g-1). In particular, the Ni-BTA film can maintain its electrochemical recharge-ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni-BTA films present a great promise for Ni-BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows.

Photothermal actuated origamis based on graphene oxide-cellulose programmable bilayers.

The design and construction of 3D architectures enabled by stimuli-responsive soft materials can yield novel functionalities for next generation soft-bodied actuating devices. Apart from additive manufacturing processes, origami inspired technology offers an alternative approach to fabricate 3D actuators from planar materials. Here we report a class of near-infrared (NIR) responsive 3D active origamis that deploy, actuate and transform between multistable structural equilibria. By exploiting the nonlinear coefficient of thermal expansion (CTE) of graphene oxide (GO), graphene oxide/ethylene cellulose (GO/EC) bilayers are readily fabricated to deliver precise origami structure control, and rapid low-temperature-triggered photothermal actuation. Complexity in 3D shapes is produced through heterogeneously patterning GO domains on 2D EC thin films, which allows us to customize 3D architectures that adapt to various robotic functions. The strategy also enables the construction of material systems possessing naturally inaccessible properties, such as remotely controlled mechanical metamaterials with auxetic behavior and bionic flowers with a rapid blooming rate. Harnessing deformability with multiple degrees of freedom (DOF) upon light irradiation, this work leads to breakthroughs in the design and implementation of shape-morphing functions with soft origamis.

Encapsulation of MnS Nanocrystals into N, S-Co-doped Carbon as Anode Material for Full Cell Sodium-Ion Capacitors.

Sodium-ion capacitors (SICs) have received increasing interest for grid stationary energy storage application due to their affordability, high power, and energy densities. The major challenge for SICs is to overcome the kinetics imbalance between faradaic anode and non-faradaic cathode. To boost the Na+ reaction kinetics, the present work demonstrated a high-rate MnS-based anode by embedding the MnS nanocrystals into the N, S-co-doped carbon matrix (MnS@NSC). Benefiting from the fast pseudocapacitive Na+ storage behavior, the resulting composite exhibits extraordinary rate capability (205.6 mAh g-1 at 10 A g-1) and outstanding cycling stability without notable degradation after 2000 cycles. A prototype SIC was demonstrated using MnS@NSC anode and N-doped porous carbon (NC) cathode; the obtained hybrid SIC device can display a high energy density of 139.8 Wh kg-1 and high power density of 11,500 W kg-1, as well as excellent cyclability with 84.5% capacitance retention after 3000 cycles. The superior electrochemical performance is contributed to downsizing of MnS and encapsulation of conductive N, S-co-doped carbon matrix, which not only promote the Na+ and electrons transport, but also buffer the volume variations and maintain the structure integrity during Na+ insertion/extraction, enabling its comparable fast reaction kinetics and cyclability with NC cathode.

Ti3 C2 MXene Paper for the Effective Adsorption and Controllable Release of Aroma Molecules.

Olfactory sensing and perception play an important role in people's daily lives and greatly affects senses, emotions, and behavior. In particular, the development of the controlled release of aroma enhances human's well-being and strengthens interactions with surroundings through olfactory display, especial when combined with visual and audial cues. Here, Ti3 C2 MXene plays a dual-function role as the adsorption site of aroma molecules and the heating source for the controlled release of aroma molecules. Due to abundant termination groups on the surface and the metallic nature, Ti3 C2 MXene provides abundant active sites for the interaction with aroma molecules; simultaneously, MXene can be electrically heated to thermally desorb the aroma molecules from the interaction sites. This approach eliminates the interface incompatibility issues between the heating source and the molecular encapsulation layer in conventional olfactory display system. This work presents the controlled release of the aroma molecule phenethyl alcohol (PA) using Ti3 C2 MXene paper. Ti3 C2 MXene paper serves as the adsorption material and a heating source that achieves 100 °C within 1 s. The relative amount of PA released reaches nearly 100% after 1 min of heating.

Leaf-inspired multiresponsive MXene-based actuator for programmable smart devices.

Natural leaves, with elaborate architectures and functional components, harvest and convert solar energy into chemical fuels that can be converted into energy based on photosynthesis. The energy produced leads to work done that inspired many autonomous systems such as light-triggered motion. On the basis of this nature-inspired phenomenon, we report an unprecedented bilayer-structured actuator based on MXene (Ti3C2T x )-cellulose composites (MXCC) and polycarbonate membrane, which mimic not only the sophisticated leaf structure but also the energy-harvesting and conversion capabilities. The bilayer actuator features multiresponsiveness, low-power actuation, fast actuation speed, large-shape deformation, programmable adaptability, robust stability, and low-cost facile fabrication, which are highly desirable for modern soft actuator systems. We believe that these adaptive soft systems are attractive in a wide range of revolutionary technologies such as soft robots, smart switch, information encryption, infrared dynamic display, camouflage, and temperature regulation, as well as human-machine interface such as haptics.