Zwitterionic Eutectogel-Based Wearable Strain Sensor with Superior Stretchability, Self-Healing, Self-Adhesion, and Wide Temperature Tolerance

Ionic conductive eutectogels have great application prospects in wearable strain sensors owing to their temperature tolerance, simplicity, and low cost. Eutectogels prepared by cross-linking polymers have good tensile properties, strong self-healing capacities, and excellent surface-adaptive adhesion. Herein, we emphasize for the first time the potential of zwitterionic deep eutectic solvents (DESs), in which betaine is a hydrogen bond acceptor. Polymeric zwitterionic eutectogels were prepared by directly polymerizing acrylamide in zwitterionic DESs. The obtained eutectogels owned excellent ionic conductivity (0.23 mS cm^-1), superior stretchability (approximately 1400% elongation), self-healing (82.01%), self-adhesion, and wide temperature tolerance. Accordingly, the zwitterionic eutectogel was successfully applied in wearable self-adhesive strain sensors, which can adhere to skins and monitor body motions with high sensitivity and excellent cyclic stability over a wide temperature range (-80 to 80 °C). Moreover, this strain sensor owned an appealing sensing function on bidirectional monitoring. The findings in this work can pave the way for the design of soft materials with versatility and environmental adaptation.

Printed Directional Bending Sensor with High Sensitivity and Low Hysteresis for Human Motion Detection and Soft Robotic Perception

We present a high-performance flexible bending strain sensor for directional motion detection of human hands and soft robotic grippers. The sensor was fabricated using a printable porous conductive composite composed of polydimethylsiloxane (PDMS) and carbon black (CB). The utilization of a deep eutectic solvent (DES) in the ink formulation induced a phase segregation between the CB and PDMS and led to a porous structure inside the printed films after being vapored. This simple and spontaneously formed conductive architecture provided superior directional bend-sensing characteristics compared to conventional random composites. The resulting flexible bending sensors displayed high bidirectional sensitivity (gauge factor of 45.6 under compressive bending and 35.2 under tensile bending), negligible hysteresis, good linearity (>0.99), and excellent bending durability (over 10,000 cycles). The multifunctional applications of these sensors, including human motion detection, object-shape monitoring, and robotic perceptions, are demonstrated as a proof-of-concept.

Self-Assembled Copper Metallogel Bearing Terpyridine and Its Application as a Catalyst for the Click Reaction in Water

Metallogels have attracted a great deal of interest because of their intriguing properties and applications in chemsensors, batteries, catalysis, and other fields. In this work, a novel ligand bearing terpyridine and hydroxyamine units was designed and synthesized. The ligand selectively gelated with copper ions in water by heating and cooling or sonication. Different physicochemical studies [Fourier transform infrared, ultraviolet-visible (UV-vis), electron paramagnetic resonance (EPR), scanning electron microscopy, X-ray diffraction, and rheology] were conducted to characterize the gels. We show that coordination interaction, π-π interaction, and noncovalent interaction had obvious effects on the properties of the gel. Additionally, a stable radical hydrogel could be obtained by ultrasound treatment, which was accompanied by color variation from green to blue. This was further confirmed by UV-vis and EPR experiments. Furthermore, the copper metallogels were developed as catalysts for the preparation of 1,2,3-triazole derivatives in water at 25 °C. Although various types of catalysts have been investigated, the use of metallogels as catalysts for the click reaction in water has been scarce. This strategy shows the process is simple, affords a high yield, and is "green" and economical.

Universal Alignment of Graphene Oxide in Suspensions and Fibers

Graphene oxide (GO) has become a key component for high-performance carbon-based films or fibers based on its dispersibility and liquid crystallinity in an aqueous suspension. While the superior performance of GO-based fiber relies on their alignment at the submicrometer level, fine control of the microstructure is often hampered, in particular, under dynamic nature of GO-processing involving shear. Here, we systemically studied the structural variation of GO suspensions under shear conditions via in situ rheo-scattering and shear-polarized optical microscope analysis. The evolution of GO alignment under shear is indeed complex. However, we found that the shear-dependent structural equilibrium exists. GO showed a nonlinear structural transition with shear, yet there is a "universal" shear threshold for the best alignment, resulting in graphene fiber achieved an improvement in mechanical properties by ∼54% without any chemical modification. This finding challenges the conventional concept that high shear stress is required for the good alignment of particles and their best performance.

Strong-Induced CPL Emission Promoted from Achiral Conjugated Polymer-Containing Emissive Nematic Liquid Crystals (P-N*-LCs)

With the rapid development on 3D printing technology, more and more works have been devoted to 3D display. 3D display will really come true by using circularly polarized luminescence (CPL)-active materials with both high quantum yield and dissymmetry factor (g_em ) in organic light-emitting diode or liquid crystals (LCs). But so far most of these CPL materials cannot meet the real application requirement because of the low g_em values in the range of 10^-5 -10^-2 . In this paper, ternary chiral emissive LCs (P-N*-LCs) is designed by doping chiral binaphthyl-based enantiomers as chiral dopant (Guest 1) and achiral conjugated polymer as induced CPL emitter (Guest 2) into nematic liquid crystal (N-LCs) Host 5CB. Both Guest 1 and Guest 2 show excellent compatibility with Host 5CB. The obtained ternary P-N*-LCs can emit strong-induced CPL signal with g_em up to 1.12 and Ф_FL up to 66.1%. This work first develops a new strategy for the smart design of excellent CPL materials from versatile achiral conjugation fluorescence polymers.

Self-Assembly of Topologically Networked Protein-Ti3C2Tx MXene Composites

Hierarchical organization plays an important role in the stunning physical properties of natural and synthetic composites. Limits on the physical properties of such composites are generally defined by percolation theory and can be systematically altered using the volumetric filler fraction of the inorganic/organic phase. In natural composites, organic materials such as proteins that interact with inorganic filler materials can further alter the hierarchical order and organization of the composite via topological interactions, expanding the limits of the physical properties defined by percolation theory. However, existing polymer systems do not offer a topological parameter that can systematically modulate the assembly characteristics of composites. Here, we present a composite based on proteins and titanium carbide (Ti₃C₂T_x) MXene that manifests a topological network that regulates the organization, and hence physical properties, of these biomimetic composites. We designed, recombinantly expressed, and purified synthetic proteins consisting of polypeptides with repeating amino acid sequences (tandem repeats) that have the ability to self-assemble into topologically networked biomaterials. We demonstrated that the interlayer distance between MXene sheets can be controlled systematically by the number of tandem repeat units. We varied the filler fraction and number of tandem repeat units to regulate the in-plane and out-of-plane electrical conductivities of these composites. Once Ti₃C₂T_x MXene sheets are separated enough to facilitate formation of cross-links in our proteins with the number of tandem repeat units reaching 11, the linear I-V characteristics of the composites switched into nonlinear I-V curves with a distinct hysteresis for out-of-plane electron transport, while the in-plane I-V characteristics remained linear. This highlights the impact of synthetic protein templates, which can be designed to modulate electronic transport in composites both isotropically and anisotropically.

Predicting whether aromatic molecules would prefer to enter a carbon nanotube: A density functional theory study

The interaction of a carbon nanotube (CNT) with various aromatic molecules, such as aniline, benzophenone, and diphenylamine, was studied using density functional theory able to compute intermolecular weak interactions (B3LYP-D3). CNTs of varying lengths were used, such as 4-CNT, 6-CNT, and 8-CNT (the numbers denoting relative lengths), with the lengths being chosen appropriately to save computation times. All aromatic molecules were found to exhibit strong intermolecular binding energies with the inner surface of the CNT, rather than the outer surface. Hydrogen bonding between two aromatic molecules that include N and O atoms is shown to further stabilize the intermolecular adsorption process. Therefore, when benzophenone and diphenylamine were simultaneously allowed to interact with a CNT, the aromatic molecules were expected to preferably enter the CNT. Furthermore, additional calculations of the intermolecular adsorption energy for aniline adsorbed on a graphene surface showed that the concavity of graphene-like carbon sheet is in proportion to the intermolecular binding energy between the graphene-like carbon sheet and the aromatic molecule.

Carbon Nanotube Chemical Sensors

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Planting carbon nanotubes onto supramolecular polymer matrices for waterproof non-contact self-healing

Supramolecular polymers show unique and excellent properties due to the reversible and designable nature of the non-covalent interactions. Herein, ureido-pyrimidinone (UPy)-based supramolecular polymers were employed to fabricate the thermo-responsive composite materials with multi-walled carbon nanotubes (MWCNTs) by planting the MWCNTs onto the supramolecular polymer matrices via a simple surface spraying procedure. The MWCNTs coating on the surface of the supramolecular polymer matrices gave the composite film superhydrophobic and conductive properties, and it had a non-contact healable ability underwater under 808 nm near-infrared light (NIR) irradiation. Moreover, the UPy-based supramolecular polymers acted as thermo-responsive matrices to guarantee the self-healing properties at a relatively low temperature, such as body temperature (33 °C-34 °C). The supramolecular polymer/MWCNTs composite materials exhibited excellent strain sensitivities and could be used to prepare human motion-monitoring devices. This line of research may find a promising practical application in healable wearable devices used in underwater environments.

Beyond Covalent Crosslinks: Applications of Supramolecular Gels

Traditionally, gels have been defined by their covalently cross-linked polymer networks. Supramolecular gels challenge this framework by relying on non-covalent interactions for self-organization into hierarchical structures. This class of materials offers a variety of novel and exciting potential applications. This review draws together recent advances in supramolecular gels with an emphasis on their proposed uses as optoelectronic, energy, biomedical, and biological materials. Additional special topics reviewed include environmental remediation, participation in synthesis procedures, and other industrial uses. The examples presented here demonstrate unique benefits of supramolecular gels, including tunability, processability, and self-healing capability, enabling a new approach to solve engineering challenges.