An ultra-soft conductive elastomer for multifunctional tactile sensors with high range and sensitivity.

Flexible tactile sensors have become important as essential tools for facilitating human and object interactions. However, the materials utilized for the electrodes of capacitive tactile sensors often cannot simultaneously exhibit high conductivity, low modulus, and strong adhesiveness. This limitation restricts their application on flexible interfaces and results in device failure due to mechanical mismatch. Herein, we report an ultra-low modulus, highly conductive, and adhesive elastomer and utilize it to fabricate a microstructure-coupled multifunctional flexible tactile sensor. We prepare a supramolecular conductive composite film (SCCF) as the electrode of the tactile sensor using a supramolecular deep eutectic solvent, polyvinyl alcohol (PVA) solution, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and MXene suspension. We employ a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) film containing 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM:TFSI) as the dielectric layer to fabricate capacitive sensors with an electrical double layer structure. Furthermore, we enhance the performance of the device by incorporating coupled pyramid and dome microstructures, which endow the sensor with multi-directional force detection. Our SCCF exhibits extremely high conductivity (reaching 710 S cm-1), ultra-low modulus (0.8 MPa), and excellent interface adhesion strength (>120 J m-2). Additionally, due to the outstanding conductivity and unique structure of the SCCF, it possesses remarkable electromagnetic shielding ability (>50 dB). Moreover, our device demonstrates a high sensitivity of up to 1756 kPa-1 and a wide working range reaching 400 kPa, combining these attributes with the requirements of an ultra-soft human-machine interface to ensure optimal contact between the sensor and interface materials. This innovative and flexible tactile sensor holds great promise and potential for addressing various and complex demands of human-machine interaction.

Bioinspired electrically stable, optically tunable thermal management electronic skin via interfacial self-assembly.

The skin is the largest organ in the human body and serves vital functions such as sensation, thermal management, and protection. While electronic skin (E-skin) has made significant progress in sensory functions, achieving adaptive thermal management akin to human skin has remained a challenge. Drawing inspiration from squid skin, we have developed a hybrid electronic-photonic skin (hEP-skin) using an elastomer semi-embedded with aligned silver nanowires through interfacial self-assembly. With mechanically adjustable optical properties, the hEP-skin demonstrates adaptive thermal management abilities, warming in the range of +3.5°C for heat preservation and cooling in the range of -4.2°C for passive cooling. Furthermore, it exhibits an ultra-stable high electrical conductivity of âˆ¼4.5×104 S/cm, even under stretching, bending or torsional deformations over 10,000 cycles. As a proof of demonstration, the hEP-skin successfully integrates stretchable light-emitting electronic skin with adaptive thermal management photonic skin.

A Review of the Carbon-Based Solid Transducing Layer for Ion-Selective Electrodes.

As one of the key components of solid-contact ion-selective electrodes (SC-ISEs), the SC layer plays a crucial role in electrode performance. Carbon materials, known for their efficient ion-electron signal conversion, chemical stability, and low cost, are considered ideal materials for solid-state transducing layers. In this review, the application of different types of carbon materials in SC-ISEs (from 2007 to 2023) has been comprehensively summarized and discussed. Representative carbon-based materials for the fabrication of SC-ISEs have been systematically outlined, and the influence of the structural characteristics of carbon materials on achieving excellent performance has been emphasized. Finally, the persistent challenges and potential opportunities are also highlighted and discussed, aiming to inspire the design and fabrication of next-generation SC-ISEs with multifunctional composite carbon materials in the future.

Highly sensitive, wide-pressure and low-frequency characterized pressure sensor based on piezoresistive-piezoelectric coupling effects in porous wood.

Lightweight and highly compressible materials have received considerable attention in flexible pressure sensing devices. In this study, a series of porous woods (PWs) are produced by chemical removal of lignin and hemicellulose from natural wood by tuning treatment time from 0 to 15 h and extra oxidation through H2O2. The prepared PWs with apparent densities varying from 95.9 to 46.16 mg/cm3 tend to form a wave-shaped interwoven structure with improved compressibility (up to 91.89 % strain under 100 kPa). The sensor assembled from PW with treatment time of 12 h (PW-12) exhibits the optimal piezoresistive-piezoelectric coupling sensing properties. For the piezoresistive properties, it has high stress sensitivity of 15.14 kPa-1, covering a wide linear working pressure range of 0.06-100 kPa. For its piezoelectric potential, PW-12 shows a sensitivity of 0.443 V·kPa-1 with ultralow frequency detection as low as 0.0028 Hz, and good cyclability over 60,000 cycles under 0.41 Hz. The nature-derived all-wood pressure sensor shows obvious superiority in the flexibility for power supply requirement. More importantly, it presents fully decoupled signals without cross-talks in the dual-sensing functionality. Sensor like this is capable of monitoring various dynamic human motions, making it an extremely promising candidate for the next generation artificial intelligence products.

Salt-induced ductilization and strain-insensitive resistance of an intrinsically conducting polymer.

High mechanical ductility and high mechanical strength are important for materials including polymers. Current methods to increase the ductility of polymers such as plasticization always cause a remarkable drop in the ultimate tensile strength. There is no report on the ductilization of polymers that can notably increase the elongation at break while not lowering the ultimate tensile strength. Here, we report the salt-induced ductilization of an intrinsically conducting polymer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS). Treating highly conductive PEDOT:PSS with a salt such as sodium perchlorate can enhance its elongation at break from 8.5 to 53.2%, whereas it hardly affects the tensile strength. Moreover, the resistance of the ductilized PEDOT:PSS films is insensitive to the tensile strain before fracture and slightly increases by only ~6% during the cyclic tensile testing with the strain up to 30%. These effects are ascribed to the decrease in the Coulomb attraction between PEDOT+ and PSS- by the salt ions.

Micropatterning of polymer substrates for cell culture.

The cell microenvironment such as substrate topology plays an important role in biological processes. In this study, microgrooves were successfully produced on surfaces of both thermoplastic and thermoset polymers using cost-effective techniques for mass production. The micropatterning of thermoplastic polystyrene (PS) petri dish was accomplished efficiently using an in-house developed low-cost hot embossing system. The high replication fidelity of the microgroove with depth and width of 2 µm and spacing of 2 µm was achieved by using silicone rubber as a soft counter mold. This patterned petri dish subsequently served as the cast to replicate the micropattern onto thermoset polydimethylsiloxane (PDMS). It was found that the micropattern increased the hydrophobicity of both PS and PDMS surfaces. The effect of the substrate micropattern on cellular behaviors was preliminarily investigated with untreated and treated PS petri dish as well as PDMS. The results show that the micropattern significantly improved cell adhesion and proliferation for cells cultured on untreated PS petri dish and PDMS substrates. Moreover, the micropattern induced obvious cell alignment along the microgrooves for culturing on all substrates which were studied.

Strategies for Stabilization of Zn Anodes for Aqueous Zn-Based Batteries: A Mini Review.

In recent years, thanks to the investigation of the in-depth mechanism, novel cathode material exploitation, and electrolyte optimization, the electrochemical performance of rechargeable Zn-based batteries (RZBs) has been significantly improved. Nevertheless, there are still some persistent challenges locating the instability of the Zn anodes that hinder the commercialization and industrialization of RZBs, especially the obstinate dendrites and hydrogen evolution reaction (HER) on Zn anodes, which will dramatically compromise the cycle stability and Coulombic efficiency. Therefore, various strategies with fundamental design principles focusing on the suppression of dendrite and the HER have been carefully summarized and categorized in this review, which are critically dissected according to the intrinsic mechanisms. Finally, pertinent insights into the challenges and perspectives on the future development of Zn anodes are also emphasized, expecting to supply potential research directions to promote the practical applications of RZBs.

Biocompatible Conductive Polymers with High Conductivity and High Stretchability.

Stretchable electronic materials have drawn strong interest due to their important applications in areas such as bioelectronics, wearable devices, and soft robotics. The stretchable electrode is an integral unit of stretchable systems. Intrinsically conductive polymers such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can have high mechanical flexibility and good biocompatibility. However, their electrical conductivity and mechanical stretchability should be greatly improved for its applications as the stretchable electrode. Here, we report highly conductive and highly stretchable PEDOT:PSS by incorporating biocompatible d-sorbitol. d-Sorbitol can serve as both the secondary dopant and plasticizer for PEDOT:PSS. It can not only significantly improve the conductivity but also the stretchability. d-Sorbitol-PEDOT:PSS (s-PEDOT:PSS) can have a conductivity of >1000 S/cm, and the conductivity could be maintained at a strain up to 60%. The resistance of s-PEDOT:PSS remains almost constant during repeated stretching-releasing cycles. The mechanism for the stretchability improvement by d-sorbitol is ascribed to the softening of PSSH chains. d-Sorbitol can position among the PSSH chains and thus destructs the hydrogen bonds among the PSSH chains. This makes the conformational change of the PSSH chains under stress become easy and thus increases the mechanical flexibility of PEDOT:PSS. This conductivity is the highest for biocompatible intrinsically conductive polymers with high stretchability.

Effect of Thiolated Ligands in Au Nanowire Synthesis.

Thiolated ligands are seldom used as morphology-directing reagent in the synthesis of Au nanostructures due to their low selectivity toward the different facets. Recently, we developed a thiolated ligands-induced synthesis of nanowires where the selective Au deposition only occurs at the ligand-deficient Au-substrate interface. Herein, the structural effect of thiolated ligands in this active surface growth is systematically investigated. It is revealed that their ability of rendering surface is closely related to the molecular structure. Ligands with aromatic backbones are capable of inducing nanowire formation, whereas those with aliphatic backbones cannot, likely because the former can pack better at short time scale of the rapid growth. The substituents of the ligands are critical for the colloidal stability of the final structure. It is further demonstrated that aromatic and aliphatic ligands could be mixed to turn on the continual lateral growth, leading to nanowires with tapered ends. The ligand generality in this growth mode also allows the creation of superhydrophobic surface, with the nanowire forest providing the nanoscale surface roughness and the hydrophobic ligand offering the surface property. These applications of the thiolated ligands in the nanosynthesis open a new approach for controlled synthesis of Au-based nanostructures with various morphologies and properties.

Exploiting Rayleigh Instability in Creating Parallel Au Nanowires with Exotic Arrangements.

New types of nanowire arrangements are explored via active surface growth, where the use of Au seeds at room temperature means that the seed shape has major impacts on the subsequent nanowire growth. When Au nanorods are used as seeds, the original stripe-shape contact line with the substrate (the active surface) splits into a series of circular dots as the result of Rayleigh instability, giving coplanar nanowire bundles. The influence of a solid system by Rayleigh instability is exceptional, permitted by the dynamic active surface. The splitting is driven by the tendency to minimize the surface of the newly emerged nanowire section, whereas Rayleigh instability is responsible for overcoming the kinetic barriers. As a result, the average distance between the nanowires is only a few nanometers, much smaller than conventional lithographic methods. Conical and tubular bundles of nanowires are formed at low seed density, where the excessive growth material available for each seed leads to expansion and splitting of the active surface under the influence of both the diffusion limited growth and Rayleigh instability. Further designs of nanowire-based Au architectures demonstrate the feasibility of combining the multiple control of the system for new synthetic advances.

General methodology of using oil-in-water and water-in-oil emulsions for coiling nanofilaments.

Hydrophobic carbon nanotubes (CNTs) and hydrophilic nanofilaments such as oxidized CNTs, Pd nanowires (NWs), and MnO(2) NWs are transformed from wires to rings by a general methodology. We show that both oil-in-water and water-in-oil emulsions, so long as their droplet size is sufficiently small, can exert significant force to the entrapped nanostructures, causing their deformation. This effect can be easily achieved by simply mixing a few solutions in correct ratios. Even preformed oil droplets can take in CNTs from the aqueous solution converting them into rings, indicating the important role of thermodynamics: The question here is not if the droplets can exert sufficient force to bend the nanofilaments, because their random vibration may be already doing it. As long as the difference in solvation energy is large enough for a nanofilament, it would "want" to move away from the bulk solution and fit inside tiny droplets, even at the cost of induced strain energy. That said, the specific interactions between a droplet and a filament are also of importance. For example, when an oil droplet rapidly shrinks in size, it can compress the entrapped CNTs in multiple stages into structures with higher curvatures (thus higher strain) than that of a circular ring, which has minimal induced strain inside a spherical droplet.

Effect of carbon nanotubes and processing methods on the properties of carbon nanotube/polypropylene composites.

The effect of multi-walled carbon nanotubes (MWCNTs) and processing methods on the morphological, crystalline, dynamic mechanical, mechanical and electrical properties of MWCNT/polypropylene (PP) composites has been investigated by using field emission scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile and electric conductivity tests. The MWCNTs have been functionalized covalently and noncovalently for better dispersion in the PP matrix. A homogeneous dispersion of MWCNTs was achieved in the PP matrix as evidenced by scanning electron microscopy. Differential scanning calorimetric (DSC) results confirmed that the incorporation of the MWCNTs effectively enhanced the crystallization of the PP matrix through heterogeneous nucleation. The glass transition temperature increased from 8 degrees C for the pure PP to 26 degrees C for the composite with 10 wt% MWCNT-COOH. The present investigation revealed that the mechanical, thermal as well as electrical properties of carbon nanotubes filled polymer composites were strongly dependent on the state of dispersion, mixing and processing methods.

Fabrication and characterization of carbon nanotube reinforced poly(methyl methacrylate) nanocomposites.

Multiwall carbon nanotube (CNT) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been successfully fabricated with melt blending. Two melt blending approaches of batch mixing and continuous extrusion have been used and the properties of the derived nanocomposites have been compared. The interaction of PMMA and CNTs, which is crucial to greatly improve the polymer properties, has been physically enhanced by adding a third party of poly(vinylidene fluoride) (PVDF) compatibilizer. It is found that the electrical threshold for both PMMA/CNT and PMMA/PVDF/CNT nanocomposites lies between 0.5 to 1 wt% of CNTs. The thermal and mechanical properties of the nanocomposites increase with CNTs and they are further increased by the addition of PVDF For 5 wt% CNT reinforced PMMA/PVDF/CNT nanocomposite, the onset of decomposition temperature is about 17 degrees C higher and elastic modulus is about 19.5% higher than those of neat PMMA. Rheological study also shows that the CNTs incorporated in the PMMA/PVDF/CNT nanocomposites act as physical cross-linkers.

Study of rheological properties of polypropylene/organoclay hybrid materials.

Polypropylene nanocomposites reinforced with organic modified montmorillonite clay have been fabricated by melt compounding using extrusion. The morphology of the composites is studied with transmission electron microscopy and X-ray diffraction. The melt-state rheological properties of the nanocomposites have been investigated as a function of temperature and organoclay loading. It is found that the organoclays are intercalated and dispersed evenly in the matrix. The storage and loss moduli of the hybrid composites decrease with temperature and increase with organoclay concentration. Both polypropylene and its composites demonstrate a melt-like rheological behavior, indicating the low degree of exfoliation of the organoclay. A shear thinning behavior is found for both polypropylene and its composites, but the onset of shear thinning for organoclay composites occurs at lower shear rates.