Yongju Gao

In situ polymerization of mechanically reinforced, thermally healable graphene oxide/polyurethane composites based on Diels–Alder chemistry

Covalently bonded graphene oxide/polyurethane (GO/PU) composites with significant reinforcement and thermally healable properties were developed via in situ polymerization based on Diels–Alder (DA) chemistry. The PU prepolymer was prepared with GO, 4,4-diphenylmethane diisocyanate, and poly(tetramethylene glycol) and blocked by using furfuryl alcohol firstly. Then the prepolymer was cross-linked by using bifunctional maleimide via DA chemistry. SEM shows that the GO was dispersed uniformly in the PU matrix. The DA and retro-DA reactions were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry separately. Tensile tests showed that with the incorporation of 0.1 wt% of GO, the tensile modulus of GO/PU composites increased from 9.80 MPa to 21.95 MPa, and the tensile strength and elongation at break of the GO/PU composites increased by more than 367% and 210%, respectively. Furthermore, the composites had thermally healable ability which was inspected by using an atomic force microscope and the strain–stress test. The healing efficiency of 78% on average was achieved which was determined by the recovery of breaking stress and a healing mechanism was tentatively proposed. Therefore, the covalently bonded self-healing GO/PU composites could be used as smart materials and structural materials.

Strain-Driven and Ultrasensitive Resistive Sensor/Switch Based on Conductive Alginate/Nitrogen-Doped Carbon-Nanotube-Supported Ag Hybrid Aerogels with Pyramid Design

Flexible strain-driven sensor is an essential component in the flexible electronics. Especially, high durability and sensitivity to strain are required. Here, we present an efficient and low-cost fabrication strategy to construct a highly sensitive and flexible pressure sensor based on a conductive, elastic aerogel with pyramid design. When pressure is loaded, the contact area between the interfaces of the conductive aerogel and the copper electrode as well as among the building blocks of the nitrogen-doped carbon-nanotube-supported Ag (N-CNTs/Ag) aerogel monoliths, changes in reversible and directional manners. This contact resistance mechanism enables the hybrid aerogels to act as strain-driven sensors with high sensitivity and excellent on/off swithching behavior, and the gauge factor (GF) is ∼15 under strain of 3%, which is superior to those reported for other aerogels. In addition, robust, elastomeric and conductive nanocomposites can be fabricated by injecting polydimethylsiloxane (PDMS) into alginate/N-CNTs/Ag aerogels. Importantly, the building blocks forming the aerogels retain their initial contact and percolation after undergoing large-strain deformation, PDMS infiltration, and cross-linking of PDMS, suggesting their potential applications as strain sensors.

A facile method to prepare highly compressible three-dimensional graphene-only sponge

Endowing graphene sponge with compressibility and conductivity offers the possibility to regenerate piezoresistivity and is therefore of great interest in the field of sensors. In this work, highly compressible three-dimensional graphene-only sponge (CGS) was prepared through a facile method by using ammonium sulfide and ammonia solutions under mild conditions. The morphologies and microstructures of the as-prepared CGSs can be controlled by adjusting the mass ratio of graphene oxide (GO) to ammonium sulfide which changed from a metallic sheen bulk with a leaf-shaped structure to a black sponge with a porous structure. Besides, by simply changing the concentrations of GO, CGSs with different porosity, conductivity as well as mechanical strength were obtained. Moreover, the resultant CGSs show ultralow density (as low as 4.9 mg cm−3), high porosity (as much as 99.8%), great compressibility (as much as the strain of 80%), and excellent stability (100 cycles) during compression. Furthermore, the sensitive variation of electrical resistance and cycle stability was validated under the compressive strain of 50% which make CGSs great candidates for pressure-responsive sensors, elastic conductors and other applications.

Percolation threshold-inspired design of hierarchical multiscale hybrid architectures based on carbon nanotubes and silver nanoparticles for stretchable and printable electronics

Conductive elastomers, an irreplaceable component of stretchable electronics, have recently gained significant attention. Herein, we report highly conductive, sensitive, stretchable, and fully printed hybrid composites comprising carbon nanotubes (CNTs), silver nanoparticles (Ag NPs) and hydroxyl-poly(styrene-block-butadiene-block-styrene) (OH-SBS) polymers. The electrically conductive composites are fabricated via direct evaporation of CNT-dispersed OH-SBS suspension under mild heating conditions, followed via an iterative process of silver precursor absorption and reduction, generating large amounts of Ag NPs on both the surface and inner regions of the CNT-embedded composites. The obtained CNT–Ag NP embedded composites possess a superior electrical conductivity of 1228 S cm−1, a high break elongation of 540%, and a high gauge factor of 26 500. The unique hierarchical multiscale hybrid architecture of CNT–Ag NPs and the utilization of OH-SBS enable the as-prepared composites to exhibit huge piezoresistive behavior with a broad range of tensile strains. Moreover, handwritten electric circuits with diverse geometries are designed, and the printed strain gauge sensor could successfully detect sign language via its strain-sensing behavior. We believe that our hierarchical multiscale hybrid design could pave the way for the simple fabrication of stretchable circuits for wearable electronics.

Binary Synergistic Sensitivity Strengthening of Bioinspired Hierarchical Architectures based on Fragmentized Reduced Graphene Oxide Sponge and Silver Nanoparticles for Strain Sensors and Beyond

Recently, stretchable electronics have been highly desirable in the Internet of Things and electronic skins. Herein, an innovative and cost-efficient strategy is demonstrated to fabricate highly sensitive, stretchable, and conductive strain-sensing platforms inspired by the geometries of a spiders slit organ and a lobsters shell. The electrically conductive composites are fabricated via embedding the 3D percolation networks of fragmentized graphene sponges (FGS) in poly(styrene-block-butadiene-block-styrene) (SBS) matrix, followed by an iterative process of silver precursor absorption and reduction. The slit- and scale-like structures and hybrid conductive blocks of FGS and Ag nanoparticles (NPs) provide the obtained FGS-Ag-NP-embedded composites with superior electrical conductivity of 1521 S cm-1 , high break elongation of 680%, a wide sensing range of up to 120% strain, high sensitivity of ≈107 at a strain of 120%, fast response time of ≈20 ms, as well as excellent reliability and stability of 2000 cycles. This huge stretchability and sensitivity is attributed to the combination of high stretchability of SBS and the binary synergistic effects of designed FGS architectures and Ag NPs. Moreover, the FGS/SBS/Ag composites can be employed as wearable sensors to detect the modes of finger motions successfully, and patterned conductive interconnects for flexible arrays of light-emitting diodes.

Layer-by-Layer Assembly of Multifunctional Porous N-Doped Carbon Nanotube Hybrid Architectures for Flexible Conductors and Beyond

Coassemble diverse functional nanomaterials with carbon nanotubes (CNTs) to form three-dimensional (3D) porous CNTs hybrid architectures (CHAs) are potentially desirable for applications in energy storage, flexible conductors, and catalysis, because of diverse functionalities and synergistic effects in the CHAs. Herein, we report a scalable strategy to incorporate various functional nanomaterials with N-doped CNTs (N-CNTs) into such 3D porous CHAs on the polyurethane (PU) sponge skeletons via layer-by-layer (LbL) assembly. To investigate their properties and applications, the specific CHAs based on N-CNTs and Ag nanoparticles (NPs), denoted as PU-(N-CNTs/Ag NPs)n, are developed. The unique binary structure enables these specific CHAs conductors to possess reliable mechanical and electrical performance under various elastic deformations as well as excellent hydrophilicity. Moreover, they are employed as strain-gauge sensor and heterogeneous catalyst, respectively. The sensor could detect continuous signal, static signal, and pulse signal with superior sustainability and reversibility, indicating an important branch of electromechanical devices. Furthermore, the synergistic effects among N-CNTs, Ag NPs, and porous structure endow the CHAs with excellent performance in catalysis. We have a great expectation that LbL assembly can afford a universal route for incorporating diverse functional materials into one structure.

In situ synthesis of silver nanostructures on magnetic Fe3O4@organosilicon microparticles for rapid hydrogenation catalysis

A novel protocol to prepare multifunctional magnetic organic–inorganic nanostructured catalysts of Fe3O4@organosilicon/Ag with tailored properties is developed. Such nanostructure design endows the catalysts with superparamagnetism (11.6 emu g−1), excellent oxidation resistance, and catalytic activity. Fe3O4 nanoparticles (NPs) are encapsulated with porous organosilicon via improved self-assembly of a flexible-bridged organosilicon precursor without templates. Subsequently, dispersed Ag NPs are in situ grown on the porous microparticles via a silver mirror reaction. The as-prepared multifunctional catalysts are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, a vibration sample magnetometer, X-ray diffraction, thermal gravimetric analysis, and nitrogen adsorption and desorption, respectively. The resultant hybrid microparticles possess micro- and nano-pores, and exhibit a small hysteresis loop and low coercivity. Meaningfully, they exhibit exceptional catalytic performance for the reduction of 4-nitrophenol in the presence of sodium borohydride and could be reused at least 9 times with excellent stability by means of convenient magnetic separation. The catalysts could be employed to reduce other dyes such as methylene blue, orange G and rhodamine B, and their corresponding reductions follow pseudo-first-order reactions. Therefore, the proposed structure design and scalable route for the synthesis of hierarchical catalysts can pave the way for synthesizing other catalyst systems to address the diverse reaction demands.

Novel adamantane-based periodic mesoporous organosilica film with ultralow dielectric constant and high mechanical strength

AbstractIn this work, a novel bridged organosilane precursor, adamantane-bridged organosilane (ADBO), was synthesized successfully which was employed to prepare adamantane-based (ADH-based) periodic mesoporous organosilica (PMO) thin film in the presence of porogen and acid catalyst via evaporation-induced self-assembly (EISA) after spin-coating procedure. The resultant ADH-based PMO thin films were characterized by FTIR, NMR, TEM, and small-angle XRD. The ADH-based PMO thin film with weight ratio of porogen to ADBO (0.75:1) possesses low dielectric constant (1.55 ± 0.04@1 MHz), excellent Young’s modulus (6.69 ± 0.54 GPa), and ideal hydrophobic property (90.2° of water contact angle) simultaneously. These outstanding properties of ADH-based PMO film can be ascribed to lower polarity, lower density, and rigid cavity structure of adamantane, which suggests its potential application as high-performance low-κ material in next-generation microelectronics.