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Flexible, lightweight sensors with a wide strain-sensing range are showing increasing significance in structural health monitoring compared with conventional hard sensors, which typically have a small strain range, are heavyweight, and have a large volume. In this work, salt particle precipitation and mechanical coating methods are used to fabricate porous graphene nanoplatelet (GNP)/polydimethylsiloxane (PDMS) flexible sensors for tension monitoring in structural health applications. The signal transformation through the Back Propagation (BP) algorithm is integrated to provide monitoring data that are comparable with other sensors. The results reveal that the flexible sensors with a low content of GNPs (0.1-0.25 wt%) possess better flexibility, allowing tensile strains over 200% to be measured. In addition, due to the enhanced deformation capacity of the pore structures, they can achieve high sensitivity (1-1000) under 65% strain, and a fast response time (70 ms) under 10% strain at 60 mm min-1. They also show high performance in the fatigue test (20 000 cycles) under 5% strain, and can effectively respond to bending and torsion. In addition, the sensors show an obvious response to temperature. Overall, the prepared flexible composite sensors in this work have the advantages of a wide strain-sensing range, a full-coverage conductive network, and being lightweight, and show potential for structural health monitoring in the near future.

Due to the rapid development of modern micro/nano electronic devices, polymer nanocomposites of high mechanical performance, and thermal conductivity and stability are increasingly important. We herein report a two-step process for preparation of similar to 3 nm-thick boron nitride (BN) nanosheets through noncovalent modification by a surfactant Triton X-100, which improves the compatibility of the nanosheets with the matrix as well as their dispersion. TEM micrographs demonstrated that the modified BN nanosheets (m-BN) were relatively uniformly dispersed in epoxy matrix and some were connected with each other. At 2.14 vol % of m-BN, the glass-transition temperature (T-g) and adhesive toughness of neat epoxy were improved by 17% and 355%, respectively. At 4.93 vol %, the thermal conductivity of neat epoxy was remarkably increased to 0.65 W.m(-1).k(-1), an increment of 335%. In addition, the epoxy/m-BN nanocomposites exhibited high thermal stability, which holds a potential as thermal interface materials for the next generation of electronic devices. Refereed/Peer-reviewed

Flexible electronics is expected to be one of the most active research areas in the next decade. In this study, a mechanically strong and flexible epoxy/GnP composite film was fabricated having a percolation threshold of electrical conductivity at 1.08 vol% GnPs and high thermal conductivity as 1.07 W m-1 K-1 at 10 vol% GnPs. The composite film shows high mechanical performance: Young's modulus and tensile strength were improved by 1344% and 66.7%, respectively, at 10 vol%. The film demonstrated high sensitivity to various mechanical loads: (i) it has gauge factors of 2 at strain range 0%-7% and 6 at range 7%-10%; (ii) it gives good electrical response with bending and twisting angles up to 180°; and (iii) it displays a good compressive load response up to 2 N where the absolute value of electrical resistance change increased by 71%. Furthermore, the film showed an excellent reliability up to 5.5 × 103 cycles with minor zero-point error. Above 20 °C, the film solely acts as a temperature sensor; upon cyclic temperature testing, the film demonstrated a stable resistive response in the range of 30-75 °C with a temperature sensitivity coefficient of 0.0063 °C-1. This flexible composite film has remarkable properties that enable it to be used as a full-fledged sensor for universal applications in aerospace, automotive and civil engineering. Refereed/Peer-reviewed

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5 vol%; for example, Young’s modulus, fracture toughness (K 1C ) and energy release rate (G 1C ) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58 vol% and thermal conductivity of 2.13 W m −1 K −1 at 6 vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7 MPa for neat epoxy to 13.57 MPa at 0.375 vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives. Refereed/Peer-reviewed

Thermosets possess diverse physical and chemical properties and thus they are widely used in various applications such as electronic packaging, construction, and automotive industries. However, their poor thermal conductivity and weak mechanical performance jeopardize their continual spread in modern industry. In this study, boron nitride nanosheets (BNNSs) were employed to promote both mechanical and thermal properties of epoxy nanocomposites. BNNSs and their epoxy nanocomposites were fabricated usingin situsolvent ultrasonication andin situpolymerization, respectively. Thermal conductivity was enhanced by 153% increment in epoxy/BNNS nanocomposite at 7 wt% in comparison with neat epoxy. In parallel, Young's modulus, lap shear strength, fracture toughness (K1C) and energy release rate (G1C) increased by 69%, 31%, 122% and 118%, respectively at 1 wt% BNNSs. Moreover, fatigue life and strength of lap shear joints were significantly improved upon adding BNNSs. A numerical model of the single lap shear joint was developed to validate the accuracy of the material constants obtained. Epoxy/BNNS nanocomposites exhibited an outstanding mechanical performance as well as high thermal conductivity giving them merits to widen their applications in electronic and automotive industry.

Porous functional materials play important roles in a wide variety of growing research and industrial fields. We herein report a simple, effective method to prepare porous functional graphene composites for multi-field applications. Graphene sheets were non-chemically modified by Triton®X-100, not only to maintain high structural integrity but to improve the dispersion of graphene on the pore surface of a sponge. It was found that a graphene/sponge nanocomposite at 0.79 wt.% demonstrated ideal electrical conductivity. The composite materials have high strain sensitivity, stable fatigue performance for 20,000 cycles, short response time of 0.401s and fast response to temperature and pressure. In addition, the composites are effective in monitoring materials deformation and acoustic attenuation with a maximum absorption rate 67.78% and it can be used as electrodes for a supercapacitor with capacitance of 18.1 F/g. Moreover, no expensive materials or complex equipment are required for the composite manufacturing process. This new methodology for the fabrication of multifunctional, durable and highly conductive graphene/sponge nanocomposites hold promise for many other applications. Refereed/Peer-reviewed