Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Two dimensional hexagonal boron nitride (2D-hBN), an isomorph of graphene with a very similar layered structure, is uniquely featured by its exotic opto-electrical properties together with mechanical robustness, thermal stability, and chemical inertness. It is thus extensively studied for application in field effect transistors (FETs), tunneling devices, deep UV emitters and detectors, photoelectric devices, and nanofillers. 2D-hBN is considered as one of the most promising materials that can be integrated with other 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), for the next generation microelectronic and other technologies. Although it is by itself an insulator, it can well be tuned by several strategies in terms of properties and functionalities, such as by doping, substitution, functionalization and hybridization, making 2D-hBN a truly versatile type of functional materials for a wide range of applications. In this review, the distinct structural characteristics of 2D-hBN, doping- and defect-induced variations in energy bands and structures, and resultant properties, are presented. There are a wide variety of processing routes that have been developed for 2D-hBN, including also those for doping, substitution, functionalization and combination with other materials to form heterostructures or h-BNC hybrid nanosheets, which are systematically elaborated for novel functions. The comprehensive overview provides the types of the state-of-the-art 2D-hBN made by new synthesis strategies, where the mainstream approaches include exfoliation, chemical vapor deposition, and gas phase epitaxy, together with several other new methods that have been successfully developed in the past few years. On the basis of the extraordinary electrical and functional properties and thermal–mechanical stability, the applications of hBN-based nanosheets as substrates and dielectrics, passivation layers, and nanofillers in nanodevices and nanocomposites are discussed, together with the peculiar optical and wetting characteristics.

Two dimensional hexagonal boron nitride (2D-hBN): synthesis, properties and applications

Research in soft matter engineering has introduced new approaches in robotics and wearable devices that can interface with the human body and adapt to unpredictable environments. However, many promising applications are limited by the dependence of soft systems on electrical or pneumatic tethers. Recent work in soft actuation and electronics has made removing such cords more feasible, heralding a variety of applications from autonomous field robotics to wireless biomedical devices. Here we review the development of functional untethered soft robotics. We focus on recent advances in soft robotic actuation, sensing and integration as they relate to untethered systems, and consider the key challenges the field faces in engineering systems that could have practical use in real-world conditions. This Review Article examines the development of functional untethered soft robotics, evaluating recent advances in soft robotic actuation, sensing, and integration in relation to untethered systems.

Untethered soft robotics

Overview of carbon nanostructures and nanocomposites for electromagnetic wave shielding

The rapid development of wearable smart devices has contributed to the enormous demands for smart flexible strain sensors. However, to date, the poor stretchability and sensitivity of conventional metals or inorganic semiconductor-based strain sensors have restricted their application in this field to some extent, and hence many efforts have been devoted to find suitable candidates to overcome these limitations. Recently, novel resistive-type electrically conductive polymer composites (ECPCs)-based strain sensors have attracted attention based on their merits of light weight, flexibility, stretchability, and easy processing, thus showing great potential applications in the fields of human movement detection, artificial muscles, human–machine interfaces, soft robotic skin, etc. For ECPCs-based strain sensors, the conductive filler type and the phase morphology design have important influences on the sensing property. Meanwhile, to achieve a successful application toward wearable devices, several imperative features, including a self-healing capability, superhydrophobicity, and good light transmission, need to be considered. The aim of the present review is to critically review the progress of ECPCs-based strain sensors and to foresee their future development.

Electrically conductive polymer composites for smart flexible strain sensors: a critical review

Anisotropic polyimide (PI)/graphene composite aerogels were fabricated by unidirectional freezing. A poly(amic acid) (PAA) ammonium salt/graphene dispersion was first synthesized by mixing together PAA, H2O, triethylamine (TEA), and graphene and then was successively subjected to one-way freezing, freeze-drying, and thermal imidization. The one-way growth of ice crystals endowed the composite aerogels with highly arranged tubular pores. The PI/graphene composite aerogels possessed anisotropic conductivity, electromagnetic interference (EMI) shielding, heat transfer, and compression performance. Moreover, the composite aerogels with low density (0.076 g·cm-3) exhibited high EMI shielding effectiveness (SE) of 26.1-28.8 dB, and its specific EMI SE value achieved 1373-1518 dB·cm2·g-1 when the graphene content was 13 wt %. The main electromagnetic interference shielding mechanism of these composite aerogels was microwave absorption. The composite aerogels had excellent thermal stability, and their 5% weight loss temperature was higher than 546 °C in nitrogen. This research provided an easy and environmentally friendly approach to prepare lightweight and anisotropic PI-based composite aerogels.

Electromagnetic Interference Shielding Performance of Anisotropic Polyimide/Graphene Composite Aerogels

Self-lubricating composites based on Polyphenylene sulfide/Polytetrafluoroethylene (PPS/PTFE) reinforced with short carbon fibers (CF) were prepared by melt-blending. The effect of CF loadings on morphology, mechanical and dry-sliding behavior of the composite were carefully investigated in expectation of providing valuable information for the application of polymer-based composites. Results indicated that the incorporation of CF apparently improved the tensile strength, flexural modulus and hardness of PPS/PTFE blends. Meanwhile, the specific wear rate and average friction coefficient of PPS/PTFE reinforced by 15 vol% CF reached to 5.2 × 10−6 mm3/Nm and 0.085, which are 88% and 47% lower than that of mono-PPS/PTFE blend at the same sliding condition. Scanning electron microscopy (SEM) observations of the worn surfaces revealed that the main wear mechanism of the PPS/PTFE composites transformed from adhesive wear to abrasive wear by the introduction of CF. X-ray photoelectron spectroscopy (XPS) analysis of worn surface and the macroscopic observations of steel ring counterpart indicated the existence of uniform, smooth and PTFE-rich transfer film for PPS/PTFE/CF trinary blends, which is responsible for the enhanced tribological properties.

Enhanced mechanical and tribological properties in polyphenylene sulfide/polytetrafluoroethylene composites reinforced by short carbon fiber

Thermally conductive composites obtained by flake graphite filling immiscible Polyamide 6/Polycarbonate blends

Co/C@cellulose nanofiber aerogel derived from metal-organic frameworks for highly efficient electromagnetic interference shielding

Electromagnetic interference shielding effectiveness of microcellular polyimide/in situ thermally reduced graphene oxide/carbon nanotubes nanocomposites

Huawei Zou

Papers

Electromagnetic Interference Shielding Performance of Anisotropic Polyimide/Graphene Composite Aerogels

Enhanced mechanical and tribological properties in polyphenylene sulfide/polytetrafluoroethylene composites reinforced by short carbon fiber

Thermally conductive composites obtained by flake graphite filling immiscible Polyamide 6/Polycarbonate blends

Co/C@cellulose nanofiber aerogel derived from metal-organic frameworks for highly efficient electromagnetic interference shielding

Electromagnetic interference shielding effectiveness of microcellular polyimide/in situ thermally reduced graphene oxide/carbon nanotubes nanocomposites