Synergistic effect of Al2O3-decorated reduced graphene oxide on microstructure and mechanical properties of 6061 aluminium alloy.

In this study, Al6061 alloy matrix composites reinforced Al2O3-decorated reduced graphene oxide (Al2O3/RGO) with 0.1, 0.3 and 0.5 weight present (wt%) were successfully fabricated using high energy ball milling and hot extrusion techniques. The microstructures of these Al2O3/RGO/Al6061 aluminum matrix composites (Al MMCs) were characterized. The results showed that Al2O3/RGO were uniformly distributed within the Al6061 matrix and tightly bonded to the matrix. Al2O3 encapsulation on RGO surface would prevent the formation of Al4C3 brittle phase in matrix, ensuring that there was no reaction between the reinforcement and the matrix Al6061. Tensile strength and Vickers hardness tests demonstrated that the mechanical properties of Al MMCs significantly increased with addition of Al2O3/RGOs. Remarkably, Al MMCs with 0.1 wt% reinforcement showed tensile yield and tensile strengths of 270 MPa and 286 MPa, respectively, which were 49% and 43% higher than those of pure Al6061 prepared using the same process. Furthermore, the 0.1 wt% Al2O3/RGO composite also showed the best plastic deformation capability in considering of the strength.

Lightweight Dual-Functional Segregated Nanocomposite Foams for Integrated Infrared Stealth and Absorption-Dominant Electromagnetic Interference Shielding.

Lightweight infrared stealth and absorption-dominant electromagnetic interference (EMI) shielding materials are highly desirable in areas of aerospace, weapons, military and wearable electronics. Herein, lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO2 (SC-CO2) foaming combined with hydrogen bonding assembly and compression molding strategy. The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity, and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures. Particularly, the segregated nanocomposite foams present a large radiation temperature reduction of 70.2 °C at the object temperature of 100 °C, and a significantly improved EM wave absorptivity/reflectivity (A/R) ratio of 2.15 at an ultralow Ti3C2Tx content of 1.7 vol%. Moreover, the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles. The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace, weapons, military and wearable electronics.

Significantly Enhanced Electromagnetic Interference Shielding Performances of Epoxy Nanocomposites with Long-Range Aligned Lamellar Structures.

High­efficiency electromagnetic interference (EMI) shielding materials are of great importance for electronic equipment reliability, information security and human health. In this work, bidirectional aligned Ti3C2Tx@Fe3O4/CNF aerogels (BTFCA) were firstly assembled by bidirectional freezing and freeze-drying technique, and the BTFCA/epoxy nanocomposites with long-range aligned lamellar structures were then prepared by vacuum-assisted impregnation of epoxy resins. Benefitting from the successful construction of bidirectional aligned three-dimensional conductive networks and electromagnetic synergistic effect, when the mass fraction of Ti3C2Tx and Fe3O4 are 2.96 and 1.48 wt%, BTFCA/epoxy nanocomposites show outstanding EMI shielding effectiveness of 79 dB, about 10 times of that of blended Ti3C2Tx@Fe3O4/epoxy (8 dB) nanocomposites with the same loadings of Ti3C2Tx and Fe3O4. Meantime, the corresponding BTFCA/epoxy nanocomposites also present excellent thermal stability (Theat-resistance index of 198.7 °C) and mechanical properties (storage modulus of 9902.1 MPa, Young's modulus of 4.51 GPa and hardness of 0.34 GPa). Our fabricated BTFCA/epoxy nanocomposites would greatly expand the applications of MXene and epoxy resins in the fields of information security, aerospace and weapon manufacturing, etc.

Aggregation-Induced Luminescence Based UiO-66: Highly Selective Fast-Response Styrene Detection.

One of the main pollutants in indoor air is volatile organic compounds (VOCs), which can cause great harm to human health. So the development of a VOC detection technology is of great significance. In this work, a tetraphenylethylene-functionalized UiO-66 based on aggregation-induced emission was successfully prepared. The UiO-66-TBPE structure exhibits the characteristic blue emission of TBPE ligands under UV excitation and can be used as a luminescence sensor for fast and efficient detection of VOCs. More importantly, UiO-66-TBPE has a high fluorescence sensing selectivity in p-xylene and styrene vapor. To further improve the practical performance, we combined UiO-66-TBPE with the polymer polyacrylate (PA) to obtain a flexible hybrid membrane with fast detection performance for styrene vapor within the 30 s. The deeper sensing mechanism of p-xylene and styrene inducing different fluorescence enhancement and fluorescence quenching is explained by a combination of modern characterization techniques and computer simulation. Finally, we applied UiO-66-TBPE/PA to leather and still maintained a good sensing performance. It provides a potential way for the application of fluorescent metal-organic frameworks (MOFs) to detect VOCs in daily life.

Flexible Ti3C2T x /(Aramid Nanofiber/PVA) Composite Films for Superior Electromagnetic Interference Shielding.

Multifunctional electromagnetic interference (EMI) shielding materials would solve electromagnetic radiation and pollution problems from electronic devices. Herein, the directional freeze-drying technology is utilized to prepare the aramid nanofiber/polyvinyl alcohol aerogel with a directionally porous structure (D-ANF/PVA), and the Ti3C2T x dispersion is fully immersed into the D-ANF/PVA aerogel via ultrasonication and vacuum-assisted impregnation. Ti3C2T x /(ANF/PVA) EMI shielding composite films with directionally ordered structure (D-Ti3C2T x /(ANF/PVA)) are then prepared by freeze-drying and hot pressing. Constructing a directionally porous structure enables the highly conductive Ti3C2T x nanosheets to be wrapped on the directionally porous D-ANF/PVA framework in order arrangement and overlapped with each other. And the hot pressing process effectively reduces the layer spacing between the stacked wavy D-ANF/PVA, to form a large number of Ti3C2T x -Ti3C2T x continuous conductive paths, which significantly improves the conductivity of the D-Ti3C2T x /(ANF/PVA) EMI shielding composite film. When the amount of Ti3C2T x is 80 wt%, the EMI shielding effectiveness (EMI SE) and specific SE (SSE/t) of D-Ti3C2T x /(ANF/PVA) EMI shielding composite film achieve 70 dB and 13790 dB·cm2·g-1 (thickness and density of 120 µm and 0.423 g·cm-3), far superior to random-structured Ti3C2T x /(ANF/PVA) (R-Ti3C2T x /(ANF/PVA)) composite film (46 dB and 9062 dB·cm2·g-1, respectively) via blending-freeze-drying followed by hot pressing technology. Meanwhile, the D-Ti3C2T x /(ANF/PVA) EMI shielding composite film possesses excellent flexibility and foldability.

Multifunctional Wearable Silver Nanowire Decorated Leather Nanocomposites for Joule Heating, Electromagnetic Interference Shielding and Piezoresistive Sensing.

Multifunctional wearable electronic devices based on natural materials are highly desirable for versatile applications of energy conversion, electronic skin and artificial intelligence. Herein, multifunctional wearable silver nanowire decorated leather (AgNW/leather) nanocomposites with hierarchical structures for integrated visual Joule heating, electromagnetic interference (EMI) shielding and piezoresistive sensing are fabricated via the facile vacuum-assisted filtration process. The AgNWs penetrate the micro-nanoporous structures in the corium side of leather constructing highly-efficient conductive networks. The resultant flexible and mechanically strong AgNW/leather nanocomposites exhibit extremely low sheet resistance of 0.8 Ω/sq, superior visual Joule heating temperatures up to 108 °C at low supplied voltage of 2.0 V due to efficient energy conversion, excellent EMI shielding effectiveness (EMI SE) of ≈55 dB and outstanding piezoresistive sensing ability in human motion detection. This work demonstrates the fabrication of multifunctional AgNW/leather nanocomposites for next-generation wearable electronic devices in energy conversion, electronic skin and artificial intelligence, etc.

High-Efficiency Electromagnetic Interference Shielding of rGO@FeNi/Epoxy Composites with Regular Honeycomb Structures.

With the rapid development of fifth-generation mobile communication technology and wearable electronic devices, electromagnetic interference and radiation pollution caused by electromagnetic waves have attracted worldwide attention. Therefore, the design and development of highly efficient EMI shielding materials are of great importance. In this work, the three-dimensional graphene oxide (GO) with regular honeycomb structure (GH) is firstly constructed by sacrificial template and freeze-drying methods. Then, the amino functionalized FeNi alloy particles (f-FeNi) are loaded on the GH skeleton followed by in-situ reduction to prepare rGH@FeNi aerogel. Finally, the rGH@FeNi/epoxy EMI shielding composites with regular honeycomb structure is obtained by vacuum-assisted impregnation of epoxy resin. Benefitting from the construction of regular honeycomb structure and electromagnetic synergistic effect, the rGH@FeNi/epoxy composites with a low rGH@FeNi mass fraction of 2.1 wt% (rGH and f-FeNi are 1.2 and 0.9 wt%, respectively) exhibit a high EMI shielding effectiveness (EMI SE) of 46 dB, which is 5.8 times of that (8 dB) for rGO/FeNi/epoxy composites with the same rGO/FeNi mass fraction. At the same time, the rGH@FeNi/epoxy composites also possess excellent thermal stability (heat-resistance index and temperature at the maximum decomposition rate are 179.1 and 389.0 °C respectively) and mechanical properties (storage modulus is 8296.2 MPa).

Structural Design Strategies of Polymer Matrix Composites for Electromagnetic Interference Shielding: A Review.

With the widespread application of electronic communication technology, the resulting electromagnetic radiation pollution has been significantly increased. Metal matrix electromagnetic interference (EMI) shielding materials have disadvantages such as high density, easy corrosion, difficult processing and high price, etc. Polymer matrix EMI shielding composites possess light weight, corrosion resistance and easy processing. However, the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance. This review firstly discusses the key concept, loss mechanism and test method of EMI shielding. Then the current development status of EMI shielding materials is summarized, and the research progress of polymer matrix EMI shielding composites with different structures is illustrated, especially for their preparation methods and evaluation. Finally, the corresponding key scientific and technical problems are proposed, and their development trend is also prospected.

Lightweight, Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities.

In order to ensure the operational reliability and information security of sophisticated electronic components and to protect human health, efficient electromagnetic interference (EMI) shielding materials are required to attenuate electromagnetic wave energy. In this work, the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide (NaOH)/urea solution, and cellulose aerogels (CA) are prepared by gelation and freeze-drying. Then, the cellulose carbon aerogel@reduced graphene oxide aerogels (CCA@rGO) are prepared by vacuum impregnation, freeze-drying followed by thermal annealing, and finally, the CCA@rGO/polydimethylsiloxane (PDMS) EMI shielding composites are prepared by backfilling with PDMS. Owing to skin-core structure of CCA@rGO, the complete three-dimensional (3D) double-layer conductive network can be successfully constructed. When the loading of CCA@rGO is 3.05 wt%, CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness (EMI SE) of 51 dB, which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites (13 dB) with the same loading of fillers. At this time, the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability (THRI of 178.3 °C) and good thermal conductivity coefficient (λ of 0.65 W m-1 K-1). Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight, flexible EMI shielding composites.

Ultraflexible and Mechanically Strong Double-Layered Aramid Nanofiber-Ti3C2Tx MXene/Silver Nanowire Nanocomposite Papers for High-Performance Electromagnetic Interference Shielding.

High-performance electromagnetic interference (EMI) shielding materials with ultraflexibility, outstanding mechanical properties, and superior EMI shielding performances are highly desirable for modern integrated electronic and telecommunication systems in areas such as aerospace, military, artificial intelligence, and smart and wearable electronics. Herein, ultraflexible and mechanically strong aramid nanofiber-Ti3C2Tx MXene/silver nanowire (ANF-MXene/AgNW) nanocomposite papers with double-layered structures are fabricated via the facile two-step vacuum-assisted filtration followed by hot-pressing approach. The resultant double-layered nanocomposite papers with a low MXene/AgNW content of 20 wt % exhibit an excellent electrical conductivity of 922.0 S·cm-1, outstanding mechanical properties with a tensile strength of 235.9 MPa and fracture strain of 24.8%, superior EMI shielding effectiveness (EMI SE) of 48.1 dB, and high EMI SE/t of 10 688.9 dB·cm-1, benefiting from the highly efficient double-layered structures, high-performance ANF substrate, and extensive hydrogen-bonding interactions. Particularly, the nanocomposite papers show a maximum electrical conductivity of 3725.6 S·cm-1 and EMI SE of ∼80 dB at a MXene/AgNW content of 80 wt % with an absorption-dominant shielding mechanism owing to the massive ohmic losses in the highly conductive MXene/AgNW layer, multiple internal reflections between Ti3C2Tx MXene nanosheets and polarization relaxation of localized defects, and abundant terminal groups. Compared with the homogeneously blended ones, the double-layered nanocomposite papers possess greater advantages in electrical, mechanical, and EMI shielding performances. Moreover, the multifunctional double-layered nanocomposite papers exhibit excellent thermal management performances such as high Joule heating temperature at low supplied voltages, rapid response time, sufficient heating stability, and reliability. The results indicate that the double-layered nanocomposite papers have excellent potential for high-performance EMI shielding and thermal management applications in aerospace, military, artificial intelligence, and smart and wearable electronics.

Highly Sensitive Strain Sensor Based on a Stretchable and Conductive Poly(vinyl alcohol)/Phytic Acid/NH2-POSS Hydrogel with a 3D Microporous Structure.

Conductive hydrogel-based wearable strain sensors with tough, stretchable, self-recoverable, and highly sensitive properties are highly demanded for applications in electronic skin and human-machine interface. However, currently, hydrogel-based strain sensors put forward higher requirements on their biocompatibility, mechanical strength, and sensitivity. Herein, we report a poly(vinyl alcohol)/phytic acid/amino-polyhedral oligomeric silsesquioxane (PVA/PA/NH2-POSS) conductive composite hydrogel prepared via a facile freeze-thaw cycle method. Within this hydrogel, PA acts as a cross-linking agent and ionizes hydrogen ions to endow the material with ionic conductivity, while NH2-POSS acts as a second cross-linking agent by increasing the cross-linking density of the three-dimensional network structure. The effect of the content of NH2-POSS is investigated, and the composite hydrogel with 2 wt % NH2-POSS displays a uniform and dense three-dimensional (3D) network microporous structure, high conductivity of 2.41 S/m, and tensile strength and elongation at break of 361 kPa and 363%, respectively. This hydrogel is biocompatible and has demonstrated the application as a strain sensor monitoring different human movements. The assembled sensor is stretchable, self-recoverable, and highly sensitive with fast response time (220 ms) and excellent sensitivity (GF = 3.44).

Enhanced Antistatic and Self-Heatable Wearable Coating with Self-Tiered Structure Caused by Amphiphilic MXene in Waterborne Polymer.

The antistatic and self-heatable flexible coating is highly desired for next-generation multifunctional clothing. MXene is a promising filler that possesses an excellent conductivity, an efficient photothermal conversion, and an outstanding compatibility with the waterborne polymer. In this study, MXene was integrated with waterborne polyacrylate by a solution-blending method. The polyacrylate/MXene composites display a self-tiered structure, and the composite coated leather possesses a surface resistivity of 7.85 × 109 Ω with 2 wt % loading, satisfying the B-level of the antistatic standard. The polyacrylate/MXene-0.5 wt % shows a higher temperature increase of 46.9 °C than that of pure polyacrylate after being irradiated by a 275 W IR light for 5 min, and the surface temperature of polyacrylate/MXene-0.5 wt % composite coated leather is 5.4 °C higher than that of polyacrylate coated leather after being irradiated by sunlight for 30 min. The tensile strength of the polyacrylate/MXene-1 wt % composite is increased by 28.3% compared with that of pure polyacrylate. All of the results prove its promising application in the multifunctional coating. Moreover, amphiphilic MXene was produced by changing the etching degree, which resulted in a self-tiered structure of the polyacrylate/MXene composite owing to the improved interfacial activity of MXene. The amphiphilic MXene possesses a decreased surface tension and can serve as a stabilizer for a Pickering emulsion, which suggests novel routes for constructing a multifunctional polymer/MXene composite.

High-Performance and Rapid-Response Electrical Heaters Based on Ultraflexible, Heat-Resistant, and Mechanically Strong Aramid Nanofiber/Ag Nanowire Nanocomposite Papers.

High-performance and rapid response electrical heaters with ultraflexibility, superior heat resistance, and mechanical properties are highly desirable for the development of wearable devices, artificial intelligence, and high-performance heating systems in areas such as aerospace and the military. Herein, a facile and efficient two-step vacuum-assisted filtration followed by hot-pressing approach is presented to fabricate versatile electrical heaters based on the high-performance aramid nanofibers (ANFs) and highly conductive Ag nanowires (AgNWs). The resultant ANF/AgNW nanocomposite papers present ultraflexibility, extremely low sheet resistance (minimum Rs of 0.12 Ω/sq), and outstanding heat resistance (thermal degradation temperature above 500 °C) and mechanical properties (tensile strength of 285.7 MPa, tensile modulus of 6.51 GPa with a AgNW area fraction of 0.4 g/m2), benefiting from the partial embedding of AgNWs into the ANF substrate and the extensive hydrogen-bonding interactions. Moreover, the ANF/AgNW nanocomposite paper-based electrical heaters exhibit satisfyingly high heating temperatures (up to ∼200 °C) with rapid response time (10-30 s) at low AgNW area fractions and supplied voltages (0.5-5 V) and possess sufficient heating reliability, stability, and repeatability during the long-term and repeated heating and cooling cycles. Fully functional applications of the ANF/AgNW nanocomposite paper-based electrical heaters are demonstrated, indicating their excellent potential for emerging electronic applications such as wearable devices, artificial intelligence, and high-performance heating systems.

Lightweight, compressible and electrically conductive polyurethane sponges coated with synergistic multiwalled carbon nanotubes and graphene for piezoresistive sensors.

Lightweight, compressible and highly sensitive pressure/strain sensing materials are highly desirable for the development of health monitoring, wearable devices and artificial intelligence. Herein, a very simple, low-cost and solution-based approach is presented to fabricate versatile piezoresistive sensors based on conductive polyurethane (PU) sponges coated with synergistic multiwalled carbon nanotubes (MWCNTs) and graphene. These sensor materials are fabricated by convenient dip-coating layer-by-layer (LBL) electrostatic assembly followed by in situ reduction without using any complicated microfabrication processes. The resultant conductive MWCNT/RGO@PU sponges exhibit very low densities (0.027-0.064 g cm-3), outstanding compressibility (up to 75%) and high electrical conductivity benefiting from the porous PU sponges and synergistic conductive MWCNT/RGO structures. In addition, the MWCNT/RGO@PU sponges present larger relative resistance changes and superior sensing performances under external applied pressures (0-5.6 kPa) and a wide range of strains (0-75%) compared with the RGO@PU and MWCNT@PU sponges, due to the synergistic effect of multiple mechanisms: "disconnect-connect" transition of nanogaps, microcracks and fractured skeletons at low compression strain and compressive contact of the conductive skeletons at high compression strain. The electrical and piezoresistive properties of MWCNT/RGO@PU sponges are strongly associated with the dip-coating cycle, suspension concentration, and the applied pressure and strain. Fully functional applications of MWCNT/RGO@PU sponge-based piezoresistive sensors in lighting LED lamps and detecting human body movements are demonstrated, indicating their excellent potential for emerging applications such as health monitoring, wearable devices and artificial intelligence.

The Synergy of Double Cross-linking Agents on the Properties of Styrene Butadiene Rubber Foams.

Sulfur (S) cross-linking styrene butadiene rubber (SBR) foams show high shrinkage due to the cure reversion, leading to reduced yield and increased processing cost. In this paper, double cross-linking system by S and dicumyl peroxide (DCP) was used to decrease the shrinkage of SBR foams. Most importantly, the synergy of double cross-linking agents was reported for the first time to our knowledge. The cell size and its distribution of SBR foams were investigated by FESEM images, which show the effect of DCP content on the cell structure of the SBR foams. The relationships between shrinkage and crystalline of SBR foams were analyzed by the synergy of double cross-linking agents, which were demonstrated by FTIR, Raman spectra, XRD, DSC and TGA. When the DCP content was 0.6 phr, the SBR foams exhibit excellent physical and mechanical properties such as low density (0.223 g/cm3), reduced shrinkage (2.25%) and compression set (10.96%), as well as elevated elongation at break (1.78 × 103%) and tear strength (54.63 N/mm). The results show that these properties are related to the double cross-linking system of SBR foams. Moreover, the double cross-linking SBR foams present high electromagnetic interference (EMI) shielding properties compared with the S cross-linking SBR foams.