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Stretchable and conductive nanocomposites are emerging as important constituents of soft mechanical sensors for health monitoring, human–machine interactions, and soft robotics. However, tuning the materials' properties and sensor structures to the targeted mode and range of mechanical stimulation is limited by current fabrication approaches, particularly in scalable polymer melt techniques. Here, thermoplastic elastomer‐based nanocomposites are engineered and novel rheological requirements are proposed for their compatibility with fiber processing technologies, yielding meters‐long, soft, and highly versatile stretchable fiber devices. Based on microstructural changes in the nanofiller arrangement, the resistivity of the nanocomposite is tailored in its final device architecture across an entire order of magnitude as well as its sensitivity to strain via tuning thermal drawing processing parameters alone. Moreover, the prescribed electrical properties are coupled with suitable device designs and several fiber‐based sensors are proposed aimed at specific types of deformations: i) a robotic fiber with an integrated bending mechanism where changes as small as 5° are monitored by piezoresistive nanocomposite elements, ii) a pressure‐sensing fiber based on a geometrically controlled resistive signal that responds with a sub‐newton resolution to changes in pressing forces, and iii) a strain‐sensing fiber that tracks changes in capacitance up to 100% elongation. [ABSTRACT FROM AUTHOR]

Graphene-carbon nanotube/copper calcium titanate (GR-CNT/CCTO) ceramic nanocomposites were prepared by spark plasma sintering (SPS) technology. The correlation between GR-CNT content and epsilon-negative property was clarified in detail. Electrical percolation behavior was confirmed in nanocomposites with GR-CNT content rising, corresponding to change from hopping conductivity to metal-like conductivity. When three-dimensional (3D) GR-CNT networks were constructed in CCTO ceramics, epsilon-negative property was obtained, originating from low-frequency collective plasma oscillation of delocalized electrons in formed networks. Epsilon-near-zero (ENZ) property was respectively obtained at ~360 MHz and ~255 MHz. The negative value of epsilon ranged from ~103 to ~104, and plasma frequency of the composites increased from 12.8 GHz to 34.6 GHz with GR-CNT content ranging from 10 wt% to 12 wt%, which was analyzed by Drude model. In addition, the dielectric loss behavior and impedance response also were discussed. The inductive character of epsilon-negative materials was expounded via equivalent circuit analysis. We provide an effective paradigm of carbon/ceramic nanocomposites with epsilon-negative property by constructing 3D GR-CNT networks, which facilitates the clarification of regulation mechanism of epsilon-negative materials. [ABSTRACT FROM AUTHOR]

Abstract Since negative permittivity demonstrated in metamaterials, how to effectively tune negative permittivity still the challenge to satisfy practical applications. Meta-composites could provide alternative routes to tunable negative permittivity. In this paper, Graphene/CaCu 3 Ti 4 O 12 (GR/CCTO) meta-composites with different GR content were fabricated by low-temperature pressureless sintering. Microstructures and compositions of GR/CCTO were investigated in detail. The electrical and dielectric properties of GR/CCTO nanocomposites were investigated at 10 kHz −1 MHz and 20 MHz - 1 GHz region respectively. AC conductivity spectra showed different variation trends which were explained by Jonscher's power law or Drude model, indicating conductive mechanism transformation from hopping conduction to metal-like conduction. Lorentz-type and/or Drude-type negative permittivity behaviors were observed at radio-frequency region. Tunable negative permittivity were realized by changing GR content in GR/CCTO nanocomposites. Correspondence between inductive characteristic and negative permittivity was manifested by equivalent circuit analysis of impedance response of GR/CCTO composites. This work not only presents novel routes to tune negative permittivity, but also further clarifies negative permittivity generation mechanism, which will greatly facilitate applications in impedance matching, electromagnetic shielding and multi-layer high- k capacitors etc. Graphical abstract Image 1 Highlights • GR/CCTO nanocomposites were fabricated by low-temperature sintering. • GR/CCTO composites were characterized by TEM, SEM, XRD, Raman and FT-IR. • Lorentz-type and/or Drude-type negative permittivity behaviors were observed. • Negative permittivity were tuned at 10 kHz - 1 MHz and 20 MHz - 1 GHz region. • Equivalent circuit analysis of impedance response were performed. [ABSTRACT FROM AUTHOR]

Abstract Metacomposites with conductive polymer matrix toward negative permittivity have promising applications in energy storage devices and electromagnetic shielding. In this paper, carbon nanotubes (CNTs)/polypyrrole (PPy) nanocomposites with different loadings of CNTs have been synthesized using a surface-initiated polymerization (SIP) method. Scanning electron microscopy (SEM) results indicate that conductive networks have constructed inside the nanocomposites by CNTs and PPy granules. A frequency switch of permittivity from positive to negative in pure PPy and CNTs/PPy nanocomposites with low CNTs loading (1 wt%) is observed, which can be analyzed by the Lorentz model. Besides, all negative permittivity behavior in the test frequency range (10–1000 MHz) is found in CNTs/PPy nanocomposites with higher CNTs content which can be easily tuned by adjusting the CNTs loading. Negative permittivity is considered arising from the plasma oscillation of delocalized electrons in conductive networks and could be fitted by Drude model. Furthermore, the equivalent circuit models, ac conductivity and dielectric loss are discussed. Graphical abstract Image Highlights • A frequency switch of permittivity from positive to negative in pure PPy and 1 wt% CNTs/PPy nanocomposite was observed. • Negative permittivity behaviors were analyzed by Lorentz model and Drude model. • Equivalent circuit analysis was applied to manifest the existence of conductive networks inside the materials. [ABSTRACT FROM AUTHOR]

• Mixed-dimensional Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs in high efficiency through a simple method. • By controlling the amount of initial reactants, Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs with different contents of CNTs were produced. • The enhanced contents of MWCNTs and RGO boosted the impedance matching characteristics, polarization and conduction loss capabilities. • Fe 3 O 4 -FeCO 3 /MWCNTs/RGO mixed-dimensional MCNCs exhibited the outstanding comprehensive EMWAPs. • Our findings took full advantage of interface and magnetic-dielectric synergy strategy to develop high-efficiency novel MAs. Interfacial and/or magnetic-dielectric synergistic effects are important avenues to boost microwave absorption properties. In order to simultaneously utilize these effects, we elaborately designed mixed-dimensional Fe 3 O 4 -FeCO 3 /multi-walled carbon nanotubes (MWCNTs)/reduced graphene oxide (RGO) multicomponent nanocomposites (MCNCs) in large scale via a facile process of hydrothermal and freeze-drying. The microstructural investigation revealed that two-dimensional RGO, one-dimensional MWCNTs and zero-dimensional Fe 3 O 4 -FeCO 3 nanoparticles were well bounded to generate the typical mixed-dimensional structure. By controlling the amounts of initial reactants, the Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs displayed improved impedance matching features, polarization and conduction loss abilities, which lead to the evidently improved electromagnetic absorption properties. The Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs simultaneously exhibited excellent absorption ability, large absorption bandwidth, low density and thin matching thickness. Generally, this work not only proposed an effective route to make the best of magnetic-dielectric synergy and interfacial strategy for exploiting novel microwave absorption materials, but also presented a simple approach to synthesize magnetic MWCNTs/RGO-based mixed-dimensional MCNCs. Interface and magnetic-dielectric synergy strategy to develop Fe 3 O 4 -Fe 2 CO 3 /multi-walled carbon nanotubes/reduced graphene oxide mixed-dimensional multicomponent nanocomposites for tunable and boosted microwave absorption [Display omitted] [ABSTRACT FROM AUTHOR]