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Carbon nanotube (CNT) aerogels and sponges are macroscopic porous materials with a unique isotropic structure. CNTs make an interconnected 3D scaffold, therefore the resulting aerogels are robust, highly conductive, and flexible, enabling a much broader range of applications than aligned arrays and thin films, especially in energy and environmental areas. A comprehensive overview of the recent progress in isotropic CNT-based macroscopic structures is provided, including their synthesis methods, structural characteristics, mechanical properties, and deformation mechanism, as well as potential applications in energy and environmental fields. In particular, this study focuses on the CNT sponges developed, which are high-performance porous materials with many distinct properties such as their versatile deformations and shape recovery. Importantly, the CNT sponges provide a universal platform for designing and manufacturing a variety of hierarchical functional composites by introducing polymers or inorganic guests, thus greatly extend application areas from highly compressible electrodes for supercapacitors and batteries, catalysis, to environmental cleanup. Future research directions and associated challenges in this field are proposed. [ABSTRACT FROM AUTHOR]

Naturally existing materials often acquire unique functions by adopting a gradient structure with gradual change in their microstructure and related properties. Imparting such an elegant structural control into synthetic materials has been a grand challenge in the fi eld. Here, the concept of gradient structure into macroscopic carbon nanotube (CNT) fi lms is employed and the CNT arrangement from well-aligned array to completely random distribution, in a continuous and smooth way, is changed. Gradient films with tailored alignedto- random transition rate or multilevel hierarchical structures with repeated transition have been fabricated. Local deformation and mechanical properties are directly related to the arrangement of CNTs and can be tailored by Herman's orientation factor; in particular, the elastic modulus and stiffness span over several orders of magnitude from aligned to random regions within a single monolithic film. Controlled synthesis of macroscopic CNT gradient structures with tunable mechanical properties opens a potential route toward manufacturing biomimetic functional materials with locally optimized design. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) and graphene-based sponges and aerogels have an isotropic porous structure and their mechanical strength and stability are relatively lower. Here, we present a junction-welding approach to fabricate porous CNT solids in which all CNTs are coated and welded in situ by an amorphous carbon layer, forming an integral three-dimensional scaffold with fixed joints. The resulting CNT solids are robust, yet still highly porous and compressible, with compressive strengths up to 72 MPa, flexural strengths up to 33 MPa, and fatigue resistance (recovery after 100,000 large-strain compression cycles at high frequency). Significant enhancement of mechanical properties is attributed to the welding-induced interconnection and reinforcement of structural units, and synergistic effects stemming from the core-shell microstructures consisting of a flexible CNT framework and a rigid amorphous carbon shell. Our results provide a simple and effective method to manufacture high-strength porous materials by nanoscale welding. [ABSTRACT FROM AUTHOR]

In order to improve the understanding of laser interactions of materials with homogeneous nano-structures, pulsed laser induced plasma from a low density, high-porosity multiwall carbon nanotube (CNT) sponge and a dense graphite block have been investigated by combinational spectroscopy approaches. We observe distinct differences in the laser-induced light emission of the CNT sponge and graphite block which we attribute to the occurrence of a phase explosion caused by the lower thermal conductivity and weaker mechanical strength of the CNT sponge. Furthermore, spectroscopy plasma analysis reveals that differences in the surface of the two systems play a key role in the generation of negative carbon ions. We observe a more effective production of negative ions for the CNT sponge as compared to the graphite block due to the greater number of surface defects of the CNT sponge. [ABSTRACT FROM AUTHOR]

We report a carbon nanotube array-encapsulatedphase change compositein which the nanotube distribution (or areal density) could be tailoredby uniaxial compression. The n-eicosane (C20) wasinfiltrated into the porous array to make a highly conductive nanocompositewhile maintaining the nanotube dispersion and connection among thematrix with controlled nanotube areal density determined by the compressivestrains along the lateral direction. The resulting electrically conductivecomposites can store heat at driven voltages as low as 1 V at fastspeed with high electro-to-heat conversion efficiencies. Increasingthe nanotube density is shown to significantly improve the polymercrystallinity and reduce the voltage for inducing the phase changeprocess. Our results indicate that well-organized nanostructures suchas the nanotube array are promising candidates to build high-performancephase change composites with simplified manufacturing process andmodulated structure and properties. [ABSTRACT FROM AUTHOR]

The anisotropy in thermoelectric properties of three-dimensional carbon nanotubes (CNTs) and CNT/polyaniline (PANI) composites have been studied by utilizing an orderly aligned CNT arrays with a self-sustained construction. In the length direction of CNT, the electrical conductivity of the CNT array is ∼5 times larger as compared to the direction vertical to the alignment of CNTs, while the difference in thermal conductivity between these two directions is ∼25 times. As a result, strong anisotropic thermoelectric transportation has been also observed in the composites composed of PANI and CNT arrays. An enhanced thermopower in the composites, as compared to the pure PANI or CNTs, is only observed in the direction along the CNTs. This study helps the fundamental understanding on the un-conventional improved thermopower, which is more likely to be realized via adjusting the carrier transportation within the interface between CNTs and PANI rather than across it. [ABSTRACT FROM AUTHOR]

A lightweight 3D Ag/CNTs/SBS composite foam was successfully fabricated by a simple freeze-drying process followed by adsorbing and in-situ reducing of silver trifluoroacetate in ethanol solution, which exhibited robust mechanical–electrical performance and high EMI shielding performance due to the synergistic contribution of the CNTs with ultra-high aspect ratio inside the SBS matrix and Ag NPs partially embedded in the superficial surface of the SBS foam skeleton. [Display omitted] • Lightweight Ag/CNTs/SBS foam was fabricated by freeze-drying and in-situ reduction. • CNTs and partially embedded Ag NPs endow the foam with excellent properties. • The foam exhibits high EMI SE of 91 dB at 4 mm in the X band. • The foam possesses enhanced EMI SE value after the cyclic compressions. The porous conductive polymer composites have received great attention owing to their superiority of being utilized in electromagnetic interference (EMI) shielding applications. Herein, lightweight and highly compressible conductive composite foam composed of poly(styrene- block -butadiene- block -styrene) (SBS) polymer matrix, carbon nanotubes (CNTs) and silver nanoparticles (Ag NPs) is fabricated by freeze-drying technology, silver precursor absorption and in-situ reduction process. Three-dimensional CNTs conductive network and partially embedded Ag NPs synergistically endow the foam with excellent mechanical, electrical and EMI shielding performance. The flexible 8Ag/4CNTs/10SBS composite foam with a low density of 0.42 g/cm3 exhibits moderate compressive strength of 169.2 kPa at strain of 50%, remarkable conductivity of 753 S/m, and prominent EMI shielding effectiveness (SE) value of around 91 dB in the electromagnetic wave frequency range of 8.2–12.5 GHz. In addition, the 4Ag/4CNTs/10SBS composite foam exhibits robust mechanical–electrical property upon 1000 compression-release cycles at strain of 50%, and its SE value increased by about 33% compared with the initial state after the cyclic compression test. These results suggest that the Ag/CNTs/SBS foams possess promising potential to be used as lightweight, flexible, and high-performance EMI shielding materials in modern electronic devices. [ABSTRACT FROM AUTHOR]

A lightweight 3D Ag/CNTs/SBS composite foam was successfully fabricated by a simple freeze-drying process followed by adsorbing and in-situ reducing of silver trifluoroacetate in ethanol solution, which exhibited robust mechanical–electrical performance and high EMI shielding performance due to the synergistic contribution of the CNTs with ultra-high aspect ratio inside the SBS matrix and Ag NPs partially embedded in the superficial surface of the SBS foam skeleton. [Display omitted] • Lightweight Ag/CNTs/SBS foam was fabricated by freeze-drying and in-situ reduction. • CNTs and partially embedded Ag NPs endow the foam with excellent properties. • The foam exhibits high EMI SE of 91 dB at 4 mm in the X band. • The foam possesses enhanced EMI SE value after the cyclic compressions. The porous conductive polymer composites have received great attention owing to their superiority of being utilized in electromagnetic interference (EMI) shielding applications. Herein, lightweight and highly compressible conductive composite foam composed of poly(styrene- block -butadiene- block -styrene) (SBS) polymer matrix, carbon nanotubes (CNTs) and silver nanoparticles (Ag NPs) is fabricated by freeze-drying technology, silver precursor absorption and in-situ reduction process. Three-dimensional CNTs conductive network and partially embedded Ag NPs synergistically endow the foam with excellent mechanical, electrical and EMI shielding performance. The flexible 8Ag/4CNTs/10SBS composite foam with a low density of 0.42 g/cm3 exhibits moderate compressive strength of 169.2 kPa at strain of 50%, remarkable conductivity of 753 S/m, and prominent EMI shielding effectiveness (SE) value of around 91 dB in the electromagnetic wave frequency range of 8.2–12.5 GHz. In addition, the 4Ag/4CNTs/10SBS composite foam exhibits robust mechanical–electrical property upon 1000 compression-release cycles at strain of 50%, and its SE value increased by about 33% compared with the initial state after the cyclic compression test. These results suggest that the Ag/CNTs/SBS foams possess promising potential to be used as lightweight, flexible, and high-performance EMI shielding materials in modern electronic devices. [ABSTRACT FROM AUTHOR]