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Carbon nanotubes (CNTs) are regarded as the next generation of one-dimensional super-strong nanomaterials due to their extraordinary mechanical properties. Recently, much attention has been dedicated into super-strong CNT-based fibers resulting from twisting operation. However, the roles of a promising compression operation on the mechanical enhancement mechanisms of CNT fibers (CNFs) are not clear. Especially, the combined twisting-compression effect has not been known. In this work, with using coarse-grained molecular dynamic simulation method, the tensile mechanical properties and mechanical enhancements of randomly-distributed CNT fibers (RDCNFs) were studied. It was found that the mechanical performances of such RDCNFs could be significantly improved by increasing CNT length or decreasing initial bending degree of CNTs. Furthermore, both specific strength and specific modulus can be effectively tuned by twisting and compressing operations, where self-locking and unhitching mechanisms of CNT knots play critical roles. On the other hand, following theoretical guidance, a super-strong CNF with the maximum specific strength up to 296 mN/tex (∼6.8 GPa) was designed and fabricated. This work provides a theoretically and experimentally support to design super-strong CNT-based fibers and lays a foundation for their future applications.

With the development of multifunction and miniaturization in modern electronics, polymeric films with strong mechanical performance and high thermal conductivity are urgently needed. Two-dimensional transition metal carbides and nitrides (MXenes) have attracted extensive attention due to their tunable surface chemistry, layered structure and charming properties. However, there are few studies on using MXenes as fillers to enhance polymer properties. In this paper, we fabricate a three-dimensional foam by the freeze-drying method to enhance the interfacial interaction between adjacent MXene sheets and polyimide (PI) macromolecules, and then a composite film with a dense and well-ordered layer-by-layer structure is produced by the hot-pressing process. Based on the secondary orientation strategy, the resultant MXene/PI film exhibits an enhanced thermal conductivity of 5.12 ± 0.37 W m−1 K−1 and tensile strength of 102 ± 3 MPa. Moreover, the composite film has good flexibility and flame retardancy owing to the synergistic effect of MXene sheets and PI chains. Hence, the MXene/PI composite film with the properties of flexibility, flame-retardancy, high mechanical strength and efficient heat transmission is expected to be used as the next thermal management material in a variety of applications.

The question of how to make artificial intelligence robots perceive the power of "light as a feather" and "heavy as a mountain" at the same time has always been a goal that people are striving to achieve. However, pressure sensors, the key components of electronic equipment, are often unable to incorporate high sensitivity and wide range performance. Here, we proposed a "gradient stiffness design" strategy to prepare a kind of carbon nanotube sponge with a stiffness difference of up to 254 times between different layers, but still maintaining an integral conductive network without delamination. This gradient stiffness structure sponge shows prominent sensing properties with ultra-broad range (from 0.0022 MPa to 5.47 MPa) and high sensitivity. The low stiffness layer can detect low stress (0.0022 MPa) with high sensitivity of 0.765 MPa-1, and the high stiffness layer can greatly extend the sensing range to an unprecedentedly high value (5.47 MPa). It can concisely detect various motions with different stress, from slight clamping of fragile fries by the robot fingers to heavily stomping motions by a 90 kg person. Moreover, a series of human movements from small-scale to large-scale can be also monitored, revealing the great potential of this gradient stiffness structure in future sensing research.