Chuanxin Weng

The disordered assembly and low conductivity of carbon nanotubes are the main problems that limit the application of electromagnetic interference (EMI) shielding. In this work, an ordered lamellar assembly structure of multiwalled carbon nanotube/Ti₃C₂T_x (MWCNT/Ti₃C₂T_x) hybrid films was achieved by vacuum-assisted filtration through the hybridization of Ti₃C₂T_x nanosheets and carbon nanotubes, where carbon nanotubes were tightly sticking on the surface of Ti₃C₂T_x nanosheets via physical adsorption and hydrogen bonding. Compared with the pure carbon nanotubes films, the hybrid MWCNT/Ti₃C₂T_x films achieved a significant improvement in conductivity of 452.5 S/cm and EMI shielding effectiveness (SE) of 44.3 dB under 50 wt% Ti₃C₂T_x with a low thickness (8.6 μm) and orderly lamellar stacking structure, which finally resulted in high specific SE (SSE/t, SE divided by the density and thickness) of 55,603.1 dB∙cm²∙g⁻¹.

Shape memory polymers (SMPs) that change shapes as designed by external stimuli have become one of the most promising materials as actuators, sensors, and deployable devices. However, their practical applications have been greatly limited due to the long recovery time, which mainly originates from their low recovery stress, inherent viscoelastic hysteresis effect and low heat transmission efficiency. In this work, a novel method is proposed to prepare fast responsive reduced graphene oxide/shape memory polyurethane/polyurethane foam (rGO/SMPU/PU foam) shape memory composites. The elastic PU foam is used as framework to be coated with SMPU and rGO by solution polymerization and self-assembly methods, which result in rGO/SMPU/PU foam with three-dimensional networks. The rGO/SMPU/PU foam exhibits a fast response (of less than 1 s) under a large compressing deformation (80%) due to the synergistic effect of the high elasticity of PU foam, the short energy transmission distance of the SMPU layer and the high thermal conductivity of the rGO layer. Moreover, owing to the outstanding shape fixity ratio (R_f) and shape recovery ratio (R_r) of SMPU and the mechanical properties of PU foam, the rGO/SMPU/PU foam shows an excellent shape memory effect (more than 98% R_f and R_r at 80% strain) and cyclic stability simultaneously. Such rGO/SMPU/PU foam material demonstrates the potential applications in high-sensitivity temperature sensors and temperature codes.

The development of electromagnetic interference (EMI) shielding materials is moving forward towards being lightweight and showing high-performance. Here, we report on lightweight silver nanowire (AgNW)/MXene hybrid sponges featuring hierarchical structures that are fabricated by a combination of dip-coating and unidirectional freeze-drying methods. The commercial melamine formaldehyde sponges (MF), designed with a buckled structure, are chosen as the template for coating with the AgNW layer (BMF/AgNW). Furthermore, the additional irregular honeycomb architecture composed of MXene assembled cell walls is introduced inside the BMF cell–matrix through unidirectional freeze-drying of MXene aqueous suspensions. Consequently, the BMF/AgNW presents a better EMI shielding effectiveness of 40.0 dB contributed by the conductive network and multiple reflections and scattering compared with the MF/AgNW. Eventually, the resulting AgNW/MXene hybrid sponge exhibits a higher EMI shielding effectiveness of 52.6 dB with a low density of 49.5 mg cm⁻³ compared with the BMF/AgNW due to synergetic effects of the AgNW and MXene both in conductivity and hierarchical structure. These results also provide a novel way to fabricate lightweight and conductive sponges as high-performance EMI shielding materials.

As an essential component of flexible optoelectronic devices, transparent conductive films made of silver nanowire (AgNW) have attracted wide attention due to the extraordinary optical, electrical and mechanical properties. However, the application of AgNW coating still faces some challenges to be overcome including large contact resistance and poor durability. Here, we induce insulating graphene oxide over silver nanowire network through solution process to modify the electrical property and provide a protective layer. Strong interaction with substrates reducing the contact resistance of AgNW junctions and extra conductive channels of graphene oxide sheets contributes to the dramatic enhancement in electric property as well as durability. The resulting coating exhibits superior and uniform optoelectronic performances (sheet resistance of ~ 38 Ω·sq⁻¹ with 91% transmittance at 550 nm), outstanding stability in harsh environments, strong adhesion, and excellent mechanical flexibility after 3,000 bending cycles at a bending radius of 2.0 mm, which imply the promising application prospects in flexible optoelectronics.

Many three-dimensional (3D) nanomaterial-based assemblies need incorporation with elastomers to attain stretchability–that also compromises their pristine advantages for functional applications. Here we show the design of elastomer-free, highly deformable silver nanowire (AgNW) conductors through dip-coating AgNW on a 3D polymeric scaffold and following a simple triaxial compression approach. The resulting 3D AgNW conductors exhibit good stability of resistance under multimodal deformation, such as stretching, compressing and bending, as well as comparable conductivity with those elastomer-based ones. Moreover, the buckled structures endow our 3D conductors with a novel negative Poisson’s ratio (NPR) behavior, which can offer good comfortability to curvilinear surfaces. The combination of mechanical properties, conductive performance, and unique deformation characteristics can satisfy multiscale conformal mechanics with soft, curvilinear human body.

Due to their extraordinary mechanical properties, nanocarbon materials (e.g. carbon nanotube and graphene) are attracting great interests in the field of nanocomposites. One unique feature in nanocarbon-based nanocomposites is their intrinsically rich interface, allowing them to adapt the microstructures in response to external loading and, in turn, to stiffen themselves. This mechanical behavior, called responsive stiffening, was usually observed in biological materials such as bones and muscles. The mechanically responsive behaviors of nanocarbon-based materials are particularly exciting because the nanocarbon-enabled huge interface area offers opportunities to tune such stiffening performance while this interface advantage is not fully exploited yet. Here, we demonstrate stiffening behaviors in graphene oxide (GO)-based film materials in response to dynamic oscillations. Through a facile method of polymer content alteration and alkali treatment, the microstructure and interlayer interaction of GO films are modified, along with the resulted responsively stiffening performance. Based on polarized Raman spectra characterizations, we attribute the stiffening mechanism to the microstructural evolution of GO films during dynamic tension as well as the polymer chains alignment. Finally, we highlight the significantly improved static mechanical properties of GO film after a simple stiffening process. Our results not only aid in the development of biomimetic, adaptive materials, but provide a mechanical way for the design of high-performance nanocarbon-based nanocomposites.

In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.