A General Approach for Buckled Bulk Composites by Combined Biaxial Stretch and Layer‐by‐Layer Deposition and Their Electrical and Electromagnetic Applications

Abstract

Fabrication of high quality stretchable conductors that show bulk structure, high electrical conductivity, and stable conductance under large deformations is crucial for wearable electronics and soft robots. A key difficulty here is to introduce buckled structure into the conductive phase of the bulk conductors and overcome the lateral crack problem in the conductive phase during buckle formation. In this paper, a general approach is introduced for fabricating novel buckled bulk composite (BBC) stretchable conductors based on common conductive nanomaterial by using sequential biaxial stretch–release and layer‐by‐layer deposition to provide alternating buckled conductive layers and elastomer layers. This biaxial stretch is used to keep the width of elastomers unchanged before and after stretching, to avoid the lateral crack formation of the conductive layer. This method can be applied to common nanoparticles, such as silver nanoparticles, silver nanowires, single‐walled carbon nanotubes, and graphenes. The BBCs exhibit high conductance, uniform structure, and stable conductance during deformation and temperature change, which are demonstrated as applications in electrical interconnects, electrothermally driven artificial muscles, electromagnetic interference shielding materials, and reconfigurable antennas.

Highly Stretchable Polymer Composite with Strain‐Enhanced Electromagnetic Interference Shielding Effectiveness

“…As presented in Figure a and Figures S25–S30, Supporting Information, a large enhancement in the average EMI SE is observed for the 3D LM composite when loading strains on the sample, for example, from 41.5 dB of 2.0 mm thick pristine film to 81.6 dB (highest value: 87 dB at 26.5 GHz) of 400% stretched film with a thickness of 1.0 mm. In comparison, the current stretchable EMI shielding materials not only present limited stretchability (i.e., <300% strain) but also suffer from a dramatic decrease or an invariant in EMI SE when stretched (Figure 3a, and Table S2, Supporting information) 6–8,12,15,16. We also measure Al and Cu plates with a thickness of 1 mm under the same conditions and conclude that their EMI SE values are around 88 dB (Figure S31, Supporting Information).…”

“…Recently, a variety of electrically conductive fillers including metallic nanowires and nanoparticles,2,5–7 liquid‐metal (LM) droplets,8–10 carbon‐based materials (e.g., graphene, carbon fibers, and carbon nanotubes)1,11,12 and 2D transition‐metal carbides13–15 have been incorporated into polymer matrix to yield EMI shielding polymer composites. While these composites are easily processable, lightweight, and mechanically flexible, their EMI shielding effectiveness (SE) is inevitably plagued by the reduction in electrical conductivity with the applied stretch,6–8,12,15,16 a common phenomenon in the current stretchable conductors 17–19. For example, the EMI SE of the LM based‐composites decreases from ≈70 dB at 0% strain to ≈60 dB at 75% strain, and further to ≈35 dB at 300% strain 8.…”

Intrinsic elastic conductors with internal buckled electron pathway for flexible electromagnetic interference shielding and tumor ablation

“…Moreover, this bi-layered structure is difficult to use when an all-directional interconnect or a uniform bulk structure is required, such as in EMI shielding and radar wave absorption [25]. In our previous work [26], a layer-by-layer technique was used to prepare a multi-layer, buckled elastic conductor, which increased the conductivity while maintaining the resistance stability under deformation. However, this structure did not show conductivity in the thickness direction, and the preparation required complicate iterative coating-stretching processes.…”

Flexible, stretchable and magnetic Fe3O4@Ti3C2Tx/elastomer with supramolecular interfacial crosslinking for enhancing mechanical and electromagnetic interference shielding performance

“…The main part of EMI SE reduction is SE A (Fig. S10), which may be the result of attenuation of the conductivity and reduction in thickness during stretching [52,53]. Fig.…”