Buckled carbon nanotube network thin-film fabricated using chemically swelled elastomer substrates

Fabrication and Functionality Integration Technologies for Small-Scale Soft Robots

Small-scale soft robots are attracting increasing interest for visible and potential applications owing to their safety and tolerance resulting from their intrinsic soft bodies or compliant structures. However, it is not sufficient that the soft bodies merely provide support or system protection. More importantly, to meet the increasing demands of controllable operation and real-time feedback in unstructured/complicated scenarios, these robots are required to perform simplex and multimodal functionalities for sensing, communicating, and interacting with external environments during large or dynamic deformation with the risk of mismatch or delamination. Challenges are encountered during fabrication and integration, including the selection and fabrication of composite/materials and structures, integration of active/passive functional modules with robust interfaces, particularly with highly deformable soft/stretchable bodies. Here, methods and strategies of fabricating structural soft bodies and integrating them with functional modules for developing small-scale soft robots are investigated. Utilizing templating, 3D printing, transfer printing, and swelling, small-scale soft robots can be endowed with several perceptual capabilities corresponding to diverse stimulus, such as light, heat, magnetism, and force. The integration of sensing and functionalities effectively enhances the agility, adaptability, and universality of soft robots when applied in various fields, including smart manufacturing, medical surgery, biomimetics, and other interdisciplinary sciences.

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes

Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable devices. Various coating strategies and testing setups have been developed to further improve their stretchability and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure is missing. In this work, the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks are studied by large-scale SEM straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, we were able to identify three fundamental deformation modes of NWs, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. Considering HRTEM and MD simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can further improve fabrication and design strategies for transparent NW network electrodes.

Synthesis of Diamond-Like Carbon Nanofiber Films

A film formed of densely packed amorphous carbon nanofibers is synthesized by chemical vapor deposition using acetylene and hydrogen gases as precursors and copper nanoparticles (<25 nm in diameter) as the catalyst at low temperatures (220-300 °C). This film has a high concentration of sp³ carbon (sp³/sp² carbon ratio of ∼1-1.9) with a hydrogen concentration of 25-44 atom %, which qualifies it as hydrogenated diamond-like carbon. This hydrogenated diamond-like carbon nanofiber film has properties akin to those of diamond-like carbon films. It has a high electrical resistivity (1.2 ± 0.1 × 10⁶ Ω cm), a density of 2.5 ± 0.2 g cm^-3, and is chemically inert. Because of its morphology, different from diamond-like carbon films on the nanometer scale, it has a higher surface area of 28 ± 0.7 m² g^-1 and has differences in mechanical properties, such as Young's modulus, hardness, and coefficient of friction. The hydrophobicity of this film is comparable to the best diamond-like carbon films, and it is wettable by oil and organic solvents. The nanofibers can also be separated from the substrate and each other and be used in a powder form.