Secondary hydration is the main driving force of autogenous self-healing and directly impacts the closure of cracks in damaged cementitious materials . In fiber-reinforced cement composites , secondary hydration also dominates the regeneration of the fiber-matrix interface during the self-healing processes. As an important factor influencing the cement hydration , silica fume (SF) addition can be crucial to the self-healing performance of cementitious materials and composites. In this paper, the effect of SF on the autogenous self-healing of ultra-high-performance fiber-reinforced concrete was investigated. With a ≥20% SF addition, the secondary hydration the cement matrix adjacent to the cracks was accelerated. The dissolution of amorphous silica and the formation of Si-containing healing phases was observed. These effects predominated the closure of the mouth and the inner part of the cracks. SF addition also enhanced the regeneration of fiber-matrix interface by promoting the growth of self-healing products in these areas. The closure of cracks and the regeneration of fiber-matrix interface are both responsible for the restoration of flexural properties.
Magnetic actuators, which use magnetic effects for actuation, are very useful in many areas, such as electrical equipment, soft robots, and medical instruments. However, they inevitably suffer damage during long-term use, leading to mechanical failure. Introduction of the self-healing concept can solve this problem to a certain extent and extend their service life. Herein, a room-temperature self-healing magnetic nanocomposite is obtained using a simple, efficient, and environmental-friendly strategy. In the authors' design, soft poly(dimethylsiloxane) (PDMS) polymeric materials are chosen as the matrix, and Fe 3 O 4 nanoparticles are utilized as a functional magnetic nanofiller to obtain a new magnetic nanocomposite. By balancing the self-healing property and mechanical performance, the optimal content of magnetic filler is determined to be 15 wt%. The optimized sample exhibits an ultimate tensile strength (0.44 MPa), a high tensile strain (400%), and an excellent self-healing efficiency (62.2% mechanical recovery of fracture strength) at 25 °C for 30 min. Furthermore, this composite material shows an excellent and healable magnetic actuation performance. This new nanocomposite provides great potential for the magnetic actuation application.
Smart reconfigurable metamaterials can better adapt to changing electromagnetic environments and broaden the range of applications. However, constructing electromagnetic reconfigurable metamaterials, especially those with large areas or applied to complex surfaces via a universal approach, is still a challenge. Here, we introduce a smart reconfigurable metamaterial consisting of a thermadapt shape memory polymer ethylene vinyl acetate copolymer (EVA) matrix and a flowable liquid–metal resonant unit. Based on the excellent self-healing properties of EVA, large-area metamaterials can be constructed by thermal assembly of metamaterial units. In addition, the original shape of the metamaterial can be reprogrammed to apply to complex three-dimensional surfaces with the reprocessing properties of EVA. Moreover, by utilizing the shape memory performance of the EVA, the temporary resonant frequency of the metamaterial can be set by programming and the resonant frequency tuning of the metamaterial can be controlled under external temperature stimulation, achieving noncontact tuning. In the future, this concept can be broadly applied in fields such as complex structure stealth layers and multifunction filters.
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