Self-Healing Nanofibers for Engineering Applications

Chemical-based Hydrogen Storage Systems: Recent Developments, Challenges, and Prospectives

Hydrogen (H2) is being acknowledged as the future energy carrier due to its high energy density and potential to mitigate the intermittency of other renewable energy sources. H2 also ensures a clean, carbon-neutral, and sustainable environment for current and forthcoming generations by contributing to the global missions of decarbonization in the transportation, industrial, and building sectors. Several H2 storage technologies are available and have been employed for its secure and economical transport. The existing H2 storage and transportation technologies like liquid-state, cryogenic, or compressed hydrogen are in use but still suffer from significant challenges regarding successful realization at the commercial level. These factors affect the overall operational cost of technology. Therefore, H2 storage demands novel technologies that are safe for mobility, transportation, long-term storage, and yet it is cost-effective. This review article presents potential opportunities for H2 storage technologies, such as physical and chemical storage. The prime characteristics and requirements of H2 storage are briefly explained. A detailed discussion of chemical-based hydrogen storage systems such as metal hydrides, chemical hydrides (CH3OH, NH3, and HCOOH), and liquid organic hydrogen carriers (LOHCs) is presented. Furthermore, the recent developments and challenges regarding hydrogen storage, their real-world applications, and prospects have also been debated.

Dual-Shell Microcapsules for High-Response Efficiency Self-Healing of Multi-Scale Damage in Waterborne Polymer-Cement Coatings

Waterborne polymer-cement coatings have been widely applied in building materials due to their organic solvent-free nature, low cost, and eco-friendliness. However, these coatings can easily crack during the drying process as a result of construction environment factors, compromising the barrier performance of the coating and limiting its large-scale application. In this study, a dual-shell self-healing microcapsule was developed, which can effectively heal damage on a macro scale in waterborne polymer-cement coatings. Specifically, this dual-shell self-healing microcapsule was designed with a silica gel shell and a tannic acid-cuprum (TA-Cu) double-shell structure embedded with an epoxy resin (EP) healing agent, which was successfully fabricated via a two-step in situ polymerization. This silica gel shell self-healing microcapsules can effectively load into waterborne polymer-cement coatings. As the coating dries and solidifies, the silica gel shell of the microcapsule also becomes loose and brittle due to dehydration. This improves the mechanical initiation efficiency of the microcapsules in the coating. This study provides a novel approach for the application of self-healing microcapsules in waterborne coating systems, which can significantly reduce cracking during the drying process of waterborne polymer-cement coatings and improve the service life of the coating under complex conditions.

Self-Healing of Polymers and Polymer Composites

This review is devoted to the description of methods for the self-healing of polymers, polymer composites, and coatings. The self-healing of damages that occur during the operation of the corresponding structures makes it possible to extend the service life of the latter, and in this case, the problem of saving non-renewable resources is simultaneously solved. Two strategies are considered: (a) creating reversible crosslinks in the thermoplastic and (b) introducing a healing agent into cracks. Bond exchange reactions in network polymers (a) proceed as a dissociative process, in which crosslinks are split into their constituent reactive fragments with subsequent regeneration, or as an associative process, the limiting stage of which is the interaction of the reactive end group and the crosslink. The latter process is implemented in vitrimers. Strategy (b) is associated with the use of containers (hollow glass fibers, capsules, microvessels) that burst under the action of a crack. Particular attention is paid to self-healing processes in metallopolymer systems.