Figure 1 The scheme of the reaction network for creating chemical fuel-driven temporary materials.
Meanwhile, the concept of DSA has been also applied to designing functional fuel-driven temporary materials. Unlike the permanent materials of which stability was considered as their advantage, temporary (transient) materials can spontaneously collapse without external destruction. The time-dependent variety brings more opportunities to realize new functions and applications. The external energy that drives the formation of temporary materials can be from light, [13-15] sound, [16-18] mechanical forces, [19] or chemical fuels, etc. However, chemical fuel-driven temporary materials are the most frequently reported among them. The principle to realize artificial fuel-driven DSA provides an effective strategy to prepare a fuel-driven temporary material. As shown in Figure 1, a well-designed precursor reacts with chemical fuel to yield an aggregated or cross-linked molecular structure which can result in the formation of a bulky material. However, the aggregation or crosslink is thermodynamically unstable in presence of a deactivator. The reaction between the material and the deactivator led to the gradual dissociation of the aggregation or cross-linking, as well as the disintegration of the material.
In recent years, a great effort has been made to investigate chemical fuel-driven temporary materials. A number of such type of materials have been reported. In this review, we will provide a brief overview of the reaction networks that can be applied to construct fuel-driven temporary materials, then systemically discuss recent examples of all kinds of fuel-driven temporary materials, such as gels, inks, nanoreactors, self-healing materials, and nanochannels. Finally, the challenges of investigating fuel-driven temporary materials and some perspectives on the function and application of such kind of materials will be discussed.
2. Chemical fuel-driven reaction networks
The key to constructing a fuel-driven temporary material is to find a reaction network (Figure 1) that contains a temporally existent intermediate product, which is usually fast produced by the reaction between the chemical fuel and the precursor in the material, then spontaneously decomposes or be consumed by the reaction with other components. [9, 20] The formation and decomposition of the temporary material rely on the existence of the intermediate product. The lifetime of the temporary material depends on the duration of the existence of the intermediate product. Recently, with the continual report on fuel-driven DSA, a number of such reaction networks have been established. They were listed in Table 1 with the relative reference.
Table 1 Reaction networks that were applied for realizing artificial DSA and fuel-driven temporary materials