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