The sacrificial bonds in natural materials have inspired the preparation of shape memory polymer (SMP), which can be prepared through the construction of dual cross-linking networks in a polymer matrix. With the rise of 4D printing technology, fine control over the shape recovery of SMPs, especially control over the recovery time, is urgently needed. In this study, the high-temperature aging method is adopted to tune the shape recovery time of dual cross-linked SMPs. Shape memory acrylonitrile butadiene rubber composite (i.e., NBR-C) is prepared by introducing Zn2+–CN coordination bonding and sulfur covalent cross-linking networks into the rubber matrix and then thermal aging at 180 °C for various time frames. Aging increases the covalent cross-linking density, ruptures rubber chains, and generates imine structures. Moreover, the composition of the coordination bonding network becomes diversified because of the formation of coordination bonds between imines and Zn2+ ions. The mechanical “tough-brittle” transition of aged NBR-C is observed, and its glassy temperature increases with aging time, which in turn changes the shape recovery time at the same recovery temperature. On the basis of these findings, the special shape memory rubber components with sequential recovery are fabricated by partially aging the NBR-C strings. This methodology provides novel solutions for the preparation of sequential SMP products without programming heating design or using redundant chemical materials. We believe that this work will be able to help promote comprehensive research of SMPs and widen applications of SMPs in the industry.

Recently, one interesting wetting phenomenon was found whereby a live frog can stably stand or easily jump on a floating lotus surface. Inspired by the floating leaf, constructing a lotus-like substrate is important to provide powerful aquatic support. In this article, a flexible and light-weight superhydrophobic paper was successfully fabricated by coating a mixture of polystyrene-poly(methyl methacrylate) copolymer (PS-co-PMMA) and silica nano-particles. The micro/nano structures from the composite coating render common papers to possess superhydrophobic surfaces with low adhesion.The coated paper restricts capillary absorption owing to its high water-repellency; moreover, it has an ultra-low absorption when completely soaked into water. A lotus-like support model with some origami frogs is made to display the floating feasibility of the coated paper. The maximum supporting force of the coated paper with an area of 30 Â 30 mm is equivalent to $68 times its own weight. The simple force analysis illustrates that the great carrying capacity of the coated paper comes from its superhydrophobicity. Importantly, the flexibility of the coated paper possibly gives rise to its good dynamic floating stability. We believe that flexible superhydrophobic paper can be practically applied to some smart designs like aquatic micro-devices.

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Under a magnetic field, the micro-robot could move directionally at air/water and oil/water interfaces in a closed system.