Microphase Separation-Driven Sequential Self-Folding of Nanocomposite Hydrogel/Elastomer Actuators

초록

Untethered stimuli-responsive soft materials with programmed sequential self-folding are of great interest due to their ability to achieve task-specific shape transformation with complex final configuration. Here, reversible and sequential self-folding soft actuators are demonstrated by utilizing a temperature-responsive nanocomposite hydrogel with different folding speeds but the same chemical composition. By varying the UV light intensity during the photo-crosslinking of the nanocomposite hydrogel, different types of microstructures can be realized via phase separation mechanisms, which allow to control the folding speeds. The self-folding structures are fabricated by integrating two dissimilar materials (i.e., a nanocomposite hydrogel and an elastomer) into hinge-based bilayer structures via extrusion-based 3D printing. It has been demonstrated that the folding kinetics can be accelerated by more than one order of magnitude due to the phase-separated microstructure formed by the relatively weaker UV intensity (≈10 mW cm-2) compared to the one formed by stronger UV intensity (≈100 mW cm-2). 3D structures with sequential self-folding capabilities are realized by prescribing actuation speeds and folding angles to specific hinges of the nanocomposite hydrogel. Sequential folding box and self-locking latch structures are fabricated to demonstrate the ability to capture and hold objects underwater.

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