Rapid Volatilization Induced Mechanically Robust Shape-Morphing Structures toward 4D Printing.

Inspired by diverse shape-shifting phenomena in nature, various man-made shape programmable materials have been developed for applications in actuators, deployable devices, and soft robots. However, fabricating mechanically robust shape-morphing structures with on-demand, rapid shape-transformation capability, and high load-bearing capacity is still a great challenge. Herein, we report a mechanically robust and rapid shape-shifting material system enabled by the volatilization of a non-fully-reacted, volatile component in a partially cured cross-linking network obtained from photopolymerization. Volume shrinkage induced by the loss of the volatile component is exploited to drive complex shape transformations. After shape transformation, the residual monomers, cross-linkers, and photoinitiators that cannot volatilize still exist in the network, which is ready for a further photopolymerization to significantly stiffen the initial material. Guided by analytic models and finite element analysis, we experimentally demonstrate that a variety of shape transformations can be achieved, including both 2D-to-3D and 3D-to-3D' transformations, such as a buckyball self-folding from a 2D hexagonal lattice sheet and multiple pop-up structures transforming from their initial compact configurations. Moreover, we show that an ultra-low-weight 3D Miura-ori structure transformed from a 2D sheet can hold more than 1600 times its weight after stiffness improvement via postcuring. This work provides a versatile and low-cost method to fabricate rapid and robust shape-morphing structures for potential applications in soft robots, deployable antennas, and optical devices.