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 robotics. 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 crosslinking 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, crosslinkers, 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 buckyballs self-folding from 2D sheets and multiple popping-up structures transforming from their initial compact configurations. Moreover, we show that an ultralow-weight 3D Miura-ori structure transformed from a 2D sheet can hold more than 1600 times its weight after stiffness improvement via post-curing. This work provides a versatile and low-cost method to fabricate rapid and robust shape-morphing structures for potential applications in soft robotics, deployable antennas, and optical devices.