Light-Driven Shape Morphing, Assembly, and Motion of Nanocomposite Gel Surfers.

Patterning of nanoparticles (NPs) via photochemical reduction within thermally responsive hydrogel films is demonstrated as a versatile platform for programming light-driven shape morphing and materials assembly. Responsive hydrogel disks, containing patterned metal NPs, form characteristic wrinkled structures when illuminated at an air/water interface. The resulting distortion of the three-phase (air/water/hydrogel) contact lines induces capillary interactions between two or more disks, which are either attractive or repulsive depending on the selected pattern of light. By programming the shapes of the NP-rich regions, as well as of the hydrogel objects themselves, the number and location of attractive interactions are specified, and the assembly geometry is controlled. Remarkably, appropriately patterned illumination enables sustained rotation and motion of the hydrogel disks. Overall, these results offer insight into a wide variety of shape-programmable materials and capillary assemblies, simply by controlling the NP patterns and illumination of these soft materials.