Laser Cutting of Polymer Templates for Water-Droplet Induced Self-Folding of Cubes: Hinge Geometry Optimization

Droplet-induced self-folding processes enable the easy and cost-effective fabrication of millimeter to submillimeter 3D structures from planar templates.These templates were fabricated by laser cutting of polymer foils that offer a high flexibility in design.The interaction of water droplets with template surfaces induces a surface tension force that causes the deformation of the laser-cut templates needed to form the 3D structures.In this study, laser patterning of 25 m thick polyimide (PI) foils by UV ultrashort pulse laser ablation was used to systematically investigate the effect of hinge geometry on the bending and self-folding process of cubes.The deposition of water droplets on the laser-structured samples leads to forces that move the side faces of the cube template causing a defined deformation of the hinges of the PI template and resulting in a bending angle between hinged template regions.The bending angle was determined as a function of hinge geometry and water droplet volume.The bending angle is increased with increasing droplet volume below a certain maximum but decreased with increasing hinge thickness and width.Finally, 2D laser cut templates with optimized v-shaped hinge structures was sucessful formed into a cube by laser droplet induced self folding.