Laser cutting of polymer templates for water-droplet induced self-folding of micron cubes: hinge geometry optimization

Droplet-induced self-folding processes enable the easy and cost-effective fabrication of submillimeter 3D structures from planar templates. These templates were fabricated by laser cutting of polymer foils that offers a high flexibility in design. The interaction of water droplets with template surfaces induces a surface tension force that causes deformation of the laser-cut templates needed to form the 3D structures. In this study, laser patterning of 25 µm thick polyimide (PI) foils by UV ultrashort pulse laser ablation was used to systematically investigate the effect of hinge thickness 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. The results provide guidelines for experimental optimization and reference data for computer-aided optimization of water droplet-induced self-folding of 3D structures.