Self-folding of thick paper via continuous solution supply analyzed by FTIR spectroscopy

Origami techniques can impart mechanical properties to sheet materials, and stimulus responsive self-folding enables their transformation into three-dimensional structures. For practical origami devices such as load bearing structures, packaging components, and soft robotic bodies, folding of thick sheets is essential because thicker materials provide the strength durability needed for reliable deployment. However, conventional one pass inkjet printing cannot achieve 180° folding even in 127 μm thick paper. We therefore set 153 μm as a challenging target thickness that exceeds the folding limit of previous inkjet-based approaches. To overcome this constraint, we propose a self-folding method based on continuous solution supply from wetted filter paper. Diffusion simulations show that continuous supply produces a deeper through thickness concentration profile that governs subsequent transport. Experiments show that this initial state strongly affects the folding outcome, enabling 180° folding under continuous supply. FTIR-ATR analysis provided key mechanistic insight, revealing that large folding angles arise when the difference in hydrogen bonding between the surfaces becomes small, indicating through-thickness homogenization of the chemical state. These findings show that continuous solution supply enables controlled folding in thick substrates, providing a route to programmable three-dimensional architectures for deployable origami devices.