Folding characteristics of membranes in capillary origami

A study was conducted to understand the effects of membrane shape, thickness, contact angle, surface tension and large deflection on capillary origami. For experiments, square and triangular membranes made of PDMS with various thicknesses and sizes were used to encapsulate different liquids. Models for membranes under pure bending were developed using the energy balance between interfacial energies (liquid-vapor, solid-liquid and solid-vapor energies) and bending energy evaluated by a small-deflection and a large-deflection assumptions. This paper is the first study to consider the large deflection for membranes as well as to include the terms for the wettability of the membrane and its shape. The developed models evaluated an important characteristic length, i.e., elasto-capillary length (L_EC), which is proportional to the critical length (L_critical) below which membranes cannot be closed to encapsulate liquid. The experimental results showed that the large-deflection model can estimate L_critical more accurately in terms of membrane shape, thickness, contact angle and surface tension for liquids with similar properties to water than the small-deflection model. The developed models should be further improved to extend the applicability to liquids with low surface tension and low contact angle.