Self-folding of polymer sheets using microwaves and graphene ink

Abstract

Self-folding represents an attractive way to convert two-dimensional (2D) material sheets into three-dimensional (3D) objects in a hands-free manner. This paper demonstrates a simple approach to self-fold thin pre-strained polystyrene (PS) sheets using microwaves. While the PS sheets are transparent to microwaves, patterns of screen-printed ink containing graphene absorb microwaves and cause the underlying printed sections of the sheet to warm up. When the local temperature in the inked region exceeds the glass transition temperature of PS (∼103 °C), the strain in the inked regions of the film relaxes gradually across the sheet thickness, which causes the PS sheet to fold. The resulting dihedral angle is proportional to the width of the hinge printed by graphene ink. The geometry and azimuthal orientation of the sample inside the microwave reactor affect the quality of the folding due to the non-uniformity of the microwave energy inside the reactor. While self-folding has previously utilized heat, light, photo-chemistry, and solvent swelling, this paper reports the use of microwaves, which can deliver large amounts of energy remotely.