Deterministic Self-Morphing of Soft-Stiff Hybridized Polymeric Films for Acoustic Metamaterials

We reported a soft-stiff hybridized polymeric film that can self-morph to dedicated three-dimensional (3D) structures for application in acoustic metamaterials. The hybridized film was fabricated by laterally adhering a soft and responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel to stiff and passive SU-8 patterns. Upon thermal stimulation, deformation of the tough PNIPAM hydrogel was locally constrained by the stiff SU-8 patterns, thereby causing laterally nonuniform strain to their interfaces for mechanically buckling the hybridized films to 3D structures. Combined with finite element analysis, we demonstrated that the stiff SU-8 patterns effectively alleviated the uncontrollability and uncertainty during the self-morphing process, which was caused by unexpected mutual deformation between the active and passive domains in the self-morphing materials. Therefore, deterministic self-buckling to dedicated 3D structures was physically realized such as a wave-shaped peak-valley structure, 3D checkerboard patterns, and Gaussian curved surfaces from the hybridized polymeric films. Finally, we demonstrated that the self-morphed 3D structures with predesigned patterns can be used as acoustic materials for subwavelength noise control. This transformative way of constructing 3D structures by self-morphing of the hybridized polymeric films will be a substantial progress in fabricating smart and multifunctional materials for widespread applications in metamaterials, soft robotics, and 3D electronics.