Development of schemes to form complex three-dimensional (3D) mesostructures in functional materials is a topic of broad interest, thanks to the ubiquitous applications across a diversity of technologies. Recently established schemes in the mechanically guided 3D assembly allow deterministic transformation of two-dimensional structures into sophisticated 3D architectures by controlled compressive buckling resulted from strain release of prestretched elastomer substrates. Existing studies mostly exploited supporting substrates made of homogeneous elastomeric material with uniform thickness, which produces relatively uniform strain field to drive the 3D assembly, thus posing limitations to the geometric diversity of resultant 3D mesostructures. To offer nonuniform strains with desired spatial distributions in the 3D assembly, this paper introduces a versatile set of concepts in the design of engineered substrates with heterogeneous integration of materials of different moduli. Such heterogeneous, deformable substrates can achieve large strain gradients and efficient strain isolation/magnification, which are difficult to realize using the previously reported strategies. Theoretical and experimental studies on the underlying mechanics offer a viable route to the design of heterogeneous, deformable substrates to yield favorable strain fields. A broad collection of 3D mesostructures and associated heterogeneous substrates is fabricated and demonstrated, including examples that resemble windmills, scorpions, and manta rays and those that have application potentials in tunable inductors and vibrational microsystems.
Keywords: buckling; heterogeneous materials; soft materials; strain engineering; three-dimensional assembly.