Curvature arising in shape memory polymer sheets via light absorption

Morphing is a process that spontaneously creates a three-dimensional (3D) curved surface shape from a two-dimensional flat sheet. It has attracted attention in various applications, ranging from flexible electronics to mechanical metamaterials. Some approaches can realize the morphing of a flat sheet through bending, folding, and buckling. Among these approaches, folding may create more complex 3D structures with a pre-strained shape memory polymer (SMP) sheet than other approaches. However, robust shape control is difficult because localized heating in the active zone when using SMP sheets presents practical challenges. In addition, the folding approach makes the edges sharp and limits the ridge pattern to create a smoothly curved shape. Here, we propose an alternative approach to morph the passive elements in an SMP sheet with two slits that define one active element and two passive elements in the sheet. These elements can buckle when shrinking the active element above the glass transition temperature via light absorption. We predict the curvature of the passive elements as a function of the shrinkage in the active zone and determine an approximate formula to describe the relationship between curvature and shrinkage. We find that the theoretical predictions agree well with the experimental results. Thus, our method could be an alternative approach for morphing techniques exploiting SMP sheets in response to light.