Thermomechanically Triggered Two-Stage Pattern Switching of 2D Lattices for Adaptive Structures

Pattern switching (or transformation) widely exists in the activities of various creatures and plays an important role in designing adaptive structures in modern materials. Utilizing the glass transition behavior in amorphous polymers, thermomechanically triggered two-stage pattern switching of 2D lattices is achieved, where components made of an amorphous polymer and a flexible elastomer are interconnected in predesigned layouts. Upon loading at room temperature, the elastomer is far more flexible than the amorphous polymer and the lattice switches into one pattern. With temperature increasing, the modulus of the amorphous polymer decreases due to glass transition. Under the proper choice of amorphous polymer whose storage modulus can decrease to below the modulus of the elastomer, a change in the relative stiffness can be achieved and can switch the overall pattern from one to another while maintaining the external load. Both the experimental and computational studies are carried out to investigate the switching mechanism. Several periodic structures are fabricated to demonstrate several switched patterns. Particularly, a proof-of-concept smart window design is fabricated to explore the potential engineering applications.