3D Multiscale Micro-/Nanofolds by Femtosecond Laser Intermittent Ablation and Constrained Heating on a Shape Memory Polymer

Spontaneous wrinkling of films with a thickness gradient offers a new opportunity for constructing various 3D hierarchical surface morphologies. Unfortunately, accurately and facilely controlling the gradient film thickness to yield multiscale and 3D hierarchical micro-/nanostructures is still difficult. Here, a rapid, facile, and highly controllable fabricating strategy for realizing 3D multiscale hierarchical micro-/nanofolds on a shape memory polymer (SMP) surface is reported. First, the nanoparticle film with gradient thickness is rapidly (100 ms to 4 s) and facilely obtained by laser intermittent ablation on the SMP, termed as laser ablation-induced gradient thickness film. Following one-time constrained heating, the 3D micropillars grow out of the substrate based on the "self-growing effect," and the nanoparticle gradient film on its top shrinks into multiscale micro-/nanofolds simultaneously. Significantly, the evolution process and the underlying mechanism of the 3D micro-/nanofolds are systematically investigated. Fundamental basis enables us to accurately regulate the gradient thickness of nanoparticle films and feature size of folds by varying laser scanning times and scanning path. Finally, desirable patterns on micro-/nanofolds can be readily realized by programmable laser cleaning technology, and the tunable adhesion of the water droplet on the multiscale structured surface is demonstrated, which is promising for microdroplet manipulation.