Remote, selective, and in situ manipulation of liquid droplets on a femtosecond laser-structured superhydrophobic shape-memory polymer by near-infrared light

Droplet manipulation plays a significant role in the fields of biomedical detection, microfluidics, and chemical engineering. However, it still remains a great challenge to simultaneously achieve remote, selective, and in situ droplet manipulation on the same surface. Here, Fe 3 O 4 nanoparticles were doped in a shape-memory polymer (SMP) to prepare a photothermal-responsive Fe 3 O 4 -SMP composite which showed remarkable near-infrared (NIR) light-triggered shape-memory property. Superhydrophobic micropillar array was constructed on such Fe 3 O 4 -SMP composite through femtosecond laser microfabrication and fluoroalkylsilane modification. The surface wettability of the as-prepared surface can transform from a low-adhesive sliding state to a high-adhesive pinning state as the micropillars are deformed by pressing. Interestingly, the deformed micropillars can stand up and restore to their original morphology under remote NIR light irradiation, resulting in the reversible and repeatable recovery of the ultralow-adhesive superhydrophobicity. With such light-triggered wettability switching, the droplets pinning on the sample surface can be remotely, selectively, and in situ released. Furthermore, the superhydrophobic Fe 3 O 4 -SMP surface is successfully applied in lossless liquid transfer, selective droplet release, and droplet-based microreactor. The as-fabricated superhydrophobic surfaces with NIR light-controlled reversible wettability will hold great promise in the fields of liquid manipulation, lab-on-a-chip, and microfluidics.