Flexible transparent hierarchical nanomesh for rose petal-like droplet manipulation and lossless transfer

Precise manipulation of water is a key step in numerous natural and synthetic processes. Here, a new flexible and transparent hierarchical structure is determined that allows ultra-dexterous manipulation and lossless transfer of water droplets. A 3D nanomesh is fabricated in one step by scalable electrospinning of low-cost polystyrene solutions. Optimal structures are composed of a mesh of dense nanofiber layers vertically separated by isolated mesoporous microbeads. This results in a highly adhesive superhydrophobic wetting that perfectly mimics rose petal-like structures. Structural-functional correlations are obtained over all key process parameters enabling robust tailoring of the wetting properties from hydrophilic to lotus-like Cassie-Baxter and rose-like Cassie-impregnating states. A mechanistic model of the droplet adhesion and release dynamics is obtained alongside the first demonstration of a mechanically induced transfer of microdroplets between two superhydrophobic coatings. This low-temperature reaction-free material structure demonstrates a facile means to fabricate impenetrable residue-less rose petal-like surfaces with superhydrophobic contact angles of 152 ± 2° and effective adhesion strength of 113 ± 20 μN. This is a significant step toward parallel, multistep droplet manipulation with applications ranging from flexible on-paper devices to microfluidics and portable/wearable biosensors.