Creation of Topological Ultraslippery Surfaces for Droplet Motion Control.

Droplet motion control on slippery liquid-infused porous surfaces (SLIPS) that mimics the peristome surface of Nepenthes alata has promising applications in the fields of energy, lab-on-a-chip device, etc., yet is limited due to the difficulty in regulating its wettability. In this work, topologies with specific functions from natural creatures, for example, grooved structures of rice leaf and wedge-shaped structures of shore bird beak with droplet transporting capability were integrated with the SLIPS. Three-dimensional topological SLIPS was fabricated on metal substrates using laser milling followed by alkaline oxidation. Fabricated rice leaflike grooved nanotextured SLIPS can properly shape the droplet footprint to achieve a sliding resistance anisotropy of 109.8 μN, which is 27 times larger than that of a natural rice leaf and can therefore be used to efficiently and precisely transport droplets; wedge-shaped nanotextured SLIPS can confine the droplet footprint and squeeze droplet to produce a Laplace pressure gradient for continuous self-driven droplet transport. The created surfaces can manipulate droplets of acid, alkali, and salt solutions. The proposed concept is believed to have potential applications for condensing heat transfer and droplet-based lab-on-a-chip devices.