RESUMEN
Unidirectional transport of liquids has attracted the attention of researchers in recent years for its wide application foreground. However, it is still a challenge to control the spreading of liquid, especially for oils with relatively high viscosity. In this paper, a flexible surface textured with branch-shaped microstructures is proposed. These asymmetric microstructures exhibit excellent unidirectional spreading behaviors for various oils. By suitably stretching the flexible surface to different stretch ratios, the spreading length of the oil droplets can be controlled. Moreover, the ongoing forward spreading of oil droplets can be suspended dynamically when the surface is stretched to 40%. Corresponding mechanism analysis demonstrates that surface stretching can narrow and close the microvalves between adjacent branches, which restrain the flow of the precursor film and the primary droplet. The switchable unidirectional spreading behavior enables the surface with such microstructures to be used for oil transportation, oil-water separation, and controllable lubrication.
RESUMEN
A surface with asymmetric microstructures for self-driven directional spreading of liquid has attracted keen interest from researchers in recent years for its great application prospects. Inspired by the jaws of tiny insects, such as ants, a surface textured with novel jaw-like microstructures as micro one-way valves is reported. These microstructures are almost two-dimensional, thus being simple and easy to fabricate. Whereas surfaces with such jaw-like micro one-way valves exhibit amazing rapid and long-distance water droplet unidirectional spreading behaviors. The maximum forward-backward distance ratio of water droplets on surfaces with the optimized microstructures is about 14.5, almost twice those of previous research. The capillary attraction at the location of the mouth of the jaws and the pinning effect brought by the sharp edge of the jaws for the precursor film are analyzed and deduced as the main mechanisms. The findings open a promising avenue for 2D asymmetric microstructure design and effective self-driven liquid unidirectional spreading.