Bioinspired Topological Surface for Directional Oil Lubrication.

Directional droplet transport widely exists in biological surfaces that greatly inspire the development of a great deal of engineered devices allowing for directional liquid transport in diverse energy and water applications. Despite extensive advances in this area, it remains a challenge to guide the directional spreading of lubricating oils by virtue of the bioinspired design of surface topography in the lubricity field. In this paper, we develop a bioinspired topological surface textured with simple V-shaped posts elegantly distributed in the parallel channels, which allows for an efficient and unidirectional transport of various lubricating oils. We also clarify the propagation of a precursor film and the coalescence effect between the original droplet and the precursor film in the preferential direction, as well as the pinning effect in the reverse direction, which integrate seamlessly to create a long-range directional oil transportation. The directional oil transportation promises a potential application of directional lubrication, creating a functional surface consisting of two zones with different lubrication properties as evidenced by different friction coefficients.