Surfaces which possess extraordinary water attraction or repellency depend on surface energy, surface chemistry and nano-and microscale surface roughness. Synergistic superhydrophilic-underwater superoleophobic surfaces were fabricated by a spray deposition of nanostructured TiO 2 on stainless steel mesh substrates. The coated meshes were then used to study gravity driven oil-water separation, where only the water from the oil-water mixture is allowed to permeate through the mesh. Oil-water separation efficiencies of up to 99 % could be achieved through the coated mesh of pore sizes 50 and 100 micron, compared to no separation at all, that was observed in the case of uncoated meshes of the same material and pore sizes. An adsorbed water on the TiO 2 coated surface, formation of a water-film between 2 the wires that form the mesh and the underwater superoleophobicity of the structured surface are the key factors that contribute to the enhanced efficiency observed in oil-water separation.The nature of the oil-water separation process using this coated mesh (in which the mesh allows water to pass through the porous structure but resists wetting by the oil phase) minimizes the fouling of mesh so that the need for frequent replacement of the separating medium is reduced. This fabrication approach presented here can be applied for coating large surface areas and to develop a large-scale oil water separation facility for oil-field applications and petroleum industries.

We employ a free-energy lattice-Boltzmann method to study the dynamics of a ternary fluid system consisting of a liquid drop driven by a body force across a regularly textured substrate, infused by a lubricating liquid. We focus on the case of partial wetting lubricants and observe a rich interplay between contact line pinning and viscous dissipation at the lubricant ridge, which become dominant at large and small apparent angles, respectively. Our numerical investigations further demonstrate that the relative importance of viscous dissipation at the lubricant ridge depends on the drop to lubricant viscosity ratio, as well as on the shape of the wetting ridge.

The transport of small amounts of liquids on solid surfaces is fundamental for microfluidics applications. Technologies allowing control of droplets of liquid on flat surfaces generally involve the generation of a wettability contrast. This approach is however limited by the resistance to motion caused by the direct contact between the droplet and the solid. We show here that this resistance can be drastically reduced by preventing direct contact with the help of dual-length scale micro-structures and the concept of “liquid-surfaces”. These new surfaces allow the gentle transport of droplets along defined paths and with fine control of their speed. Moreover, their high adhesion permits the capture of impacting droplets, opening new possibilities in applications such as fog harvesting and heat transfer.

The current paradigm of self-propelled motion of liquid droplets on surfaces with chemical or topographical wetting gradients is always mono-directional. In contrast, here, we demonstrate bidirectional droplet motion, which we realize using liquid infused surfaces with topographical gradients. The deposited droplet can move either toward the denser or the sparser solid fraction area. We rigorously validate the bidirectional phenomenon using various combinations of droplets and lubricants, and different forms of structural/topographical gradients, by employing both lattice Boltzmann simulations and experiments. We also present a simple and physically intuitive analytical theory that explains the origin of the bidirectional motion. The key factor determining the direction of motion is the wettability difference of the droplet on the solid surface and on the lubricant film.

We theoretically investigate the apparent contact angle of droplets on liquid infused surfaces as a function of the relative size of the wetting ridge and the deposited droplet. We provide...