Sprayable Superoleophobic Coatings for Pumpless Handling of Low-Surface-Tension Liquids

Limited attention has been paid to repellency and wettability-confined transport of low-surface-tension liquids, such as oils, alcohols, and hydrocarbons. This is because repellency becomes very difficult for fluids with surface tension below 30 mN m-1. This situation is encountered in many engineering applications using organic liquids and thus, oleophobic surfaces are of high technological importance. In this work, a nanocomposite coating comprising of fluorinated silica micro- and nanoparticles (filler), a copolymer (binder), and traces of fluorinated polyhedral oligomeric silsesquioxane (additive, lowest surface-energy crystalline material reported to date) is spray-deposited on a surface pretextured by laser etching, a technique that requires no lithographic processing. The approach results in surfaces that can repel liquid hydrocarbons with surface tension as low as 21.14 mN m-1 and also hinder the spreading of heptane (19.74 mN m-1) at room temperature. The repellency of several organic liquids with surface tensions in the range of 19.7 - 27 mN m-1 is experimentally investigated and compared with water (baseline case). To study the effect of fluid properties, comparisons are performed between the distances traveled and the velocities of microliter droplets transported pumplessly on wedge-shaped wettability-patterned tracks that confine the liquids by the superoleophobic background surrounding the wettable tracks. Facile superoleophobic coatings are formulated to repel low surface-tension liquids, such as octane (21.1 mN m-1), and also inhibit the spreading of even lower surface-tension liquids, such as heptane (19.7 mN m-1). Microfluidic functionality is demonstrated in terms of pumpless droplet transport of such fluids on wedge-shaped wettable tracks laid in a superoleophobic background made of the novel coating reported herein. image