Wetting resistance of heterogeneous superhydrophobic coatings with orthogonally layered fibers

Abstract

a b s t r a c tSuperhydrophobic coatings comprised of electrospun nanofibers are a low-cost alternative to micro-fabricated surfaces, and can be applied to substrates of any arbitrary geometry. Such coatings with orthogonally oriented layers have properties that allow their wetting resistance to be predictable for a range of solid volume fractions, fiber diameters, and contact angles. In this paper, we have presented a modeling strategy that solves for the airwater interface shape over several layers of such coatings to predict the resistance of superhydrophobic fiber coatings to hydrostatic pressures and to quantify the relationship between microstructure, meniscus penetration depth, and wetted surface area of the fibers. Slip length predictions are also provided to shed some light on the performance of such coatings in drag reduction applications. It was found that while failure pressure for a coating rises with reducing fiber spacing, there is a tradeoff with wetted fiber surface area relative to a bare substrate. This tradeoff can be offset, however, by using smaller fibers for an intended coating. This results in a higher failure pressure for the same wetted area fraction. The results generated in this work are discussed in relation to those reported in the literature whenever possible.

Droplet Mobility on Hydrophobic Fibrous Coatings Comprising Orthogonal Fibers

“…The easiest way to produce a fibrous coating with directional fibers is to deposit parallel fibers in orthogonal layers. This helps to produce coatings with a reasonably controlled thickness or porosity. − As will be discussed in the next section, we produce electrospun polystyrene (PS) coatings comprising orthogonally oriented layers of aligned fibers and use these coatings in studying the role of surface microstructure on droplet mobility. Our study is also accompanied by numerical simulations to provide additional insight into the physics of droplet mobility on a surface.…”

Contribution of Interfacial Bonding towards Geopolymers Properties in Geopolymers Reinforced Fibers: A Review

“…To the best of our knowledge, there has been no research on using mathematical functions to simulate or quantify fiber roughness. Although the shape and arrangement of the actual roughness are arbitrary, for the sake of simplicity, the sine roughness (the sine function is also used to describe the roughness on the plane) is used [54][55][56][57]. In each cross-section of the fibers, the rose function (sine curve in polar coordinates) can cause sinusoidal roughness [58].…”

Effects of roughness on droplet apparent contact angles on a fiber

“…The surface energy minimization method implemented in the Surface Evolver (SE) finite element code is used to simulate the 3-D shape of a droplet deposited on a rough fiber. SE has shown to be accurate in predicting the airwater interface stability (see e.g., [25][26][27][28]). In this section, we first present the equations for producing a fiber having an arbitrary 3-D roughness, and then derive an equation for the energy of a droplet deposited on such a fiber.…”