Contact Angle Hysteresis and Work of Adhesion of Oil Droplets on Nanosphere Stacking Layers

Abstract

Surface repellency of liquid droplets with different surface tensions (23.4-73.2 mN/m) on nanostructured surfaces built of one-and two-tier silica sphere stacking surfaces were investigated, and contact angle hysteresis (CAH) and work of adhesion were analyzed. It was shown that the binary nano-and sub-micrometer-scaled roughened surfaces exhibited better repellency toward oil drops with surface tension of 30 mN/m, and the CAH behavior strongly depended on both liquid types and density of three-phase contact line. This improvement of hysteresis from the two-tier texture is attributed to the facts that (i) the arrangement of submicrometer spheres generates a primary roughness that allows air cushion in the texture and (ii) the deposition of nanospheres creates a large number of point contact fashion to repel the oil penetration, reducing the length of the liquid-solid contact line (i.e., Cassie state). The existing air layer tends to impart the fraction of vapor-solid contact, which decreases the kinetic barrier of drop movement. Incorporated with the Young-Dupre `equation, it has shown a linear relationship between the difference between cosines of advancing and receding angles and the work of adhesion. Accordingly, it reveals that the adhesion of solid-oil contact interface is reduced due to the design of surface topography.

Recent developments in polymeric superoleophobic surfaces

“…Generally, they are composed of inorganic nanoparticles, which enhance the roughness, and organic fluoropolymers, which provide a low surface energy. 66 nanoparticles are the most common inorganic materials. There are three typical approaches: (1) the nanoparticles are first blended with the fluoropolymer, then the solution is coated onto the substrates; 83,85,91,93 (2) the nanoparticles are first modified with low surface energy compounds, then the modified particles are coated on the substrates; 84,88,92 (3) the nanoparticles are first stacked on the substrates, then coated with fluoropolymers.…”

“…There are three typical approaches: (1) the nanoparticles are first blended with the fluoropolymer, then the solution is coated onto the substrates; 83,85,91,93 (2) the nanoparticles are first modified with low surface energy compounds, then the modified particles are coated on the substrates; 84,88,92 (3) the nanoparticles are first stacked on the substrates, then coated with fluoropolymers. 66,86,87 Schutzius et al followed the first approach, and made dispersions by combining fluoropolymer blends with clay nanoparticles or carbon nanowhiskers. 93 After spray processing onto substrates, the composite coatings showed water and water-alcohol repellent properties.…”

“…4(C)]. 66,86,87 Plasma Treatment Plasma treatments used to create superoleophobic surfaces include plasma etching and plasma polymerization. They can be adopted as the only technique or coupled with other techniques as a combination to create superoleophobic surfaces.…”

Superoleophobic surfaces: design criteria and recent studies

“…Hsieh et al 58 prepared silica sphere stacks with two-tier roughness by using a two-stage spin-coating technique (Figure 8a-8c). When the surfaces were further spin-coated with a perfluoroalkyl methacrylic copolymer, they displayed an advancing contact angle θ adv * ≈ 150° and contact angle hysteresis Δθ * ≈ 3° for hexadecane.…”

Enhancing Water and Oil Repellency of Teflon Surface By Imparting Micro-Rough Structures Using Simple One-Step

“…Lotus effect (Nosonovsky et al, 2009;Cheng et al, 2006) is the best example of surfaces with high CA but small CAH, small SA, while Petal effect (Feng et al, 2008;Bhushan et al, 2010) is the best example of high CA and large CAH as well, and consequent large SA. For the liquid droplet to slide by the effect of its weight ( ) after tilting the substrate (SA) by a specific angle of ( ), can be expressed as (Xiu et al, 2008;Hsieh et al, 2009):…”