Design principles for superamphiphobic surfaces

Abstract

To predict the properties of superamphiphobic layers we analyzed the wetting of a square and a hexagonal array of vertical pillars composed of spheres (radius R) partially sintered together. Apparent contact angles above 150 are obtained by pinning of a non-polar liquid surface at the underside of the top sphere resulting in a Fakir or Cassie state. Analytical equations are derived for the impalement pressure in the limiting case A 0 [ R 2 , where A 0 is the area of the regular unit cell containing a single pillar. The case of close pillars is investigated numerically. By balancing forces at the rim of a drop, we calculate the apparent receding contact angle. To describe drag reduction of a flowing liquid we calculate the apparent slip length. When considering pressure-induced flow through cylindrical capillaries of radius r c , significant drag reduction occurs only for thin capillaries. The mechanical stability with respect to normal forces and shear is analyzed. Nanoscopic silica glass pillars would be able to sustain the normal and shear stresses caused by capillary and drag forces. For a high impalement pressure and good mechanical stability A 0 should be small and R (respectively the neck diameter) should be large, whereas a large A 0 and a small R imply low contact angle hysteresis and high slip length.

Superamphiphobic surfaces

“…Interestingly,  Adv ,  Rec , and  SA for hexadecane on the beadsonly surface are 156°, 150° and 5°, respectively. In comparison, the beads-on-strings and fibers-only surfaces shows a slightly 10 higher CAH with  Adv / Rec values of 153°/141° and 153°/134°, respectively. Recently, the same research group demonstrated that similar textured surfaces can also be fabricated by spraying the FD-POSS/PMMA blend.…”

“…The surface can be roughly deemed as superantiwetting if both water and 'oils' can move freely on the surface without any sticking. However, to characterize a superantiwetting surface quantitatively, precise determinations of static 10  CA and CAH, which are normally performed with commercial instruments, are needed. More than 200 years ago, Thomas Young, the genius polymath who made major contributions to vision, physiology, sound, light, 20 language, solid mechanics, and Egyptology, described the forces acting on a liquid droplet spreading on a surface (Fig.…”

“…[23][24][25] For example, Leng et al 23 functionalized woven fibers with a layer of microscale silica via in situ Stöber reaction, 5 followed by further modification with another layer of nanoscale silica via physical adsorption. Briefly, a piece of cotton textile was immersed in a room temperature mixture of methanol, isopropanol, and ammonium solution in the presence of tetraethylorthosilicate for several hours, and then cleaned with 10 methanol in an ultrasonic bath repeatedly so as to remove the physically adsorbed particles. Subsequently, the obtained textile was soaked in 3-aminopropyltriethoxysiloxane solution to generate surface amine groups which were then protonated with hydrochloric acid.…”

“…Differently, n-type Si (100) film with surface pyramid structure can be prepared by etching the substrate in a aqueous solution of KOH and isopropanol at 85 °C for 20-30 min. 38 Glass can be 10 tailored by ion etching, and subsequently chemical etching in aqueous HF. 39 Besides the etching techniques discussed above, other etching methods such as plasma etching 40 and water etching 41 can also be applied, depending on the chemical property of the substrate.…”

“…50 Briefly, Zn plates, either those without any pretreatment or those treated for 2 h in a -20 °C refrigerator or in a 10 80 °C oven, could be used as the substrates. The galvanic replacement reactions were carried out by simply immersing the substrates in aqueous AgNO 3 for various time intervals, followed by cleaning with deionized water and drying in air.…”