Design and Fabrication of Micro-textures for Inducing a Superhydrophobic Behavior on Hydrophilic Materials

Abstract

Artificial superhydrophobic surfaces are typically fabricated by tuning the surface roughness of intrinsically hydrophobic surfaces. We report here the design and fabrication of micro-textures for inducing a superhydrophobic behavior on hydrogen-terminated Si surfaces with an intrinsic water contact angle of approximately 74 degrees . The micro-textures consist of overhang structures with well-defined geometries fabricated by microfabrication technologies, which provide positions to support the liquid and prevent the liquid from entering into the indents between the micro-textures. As a result, water is in contact with a composite surface of solid and air, which induces the observed macroscopic superhydrophobic behavior.

Plastron induced drag reduction and increased slip on a superhydrophobic sphere

“…By contrast, biomimetic engineered surfaces are typically characterized by a regular array of indentations and/or protrusions. 42 In either circumstance, the presence of these micro-scale features is expected to depress air velocities within the plastron due to the additional viscous drag associated with flow past this micro-topography. So whereas the curves of figure 2 exhibit unambiguous minima corresponding to the smallest possible drag experienced by a plastron-retaining superhydrophobic sphere, the associated predictions of (ξ SH ) min and h * /b may be conservative.…”

Fabrics with Tunable Oleophobicity

“…The liquid repellency of the dip-coated fabric is highlighted in Fig. 3e which shows that this fabric is able to support a composite interface and display high apparent contact angles (" * It should however be noted that when the equilibrium contact angle " < 90°, the composite interface is necessarily metastable, [4,19,20,25,[41][42][43] i.e. it corresponds to a local minimum in the overall Gibbs free energy for the system, while the fully-wetted Wenzel state corresponds to the global minimum.…”

Tunable nano-replication to explore the omniphobic characteristics of springtail skin

“…Thus, our data prove the recently proposed geometrical control over wetting of Collembola skin, 10 supporting and extending findings on engineered omniphobic surfaces. [37][38][39] Furthermore, the CassieWenzel transition at elevated pressures was observed to occur as a stepwise process, enabling a reversible partial wetting due to nanoplastrons remaining entrapped inside the skin nanocavities, which facilitates recovery of the de-wetted state upon pressure reduction. The resulting last barrier against complete wetting can, for example, effectively protect springtails against suffocation in rain (rain droplets have a dynamic pressure in the range from 100 to 1000 hPa).…”