Wetting of anisotropic sinusoidal surfaces—experimental and numerical study of directional spreading

Abstract

Directional wettability, i.e. variation of wetting properties depending on the surface orientation, can be achieved by anisotropic surface texturing. A new high precision process can produce homogeneous sinusoidal surfaces (in particular parallel grooves) at the microscale, with a nano-scale residual roughness five orders of magnitude smaller than the texture features. Static wetting experiments have shown that this pattern, even with a very small aspect ratio, can induce a strong variation of contact angle depending on the direction of observation. A comparison with numerical simulations (using Surface Evolver software) shows good agreement and could be used to predict the fluid-solid interaction and droplet behaviour on textured surfaces. Two primary mechanisms of directional spreading of water droplets on textured stainless steel surface have been identified. The first one is the mechanical barrier created by the textured surface peaks, this limits spreading in perpendicular direction to the surface anisotropy. The second one is the capillary action inside the sinusoidal grooves accelerating spreading along the grooves. Spreading has been shown to depend strongly on the history of wetting and internal drop dynamics.

Polymer Spreading on Unidirectionally Nanotextured Substrates Using Molecular Dynamics

“…From Figure 6, we observe that spreading is nonlinear with time; steps form such that d ⊥ is constant as a function of time when the polymer spreading front reaches texture grooves and peaks. Thus, in agreement with Kubiak and Mathia 9 and Fischer et al, 10 both peaks and grooves modify spreading, and we observe the pinning-depinning-repinning spreading mechanism previously described. 10,11,14,19,20 We also observe that the sharp θ = 60°substrate grooves and peaks inhibit perpendicular spreading longer than the sinusoidal wave grooves and peaks.…”

“…Thus, in agreement with Kubiak and Mathia 9 and Fischer et al, 10 both peaks and grooves modify spreading, and we observe the pinning-depinning-repinning spreading mechanism previously described. 10,11,14,19,20 We also observe that the sharp θ = 60°substrate grooves and peaks inhibit perpendicular spreading longer than the sinusoidal wave grooves and peaks.…”

“…Alternatively, the liquid may only be slowed by texture peaks, causing the contact line to advance in a stick-slip manner, pinning-depinning-repinning on subsequent texture peaks. 10,11,14,19,20 Conversely, others propose that anisotropic spreading is caused by texture grooves that accelerate spreading along the direction parallel to the texture, i.e., along the grooves. 9,10,15−18 Fischer et al 10 this accelerated spreading in part to capillary action inside the grooves, based on experiments with sinusoidal textures (height of 8 or 16 μm).…”

“…10,11,14,19,20 Conversely, others propose that anisotropic spreading is caused by texture grooves that accelerate spreading along the direction parallel to the texture, i.e., along the grooves. 9,10,15−18 Fischer et al 10 this accelerated spreading in part to capillary action inside the grooves, based on experiments with sinusoidal textures (height of 8 or 16 μm). In addition, Zhang et al 17 used Monte Carlo simulations and experiments (square-shaped textures with a height of 0.03-0.05 μm) to explain that an increased surface force exists inside a groove because it is surrounded by as many as three surfaces; i.e., a square groove is composed of a base and two side-walls.…”

Analysis of surface roughness morphology with TRIZ methodology in automotive electrical contacts: Design against third body fretting-corrosion

“…However, it is known that high surface quality promotes friction damage [32]. Kubiak et al [30,[33][34][35] report that surface geometry influences friction conditions due to the increased contact force on rough surfaces [36]. This makes it possible to control the friction between the partial slip (only the outer contact area is exposed to the slip, while the central area remains in an adhesive state) and the total slip (the entire contact surface is exposed to the slip).…”