Effect of topography on the wetting of nanoscale patterns: experimental and modeling studies

Abstract

We investigated the influence of nanoscale pattern shapes, contours, and surface chemistry on wetting behavior using a combination of experimental and modeling approaches. Among the investigated topographical shapes, re-entrant geometries showed superior performance owing to their ability to restrain the liquid-air interface in accordance with Gibbs criteria. The wetting state is also controlled by the surface texture in addition to the surface chemistry. Topographies with smaller intrinsic angles are better able to support the liquid droplet. Based on these observations, two geometrical relationships for designing superhydrophobic patterns exhibiting the Cassie-Baxter state are proposed. A detailed analysis of the simulation results showed the presence of viscous forces during the initial transient phase of the droplet interaction with the solid surface even at negligible normal velocity, which was verified experimentally using a high-speed imaging technique. During this transient phase, for a polystyrene surface, the liquid front was observed to be moving with a radial velocity of 0.4 m s(-1), which gradually decreased to almost zero after 35 ms. We observed that the viscous energy dissipation density is influenced by the surface material and topography and the wetting state. The viscous energy dissipation density is minimal in the case of the Cassie-Baxter state, while it becomes quite significant for the Wenzel state. The viscous effects are reduced for topographies with smooth geometries and surfaces with high slip length.

Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study

“…From phase diagrams in Figs 6 and 7, we conclude that the dewetting behavior in small wetting angle condition is relatively simple: the film can only be stable in pits, this is consistent with many of previous studies for liquid layers on substrates with either chemically313233343536373839404142 or topologically4142434445464748 patterned. However, for large wetting angle, the dewetting behavior is much more complex even in the simple deep pit condition as considered in current paper: the film can be either stable in pits or on mesas, which gives us an alternative method to control the position and arrangement of the desired nanostructure by operating on the substrate geometry and film thickness in addition to on the wetting angle as in cases of chemically patterned substrate.…”

“…In contrast to the lack of theoretical understanding for SSD, the morphological evolution of liquid wetting layers on chemically313233343536373839404142 or topographically4142434445464748 structured substrates has been studied extensively and detailed morphological phase diagrams have also been given31323335. In general, there are mainly two types of liquid wetting processes.…”

Combining the lotus leaf effect with artificial photosynthesis: regeneration of underwater superhydrophobicity of hierarchical ZnO/Si surfaces by solar water splitting

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In recent years, the non-wetting property of superhydrophobic surfaces submerged in water has attracted much attention because it has potential applications in drag reduction, anti-fouling, anti-corrosion, waterproof devices, microchannels, anti-icing and other non-wetting related applications. [16][17][18][19][20][21][22][23][24][25] Practical applications of non-wetting surfaces, however, have been impeded by the limited stability of their underwater superhydrophobicity.…”

Questions and Answers on the Wettability of Nano‐Engineered Surfaces

“…This corresponds, for a liquid‐air system, to velocities below 0.01 m/s. Therefore, both viscous and capillary forces govern the quasi static wetting regime, while surface tension forces dominate in static wetting states . Nevertheless, it is well known that the final macroscopic value of the apparent contact angle depends on its dynamic history .…”