Impact of Small-Scale Geometric Roughness on Wetting Behavior

Abstract

We examine the extent to which small-scale geometric substrate roughness influences the wetting behavior of fluids at solid surfaces. Molecular simulation is used to construct roughness wetting diagrams wherein the progression of the contact angle is traced from the Cassie to Wenzel to impregnation regime with increasing substrate strength for a collection of systems with rectangularly shaped grooves. We focus on the evolution of these diagrams as the length scale of the substrate features approaches the size of a fluid molecule. When considering a series of wetting diagrams for substrates with fixed shape and variable feature periodicity, we find that the diagrams progressively shift away from a common curve as the substrate features become smaller than approximately 10 fluid diameters. It is at this length scale that the macroscopic models of Cassie and Wenzel become unreliable. Deviations from the macroscopic models are attributed to the manner in which the effective substrate-fluid interaction strength evolves with periodicity and the important role that confinement effects play for substrates with small periodicities.

Passive water collection with the integument: mechanisms and their biomimetic potential

“…2) (Extrand, 2002;Quéré, 2008;Spori et al, 2008). Besides random roughness, specific geometric roughness in the range of nanometres and micrometres can also be used to control the wetting behaviour of a specific liquid-material combination (Zu et al, 2010;Kumar and Errington, 2013). The more precisely that a material surface can be manufactured, the more specific the modification of its wetting properties.…”

Molecular dynamics study of oil detachment from an amorphous silica surface in water medium

“…But the mechanism is different from this research about the surface roughness [14][15][16][17]. They studied the effect of roughness on adsorption [14,15], wetting [16,17]. While the roughness they created is artificial.…”

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“…One of the most fascinating wetting behaviour on nanorough substrates is the deviation from the predicted wetting diagram, such as the adoption of a Cassie‐like wetting state despite an unfavorable energy balance. Metastable Cassie state have intrigued researchers over the years and several approaches have been brought forwards to explain their occurrence first on micro and now on nano textured surfaces . These metastable states arise from the presence of high free energy barrier between local and absolute energy minima .…”