Does surface roughness amplify wetting?

Abstract

Any solid surface is intrinsically rough on the microscopic scale. In this paper, we study the effect of this roughness on the wetting properties of hydrophilic substrates. Macroscopic arguments, such as those leading to the well-known Wenzel's law, predict that surface roughness should \emph{amplify} the wetting properties of such adsorbents. We use a fundamental measure density functional theory (DFT) to demonstrate the opposite effect from roughness for microscopically corrugated surfaces, i.e., wetting is \emph{hindered}. Based on three independent analyses we show that microscopic surface corrugation increases the wetting temperature or even makes the surface hydrophobic. Since for macroscopically corrugated surfaces the solid texture does indeed amplify wetting there must exist a crossover between two length-scale regimes that are distinguished by opposite response on surface roughening. This demonstrates how deceptive can be affords to extend the thermodynamical laws beyond their macroscopic territory.

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• When does Wenzel's extension of Young's equation for the contact angle of droplets apply? A density functional study
• Wetting in the presence of the electric field: The classical density functional theory study for a model system
• Phase behaviour of fluids in undulated nanopores
• Contact angle of water on a model heterogeneous surface. A density functional approach
• Geometry-induced interface pinning at completely wet walls