  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.
