Spreading of a water droplet on a vertically aligned Si nanorod array surface

The dynamics of spreading of a water drop on a vertically aligned Si nanorod array surface is studied with a fast charge coupled device camera. Four dynamic spreading regimes are identified, with a precursor rim advancing ahead of the contact line. The diameters of the precursor rim $Dp$⁠, the precursor length $δ$⁠, and the contact line $Dc$ obey dynamic scaling laws, $Dc,p∝tnc,p∕2$⁠, with $nc≈0.216$ and $np≈0.272$⁠, and $δ≈t1∕2$⁠. The exponents do not vary significantly with the nanorod height and are consistent with the dynamic spreading behavior on a rough or porous surface.