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 D-p, the precursor length delta, and the contact line D-c obey dynamic scaling laws, D-c,D-p proportional to t(c,p)(n)/2, with n(c)approximate to 0.216 and n(p)approximate to 0.272, and delta approximate to t(1/2). The exponents do not vary significantly with the nanorod height and are consistent with the dynamic spreading behavior on a rough or porous surface. (c) 2007 American Institute of Physics.