Drop impact on chemically structured arrays

We describe recent investigations on the impact behaviour of liquid drops onto chemically structured surfaces. The surface patterns were prepared via photochemical attachment of polymer molecules with different hydrophilicities using self-assembled monolayers of benzophenone bearing silanes. Immobilization of the polymer monolayers was followed by an ablation process to generate a chemical surface pattern. Impact experiments on systems consisting of very hydrophobic poly(perfluoroalkylethyl)acrylate coatings and hydrophilic areas show that within certain limitations the water drop has a strong tendency to reach the hydrophilic spots, even for inclined substrates. Impact experiments of drops on arrays of hydrophilic spots on the background of a perfluorinated polymer show that the drops spontaneously self-centre on the lithographically generated pattern. The obtained results suggest that the process can be used to circumvent some of the current problems in micro-array fabrication.