Investigation of capillary forces using atomic force microscopy

An atomic force microscope tip, coated with a small amount of liquid silico ne, was used to investigate the wetting and capillary bridging forces on va rious low- and high-energy surfaces. The low-energy surfaces were prepared by reacting alkyl and perfluoroalkyl functional silanes with a silicon wafe r (Si/SiO2). Force-distance scans in air revealed that the silicone fluid f orms ductile capillary bridges on the low-energy methyl and perfluoromethyl surfaces, whereas a tight bridge is formed on silica. Further studies on a silicon wafer possessing a gradient of surface energy shed more light on t he relationship between surface wettability and capillary forces, These obs ervations can be modeled in a general way using the Young-Laplace equation. The understanding of these capillary interactions at nanoscopic levels may have important applications, especially in the controlled deposition of li quid droplets on surfaces.