Surface characteristics of water-repellent polyelectrolyte multilayer films containing various silica contents

Water-repellent films were dip-coated onto glass substrate by mimicking a unique surface feature of the lotus leaf by a layer-by-layer deposition of polyelectrolyte, followed by SiO₂ particle to modify surface roughness, and finally a semifluorinated silane to lower the surface energy. Two types of the SiO₂, a fine-sized Aerosil^® 200 and a coarse-sized Aeroperl^® 300/30, were employed at various contents to modify the films' surface roughness. SEM and AFM analysis revealed that the Aerosil^® 200 had more uniform deposition onto the etched polyelectrolyte layer due to its very fined size while the Aeroperl^® 300/30 had less uniform deposition due to its coarser size. In both cases, higher SiO₂ content in the films led to more surface roughness and more hydrophobicity, although the effect was not dramatic in the case of Aerosil^® 200. The films containing the Aerosil^® 200 had very high contact angles of 167-175°and very low surface energy of 0.03-0.51 mJ m^− 2, while the films containing the Aeroperl^® 300/30 had lower contact angles of 132-154°and higher surface energy of 3.07-11.29 mJ m^− 2.