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 (R) 200 and a coarse-sized Aeroperl (R) 300/30, were employed at various contents to modify the films' surface roughness. SEM and AFM analysis revealed that the Aerosil (R) 200 had more uniform deposition onto the etched polyelectrolyte layer due to its very fined size while the Aeroperl (R) 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 (R) 200. The films containing the Aerosil (R) 200 had very high contact angles of 167-175 degrees and very low surface energy of 0.03-0.51 mJ m(-2), while the films containing the Aeroperl (R) 300/30 had lower contact angles of 132-154 degrees and higher surface energy of 3.07-11.29 mJ m(-2). (c) 2009 Elsevier B.V. All rights reserved.