Optical analysis of a transparent slippery surface by controlling the refractive index of the porous structure

This report demonstrates the fabrication of a transparent slippery surface and an investigation of its transparent property by systematically controlling the refractive index. The slippery surface, fabricated by a simple method, was shown to have a water-repellent property similar to those of captured insects sliding into the pitcher of Nepenthes. The as-fabricated opaque porous structures were covered by a siloxane lubricant and showed high optical transmittance in the visible light region. In particular, the difference in the refractive indices between the lubricant and porous structure served as a crucial variable for obtaining a transparent surface. Slippery surfaces were fabricated by using various kinds of nanoparticles (SiO₂, Al₂O₃, ZrO₂, and TiO₂), and the mechanism behind the transparency of these surfaces was investigated by comparing their transmittances using a UV spectrophotometer. The results show that SiO₂ nanoparticle, with a refractive index of 1.46, is the most suitable material for use with the siloxane lubricant. The average transmittance of the slippery surface composed of SiO₂ nanoparticle is approximately 80% in the visible light region. Through this study, the transparency of slippery surfaces can be further understood.