Fabrication of the hierarchically roughened bumpy-surface topography for the long-lasting highly oleophobic “lotus effect” on cotton fibres

In this study, a long-lasting highly oleophobic “lotus effect” was developed on the cotton fabric surface by fabricating the hierarchically roughened bumpy-surface topography with a low surface energy. The process was performed in two stages, where the three following approaches were used for the first stage: (1) surface incorporation of Stöber silica particles, which were prepared in advance with average diameters of 50 ± 15, 230 ± 20 and 780 ± 30 nm, (2) in situ generation of a particle-containing polysiloxane layer, (3) in situ generation of the particle-containing polysiloxane layer on the cotton fibres with the previously incorporated Stöber silica particles. In the second stage, the nanometre-scale structures with a simultaneous reduction of surface free energies were obtained using the sol–gel processing of fluoroalkylfunctional water-born oligosiloxane (FAS). The static contact angle measurements with water θ(W) and n-hexadecane θ(C16) and sliding (roll-off) (α) angle measurements with water on the FAS-coated surfaces show that the in situ created particle-containing polysiloxane layer on the cotton fibres with surface-incorporated Stöber particles remarkably minimized the solid/water interface and maximized the water/air interface, which enabled the fabrication of the artificial “Lotus effect”. This effect was characterized with the extremely low roll-off angle, i.e., α = 2°, and was accompanied by an exceptionally high oleophobicity, where θ(C16) approaches the value of 150°. The noteworthy high durability of these coatings successfully preserves their outstanding performances even after two laboratory washings that correspond to ten domestic washings.