Ultra-hydrophobic biomimetic transparent bilayer thin film deposited by atmospheric pressure plasma

Abstract

An open-air atmospheric pressure plasma was used to deposit ultrahydrophobic bilayer coatings. The plasma set-up was tuned, allowing the successive injection in the post-discharge of two monomers. To the best of our knowledge, no study describes the successive deposition by atmospheric plasma of two precursors, which could work in synergy and allow designing composite coatings of high added value. In this study, two liquid precursors were chosen for the deposition of single and bilayer coatings: (i) hexamethyldisiloxane (HMDSO) and (ii) 1H,1H,2H,2H-perfluorooctyltriethoxysilane (pFOTES). Single layer coatings (HMDSO and pFOTES) as well as bilayer coating (HMDSO/pFOTES) were analysed using multiscale techniques: Scanning Electron Microscopy (SEM), profilometer, Atomic Force Microscopy (AFM), Fourier-Transformed Infrared Spectroscopy (FTIR), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and drop shape analysis. The bilayer system (HMDSO/pFOTES), resulting from the successive deposition of HMDSO and pFOTES precursors, was confirmed by ToF-SIMS characterization while contact angle measurements highlighted the ultrahydrophobic property of the bilayer: water was fully repelled, with a zero contact angle hysteresis. This resulted from the combination of the multiscale roughnesses of the HMDSO-based and pFOTES based layers, combined with the intrinsic hydrophobicity of the pFOTES layer.