Influence of long alkyl spacers in the elaboration of superoleophobic surfaces with short fluorinated chains

Abstract

In order to produce extremely high oleophobic properties with a low fluorine content, long dodecyl spacers were introduced between a polymer and fluorinated chains in order to reduce the mobility of the fluorinated chains, especially short perfluorobutyl (F-butyl) chains. We report the synthesis and characterization of electrodeposited polymer surfaces obtained from original fluorinated 3,4-ethylenedioxypyrrole (EDOP) derivatives. Semi-fluorinated chains of three different lengths (F-octyl: PEDOPC₁₂F₈, F-hexyl: PEDOPC₁₂F₆ and F-butyl: PEDOPC₁₂F₄) were grafted to EDOP and separated with a n-dodecyl chain in order to reduce the mobility of F-butyl chains. For the first time, a surprisingly high contact angle of 138° was measured with hexadecane on PEDOPC₁₂F₄, although F-octyl tails are necessary to produce robust superoleophobic surfaces. By producing smooth surfaces, we successfully separate the influence of the intrinsic hydro- and oleophobicity and the surface structuration on the static contact angles of water and hexadecane. Here, the surface structuration increases the contact angle of hexadecane by 90° for PEDOPC₁₂F₄. The Cassie–Baxter equation predicts a porosity of 84.5% between the surface and a hexadecane droplet.