Superoleophobic surfaces with short fluorinated chains?

Abstract

Due to the extremely low surface tension of oils, the elaboration of superoleophobic surfaces implies the development of well-defined strategies to impede their tendency to spread. Usually, these strategies combine the presence of re-entrant structures (overhang, mushroom-like, T-like structures, etc.) with perfluorinated compounds containing long perfluorinated tails. Due to the toxicity (bioaccumulative potential) of long perfluorinated tails, our strategy is to develop superoleophobic properties with short perfluorinated tails (perfluorobutyl or F-butyl). However, almost all our strategies failed because of their much lower intrinsic oleophobicity. Here, we show the possibility to reach superoleophobic properties by electrodeposition of original fluorinated (F-butyl, F-hexyl and F-octyl) 3,4-ethylenedioxythiophene derivatives containing an amide connector. Surprisingly, if superhydrophobic properties are obtained whatever the fluorinated chain length, superoleophobic properties are only obtained with F-butyl tails (θ_{sunflower oil} = 150.0° and θ_hexadecane = 132.1°). Here, the fibers, only obtained with F-butyl chains, have a much higher tendency to repel oils than spherical particles. It seems that the presence of nanofibrils (re-entrant structures) and amide connectors allow the stabilization of the Cassie–Baxter state (fakir state) to be increased with oil droplets, which makes it possible to reach a state close to the Cassie–Baxter state with a polymer containing F-butyl tails. We think that the amide connectors increase the presence of the F-butyl tails at the extreme surface by reducing their mobility.