Versatile Superhydrophobic Surfaces from a Bioinspired Approach

We report the surface wettability and morphology of conductive polymer films obtained by electrodeposition of poly(3,4-ethylenedioxythiophene) (i.e., PEDOT) derivatives containing an alkyl chain (PEDOTHn with n = 4, 6, 8, 10, and 12) or a phenyl (PEDOTPh) group in the 2-position. Even if the general approach in the literature is the use of highly fluorinated tail to reach superhydrophobic materials, we point out that versatile surfaces (from hydrophilic to superhydrophobic) can be obtained, in one step, without any fluorinated chemistry. Indeed, superhydrophobic surfaces were formed, using Bu4NPF6 and acetonitrile as electrolyte, by electrodeposition of PEDOT derivatives substituted with n-C10H21 and n-C12H25 chains, while the polymer films substituted with n-C8H17 and n-C6H13 were hydrophobic and those substituted with n-C4H9 and phenyl were hydrophilic. In the PEDOTHn series, the polymer films were structured only from n-C8H17, which proves the influence of long alkyl chains on both the surface wettability and the surface morphology due to the increase in polymer insolubility. By changing acetonitrile by dichloromethane, as solvent of electropolymerization, it is possible to produce smooth surfaces and as a consequence to determine the chemical and physical parts of the contact angles as well as roughness factors or air fractions following the Wenzel and Cassie-Baxter theories. By changing the salt for the electrodeposition, it also was possible to reach superhydrophobic surfaces even with short alkyl chains as well as without alkyl chains but using perfluorinated salts. In this work the mechanism to reach structured surfaces is also discussed. This work contributes to the formation of bioinspired superhydrophobic surfaces.