Exceptionally Strong Effect of Small Structural Variations in Functionalized 3,4-Phenylenedioxythiophenes on the Surface Nanostructure and Parahydrophobic Properties of Their Electropolymerized Films

Abstract

Electropolymerization of electron-rich aromatics/heteroaromatics to form conducting polymers is an easy and powerful technique to form surfaces of different nanostructures and hydrophobicity/wettability. Understanding the factors governing the growth of the polymer nanostructures and controlling the surface morphology are the big challenges for the surface and materials science. In this paper, we report the design and synthesis of a series of 3,4-phenylenedioxythiophenes (PheDOTs) substituted at the benzene ring with 2-naphthylmethyl-, 1-naphthylmethyl-, and 9-anthracenylmethyl-groups (2Na-PheDOT, 1Na-PheDOT, and 9Ant-PheDOT). They have been electropolymerized in either potentiostatic or potentiodynamic conditions to form the polymer surfaces of different morphologies. Even small changes in the structure of PheDOT monomers by varying the side groups (2-/1-naphthyl-or 9-anthracenyl-) result in the formation of very different polymer surface nanostructures: From monodirectionally growing (one-dimensional) vertically aligned nanotubes for 2Na-PheDOT to ribbonlike nanostructures (two-dimensional) for 1Na-PheDOT, and a mixture of these two structures for 9Ant-PheDOT. Moreover, the surfaces of the p[2Na-PheDOT] polymer, electrodeposited from the monomer 2Na-PheDOT and the dimer (2Na-PheDOT)2 (which have different solubilities and the reactivities on electropolymerization, but formally lead to the polymer of the same chemical structure), show very different nanostructures. In contrast to 2Na-PheDOT, which forms vertically aligned nanotubes of the polymer on the surface, the polymerization of (2Na-PheDOT)2 leads to spherical particles [three-dimensional (3D)] when Bu4NClO4 is used as an electrolyte and a membrane structure with spherical holes (3D) in the case of more hydrophobic Bu4NPF6. The importance of water for gas bubble formation (O2 and H2) during electropolymerization and creation of the surface nanostructures has been demonstrated and discussed. The formation of these different nanostructures is accompanied by different wettability of the surface, from hydrophilic (with an apparent water droplet contact angle of θw ∼40-70°) to highly hydrophobic (θw up to 129-134°). The sticky, parahydrophobic surface formed from 1Na-PheDOT showed high adhesion to water, with no water droplets moving after inclination of the surface to 90° (rose-petal effect). Copyright © 2019 American Chemical Society.