Controlling water adhesion on superhydrophobic surfaces with bi-functional polymers

With an aim to control the surface hydrophobicity and water adhesion, as observed on various natural surfaces, novel 3,4-propylenedioxythiophene (ProDOT) monomers having one and two 3-trimethylsilylpropyl (TMS) groups were synthesized and subjected to electropolymerization to form surface coatings. The monomer ProDOT is employed owing to its tendency to form fibrous structures by electropolymerization [T. Darmanin, F. Guittard, Mater. Chem. Phys. 146 (2014) 6–11], whereas the TMS groups generate very low surface energies comparable to short chain fluorocarbons [N. M. Kovalchuk, et al., Colloids Surfaces A 604 (2020) 125277.]. It is shown that even though these two types of monomer lead to fibrous structures, the dimensions of the fibers as well as the wetting properties are different. The monomer with only a single TMS group (ProDOTSiMe₃) generates extremely long nanofibers with only low surface roughness. The resulting surfaces have extremely high apparent contact angles (θ_w) up to 141.7° and strong water adhesion, similar to rose petals or gecko feet. On the other hand, the analogue with two TMS groups (ProDOT(SiMe₃)₂) forms short nanofibers but with extremely high surface roughness. The resulting surfaces are superhydrophobic with θ_w > 160° and ultra-low water adhesion (hysteresis and sliding angles < 1°), similar to lotus leaves. These results point to interesting applications offering control over water adhesion whilst maintaining high hydrophobicity.