Bioinspired silica-containing polyurethane-acrylate films: Towards superhydrophobicity with tunable water adhesion

In this paper, a convenient, straightforward, and large-scale transferable approach for the preparation of fluorine-free bioinspired superhydrophobic silica-filled photo-crosslinked polyurethane-acrylate (PUA) nano-composite films is reported. The enrichment of the hydrophobic fumed silica at the film surface and especially its inherent dual scale dimension, related to its synthesis, enables to endow the film with super water-repellent features. Particularly, the effect of the silica content from 0 to 60 wt% is studied and the wettability properties of the resulting nanocomposite films are investigated in link with the chemical composition and the surface morphology at different scales. It is shown that different wetting states can be achieved from Wenzel to Cassie impregnating and then Cassie-Baxter regime, dictated by the silica content present at the air surface. Thus, by simply varying the silica content, the water adhesion can be adjusted from very high for a silica content equal to 50 wt% to extremely low for a silica content equal to 60 wt%, imparting the film with "Lotus" or "rose petal" effect, respectively. The as-prepared slippery or sticky nanocomposite films are shown to exhibit long-lasting wettability performances.