Preparation and characterization of a durable superhydrophobic hyperbranched poly(dimethylolbutanoic acid-glycidyl ester of versatic acid)/nano-SiO2 coating

Abstract A novel method combining the use of nano-SiO2 and the hydrophobic hyperbranched polymer, poly(dimethylolbutanoic acid-glycidyl ester of versatic acid) (poly(di-MBA-TM10)), as a binder was proposed for the fabrication of superhydrophobic coatings. The structure of hyperbranched poly(di-MBA-TM10) was characterized along with surface morphology and elemental analysis of coatings via 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared (FTIR), water contact angle (WCA), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The resulting superhydrophobic coatings have water contact angles of 169.7° and showed resistance to acidic, alkaline, and neutral media. The superhydrophobic surface was prepared by the embedding method, and it retains its hydrophobicity even after 100 cycles of sanding and knife-scoring. The surface of the coating consists of binary nano and microstructure. SEM showed that the thorn-like protrusions that provide sufficient roughness required for superhydrophobicity were observed on the surface. The XPS and AFM data show that these protrusions are mainly composed of nano-SiO2 aggregates and alkyl chains of hyperbranched poly(di-MBA-TM10). Uniformity of the surface roughness is a key factor to obtain a superhydrophobic coating. A possible mechanism was briefly described here in which the nucleation of nano-SiO2 aggregates provided a synergistic effect for the superhydrophobicity. The results from SEM and AFM showed that the nano-aggregates detected on the superhydrophobic surfaces were the aggregates of individual nano-SiO2. Superhydrophobic surfaces prepared from our embedded method can be used as coatings for funnels to collect rainwater in precision rain gauges.