Superhydrophobic nanocomposite coatings based on different polysiloxane matrices designed for electrical insulators

The present paper describes for the first time the influence of three different kinds of polysiloxane as hydrophobic agent on superhydrophobic coatings for electrical insulators: a trimethoxy (2,2,4-trimethyl pentyl)-based silane; a mixture of methyl methoxy siloxane with methylsilsesquioxane; a mixture of dimethyl siloxane, methylsilsesquioxanes and n-octyl silsesquioxanes. The polysiloxane properties were investigated by thermogravimetric (TGA) and hydrophobic (contact and sliding angles) analysis, indicating great differences on thermal properties and surface free energy. The polysiloxane binders were loaded with different sizes of microsized alumina trihydrate (ATH) and organophilic nanosilica functionalized with octyl-silane and polydimethylsiloxane (PDMS). The hydrophobicity of the coating was evaluated by water contact angle (WCA) and sliding angle (SA). The morphology and roughness of the coatings were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover the superhydrophobic durability of the coatings was evaluated by water immersion, hydrophobicity recovery, hydrophobicity transfer and adhesion. The effectiveness of these materials as coatings for glass electrical insulator was evaluated by tracking and erosion resistance using the inclined plane test (IPT). The results showed that the polysiloxane based on a mixture of methyl methoxy siloxane with methylsilsesquioxanee loaded with ATH and PDMS-treated silica exhibited the most promising characteristics as high contact angle, self-cleaning ability, good adhesion to the substrate and low number of leakage current peaks during the tracking and erosion resistance test. Such characteristics can bring benefits on electrical insulators like reducing the formation of conductive surface paths and the consequent degradation of the coating by dry band arcs, increasing its resistance when exposed to the electric field. • Hybrid nanosilica and alumina were used to create superhydrophobic coatings for electrical insulator applications. • Silica functionalized with PDMS provided better hydrophobic behavior than octyl-silane functionalized silica. • Hydrophobic stability was studied in detail for designed superhydrophobic coatings. • PDMS-base coatings with promising tracking and erosion resistance, self-cleaning ability and adhesion were reported.