Long-living, stress- and pH-tolerant superhydrophobic silica particles via fast and efficient urethane chemistry; facile preparation of self-recoverable SH coatings

Abstract

Superhydrophobic (SH) and water-rolling oligomer wrapped silica particles (OWS) were synthesized using a one-step method by employing the quick and efficient silanol–isocyanate surface reaction. The presence of urethane/allophanate linkages and oligomer formation over the silica surface was confirmed using FTIR and MALDI-TOF-MS analyses. The thin coating of the particles displayed a static contact angle of >160°, a roll-off angle of ∼3° and exhibited a micro-nano structure as shown in the FESEM images. The OWS particles are tolerant to variations in pH either side of the pH scale, from 1 to 13, exhibiting water roll-off properties when exposed to harsh acidic and basic conditions. The pH tolerance was observed after mechanical damage. The rapidity and efficiency of the method was demonstrated with a low extent of grafting also. The superhydrophobic particles are long-living as they retained SH properties in different pH conditions even after one year of continuous exposure to ambient conditions. Furthermore, the SH particles with an incorporated cross-linked poly(dimethylsiloxane) coating displayed excellent pH and stress resistance. Surprisingly, the SH coating exhibits self-recoverable superhydrophobicity without an external stimulus (under ambient conditions) or heat treatment after water impalement, pH, boiling water and stress tests.