High-valued utilization of fly ash for preparing mechanically robust and multi-scale superhydrophobic coatings

Fly ash (FA) is an industrial solid waste which adds burden to the environment. Superhydrophobic surfaces (SHSs) are widely or potentially applied in various fields, like self-cleaning, drag reduction, oil/water separation, anti-corrosion, anti-icing, and so on. This paper proposes a novel and facile way to reutilize varisized FA particles to prepare superhydrophobic coatings which exhibit excellent water-repellency and mechanical wear resistance. The FA particles undergo chemical modification (MFA), then physically mixing with polydimethylsiloxane (PDMS), and finally spraying or dipping to obtain the nano/micro, nano-micro, and nano-micro-submillimeter hydrophobic/superhydrophobic surfaces (MFA@PDMS) on versatile substrates. The MFA@PDMS coating shows that the nano-micro co-existed particles could achieve the best superhydrophobic property with excellent water-repellency and mechanical wear resistance. The results of SEM, FITR and contact angle indicate that the surface of FA was roughened after modification and the wettability of MFA particles transferred from hydrophilic to hydrophobic. The prepared nano-micro MFA@PDMS coating remains superhydrophobic even after 60 times unidirectional abrasion under 500 g weight, due to the fact that the presence of polydimethylsiloxane enhanced the binding force between inter-particles as well as particle-substrate. In addition, it was demonstrated that the nano-micro MFA@PDMS SHSs could effectively separate the oil/water mixtures.