Fabrication and characterization of high performance superhydrophobic organosilane-coated fly ash composites with novel micro–nano-hierarchy roughness

High hydrophobicity and environmental adaptability are the key performance indicators for the application of fly ash (FA) as waterproof filling material in landfill and building engineering. However, the current hydrophobic modification of fly ash is mainly based on the simple mixing or coating of hydrophobic agent and adhesive. This physical adsorption hydrophobic modification method based on weak intermolecular force such as van der Waals force will lead to poor hydrophobic stability and environmental adaptability. In this study, a preparation method of superhydrophobic FA with micro–nano-hierarchy roughness by coupling polydimethylsiloxane (PDMS) and FA through siloxane covalent bond (–Si–O–Si–) under the action of catalyst and mechanical external force was explored for the first time, and the microstructure, chemical properties and wettability of FA and superhydrophobic FA were characterized. The environmental resistance of superhydrophobic FA, such as acid and alkali resistance, high temperature resistance and ultraviolet resistance, were evaluated. The results show that PDMS is successfully grafted to the surface of FA particles by means of Si–O–Si covalent bond, and the mechanical external force gives the superhydrophobic FA greater micro–nano-roughness. The combination of low surface energy and micro-roughness successfully changes the FA from superhydrophilic to superhydrophobic, where the water contact angle (WCA) increases from 21° to 155°, and the water sliding angle (WSA) reaches 8°. The robustness of acid and alkali resistance, high temperature and ultraviolet resistance show that superhydrophobic FA has good environmental tolerance.Graphical abstract A preparation method of superhydrophobic fly ash which can endow fly ash with low surface energy and micro–nano-roughness is proposed for the first time. PDMS was grafted onto the surface of fly ash particles by siloxane covalent bond. The super hydrophobic fly ash obtained has good environmental adaptability.