Preparation of superhydrophobic porous coating film with the matrix covered with polydimethylsiloxane for oil/water separation

Abstract

In this work, an organic coating film was designed to have a porous microstructure together with a rough surface, and its matrix was covered with a low surface energy layer, so that it can be employed for oil/water separation based on its superhydrophobicity and superoleophilicity. First, a mixture solution of poly(styrene-block-butadiene-block-styrene) (SBS) and polydimethylsiloxane (PDMS) prepolymer was sprayed onto stainless steel mesh in a non-solvent vapor atmosphere of ethanol. After solvent evaporation, a porous coating film has been obtained. The film matrix was formed from SBS to have a nodular-microstructure, which was covered by the highly flexible PDMS prepolymer. Then, the PDMS prepolymer was cured to cover the nodular microstructure at 60 °C, which was chosen to be far below the glass transition temperature of polystyrene block of SBS in order to maintain the formed nodular microstructure. The microstructures of the obtained coating films were carefully characterized and analyzed. Water and oil contact angles on the coating films were measured to indicate their wetting properties of superhydrophobicity and superoleophilicity. The oil diffusion speed along the coating film and the oil swelling behavior were examined to suggest the advantages of the covering PDMS layer. The coating films have been employed for oil/water separation through self gravity-driven filtration, where oil could penetrate the coating film automatically while water retained. The oil separation rate was found to be higher than 99.0% and the flux was estimated to be greater than 162 L∙h−1 m−2. Moreover, the cycling tests suggest the satisfactory reusability of the coating film, implying its potential applications in oily wastewater treatment or oil spill recovery.