Smart PDMS sponge with switchable pH-responsive wetting surface for oil/water separation

A smart sponge with porous structures and switchable hydrophobic-oleophilic or hydrophilic-underwater-oleophobic properties by varying the medium pH is successfully fabricated. This special sponge with a controllable wetting surface is prepared simply by introducing active hydroxyls on the surface of a fabricated poly(dimethylsiloxane) (PDMS) sponge and then esterifying it with picolinic acid. Under the synergistic action of raw PDMS chains and functionalized chains in different media the water contact angles decrease from 138 degrees (pH = 7.0) to 10 degrees (pH = 2.0), whereas the oil contact angles increase from 0 degrees (pH = 7.0) to 140 degrees (pH = 2.0) from neutral or alkaline to very acidic media underwater. The basic structure, chemical components, element type, contact angle and restorability of the sponge are also investigated. Owing to its stability and great practicability, this functionalized pH-responsive sponge can be directly used for oil/water separation. The switchable oil capture and release in aqueous media by our functionalized sponge can provide a new avenue to avoid secondary pollution in oil/water separation processes.