PH ‐Responsive PDMS ‐ AA ‐ UA ‐ SiO ₂ @ MS Sponge With Switchable Wettability for Efficient and Recyclable Oil‐Water Separation

Oily wastewater poses significant threats to environmental ecosystems and human health, and the inherent complexity of oil–water mixtures underscores the urgent need for advanced, intelligent separation materials. In this study, we report the development of a pH‐responsive sponge with reversible wettability switching, designed for efficient and adaptive oil–water separation. Acrylic acid‐terminated polydimethylsiloxane (PDMS‐AA) was synthesized via sodium ethoxide‐initiated ring‐opening polymerization of octamethylcyclotetrasiloxane (D 4 ), followed by end‐capping with acrylic acid. Subsequently, a bifunctional copolymer (PDMS‐AA‐UA) was prepared through free‐radical copolymerization of PDMS‐AA and 10‐undecenoic acid (UA), which was then grafted onto hydrophilic SiO 2 nanoparticles to form a micro‐/nano‐structured composite coating. The resulting sponge exhibits reversible, pH‐driven wettability transitions. Under acidic (pH 1) and neutral (pH 7) conditions, the surface displays superhydrophobicity with a water contact angle (WCA) of approximately 160°, enabling selective oil absorption. Upon exposure to alkaline conditions (pH 14), deprotonation of carboxyl groups renders the surface hydrophilic, facilitating rapid release of absorbed oil and demonstrating controllable desorption behavior. This switchable wettability enables on‐demand separation of various oil–water mixtures.