Three-Dimensional Thermoresponsive Polydimethylsiloxane Sponge with Reversible Superwettability for Switchable Oil/Water Separation and Particulate Matter Filtration

Recently, researchers’ attention has been drawn to reversible surface superwettability with ultrafast responsiveness to environmental stimuli, since these platforms show great promise for a variety of applications. Herein, thermoresponsive electroconductive PDMS modified by poly(N-isopropylacrylamide) (PNIPAAm) and carbon black has been developed (PNIPAAm@C@PDMS sponge). The incorporation of PNIPAAm rendered the fluoride-free PDMS sponge temperature-sensitive, enabling a convertible wettability. The porous structure of the PDMS sponge facilitated the addition of carbon black to enhance surface roughness and impart electrical conductivity, creating numerous active sites capable of adsorbing PM pollutants. The carbon black composition has endowed the obtained sponge with a certain conductivity, exhibiting excellent Joule heating performance at a voltage of 24 V. Dependent upon this property, a smart switch of superwettability can be achieved for PNIPAAm@C@PDMS by self-induced joule heating. The composite sponge shows superhydrophilicity and underwater superoleophobicity below the lower critical solution temperature (LCST, ca. 25 °C), which can be used to separate different types of water-in-oil mixtures. However, the reverse characteristic above the LCST (ca. 45 °C) can be observed, displaying superhydrophobicity and underwater superoleophilicity, which allows it to separate a stabilized oil-in-water mixture. Besides, the composite sponge also shows excellent potential recyclable filtration performance for PM2.5. Importantly, the PNIPAAm coating provides a stable superhydrophobic surface that ensures long-term PM filtration stability under high-humidity conditions, demonstrating that the smart wettability design indirectly but crucially supports air purification applications. Therefore, the smart switchable sponge can be a promising candidate for developing multifunctional superwettable surfaces for water and air pollution treatment.