Thermoresponsive Polyurethane Sponges with Temperature-Controlled Superwettability for Oil/Water Separation

Here we have obtained a thermoresponsive three-dimensional (3D) polyurethane (PU) sponge with temperature-controlled superwettability. First, silanization was used to enhance the surface roughness of the PU sponge and reactive vinyl groups were provided. We then grafted a polyisopropylacrylamide (PNIPAAm) hydrogel to the PU skeleton, resulting in the preparation of a temperature-responsive 3D PU material showing useful oil–water separation performance. The surface morphology, chemical composition, and wettability of the prepared modified PU sponge were clarified. The surface wettability of the modified sponge changed with temperature. Under ambient conditions with a temperature of 25 °C, which is lower than the low critical solution temperature of PNIPAAm (LCST, about 32 °C), the product showed superhydrophilicity in air and superoleophobicity under water, while when the outside temperature (45 °C) became higher than the LCST, the product changed to show high hydrophobicity in air and superlipophilicity under water. After 8 cycles of temperature variation, the product still showed impressive responsiveness. In addition to the smart responsive properties, the modified PU sponge could absorb and automatically desorb oil at 45 and 20 °C, respectively, showing good oil–water separation ability, together with the capability of oil recycling.