Popcorn-based dual-monomer copolymerized temperature/pH-sensitive core-shell hydrogels

Temperature/pH-responsive hydrogels are one of the most studied environmental-responsive hydrogels, with sensitivity and rapid response being the sought-after properties, while sensitivity and reusability are generally poor. This study prepared a hydrogel with a temperature/pH-responsive core-shell structure by static template polymerization, using the temperature-sensitive monomer dimethylaminoethyl methacrylate polymerized with 2-acrylamide-2-methylpropanesulfonic acid as the temperature-sensitive shell and popcorn with acrylic acid as the pH-responsive core-layer hydrogel. The chemical structure, thermal stability, and morphology of the core-shell structure hydrogels were characterized by Infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller surface (BET), Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Thermogravimetric analysis (TG), respectively. The pH responsiveness well as the temperature responsiveness of the shell structure was tested. The results showed that the lowest critical solution temperature (LCST) of the core-shell hydrogel is 43 ℃, with good temperature responsiveness in the range of 25–55 ℃, pH responsiveness from pH= 4 to pH= 13, and a short response time. From SEM, AFM, and BET, it can be concluded that the hydrogel has a rough surface and pore structure with a root mean square roughness value of 0.787 nm, a specific surface area of 1.3381 m²/g, and an average pore size of 4.0911 nm. FTIR and XRD can show that popcorn (PCP) is well-doped in the core-shell structure hydrogel, which also proves the existence of the core-shell structure. The design of the core-shell structure enhanced the stability performance of the shell temperature-sensitive hydrogel so that the retention rate of the sample was still 37% at 800 °C, and the water retention rate was still 80.7% after repeated immersion in distilled water 7 times, which has good prospects for agricultural and pharmaceutical applications.