Synthesis of Temperature-Responsive SiO2 Nanoparticles for Switchable Emulsification and Demulsification in Enhanced Oil Recovery.

Temperature-responsive SiO2 nanoparticles are regarded as promising flooding agents in enhanced oil recovery (EOR). Herein, hydrophilic poly(sulfobetaine methacrylate) (PSBMA) and thermosensitive poly(N-isopropylacrylamide) (PNIPAM) layers were sequentially grafted onto SiO2 nanoparticles via two-step activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP), yielding six functionalized SiO2 nanoparticles (FSNPs) with varying SBMA/NIPAM weight ratios. The structures of the FSNPs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). FSNP3:2 with the optimal SBMA/NIPAM weight ratio effectively emulsified model oil at 50 °C and demulsified upon cooling to 20 °C. Interfacial tension and contact angle measurements indicated that the thermally triggered hydrophobic transition of PNIPAM enhanced the interfacial activity of FSNP3:2 and its dispersion viscosity. Core flooding tests showed that FSNP3:2 nanofluid and its Pickering emulsion achieved additional oil recovery of 12.78% and 18.94% at 50 °C, respectively. The produced emulsion completely demulsified upon cooling and was readily regenerated for reuse. This study offers a novel design strategy for temperature-responsive SiO2 nanoparticles in EOR.