Nitrogen-aeration tuned ultrasonic synthesis of SiO₂@PNIPAm nanoparticles and preparation of temperature responsive Pickering emulsion

Ultrasonic synthesis has shown great potential applications in preparing varieties of nanostructured materials. However, fabrication of nanomaterials with tunable structures and desirable properties is still challenging because of the instability and nonuniform distribution of cavitation effect in liquid phase. In this study, a novel aeration tuned ultrasonic synthesis approach is proposed for optimizing the cavitation effect in both time and space scales and fabricating SiO₂@PNIPAm NPs. By alternation of ultrasonication and N₂ aeration, more and more gas bubbles are formed in the reaction liquid, and the collapse of those bubbles is further enhanced by the reactants of solid SiO₂ and intermediate functionalized SiO₂ NPs. As a result, SiO₂@PNIPAm NPs with various grafting ratios are successfully synthesized simply by changing the number of ultrasonic synthesis cycle. The SiO₂@PNIPAm NPs are subsequently used as stabilizer to form Pickering emulsions with different temperature response. This work provides a potential facile sonochemical synthesis method with high efficiency in obtaining inorganic/organic NPs of well determined structures.