Surface grafting polymerization via cavitation regulated sonochemistry

Due to the generation of reactive radicals during the collapse of acoustic cavitation bubbles, various polymerization reactions can be effectively carried out within homogeneous solution. However, hybrid nanostructured materials with controllable polymer grafting density through sonochemical polymerization remains challenging, primarily attributed to the complexity of the dynamic behavior of cavitation bubbles within heterogeneous polymerization system. In this study, a series of SiO₂ hybrid NPs (SiO₂@PNIPAM and SiO₂@PDEAEMA) with tunable grafting density are synthesized by the cavitation regulated sonochemical approach, and the surface grafting mechanism is interpreted. In specific, the incorporation of SiO₂ nanoparticles to the sonochemical solution not only modulates the dynamics of transient cavitation bubbles but also correspondingly increases the concentration of ultrasound induced-free radicals and the monomer conversion rate. In this scenario, the presence of ultrasound-generated free radicals facilitates rapid polymerization on the surface of SiO₂ and in the liquid phase at the same time, regardless of the chemical composition of monomer. Under the combined action of the two, the long-linked polymers with uniform distribution are formed by coupling. Besides, by adjusting the ultrasound-aeration cycle, the active sites on the surface of the SiO₂ gradually increase, which also promotes the density of the grafted polymer to gradually increase. This study offers the possibility for sonochemical polymerization of organic-inorganic hybrid nanomaterials with tunable structure.