Synthesis of non-collapsed hollow polymeric nanoparticles with shell thickness on the order of polymer gyration radius
The hollow polymeric nanoparticles of poly(styrene-co-divinylbenzene) of ultra-thin shell were synthesized by the interfacial RAFT miniemulsion polymerization with various particle sizes, void fractions and crosslinking degrees. With the void fraction increased, the hollow nanoparticles were more likely to collapse once dried. This collapse could be suppressed by simply increasing the level of crosslinker. The fraction of the collapsed hollow particles decreased nearly linearly with the increasing level of crosslinker. The non-collapsed hollow nanoparticles with a void fraction about 60% and shell thickness of 11.5 nm were fabricated with the crosslinker (divinylbenzene) of 0.67 mass fraction based on monomers. The resulted polymeric shell of the hollow nanoparticles was mesoporous, which had high surface area 514 m2/g, extremely large pore volume 2.74 ml/g and a most probable pore diameter of 9 nm. The structures of the hollow nanoparticles were mechanically stable not only in the solvent but also under harsh conditions like high temperature (200 °C) and strong shear. Additionally, the hollow nanoparticles were able to be fully re-dispersed in the solvent. The average hollow particle diameter was tuned from 70 nm to 199 nm by decreasing the level of the amphiphilic RAFT agent. The shell thickness was tuned from 10.6 nm to 19.3 nm by changing the core/shell ratios.