Polymeric Toroids Derived from the Fusion-Induced Particle Assembly of Anisotropic Bowl-Shaped Nanoparticles

Polymeric toroids are fascinating soft nanostructures due to their unique geometry and properties, which have shown potential applications in the fields of nanoreactors, drug delivery, cancer therapy, etc. However, facile preparation of polymeric toroids is still challenging. Herein, we propose a fusion-induced particle assembly (FIPA) strategy to prepare polymeric toroids using anisotropic bowl-shaped nanoparticles (BNPs) as a building block. The BNPs are prepared in ethanol by the self-assembly of an amphiphilic homopolymer, poly(N-(2,2'-bipyridyl)-4-acrylamide) (PBPyAA), synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Upon incubation in ethanol above the glass transition temperature (Tg) of PBPyAA, the BNPs gradually aggregate to form trimers and tetramers due to the disturbance of the colloidal stability. With the increase in incubation time, the aggregated BNPs fuse with each other and then form toroids. Notably, we find that only anisotropic BNPs can aggregate and fuse to form toroids rather than spherical compound micelles due to high surface free energy and curvature at the edge of the BNPs. Besides, mathematical calculations further confirm the formation of trimers and tetramers during the FIPA process and the driving force for the formation of toroids. Overall, we propose a fresh insight for the facile preparation of polymeric toroids by the FIPA of anisotropic BNPs.