Controlling size, shape, and charge of nanoparticles via low-energy miniemulsion and heterogeneous RAFT polymerization

Size, shape, and charge are key parameters of nanoparticles, and variations in these parameters can significantly impact their properties and applications. Among various nanoparticle synthesis methods, the combination of low-energy miniemulsions with reversible addition-fragmentation chain-transfer (RAFT) polymerization allows for the facile, rapid, and environmentally friendly preparation of uniform nanoparticles. However, this method cannot, yet, simultaneously control the size, shape, and charge of nanoparticles, thereby limiting its potential applications. Here we report the synthesis of polymeric nanoparticles with concurrent control over particle size, shape, and charge via low-energy miniemulsion and heterogeneous RAFT polymerization. Key to our approach is the combination of (i) a macromolecular surface-active agent to facilitate the formation of nanodroplets, (ii) various small-molecule surfactants with different charges to control the size and charge of nanodroplets, and (iii) a molecular transformer to control the morphology of the final polymeric nanoparticles. In particular, negatively charged polystyrene nanoparticles of different sizes (from ∼100 to ∼500 nm) and shapes (sphere, worm, and vesicle) were obtained by simply tuning the amount of added sodium dodecyl sulfate (SDS) and toluene. The nanoparticle charge was then switched from negative to positive by replacing SDS with cetyltrimethylammonium bromide (CTAB), a positively charged surfactant. In addition, biocompatible and neutral surfactants (including Tweens and Span 80) were employed to tune the nanoparticle size yielding challenging-to-synthesize nanoworms. This work provides a simple but powerful approach to produce nanoparticles of different properties, thus expanding the scope of nanomaterials made by RAFT low-energy miniemulsion polymerization.