CO2 responsive reversible aggregation of nanoparticles and formation of nanocapsules with an aqueous core

Abstract

We report the use of commercially available long-chain tertiary amines as smart switchable surfactants or hydrophobic oils in miniemulsions. Miniemulsion droplets were stabilized by employing the charged tertiary amine as surfactants to prevent coalescence. PMMA and PS nanoparticles were obtained by polymerizing the monomer droplets. Furthermore, the dispersions could be aggregated by bubbling argon (Ar) at 60 °C or by increasing their pH. In both cases, the nanoparticles could be re-dispersed by charging the dispersions with CO₂ at room temperature. The same tertiary amines in their neutral form were used as soft liquid templates in miniemulsion droplets. Core–shell nanoparticles, with the hydrophobic tertiary amine as the core and polyvinylformal (PVF) as the shell, were prepared by the emulsion-solvent evaporation technique. By charging the nanocapsules with CO₂, the hydrophobic core was transformed to the water soluble ammonium bicarbonate salt. Thus, aqueous dispersions of polymer nanocapsules with a hydrophilic core could be prepared without the conventional transfer of capsules from oil to aqueous dispersions. This method provides a direct pathway to synthesize polymer nanocapsules mimicking natural compartmentalized systems such as liposomes and cells, with aqueous media present inside and outside the compartments.