Liquid-core polymer nanocapsules prepared using flash nanoprecipitation.

Hypothesis: Nanocapsules, consisting of a solid shell and a liquid core, are an interesting class of materials with numerous applications and various methods of synthesis. One common method for synthesis of nanoparticles is flash nanoprecipitation. For a multicomponent system consisting of a liquid (n-hexadecane) and solid (polystyrene), we hypothesize that nanocapsules will form from droplets created by the turbulent mixing in the nanoprecipitation process. We anticipate n-hexadecane molecules should phase-separate more rapidly from the non-solvent, thus becoming the core, while the more slowly diffusing polystyrene forms the shell. Additionally, we predict that the amount of both n-hexadecane and polystyrene used in creating these nanocapsules will influence capsule size. Experiments: Using flash nanoprecipitation, we synthesized nanocapsules of a polystyrene shell and liquid core of n-hexadecane. We varied the concentrations of both polystyrene and n-hexadecane and characterized the resulting dispersions using dynamic light scattering and scanning electron microscopy. Findings: Our experiments demonstrate that flash nanoprecipitation can be employed to create nanocapsules with radii ranging from 50 to 200 nm, with radii of the n-hexadecane cores between 35 and 175 nm and polystyrene shells with thickness ranging from 7 to 62 nm. We used various methods of analysis to confirm this core/shell morphology and applied a droplet model to explain the dependence of particle size on initial concentrations of n-hexadecane and polystyrene.

Particle Formation Mechanisms in the Nanoprecipitation of Polystyrene.

Numerous precipitation methods for creating nanoparticle dispersions that are based on mixing a solution with a miscible nonsolvent have been developed. Here, we show that for polymer particles, the formation is highly dependent on the rate of mixing. We also demonstrate the importance of the glass transition of the polymers on particle formation. A simple model of droplet formation during mixing provides a satisfactory description of the observed dependence of particle size on polymer molecular weight, concentration, solvent ratio, and mixing conditions.