Reprecipitation

Reprecipitation is a synthesis technique used to form colloidal nanoparticles by dissolving a material in a good solvent and subsequently precipitating it by introducing this solution into a poor solvent or by rapid dilution, causing supersaturation and nucleation. The method is particularly common in producing polymeric nanoparticles and has also been applied to inorganic nanomaterials and quantum dots.

Typically, the process involves preparing a stock solution of the material in a suitable good solvent. The solution is rapidly injected into a non-solvent with vigorous stirring, or the non-solvent is added to the good solvent under controlled conditions. As the solvent quality decreases, the solute supersaturates and nucleates, and particles grow until stabilization by surface-active agents or inherent charges halts growth. After formation, the suspension is often aged briefly and particles are collected by centrifugation or filtration; solvents are removed by evaporation or dialysis.

Particle size and distribution are influenced by the choice of solvent and non-solvent, solute concentration, temperature, rate of mixing, and the presence of stabilizers such as surfactants or polymers that provide steric or electrostatic stabilization. The method is generally simple and scalable, but achieving highly uniform particles requires careful optimization of mixing and solvent pair.

Applications include fabrication of polymeric nanoparticles for drug delivery, imaging, and coatings, as well as preparation of colloidal inorganic nanoparticles and quantum dots. Limitations include possible residual solvent, sensitivity to aggregation, and limited crystallinity or control for certain materials. Reprecipitation is often contrasted with other nanoparticle synthesis routes such as precipitation polymerization or hot-injection methods.