Purpose. The aim of this work was to relate the physicochemical properties of the aqueous and organic phases used for nanoparticle (NP) preparation to the formation of NP produced by salting-out, emulsification-diffusion, and nanoprecipitation.

Methods. Methacrylic acid copolymer and poly(vinyl alcohol) (PVAL) were selected as NP polymer and emulsifying agent, respectively. Salting-out and emulsification-diffusion NP batches were prepared modifying the PVAL content in the aqueous phase. For nanoprecipitation, NP were produced with variation of the polymer content and type of solvent in the organic phase.

Results. For salting-out and emulsification-diffusion, NP formation was discussed in terms of the emulsification theory. The nanoemulsion obtained during NP preparation was visualized by scanning electron microscopy. Aqueous and organic phases used for NP preparation were characterized by their viscosity and surface tension. NP characteristics such as particle mean size, residual surfactant, suspendability in water after freeze-drying, and morphology were explained in terms of these properties. For nanoprecipitation, NP formation was analyzed considering the diffusion-stranding phenomenon.

Conclusions. NP formation by salting-out and emulsification-diffusion was related to PVAL chain interactions at the droplet interface (e.g., reduction in the interfacial tension, mechanical sta- bilization, and steric stabilization) and in the bulk solution (hy- drodynamic stabilization). For nanoprecipitation, X_{solvent-water} and Δδ_{solvent-water} of the organic phase solvents were well related to the NP characteristics.