Investigating the Synergistic Anionic/Nonionic Surfactant Interaction on Nanoparticle Synthesis with Solvent-Free Extrusion Emulsification

This paper examines different binary mixtures of anionic/nonionic surfactants using a new technique known as solvent-free extrusion emulsification (SFEE) to control the surface charge in resulting nanosized polyester particles. Five similar nonionic surfactants with only minor structural differences from one another, along with an anionic surfactant (Calfax DB-45), were considered. The optimal hydrophilic end for the nonionic species was found to be 10–12 ethoxy units, whereas with respect to their hydrophobic end group, a more hindered branched alkyl structure was more desirable in preparing particles in the desired size range of 100–200 nm for this polymer. The preferred blend of Calfax/Igepal CA-630, found in a preliminary study, was shown to exhibit a synergistic interaction in SFEE in subsequent trials. The synergistic interaction was considered to arise from the high viscosity of the system, keeping the two surfactants partitioned across the interface of the emulsifying phases, which allowed a lower total surfactant concentration to be used than possible in a comparable solvent-based emulsification method. This partitioning across the interface decreased the nonextractable amount of Calfax left in the polyester latex. This approach of blending anionic and nonionic species shows an important step in preparing nanosized particles with controlled charge.