Influence of the PAA concentration on PAA/NH3 emulsion template method for synthesizing hollow silica nanoparticles

This paper describes the synthesis mechanism of the hollow silica nanoparticles (HSNPs) with various concentrated poly acrylic acid (PAA) solutions, and the effect of the PAA concentration on the morphology of the HSNPs was investigated. The PAA interacting with ammonium hydroxide (NH3 aq.) acts as the template for the silica coating in ethanol, and the template is easily removed by water to obtain the HSNPs. When a low PAA solution (<1 mM) was used as the template, the silica shell was hardly formed on the PAA aggregates because of high molecular motion of the PAA aggregate’s surface. When a highly concentrated PAA solution (>15 mM) was used as the template, the dense silica nanoparticles coexisted with the HSNPs because of the high solubility of the PAA aggregates in the ethanol. As a result, the stable PAA aggregates could be prepared at PAA concentrations from 3 mM to 15 mM. In this range, the HSNPs became smaller and more monodispersed with the decreasing PAA concentration. As a result, the interaction between PAA and NH3 was the most important factor for controlling the HSNP’s morphologies.