Synthesis of silica nanoparticles using oil-in-water emulsion and the porosity analysis

A set of silica particles was synthesized in oil-in-water emulsion with particle diameters ranging from ~42 nm to ~115 nm approximately. The porosity of the nanoparticles was analyzed using conventional nitrogen sorption and positron annihilation lifetime spectroscopy (PALS) techniques. The isotherm obtained using nitrogen sorption indicated that the particles were 'non-porous', however fitting data with Density Functional Theory model revealed a low concentration pore with diameters from 1.4 nm to 1.7 nm. The pore size was independent of the particle size. In contrast, analysis with PALS revealed a single pore size of ~0.6 nm present in all samples. Difference in results obtained for micropores <4 nm diameter is proposed to be dependent on models used and sample conditions for analysis.