Altering Surface Charge of Silica Nanoparticles through Co-condensation of Choline Chloride and Tetraethyl Orthosilicate (TEOS)

ABSTRACTWe demonstrate an alternative route to synthesize functionalized silica nanoparticles through incorporation of alcohol compounds in the Stöber process. The Stöber process has been widely utilized for the synthesis of silica nanoparticles due to its simplicity and reliability. Silane based compounds have been incorporated in this process in order to tailor surface properties of the silica nanoparticles. These compounds do, however, have limitations in their utility due to side reactions with water and intermolecular polymerization. In this article, we report the incorporation of alcohol based reagents in the Stöber process as an alternative means of synthesis and functionalization of silica nanoparticles. In particular, choline chloride was chosen as an exemplary alcohol to be incorporated in the process for tuning overall surface charge of the silica nanoparticles. These silica nanoparticles with incorporated choline chloride were characterized by atomic force microscopy (AFM), zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) in comparison with silica nanoparticles synthesized from the traditional Stöber process. While the size and shape of the nanoparticles exhibited little difference between the two synthetic routes, the zeta potential of the choline chloride incorporated nanoparticle was ∼10 mV higher than that of the traditional silica nanoparticles. Composition of the choline chloride containing silica nanoparticles was verified by XPS with the observation of strong N1s and C1s signals. The methods introduced in this article could be expanded to incorporate a range of alcohol containing compounds including choline chloride for the synthesis of silica nanoparticles with a tuned surface chemistry.