Electrospray as an Atomized Precursor-Delivery Strategy for Stöber Silica Nanosphere Synthesis

Electrospray provides an atomized precursor delivery strategy for controlling silica particle formation during Stöber synthesis. In this study, electrospray and drop-by-drop precursor delivery were compared across 0.1–0.5 mL/min to evaluate delivery-mode effects on particle size and size distribution. The mean particle size increased with flow rate under electrospray delivery, whereas the opposite trend was observed under drop-by-drop delivery. Electrospray maintained relatively narrow particle size distributions, with coefficients of variation ranging from 5.6 to 6.7%. These contrasting behaviors were interpreted in terms of differences in local precursor supply conditions and their possible influence on the relative contributions of particle growth and secondary nucleation. Under stable cone-jet electrospray conditions, the mean particle size increased progressively with reaction time at both 7.8 and 9.3 kV, while the coefficient of variation remained approximately 7% throughout. In addition, particles synthesized at 9.3 kV exhibited smaller mean diameters than those obtained at 7.8 kV at all investigated reaction times, while maintaining relatively narrow particle size distributions under both stable cone-jet conditions. Overall, these findings suggest that electrospray offers an additional process-based approach for adjusting silica particle size through control of precursor supply rate and atomization characteristics.