Continuous synthesis of monodisperse silica microspheres over 1 μm size

This study presents a robust and scalable method for synthesizing continuously the silica microspheres via the Stöber method. Owing to the superb mixing accessible with gas-liquid segmented flow in coiled microtube, satisfactory morphology and mono-dispersity of silica spheres was obtained. The continuous method was firstly optimized through investigating the effects of various operation parameters on the morphology, particle size, size distribution and chemical structure of silica spheres. Without the surfactant, the size of silica spheres was limited < 850 nm due to the partial blockage of microchannel when synthesizing larger silica spheres. The addition of surfactant migrated the clogging issue, enabling the reliable synthesis of microspheres with diameters over 1 μm within a four times shorter residence time (30 min). Moreover, the mono-dispersity of silica microspheres could be further improved by increasing the gas/liquid ratio in segmented flow due to the more intensified mixing in liquid segments, as verified in visual flow field investigation.