Microfluidic-assisted Sol-gel Preparation of Monodisperse Mesoporous Silica Microspheres with Controlled Size, Surface Morphology, Porosity and Stiffness

The controllable synthesis of monodisperse mesoporous silica microspheres with unique physicochemical properties is becoming increasingly important for a variety of applications such as catalysts, chromatography, drug delivery and sensors. Here, we report a facile microfluidic-assisted sol-gel method for preparation of silica microspheres with precisely controlled properties such as the size of the microspheres, the surface morphology, porosity and stiffness. All these properties can be manipulated by changing specific synthesis parameters, such as changing the microfluidic channels to tune the size of the microdroplets (tens to hundreds of microns), changing the contents of the precursor solution to manipulate the surface morphology (wrinkled to smooth surface) and changing the gelation/annealing conditions to tune the porosity (surface area up to 1021 m²/g) and stiffness of the microspheres (elastic modulus tunable from 0.9 GPa to 144.3 GPa). Further investigations indicate rapid solvent diffusion promotes formation of condensed microspheres while gelation of silica sol induces mesoporous structures, tuning the solvent diffusion and gelation rates enable the modulation of the porous structure and surface morphology, and the surface status further determines the stiffness of the microspheres. The strategy presented here may provide new tools for on-demand design of the next generation monodisperse silica microspheres with precisely controlled properties, it may also bring new insights to preparation of other monodisperse microspheres with desired functionalities.