Microdroplet-based synthesis of polymethylsilsesquioxane microspheres with controllable size, surface morphology, and internal structure.

[Display omitted] • Large-sized polymethylsilsesquioxane spheres were prepared by microdroplet method. • A step T -junction microchannel was used to generate monodispersed microdroplets. • The microdroplets were solidified via rapid in-situ interfacial polycondensation. • Corrugated/smooth surface and loose/dense internal structure could be obtained. • Particle size could be tuned from tens of microns (∼20 μm) to hundreds of microns. Monodispersed polysilsesquioxane (PSQ) microspheres are generally synthesized by the classical sol–gel method. Using this method, the particle size is limited to the range of several hundred nanometers to several microns. The preparation of monodispersed large-sized PSQ microspheres remains technically challenging. Herein, with the polymethylsilsesquioxane (PMSQ) microspheres as the model product, a microdroplet-based strategy was developed for the synthesis of PSQ microspheres with larger particle sizes. According to the properties of the reactants, a W/O microdroplet reaction system was realized, i.e., with the mixture of methyltrimethoxysilane (MTMS) and liquid paraffin as the continuous phase and ammonia solution as the dispersed phase. The monodispersed W/O microdroplets were generated in a step T -junction microfluidic device, and solidified into PMSQ microspheres via in-situ interfacial polycondensation (∼2 min) in a microtube reactor. The size, surface morphology and internal structure of the PMSQ microspheres could be tuned by adjusting the synthesis conditions, mainly including the two-phase flow rates, MTMS concentration, NH 4 OH concentration, and the structural parameters of the microfluidic device. Various PMSQ microspheres with corrugated or smooth surface morphology, and loose or dense internal structure could be synthesized. The microsphere size could be tuned from tens of microns (∼20 μm) to hundreds of microns. [ABSTRACT FROM AUTHOR]