硅基微球因具有良好的化学稳定性、生物相容性、孔结构可调且易于功能化等优点，被广泛应用于化工、环境、电子信息、生命科学等领域，其应用效果与颗粒的形貌、粒径、孔结构及分散性密切相关，发展硅基微球的可控制备技术具有重要的研究意义和应用价值。论文以二氧化硅微球（SiO2）和聚倍半硅氧烷微球（PSQs）的可控合成和规模生产为目标，基于微反应技术，发展硅基微球的连续合成新工艺和新方法，深入探究合成过程的内在规律和颗粒调控机制，为新技术的产业化应用奠定基础。发展了喷雾辅助-碳化微反应制备SiO2微球的新工艺，发明了碳化反应、微分散技术及喷雾技术相结合的球形二氧化硅连续合成策略，揭示了碳化反应过程强化及颗粒形貌的调控机制。合成的SiO2颗粒具有良好的球形度和分散性，平均粒径1-2 μm，比表面积在300-1100 m2/g范围内可调，孔容在0.21-1.82 cm3/g之间可调。新工艺解决了传统沉淀法产品分散性欠佳、副产硫酸钠废盐等难题。采用原位拉曼光谱定量研究了甲基三甲氧基硅烷（MTMS）、3-巯丙基三甲氧基硅烷（MPTMS）的碱催化水解与缩合动力学，同时测定了MTMS和MPTMS在水中的溶解度。根据水解动力学及溶解度数据，建立了有机硅源微液滴的非均相水解模型，该模型可预测微液滴完全水解所需时间。揭示了一步溶胶-凝胶法中单分散PSQs微球的形成机理，采用透射电镜和动态光散射表征了PSQs微球合成过程中颗粒形貌、粒径及粒径分布随反应时间的变化，提出PSQs微球的四阶段形成机理，即：（i）碱催化下有机硅源快速水解，寡聚体胶束成核，（ii）形成核颗粒及其聚集体，（iii）热力学不稳定的颗粒溶解，热力学稳定的颗粒快速生长，（iv）颗粒缓慢生长，粒径趋于稳定。发展了PSQs微球的连续合成微反应系统，采用微分散技术强化有机硅源与水相的传质，加速其水解，并实现了颗粒在管式反应器中快速生长。该方法所合成的聚甲基硅氧烷微球（PMSQ）及罗丹明B-聚甲基硅氧烷复合荧光微球（RhB-PMSQ）具有良好的单分散性（CV~5%），微球粒径在几百纳米~数微米之间可调。微反应系统具有良好的运行稳定性，解决了间歇釜式工艺产品批次稳定性差、过程难以放大的问题，为颗粒材料连续制备技术的发展提供了示范。
By virtue of good chemical stability, excellent biocompatibility, diverse pore structures, and easy functionalization, silica-based microspheres have been widely used in chemical industry, environment, electronic information, bioscience, etc. Their applications are closely related to particle size, morphology, pore structure, and dispersity. Therefore, it is of great significance to develop novel technologies for the controllable synthesis for silica-based microspheres. Herein, with silica (SiO2) and polysilsesquioxanes (PSQs) microspheres as the research objectives, we aim to develop controllable, reproducible, and scalable synthetic methods based on the microchemical and continuous flow technologies. The underlying fundamentals of the synthetic processes were systematically investigated, including reaction kinetics, particle formation mechanism, and product regulation strategies, which would lay a solid foundation for the industrial applications of the developed novel technologies.A facile spray-assisted carbonation microreaction method was developed for the synthesis of mesoporous silica microspheres. The effects of reaction conditions on the morphology and pore structure of silica particles were systematically studied. The resultant silica particles show highly spherical morphology, excellent dispersity, and narrow particle size distribution, with average diameters of 1-2 μm. The specific surface area and total pore volume of the silica microspheres can be regulated in the range of 300-1100 m2/g and 0.21-1.82 cm3/g, respectively. With methyltrimethoxysilane (MTMS) and 3-mercaptopropyl trimethoxysilane (MPTMS) as the model silicon sources, the formation mechanism of PSQs microspheres in one-step sol-gel method was revealed for the first time by monitoring the time evolution of particle morphology, size, and size distribution via transmission electron microscopy (TEM) and dynamic light scattering (DLS). A four-stage formation mechanism was proposed: (i) fast base-catalyzed hydrolysis of alkoxysilanes and subsequent formation of polydisperse hollow nanoparticles via oligomer micelle nucleation mechanism, (ii) growing nuclei particles and their aggregates, (iii) fast growth of thermodynamically stable particles by absorbing hydrolytic monomers and oligomers, (iv) slow diffusion growth of particles ending with a constant particle size and narrow size distribution.The base-catalyzed hydrolysis and condensation kinetics of MTMS and MPTMS and their solubilities in H2O were quantitatively determined using in-situ Raman spectroscopy. A heterogeneous hydrolysis model of alkoxysilane microdroplets was further established, which could predict the time required for the disappearance of alkoxysilane microdroplets.Based on the above fundamental research, a continuous flow microreaction system for the synthesis of polymethylsilsesquioxane microspheres (PMSQ) and rhodamine B-doped PMSQ fluorescent microspheres (RhB-PMSQ) was developed. The hydrolysis reaction of MTMS was greatly accelerated by generating MTMS microdroplets in a microdispersion device, and the subsequent growth of PMSQ microspheres was performed in a tubular reactor with a millimeter-scale diameter. The as-synthesized PMSQ and RhB-PMSQ microspheres show excellent monodispersity (CV~5%), and the particle size could be tuned from hundreds of nanometers to several microns. Meanwhile, the optimized continuous flow microreaction system demonstrates a high level of controllability, stability, and robustness, which addresses the challenges of conventional batch processes, such as poor reproducibility of the product quality and great difficulty in scale-up, etc. The developed microreaction system provides a new platform for the continuous flow synthesis of nano/micro particles.
