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<p>Reliable control of particle size and modality in the Stöber synthesis of silica particles requires understanding when supersaturation is relieved by nucleation and when it is consumed exclusively by growth on existing surfaces. Despite decades of investigation, it has remained experimentally unresolved under classical Stöber conditions whether nucleation proceeds continuously throughout synthesis or is confined to a finite temporal window, and whether aggregation contributes significantly to particle growth. Here, we establish an experimentally validated mechanistic framework for nucleation and growth in ammonia-catalyzed Stöber silica synthesis using a canonical and widely employed reaction composition. By combining seed-free, seeded, and time-resolved experiments with controlled TEOS addition, we show that nucleation is confined to a finite temporal interval governed by the dynamic balance between monomer-generation rate (rate of formation of hydrolyzed silica species from TEOS) and surface-mediated monomer uptake. Rapid TEOS delivery produces a short nucleation burst, whereas slower addition limits supersaturation buildup and extends the nucleation interval. In seeded systems, pre-existing silica surfaces act as efficient monomer sinks. Once the available seed surface area exceeds a critical threshold, incoming TEOS is consumed predominantly by seed growth, supersaturation does not reach the nucleation threshold, and secondary nucleation is suppressed. Quantitative seed surface-area thresholds for nucleation suppression are identified and shown to depend systematically on TEOS addition rate. Time-resolved SEM imaging directly captures the appearance, growth, and termination of fresh nuclei, providing direct experimental evidence for a finite nucleation window. Hydrodynamic and colloidal stability analyses further demonstrate that growth is diffusion-dominated at the particle scale and that aggregation between mature particles is kinetically inhibited by electrostatic repulsion. Together, these results show that silica formation in the Stöber system is governed by supersaturation-limited nucleation and surface-mediated growth rather than continuous nucleation or aggregation-driven mechanisms. The experimentally established mechanistic boundaries reported here provide essential constraints for predictive models of silica formation and practical design rules for achieving narrowly distributed, modality-controlled silica particles.</p> Graphical abstract <p></p>

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Finite nucleation and surface-controlled growth in the Stöber synthesis of silica particles

  • 期刊论文

  • 发表日期：

    2026年7月6日

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  • Hürriyet Polat,
  • Elif Suna Sop Koçyiğit,
  • Mehmet Polat

摘要

Reliable control of particle size and modality in the Stöber synthesis of silica particles requires understanding when supersaturation is relieved by nucleation and when it is consumed exclusively by growth on existing surfaces. Despite decades of investigation, it has remained experimentally unresolved under classical Stöber conditions whether nucleation proceeds continuously throughout synthesis or is confined to a finite temporal window, and whether aggregation contributes significantly to particle growth. Here, we establish an experimentally validated mechanistic framework for nucleation and growth in ammonia-catalyzed Stöber silica synthesis using a canonical and widely employed reaction composition. By combining seed-free, seeded, and time-resolved experiments with controlled TEOS addition, we show that nucleation is confined to a finite temporal interval governed by the dynamic balance between monomer-generation rate (rate of formation of hydrolyzed silica species from TEOS) and surface-mediated monomer uptake. Rapid TEOS delivery produces a short nucleation burst, whereas slower addition limits supersaturation buildup and extends the nucleation interval. In seeded systems, pre-existing silica surfaces act as efficient monomer sinks. Once the available seed surface area exceeds a critical threshold, incoming TEOS is consumed predominantly by seed growth, supersaturation does not reach the nucleation threshold, and secondary nucleation is suppressed. Quantitative seed surface-area thresholds for nucleation suppression are identified and shown to depend systematically on TEOS addition rate. Time-resolved SEM imaging directly captures the appearance, growth, and termination of fresh nuclei, providing direct experimental evidence for a finite nucleation window. Hydrodynamic and colloidal stability analyses further demonstrate that growth is diffusion-dominated at the particle scale and that aggregation between mature particles is kinetically inhibited by electrostatic repulsion. Together, these results show that silica formation in the Stöber system is governed by supersaturation-limited nucleation and surface-mediated growth rather than continuous nucleation or aggregation-driven mechanisms. The experimentally established mechanistic boundaries reported here provide essential constraints for predictive models of silica formation and practical design rules for achieving narrowly distributed, modality-controlled silica particles.

Graphical abstract