The physical and chemical properties of metal nanoparticles are strongly dependent on their size and shape. In this work, we present a flexible manufacturing approach for the synthesis of spherical silver nanoparticles with tuneable sizes between 5 to 80 nm. This unique size flexibility is enabled by rapid online characterisation coupling spectroscopy and a mathematical Mie theory-based algorithm for size and shape evaluation. While it is conventionally believed that narrow size distributions require a fast nucleation step, herein, we demonstrate that fast and controllable growth is also required. To achieve this, a combination of chemical and engineering approaches is presented to limit thermodynamically driven size focus, coalescence and secondary nucleation. We show that an optimum reducing agent to silver precursor to seeds ratio and pH range need to be maintained throughout the growth stage. Such demanding conditions can be achieved by accurate control of the feed points and fluid dynamics across a series of microfluidic helical reactors leading to low mixing times. In this way, particle sizes with narrow size distributions and spherical shapes can be easily tuned by just varying the reducing agent-to-precursor concentration in the growth stage in an approach directly applicable to other metal nanoparticles.

中文翻译：

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连续制造5至80 nm之间的银纳米颗粒，具有快速的在线光学尺寸和形状评估

金属纳米粒子的物理和化学性质在很大程度上取决于其大小和形状。在这项工作中，我们提出了一种灵活的制造方法，用于合成尺寸可调节的5至80 nm球形银纳米颗粒。快速在线表征耦合光谱法和基于数学Mie理论的尺寸和形状评估算法可实现这种独特的尺寸灵活性。尽管通常认为窄尺寸分布需要快速成核步骤，但是在本文中，我们证明了还需要快速且可控的生长。为实现此目的，提出了化学和工程方法的组合，以限制热力学驱动的尺寸聚焦，聚结和二次成核。我们表明，在整个生长阶段都需要保持最佳的还原剂对银前体与种子的比例和pH范围。可以通过精确控制一系列微流体螺旋反应器中的进料点和流体动力学来实现这种苛刻的条件，从而缩短混合时间。通过这种方式，可以通过直接适用于其他金属纳米粒子的方法，只需在生长阶段改变还原剂与前体的浓度，即可轻松调整具有窄尺寸分布和球形的粒径。