Abstract The growing interest in polydopamine (PDA) nanospheres leads to a strong increase in demand for size-controllable synthesis strategies. Understanding the formation pathways of PDA nanosphere is of utmost importance in order to predictably synthesize these nanoparticles with the desired diameters. In the present study we synthesized PDA nanospheres with various diameters by the self-oxidative polymerization of dopamine (DA) in an alkaline solution. The diverse reaction conditions including the DA:NaOH molar ratio, the DA concentrations, the reaction time and temperature as well as the oxidant types were extensively investigated, and the results of the TEM and DLS analysis clearly showed the dependence of the diameters of the PDA nanospheres on reaction conditions. In addition, the relationships between the polymerization kinetics of DA and the particle size of PDA nanospheres were examined by UV–vis spectroscopy. The polymerization kinetics of DA were significantly accelerated by the presence of more hydroxide ions (OH−) or a strong oxidizing agent, which increased the nucleation rate of PDA, resulting in PDA nanospheres of smaller diameter. The increasing DA concentrations cause the PDA cores to grow, resulting in an increase in diameter. Moreover, the size of the PDA nanospheres increased with the prolonged reaction until a certain time and as long as sufficient precursors are available. It was also found that higher temperatures not only accelerate the nucleation of PDA particles but also promote the diffusion of DA monomers. Based on the results we suggest the DA:NaOH molar ratio as the most promising tool to affect the diameter and the size distribution of PDA spheres due to its influence at the very beginning of the reaction pathway.

中文翻译：

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聚多巴胺纳米球的可调合成及其成核和生长

摘要 对聚多巴胺 (PDA) 纳米球日益增长的兴趣导致对尺寸可控合成策略的需求大幅增加。了解 PDA 纳米球的形成途径对于预测合成具有所需直径的这些纳米颗粒至关重要。在本研究中，我们通过多巴胺 (DA) 在碱性溶液中的自氧化聚合合成了各种直径的 PDA 纳米球。广泛研究了多种反应条件，包括 DA:NaOH 摩尔比、DA 浓度、反应时间和温度以及氧化剂类型，TEM 和 DLS 分析的结果清楚地显示了 PDA 直径的依赖性反应条件下的纳米球。此外，DA 的聚合动力学与 PDA 纳米球的粒径之间的关系通过 UV-vis 光谱检查。更多的氢氧根离子 (OH−) 或强氧化剂的存在显着加速了 DA 的聚合动力学，这增加了 PDA 的成核速率，导致 PDA 纳米球的直径更小。DA 浓度的增加导致 PDA 核生长，导致直径增加。此外，PDA 纳米球的尺寸随着反应时间的延长而增加，直到有足够的前体可用。还发现较高的温度不仅加速了 PDA 颗粒的成核，而且还促进了 DA 单体的扩散。根据结果​​，我们建议 DA：