发表机构
Institute of Physics, Martin-Luther-University Halle-Wittenberg（马丁·路德·哈雷-维滕贝格大学物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究系统比较了聚合物在不同基底上的预冻结与异相成核，发现预冻结能显著提升结晶动力学和晶体取向，使石墨烯成为理想成核剂。
AI 中文摘要
液体的结晶通常发生在固体表面，通过异相成核或预冻结机制进行。理解这一过程对于控制薄膜中的晶体形态以及开发高效的成核剂至关重要——尤其是对于通常在熔融状态下加工的聚合物而言。然而，成核和预冻结相对于结晶动力学和半结晶聚合物形态的效率尚未得到充分研究，且仍不明确。在此，我们通过系统研究模型聚合物聚（ε-己内酯）（PCL）在各种结晶性和无定形基底上的去润湿液滴中的基底诱导结晶来应对这一挑战。利用偏振光光学显微镜，监测了液滴的结晶温度，并发现其在不同基底上有所变化，揭示了三种情形：在玻璃和硅上接近均相成核；在有序和无序富碳基底上发生异相成核；以及在石墨烯上发生预冻结。对温度依赖性成核速率进行了分析，发现除PCL在石墨烯上的情况外，所有体系均符合经典成核理论；在石墨烯上，由于所有液滴同时结晶，成核速率出现发散。在石墨烯上观察到PCL晶体最高的面内和面外取向，其中外延生长的片晶垂直延伸达数百纳米。这些结果表明，预冻结对结晶动力学和晶体形态具有卓越的影响，使得预冻结基底成为完美的成核剂。
英文摘要
Crystallisation of liquids often occurs at solid surfaces, via heterogeneous nucleation or prefreezing. Understanding this process is crucial for controlling crystal morphology in thin films and developing efficient nucleating agents - especially for polymers, typically processed in a molten state. However, the efficiency of nucleation and prefreezing with respect to crystallisation kinetics and semicrystalline polymer morphology has not been well studied and remains unclear. Here, we address this challenge by conducting a systematic study of substrate-induced crystallisation in dewetted droplets of the model polymer poly($\varepsilon$-caprolactone) (PCL) on various crystalline and amorphous substrates. Using polarized light optical microscopy, droplet crystallisation temperature was monitored and varied across the substrates, revealing three scenarios: close-to-homogeneous nucleation on glass and silicon; heterogeneous nucleation on ordered and disordered carbon-rich substrates; and prefreezing on graphene. The temperature-dependent nucleation rate was analysed and found to obey classical nucleation theory for all systems except PCL on graphene, where it diverges as all the droplets crystallise simultaneously. The highest in- and out-of-plane PCL crystal orientation is found on graphene, where the epitaxially grown lamellae extend vertically over several hundred nanometres. These results demonstrate that prefreezing has a superior influence on crystallisation kinetics and crystal morphology, making prefreezing substrates perfect nucleating agents.
