Two-step nucleation pathways in which disordered, amorphous, or dense liquid states precede the appearance of crystalline phases have been reported for a wide range of materials, but the dynamics of such pathways are poorly understood. Moreover, whether these pathways are general features of crystallizing systems or a consequence of system-specific structural details that select for direct versus two-step processes is unknown. Using atomic force microscopy to directly observe crystallization of sequence-defined polymers, we show that crystallization pathways are indeed sequence dependent. When a short hydrophobic region is added to a sequence that directly forms crystalline particles, crystallization instead follows a two-step pathway that begins with the creation of disordered clusters of 10–20 molecules and is characterized by highly non-linear crystallization kinetics in which clusters transform into ordered structures that then enter the growth phase. The results shed new light on non-classical crystallization mechanisms and have implications for the design of self-assembling polymer systems.

中文翻译：

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通过仿生聚合物的序列工程调整结晶途径

对于多种材料，已经报道了两步成核途径，其中无序，无定形或致密液态先于结晶相出现，但对这种途径的动力学了解甚少。此外，这些途径是结晶系统的一般特征还是直接或两步法选择的系统特定结构细节的结果尚不清楚。使用原子力显微镜直接观察序列定义的聚合物的结晶，我们表明结晶途径确实是序列依赖性的。当将短的疏水区域添加到直接形成结晶颗粒的序列中时，相反，结晶过程遵循两步途径，即从创建10-20个分子的无序团簇开始，其特征是高度非线性的结晶动力学，其中，团簇转变为有序结构，然后进入生长期。结果为非经典的结晶机理提供了新的思路，并对自组装聚合物系统的设计产生了影响。