Direct observation of crystallization behavior of isolated polymer chains by atomic force microscopy

我们成功地用原子力显微镜(AFM)在分子水平上可视化了单个孤立的高分子链的结晶行为。此前，我们发现等规聚(甲基丙烯酸甲酯)(it-PMMA)在其Langmuir单分子膜的压缩下形成了二维折叠链状晶体，并通过AFM清晰地显示了晶体的分子图像。在本研究中，将高分子量的it-PMMA稀释到由于低分子量而不能结晶的it-PMMA的单层中。在较低的表面压力下，观察到高相对分子质量的it-PMMA在齐聚物单分子膜中有孤立的无定形链增溶。在压缩时，孤立的链转变为由单链组成的晶体。详细的AFM观察表明，结晶核优先形成在链的末端，并且核的大小几乎与it-PMMA的相对分子质量无关。

We successfully visualized crystallization behavior of a single isolated polymer chain at a molecular level by atomic force microscopy (AFM). Previously, we found that isotactic poly(methyl methacrylate) (it-PMMA) formed two-dimensional folded chain crystals upon compression of its Langmuir monolayer, and the molecular images of the crystals were clearly visualized by AFM. In the present study, a high-molecular-weight it-PMMA was diluted in a monolayer of an it-PMMA oligomer which cannot crystallize due to the low molecular weight. At a low surface pressure, isolated amorphous chains of the high-molecular-weight it-PMMA solubilized in the oligomer monolayer were observed. On compression, the isolated chains converted to crystals composed of the single chain. Detailed AFM observations of the crystals indicated that the crystalline nuclei preferably formed at the ends of the chains, and the size of the nuclei was almost independent on the molecular weight of the it-PMMA.