Wang Tianchang, Wang Haijun, Li Huihui, Gan Zhihua, Yan Shouke
Beijing National Laboratory of Molecular Sciences, Institute of Chemistry, The Chinese Academy of Sciences, Beijing, 100080, China.
Phys Chem Chem Phys. 2009 Mar 14;11(10):1619-27. doi: 10.1039/b817597g. Epub 2009 Jan 21.
Banded spherulites of PEA, PBS and their PBS-PEA blends were studied by optical and atomic force microscopies. It was found that PEA forms a regular banded structure within the temperature range 23 degrees C to 36 degrees C, otherwise only Maltese-cross spherulites are observed. The banded PEA spherulites exhibit a double ring feature with band spacing between two equivalent birefringent rings increasing with temperature. The ring extinction in PEA banded spherulites is caused by a lamellar twist. There exist two equivalent positions in one twisting period, which show no birefringence. The PBS can also grow in ring-banded spherulites in a wide temperature window with the high temperature threshold for forming banded structures that are not sharply delineated, as in the case of PEA. Also the double ring feature is not so pronounced for the spherulites of pure PBS. Blending PBS with PEA is found to favor the formation of PBS banded structures. During the crystallization process, the early growing PBS spherulites at 75 degrees C show weak birefringence with an evident ring-banded structure. The crystallization of PEA at 0 degrees C makes a great contribution to the birefringence increment of the initially-birefringent rings. This is caused by the analogic crystal orientation of PBS and PEA based on interlamellar phase separation as revealed by AFM observation. The band spacing of PBS spherulites is found to be increase with both increasing temperature and increasing PEA content. This stems from an increment in chain mobility of PBS both with temperature and addition of the PEA component.
通过光学显微镜和原子力显微镜对聚（ε-己内酯）（PEA）、聚丁二酸丁二醇酯（PBS）及其PBS-PEA共混物的带状球晶进行了研究。结果发现，PEA在23℃至36℃的温度范围内形成规则的带状结构，否则仅观察到马尔他十字球晶。带状PEA球晶呈现出双环特征，两个等效双折射环之间的带间距随温度增加。PEA带状球晶中的环消光是由片层扭曲引起的。在一个扭曲周期内存在两个等效位置，它们不显示双折射。PBS在很宽的温度窗口内也能生长成环带状球晶，其形成带状结构的高温阈值不像PEA那样清晰界定。而且纯PBS球晶的双环特征也不那么明显。发现将PBS与PEA共混有利于形成PBS带状结构。在结晶过程中，75℃下早期生长的PBS球晶显示出弱双折射，具有明显的环带状结构。0℃下PEA的结晶对初始双折射环的双折射增量有很大贡献。这是由原子力显微镜观察揭示的基于层间相分离的PBS和PEA类似晶体取向引起的。发现PBS球晶的带间距随温度升高和PEA含量增加而增大。这源于PBS的链迁移率随温度和PEA组分的加入而增加。
