学术报告
高分子科学系列讲座136讲：Dr. Jianjun XU, Coupled crystallization in a diblock copolymer of lamellar morphology
文章来源： 发布时间：2012-06-04
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报告题目：Coupled crystallization in a diblock copolymer of lamellar morphology（No. PSLAB136-PS2012-14） |
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报 告 人：Dr. Jianjun XU |
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单 位：DSM Resolve / Research, Netherlands |
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报告时间：2012年6月11日（星期一）上午9:30 |
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报告地点：主楼四楼学术厅（410房间) |
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报告内容摘要：
Interesting crystallization behaviour in an amorphous-semicrystalline diblock copolymer [1] will be presented. The copolymer locates in weak segregation limit of the phase diagram and has a lamellar morphology. The amorphous block is polystrene (PS) and the crystalline block is poly(ferrocenyl dimethylsilane) (PFS) which has a small driving force for crystallization [1-3]. The contrast in electron densities of the PS and the PFS phases is large and thus the block copolymer is ideal for TEM and in-situ SAXS studies.
Isothermal crystallization of the lamellar PS-b-PFS dilock copolymer is shown to proceed in a confined and grain-by-grain fashion. Here a ‘grain’ is defined as an ensemble of stacked lamellae wherein the PFS crystallization was found to spread quickly but stop at its surroundings. The in situ SAXS investigations were only able to resolve partially crystallized grains at very high temperatures. In all other cases, the SAXS patterns represent superposition of the scattering features of either fully amorphous or fully crystallized grains. We assume that one single nucleation event is sufficient to induce rapid crystallization of the whole grain. The high rate of crystal growth within a grain – in combination with considerable spatial changes associated with the PFS crystallization – indicate that a highly efficient pathway is accessible which allows spreading of the crystallization even perpendicular to the lamella planes, i.e., passing through the amorphous PS layers. We suggest that conformational changes in the PS as induced by the PFDMS crystallization (‘squeezing transfer’) are responsible for this fast spreading of the crystallization in the grain. The process is thus called ‘coupled crystallization’. References: [1] J. Xu, V. Bellas, B. Jungnickel, B. Stühn, M. Rehahn. Macromol. Chem. Phys. 2010, 211, 2276. [2] J. Xu, V. Bellas, B. Jungnickel, B. Stühn, M. Rehahn. Macromol. Chem. Phys. 2010, 211, 1261. [3] J. Xu, Y. Ma, W. Hu, M. Rehahn and G. Reiter. Nature Materials. 209, 8, 348. |
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Dr. Jianjun XU |
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Jianjun Xu is senior scientist at DSM Resolve in DSM Material Science Research Campus in the Netherlands. He obtained PhD in Polymer Chemistry in Institute of Chemistry, Chinese Academy of Sciences in 1998, in group of Prof. Yunzhao Yu. |
