Understanding the growth rates of polymer cocrystallization in the binary mixtures of different chain lengths.
Understanding the growth rates of polymer cocrystallization in the binary mixtures of different chain lengths.
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DOI：
10.1021/jp800500g
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
T. Cai;Yu Ma;Pengcheng Yin;Wenbing Hu
中科院分区：
文献类型：
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作者：
T. Cai;Yu Ma;Pengcheng Yin;Wenbing Hu
聚合物材料通常含有分子长度的多分散性。采用动态蒙特卡罗模拟方法研究了不同链长的二元混合物中聚合物层状晶体的线性生长速率。两种链长都选择足够大以在晶体生长时进行链折叠，但不是非常大以避免体相中链缠结的影响。我们发现，晶体生长速率表现出线性依赖于混合物的组成。这种线性关系意味着整体晶体生长速率是由可变长度的单一聚合物的单独贡献集成，支持分子内晶体成核的模型。在单个聚合物的晶体生长的每个事件中，长链比短链产生更多的结晶度。这种高效率解释了长链晶体生长速率高于短链晶体生长速率的原因，这与传统的基于熔点不同的观点有很大不同。此外，与部分释放的滑动扩散的晶体增厚，一个新的依赖性的晶体生长速率发生在附近的稀释端的长链组合物在高温下，这可以归因于在晶体生长前沿的整数链折叠的偏好。优选的折叠长度可以随链长度而变化，从而影响晶体生长速率。
Polymer materials often contain a polydispersity of molecular lengths. We studied the linear growth rates of polymer lamellar crystals in the binary mixtures of different chain lengths by means of dynamic Monte Carlo simulations. Both chain lengths were chosen large enough to perform chain folding upon crystal growth but not very large to avoid the effect of chain entanglement in the bulk phase. We found that the crystal growth rates exhibit a linear dependence upon the compositions of mixtures. This linear relation implies that the overall crystal growth rates are integrated by the separate contributions of variable-length single polymers, supporting the model of intramolecular crystal nucleation. In each event of crystal growth of single polymers, long chains yield more crystallinity than short chains. This high efficiency explains higher crystal growth rates of long chains than that of short chains, and the explanation is quite different from the traditional view on the basis of their different melting points. In addition, with a partial release of sliding diffusion for crystal thickening, a new dependence of crystal growth rates occurs near the dilute end of long-chain compositions at high temperatures, which can be attributed to the preference of integer-number chain folding at the crystal growth front. The preferred fold lengths may vary with chain lengths and thus influence the crystal growth rates.