Molecular dynamics simulations of crystal nucleation in entangled polymer melts under start-up shear conditions
Molecular dynamics simulations of crystal nucleation in entangled polymer melts under start-up shear conditions
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DOI：
10.1063/1.5082244
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发表时间：
2019-02-28
影响因子：
4.4
通讯作者：
Graham, Richard S.
中科院分区：
文献类型：
--
作者：
Anwar, Muhammad;Graham, Richard S.
了解流动诱导结晶过程是必要的，因为它与聚合物加工技术相关。聚合物结晶控制了半结晶聚合物的形态，从而控制了最终产品的性能。我们进行了分子动力学模拟的聚合物熔体组成的充分纠缠的线性链在剪切流动。我们利用已建立的流变模型确定了线性聚合物链在不同温度下的劳斯弛豫时间（tau(R)），并将模拟数据与Arrhenius和Williams-Landel-Ferry方程拟合。我们模拟了不同温度下不同的劳斯-魏森伯格数(W-iR = （γ) /点tau(R)）值的结晶诱导时间。我们观察到，诱导结晶所需的应变和拉伸水平随着温度的升高而增加。我们发现感应时间在剪切速率中遵循幂律，并且在较高温度下比在较低温度下观察到更明显的流量影响。此外，我们确定成核事件发生相对较早的剪切瞬态和在一个拉伸值小于其稳态值。我们还报告了应变的值，其中一个成核事件的发生是最有可能发生的。由AIP出版社授权出版。
Understanding the flow induced crystallisation process is necessary due to its technological relevance to polymer processing. Polymer crystallisation controls the morphology of semi-crystalline polymers and hence the properties of the end product. We perform molecular dynamics simulations of polymer melts consisting of sufficiently entangled linear chains under shear flow. We determine the Rouse relaxation time (tau(R)) for linear polymer chains using an established rheological model at different temperatures and fit the simulation data with the Arrhenius and Williams-Landel-Ferry equations. We simulate the crystallisation induction times for different values of the Rouse-Weissenberg number (W-iR = (gamma) over dot tau(R)) at different temperatures. We observe that the level of strain and stretch required to induce crystallisation increases with temperature. We find that the induction times follow a power law in shear rate and observe a more pronounced effect of flow rate for higher temperatures than at lower temperatures. Moreover, we determine that nucleation events occur relatively early in the shear transient and at a stretch value that is smaller than its steady state value. We also report the values of strain at which the occurrence of a nucleation event is most likely to happen. Published under license by AIP Publishing.