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The Role of the Functionality in the Branch Point Motion in Symmetric Star Polymers: A Combined Study by Simulations and Neutron Spin Echo Spectroscopy

机译:对称星聚合物分支点运动中的功能在分支点运动中的作用:模拟和中子旋转回波光谱的组合研究

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摘要

We investigate the effect of the number of arms (functionality f ) on the mobility of the branch point in symmetric star polymers. For this purpose we carry out large-scale molecular dynamics simulations of simple bead–spring stars and neutron spin echo (NSE) spectroscopy experiments on center labeled polyethylene stars. This labeling scheme unique to neutron scattering allows us to directly observe the branch point motion on the molecular scale by measuring the dynamic structure factor. We investigate the cases of different functionalities f = 3, 4, and 5 for different arm lengths. The analysis of the branch point fluctuations reveals a stronger localization with increasing functionality, following 2/ f scaling. The dynamic structure factors of the branch point are analyzed in terms of a modified version, incorporating dynamic tube dilution (DTD), of the Vilgis–Boué model for cross-linked networks [ J. Polym. Sci., Part B 1988 , 26 , 2291?2302]. In DTD the tube parameters are renormalized with the tube survival probability Φ( t ). As directly measured by the simulations, Φ( t ) is independent of f , and therefore the theory predicts no f dependence of the relaxation of the branch point. The theory provides a good description of the NSE data and simulations for intermediate times. However, the simulations, which have access to much longer time scales, reveal the breakdown of the DTD prediction since increasing the functionality actually leads to a slower relaxation of the branch point.
机译:我们研究了武器(功能f)的效果对对称星聚合物中分支点的迁移率。为此目的,我们在标有标记的聚乙烯恒星的中心进行简单的珠子春天恒星和中子旋转回声(NSE)光谱实验的大规模分子动力学模拟。该标记方案是中子散射独特的标记方案使我们通过测量动态结构因子来直接观察分子尺度的分支点运动。我们研究了不同臂长度的不同功能F = 3,4和5的情况。分支点波动的分析揭示了越来越多的函数,在2 / f缩放之后呈现出更强的本地化。分支点的动态结构因子在改进的版本中分析了一种用于交联网络的Vilgis-Boué模型的动态管稀释(DTD)的改进版本[​​J.Colomm。 SCI。,B部分1988,26,2291?2302]。在DTD中,管参数用管生存概率φ(t)重整。通过模拟直接测量,φ(t)与f无关,因此理论预测分支点的松弛的不依赖性。该理论提供了NSE数据和中间时间模拟的良好描述。然而,可以访问更长的时间尺度的模拟,揭示了DTD预测的击穿,因为增加功能实际上导致分支点的较慢松弛。

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  • 来源
    《Macromolecules》 |2018年第1期|共12页
  • 作者单位

    Forschungszentrum Jülich GmbH 52425 Jülich Germany;

    Centro de Física de Materiales (CSIC UPV/EHU) and Materials Physics Center MPC Paseo Manuel de Lardizabal 5 20018 San Sebastián Spain;

    Forschungszentrum Jülich GmbH 52425 Jülich Germany;

    Centro de Física de Materiales (CSIC UPV/EHU) and Materials Physics Center MPC Paseo Manuel de Lardizabal 5 20018 San Sebastián Spain;

    Forschungszentrum Jülich GmbH 52425 Jülich Germany;

    Department of Chemistry University of Athens Panepistimiopolis Zografou 15771 Athens Greece;

    Institut Laue-Langevin 71 Avenue des Martyrs CS 20156 Cedex 9 38042 Grenoble France;

    Forschungszentrum Jülich GmbH 52425 Jülich Germany;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 高分子化学(高聚物);
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