Effect of excluded volume on segmental orientation correlations in polymer chains.
Effect of excluded volume on segmental orientation correlations in polymer chains.
复制标题
排除体积对聚合物链中链段取向相关性的影响。
DOI：
--
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
K. Saalwächter
中科院分区：
文献类型：
--
作者：
J. Sommer;Walter Chassé;J. L. Valentín;K. Saalwächter
我们研究了排除体积相互作用对聚合物凝胶中链段取向统计的影响，并表明核磁共振（NMR）实验提供了排除体积效应对链统计的直接和独特的测量。我们特别考虑张量序参数，它可以表示为段方向相对于固定的端到端距离向量的第二个Legendre多项式，它与NMR实验中获得的剩余耦合常数直接相关。我们提供了单链在良好溶剂和半稀溶液中的分析结果。利用化学键波动模型进行了计算机模拟，并与分析预测结果进行了比较。考虑到聚合物凝胶处于膨胀平衡状态，我们预测了张量阶参数与凝胶的相关长度（团大小）之间的独特关系。将多量子核磁共振方法应用于端链和随机交联聚合物网络的实验与这一预测非常吻合。实验中观察到的张量阶参量在中低程度膨胀时的初始衰减可以解释为溶剂效应，而无需对膨胀过程中的约束释放过程进行额外假设。
We study the impact of excluded volume interactions on the orientation statistics of chain segments in polymer gels, and show that nuclear magnetic resonance (NMR) experiments provide a direct and unique measure of excluded-volume effects on the chain statistics. In particular we consider the tensor order parameter, which can be expressed as the second Legendre polynomial of the segment orientation with respect to a fixed end-to-end distance vector and which is directly related to the residual coupling constant obtained in NMR experiments. We provide analytical results for the case of single chains in a good solvent and for semidilute solutions. Computer simulations using the bond fluctuation model are applied to compare with the analytical predictions. Considering polymer gels at the equilibrium state of swelling we predict a unique relation between the tensor order parameter and the correlation length (blob size) of the gel. Experiments applying multiple-quantum NMR methods to both end-linked and randomly cross-linked polymer networks are in excellent agreement with this prediction. The initial decay of the tensor order parameter as observed in experiments at low and intermediate degrees of swelling can be explained as a solvent effect without making additional assumptions about constraint release processes during swelling.