Brodin Alexander
Experimentalphysik II, Universität Bayreuth, Bayreuth, Germany.
J Chem Phys. 2008 Mar 14;128(10):104901. doi: 10.1063/1.2835603.
Segmental dynamics of relatively short linear polymers are discussed in terms of two distinct contributions, one related to the local segmental motion (alpha relaxation) and the other to polymer-specific effects that reflect Brownian dynamics of the polymer under chain connectivity constraints (Rouse relaxation modes). These two aspects of polymer dynamics are reflected, though differently, in relaxation spectra of different experimental techniques. Two contrasting cases of the (collective) dipolar response (dielectric techniques) versus the individual segmental response (e.g., NMR spin-lattice relaxation spectroscopy) are considered. The second-rank orientational correlation function of an elementary (Kuhn) segment, directly related to NMR observables, is derived in terms of Rouse normal modes. The effect of alpha dynamics is estimated under the assumption of a separation of time scales which, as it is argued, is a necessary precondition of the Rouse approach. The relative magnitude of the polymer-related dynamics is expressed through the number of elementary Rouse units in the chain and the number of Kuhn segments in a Rouse unit. The results are discussed in the context of recent literature.
相对较短的线性聚合物的链段动力学是根据两种不同的贡献来讨论的，一种与局部链段运动（α弛豫）有关，另一种与聚合物特定效应有关，该效应反映了在链连接性限制下聚合物的布朗动力学（Rouse弛豫模式）。聚合物动力学的这两个方面，尽管方式不同，但在不同实验技术的弛豫谱中都有所体现。考虑了（集体）偶极响应（介电技术）与单个链段响应（例如，NMR自旋晶格弛豫光谱）这两种对比情况。根据Rouse简正模式推导了与NMR可观测量直接相关的基本（Kuhn）链段的二阶取向相关函数。在时间尺度分离的假设下估计了α动力学的影响，如所论证的，这是Rouse方法的必要前提条件。聚合物相关动力学的相对大小通过链中基本Rouse单元的数量和一个Rouse单元中Kuhn链段的数量来表示。在近期文献的背景下对结果进行了讨论。
