Dynamics of Dipole-Inverted cis-Polyisoprene Chains in a Matrix of Long, Entangling Chains. 2. Effects of Constraint Release on the Coherence of the Subchain Motion
Dynamics of Dipole-Inverted cis-Polyisoprene Chains in a Matrix of Long, Entangling Chains. 2. Effects of Constraint Release on the Coherence of the Subchain Motion
复制标题
长缠结链矩阵中偶极反向顺式聚异戊二烯链的动力学。
作者：
H. Watanabe;Yumi Matsumiya;K. Osaki;Ming
对于顺式聚异戊二烯（PI）链具有沿其主链沿着平行的偶极，粘弹性弛豫反映了子链（应力产生单元）在相应时间的取向各向异性，而介电弛豫反映了子链在两个单独时间的取向相关性。粘弹性和介电弛豫过程之间的这种差异，使我们能够通过比较这些过程来检查在单个链中的子链运动的短时间相干性。具体地说，对于完全相干或不相干的子链运动的两种极端情况下，粘弹性模量G * coh和G * incoh显式计算的弛豫时间τ p和特征函数fp定义的局部相关函数描述的介电弛豫的基本特征。在这些背景的基础上，计算了PI链（M = 48800）在高M缠结聚丁二烯（PB）基质（M = 263000）中稀释共混的G * coh和G * incoh。(The计算所需的τ p和fp数据在本系列论文的第1部分中得到。）G * coh与PI链的G * 数据非常一致，而G * incoh与数据显著不同，这意味着在高M PB基质中PI链的子链运动是高度一致的。相比之下，在M较小（=9240）的纠缠PB矩阵中，同一PI链的子链运动被发现是不相干的。在高M矩阵中，约束释放机制对PI链的全局动力学行为的贡献可以忽略不计，而在低M矩阵中，约束释放机制对PI链的全局动力学行为起主导作用。这些结果表明，约束释放是决定子链运动相干程度的重要因素。
For cis-polyisoprene (PI) chains having dipoles parallel along their backbone, viscoelastic relaxation reflects orientational anisotropy of subchains (stress-generating units) at respective times while the dielectric relaxation reflects orientational correlation of the subchains at two separate times. This difference between viscoelastic and dielectric relaxation processes enables us to examine the short-time coherence of subchain motion in individual chains through comparison of these processes. Specifically, for the two extreme cases of perfectly coherent or incoherent subchain motion, viscoelastic moduli G * coh and G * incoh are explicitly calculated from the relaxation times τ p and eigenfunctions f p defined for a local correlation function describing fundamental features of the dielectric relaxation. On the basis of these backgrounds, the G * coh and G * incoh were calculated for a PI chain (M = 48800) dilutely blended in a high-M entangling polybutadiene (PB) matrix (M = 263000). (The τ p and f p data necessary for this calculation were obtained dielectrically in Part 1 of this series of papers.) The G * coh was in excellent agreement with the G * data of the PI chain while G * incoh , was significantly different from the data, meaning that the subchain motion was highly coherent for the PI chain in the high-M PB matrix. In contrast, the subchain motion of the same PI chain was found to be incoherent in an entangling PB matrix of smaller M (=9240). The constraint release mechanism made a negligible contribution to the global dynamics of the PI chains in the high-M matrix while it dominated the dynamics in the low-M matrix. These results indicate that the constraint release is an important factor that determines the degree of coherence of the subchain motion.