Glass transition of polymers: Memory effects in structural relaxation of polystyrene
Glass transition of polymers: Memory effects in structural relaxation of polystyrene
复制标题
聚合物的玻璃化转变：聚苯乙烯结构松弛的记忆效应
DOI：
10.1103/physreve.56.741
复制
发表时间：
1997
影响因子：
2.4
通讯作者：
H. Spiess
中科院分区：
文献类型：
--
作者：
S. Kuebler;A. Heuer;H. Spiess
本文采用多维固体核磁共振回波技术研究了聚苯乙烯的α弛豫动力学。一个广泛的分布的相关时间特性的无定形聚合物的玻璃化转变温度以上的弛豫时间分布内的时间波动进行了分析。这些波动由速率记忆参数Q量化。实验相关函数显示Q几乎是在其理论最小值，证明了不同的弛豫模式之间的强耦合。对于聚乙酸乙烯酯和邻三联苯得到的类似结果表明，这种行为是在玻璃化转变以上的无定形系统中的动力学的特征，如通过NMR实验所看到的。此外，多时间相关函数允许一个量化的异质性和同质性的松弛过程的贡献，并确定在何种程度上可以被视为不同的松弛过程，而不是一个同质的情况下，其中的nonexponentiality是内在的异构叠加的松弛。分析表明，放松是接近的异质极限，其余的偏差表明存在一小部分相关的来回跳跃。
The dynamics of the α relaxation in polystyrene is investigated by applying specific multidimensional solid-state NMR echo techniques to evaluate multitime correlation functions. A broad distribution of correlation times characteristic for amorphous polymers above the glass transition temperature is analyzed with respect to temporal fluctuations within the relaxation time distribution. These fluctuations are quantified by a rate memory parameter Q. The experimental correlation functions reveal Q to be almost at its theoretical minimum, proving a strong coupling among different relaxation modes. Similar results obtained for polyvinylacetate and ortho-terphenyl indicate that this behavior is a characteristic feature of the dynamics in amorphous systems above the glass transition as seen by NMR experiments. Furthermore, the multitime correlation functions allow one to quantify the heterogeneous and homogeneous contributions to the relaxation process and to determine to what extent the relaxation can be regarded as a heterogeneous superposition of different relaxation processes as opposed to a homogeneous scenario, in which the nonexponentiality is intrinsic. The analysis reveals that the relaxation is close to the heterogeneous limit and that remaining deviations indicate the presence of a small fraction of correlated back-and-forth jumps.