Mechanical Relaxation Studies of Sub-Rouse Modes in Amorphous Polymers
Mechanical Relaxation Studies of Sub-Rouse Modes in Amorphous Polymers
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DOI：
10.4028/www.scientific.net/ssp.184.52
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发表时间：
2012-01
期刊：
影响因子：
--
通讯作者：
Xuebang Wu;Hua Guang Wang;Changsong Liu;Zhen-Gang Zhu
中科院分区：
文献类型：
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作者：
Xuebang Wu;Hua Guang Wang;Changsong Liu;Zhen-Gang Zhu
力学谱是研究大温频范围内非晶态聚合物分子动力学的有力工具。本工作利用高精度剪切力学谱工具，研究了一系列非晶态聚合物从局部链段弛豫到亚Rouse模的链段动力学。我们已经证明了在无定形聚合物中存在慢于局部链段运动的子劳斯模式。在相同的温度TB ~1.2 Tg下，亚Rouse模式表现出与局部链段弛豫相似的动力学变化，表现为弛豫时间和弛豫强度随温度的变化。此外，所有聚合物的亚Rouse模在TB处的交叉弛豫时间几乎相同，即τ ′（TB）= 10 ~（-1）±0.5 s，与分子量和分子结构无关。这一显着的发现表明，只有时间尺度的放松决定的子劳斯模式的动态变化。根据耦合模型，交叉被建议是由TB以下的强分子间协同性的开始引起的。结果表明，亚劳斯模式及其性质普遍存在于无定形聚合物的力学光谱，揭示了亚劳斯模式的合作性质。
Mechanical spectroscopy is a powerful tool for the investigation of molecular dynamics of amorphous polymers over a large temperature range and frequency scale. In this work, by using high precision shear mechanical spectroscopy tool, we have investigated the segmental dynamics from local segmental relaxation to sub-Rouse modes in a series of amorphous polymers. We have demonstrated the existence of sub-Rouse modes slower than the local segmental motion in amorphous polymers. The sub-Rouse modes exhibit a similar change of dynamics at the same temperature TB ~1.2 Tg, as the local segmental relaxation through the temperature dependence of relaxation time and relaxation strength. Furthermore, the crossover relaxation time of the sub-Rouse modes at TB is almost the same for all the polymers investigated, i.e. τα'(TB) = 10-1±0.5 s, which is independent of molecular weight and molecular structure. This remarkable finding indicates that solely the time scale of the relaxation determines the change in dynamics of the sub-Rouse modes. According to the coupling model, the crossover is suggested to be caused by the onset of strong intermolecular cooperativity below TB. Hence the results suggest that the sub-Rouse modes and their properties are generally found in amorphous polymers by mechanical spectroscopy, and reveal the cooperative nature of the sub-Rouse modes.