Dynamic crossover of alpha' relaxation in poly(vinyl acetate) above glass transition via mechanical spectroscopy.
Dynamic crossover of alpha' relaxation in poly(vinyl acetate) above glass transition via mechanical spectroscopy.
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DOI：
10.1021/jp903523x
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发表时间：
2009-08
期刊：
影响因子：
--
通讯作者：
Xuebang Wu;Zhen-Gang Zhu
中科院分区：
文献类型：
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作者：
Xuebang Wu;Zhen-Gang Zhu
在玻璃化转变温度(T(G))以上，在1 MHz~100 Hz的频率范围内，用机械能谱研究了聚乙酸乙烯酯(PVAc)的分子弛豫动力学。随温度变化的力学谱揭示了两种弛豫模式的存在：一种是由玻璃化转变引起的α模式，另一种是可能与软化弥散有关的α‘模式，它由子Rouse模式和Rouse模式组成。与α模式相比，α‘模式具有更弱的温度依赖性。此外，通过弛豫时间、弛豫强度和形状参数的温度依赖关系，从频域谱得到的α‘模在温度T(B)约387K处表现出与α模相似的动态交叉。而α‘模的交叉时间约为0.08 S，比α模的10(-6)-10(-7)S长。根据耦合模型，认为这种交叉是由于T(B)以下分子间的协作性大大增加所致。
The molecular relaxation dynamics of poly(vinyl acetate) (PVAc) has been studied by mechanical spectroscopy above the glass transition temperature (T(g)) within a frequency range from 1 mHz to 100 Hz. The temperature-dependent mechanical spectra reveal the existence of two relaxation modes: alpha, ascribed to the glass transition, and alpha', which may be related to the softening dispersion, composed of the sub-Rouse modes and the Rouse modes. The alpha' mode has a weaker temperature dependence than the alpha mode. Furthermore, the alpha' mode from the frequency-domain spectra exhibits a similar dynamic crossover at temperature T(B) approximately 387 K as the alpha mode through the temperature dependence of relaxation time, relaxation strength, and shape parameter. However, the crossover of the alpha' mode occurs at a time of about 0.08 s, longer than 10(-6)-10(-7) s for the alpha mode by dielectric spectroscopy. According to the coupling model, the crossover is suggested to be caused by the strong increase of intermolecular cooperativity below T(B).