structural relaxation

结构弛豫
  • 文章类型: Journal Article
    部分结晶度对低分子有机玻璃结构弛豫行为的影响,相反,例如,聚合材料,一个很大程度上未开发的领域。在本研究中,采用差示扫描量热法制备了一系列结晶到不同程度的无定形吲哚美辛粉末。制剂源于两个不同的粒径部分:50-125µm和300-500µm。根据现象学工具-Narayanaswamy-Moynihan模型描述了来自循环量热测量的结构松弛数据。对于300-500微米的粉末,在0-70%结晶度范围内,主要在表面上形成的结晶相导致玻璃化转变单调降低〜6°C。松弛运动的活化能和松弛基质内的异质性程度不受结晶度增加的影响,而互联互通略有增加。这种行为归因于淬火应力的释放以及随之而来的结构互连性的轻微增加。对于50-125微米的粉末,观察到明显不同的弛豫动力学。这得出的结论是,结晶相沿内部微裂纹在整个玻璃质基体中生长。在较高的结晶度,Tg的急剧增加,互联互通的增加,并且观察到参与松弛运动的结构单元的变异性增加。
    The influence of partial crystallinity on the structural relaxation behavior of low-molecular organic glasses is, contrary to, e.g., polymeric materials, a largely unexplored territory. In the present study, differential scanning calorimetry was used to prepare a series of amorphous indomethacin powders crystallized to various extents. The preparations stemmed from the two distinct particle size fractions: 50-125 µm and 300-500 µm. The structural relaxation data from the cyclic calorimetric measurements were described in terms of the phenomenological Tool-Narayanaswamy-Moynihan model. For the 300-500 µm powder, the crystalline phase forming dominantly on the surface led to a monotonous decrease in the glass transition by ~6 °C in the 0-70% crystallinity range. The activation energy of the relaxation motions and the degree of heterogeneity within the relaxing matrix were not influenced by the increasing crystallinity, while the interconnectivity slightly increased. This behavior was attributed to the release of the quenched-in stresses and to the consequent slight increase in the structural interconnectivity. For the 50-125 µm powder, distinctly different relaxation dynamics were observed. This leads to a conclusion that the crystalline phase grows throughout the bulk glassy matrix along the internal micro-cracks. At higher crystallinity, a sharp increase in Tg, an increase in interconnectivity, and an increase in the variability of structural units engaged in the relaxation motions were observed.
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