Low-frequency molecular relaxations in disordered solids
Low-frequency molecular relaxations in disordered solids
复制标题
无序固体中的低频分子弛豫
DOI：
10.1051/jcp/1985820283
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
G. P. Johari
中科院分区：
文献类型：
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作者：
G. P. Johari
各向同性和各向异性液体的玻璃态以及取向无序晶体的类玻璃态中原子或分子的运动通常可以通过介电和机械弛豫光谱在10-4 Hz — 107 Hz频率范围内观察到。原子或分子在玻璃的刚性基体中的这些平移和/或旋转扩散表现出与原子或分子的扩散运动相关的弛豫特性，这些扩散运动使液体在玻璃化转变温度下变得宏观刚性。这种局部构型态（对于原子或分子的集合）的可用性也具有热力学结果，因为对材料的玻璃态和无序冻结态的热容和熵的分析表明，非振动对这些热力学性质有很大的贡献。参与此类运动的原子或分子团的数量随着温度的增加而增加，但随着玻璃的物理老化而减少。在玻璃物理老化过程中，致密化对这些运动的影响与压缩的影响不同。这些局部运动的存在可能是由于松散堆积区域的存在，这是由玻璃化转变温度下密度波动的冻结引起的，这导致玻璃中分子水平的异质结构。
Motions of atoms or molecules in the glassy state of isotropic and anisotropic liquids and in the glass-like state of orientationally disordered crystals can be generally observed by dielectric and mechanical relaxation spectroscopy in the frequency range 10-4 Hz — 107 Hz. These translational and/or rotational diffusions of atoms or molecules in the otherwise rigid matrix of a glass show relaxational characteristics quite different from those associated with the diffusional motion of atoms or molecules whose freezing out causes a liquid to become macroscopically rigid at the glass transition temperature. This availability of localized configurational states (to an ensemble of atoms or molecules) also has a thermodynamic consequence, for an analysis of the heat capacity and entropy of the glassy and disorder frozen-in state of materials shows a substantial nonvibrational contribution to these thermodynamic properties. The number of atomic or molecular groups involved in such motions increases with temperature, but decreases on the physical ageing of a glass. The effect of densification on these motions during the physical ageing of a glass differs from that of compression. The existence of these localized motions is likely to be due to the presence of loosely packed regions, caused by the freezing-in of the density fluctuations at the glass transition temperature which leads to a heterogeneous structure at a molecular level in a glass.