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首页> 外文期刊>Journal of Non-Crystalline Solids: A Journal Devoted to Oxide, Halide, Chalcogenide and Metallic Glasses, Amorphous Semiconductors, Non-Crystalline Films, Glass-Ceramics and Glassy Composites >Physical ageing and the Johari-Goldstein relaxation in molecular glasses
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Physical ageing and the Johari-Goldstein relaxation in molecular glasses

机译：物理衰老和约翰尼 - 戈德斯坦在分子玻璃中放松

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摘要

Based on some of our earlier dielectric relaxation studies during structural relaxation of molecular glasses, we describe certain features specific to the change in the Johari-Goldstein (JG) relaxation and examine their consequences for understanding of the molecular mechanism of the JG process. The parameter for the distribution of relaxation times increases slightly (loss curve becomes narrower) and the relaxation rate either remains constant or increases on ageing. In all cases, contribution to permittivity from the JG relaxation, ΔεJG decreases with time, with a rate constant k according to a relation, Δε_(JG) (t) = Δε_(JG) (t → ∞) - [Δε_(JG) (t = 0) - Δε_(JG) (t → ∞)][1- exp[-(kt)]. This reduces to an equation of the type Δε_(JG)(t) = a + b exp(- kt) where a and b are constants of the glass as well are dependent on the thermal history of quenching of the glassy system. On decreasing the temperature, the relaxation rate for a rigid molecular glass follows the Arrhenius equation in a range that extends from liquid to glass, but deviates from it as a result of structural relaxation of the two alcohols, while the distribution of relaxation times decreases. The variation of Δε_(JG) with temperature shows an increase in slope on heating through T_g or else a deep and broad minimum before T_g is reached and the slope increases are remarkably similar to the changes observed for volume and thermodynamic properties on heating a glass. These findings need to be considered for a molecular mechanism in the potential energy view of JG relaxation, in analyzing the physical ageing of the α-relaxation process. It is argued that a recent suggestion for considering the JG relaxation within the picture of potential energy landscape may not be inconsistent with its molecular origin and dynamics in localized regions of structurally inhomogeneous glass. But there is still need to determine how the apparent dynamic heterogeneity evident from the broad distribution of the JG relaxation times can be reconciled with the dynamic heterogeneity used to explain less-broad spectra of the α - relaxation process.
机译：基于我们在分子玻璃的结构松弛过程中的一些早期介电放松研究中，我们描述了特定于约翰尼 - 戈德斯坦（JG）放松的变化的特征，并检查了对JG过程的分子机制的影响。用于弛豫时间分布的参数略微增加（损耗曲线变窄），并且弛豫速率保持恒定或增加老化。在所有情况下，从JG弛豫到允许率的贡献，Δεjg随时间减少，速率常数k根据关系，Δε_（jg）（t）=Δε_（jg）（t→∞） - [Δε_（jg） （t = 0） - Δε_（jg）（t→∞）] [1- exp [ - （kt）]。这减小到Δε_（jg）（t）（t）= a + b exp（ - - kt）的等式，其中a和b也是玻璃的常数，也取决于玻璃系统的淬火的热历史。在降低温度下，刚性分子玻璃的弛豫率在从液体到玻璃延伸的范围内遵循Arrhenius方程，但由于两种醇的结构松弛而偏离它，而松弛时间的分布降低。温度的Δε_（JG）的变化显示通过T_G加热的斜率增加，或者在达到T_G之前的深层和宽的最小值，并且斜率增加非常类似于在加热玻璃上观察到的体积和热力学性能的变化。在分析α-松弛过程的物理老化时，需要考虑这些调查结果在JG弛豫的潜在能量观点中进行分子机制。有人认为，最近关于考虑潜在能量景观图片内的JG放松的建议可能与结构不均匀玻璃的局部区域中的分子来源和动态不一致。但仍然需要确定如何从JG弛豫时间的广泛分布中明显明显的可观的动态异质性可以与用于解释α - 松弛过程的较少广谱的动态异质性协调。

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