Merabia Samy, Long Didier
Laboratoire de Physique des Solides, Université de Paris XI, Batiment 510, 91405 Orsay Cédex, France.
J Chem Phys. 2006 Dec 21;125(23):234901. doi: 10.1063/1.2399527.
It has been shown over the past ten years that the dynamics close to the glass transition is strongly heterogeneous: fast domains coexist with domains three or four decades slower, the size of these regions being about 3 nm at T(g). The authors extend here a model that has been proposed recently for the glass transition in van der Waals liquids. The authors describe in more details the mechanisms of the alpha relaxation in such liquids. It allows then to interpret physical ageing in van der Waals liquids as the evolution of the density fluctuation distribution towards the equilibrium one. The authors derive the expression of macroscopic quantities (volume, compliance, etc.). Numerical results are compared with experimental data (shape, times to reach equilibrium) for simple thermal histories (quenches, annealings). The authors explain the existence of a "Kovacs memory effect" and the temporal asymmetry between down jump and up jump temperatures experiments, even for systems for which there is no energy barriers. Their model allows also for calculating the evolution of small probe diffusion coefficients during ageing.
在过去十年中已经表明，接近玻璃化转变的动力学是强烈非均匀的：快速区域与慢三到四个数量级的区域共存，这些区域在玻璃化转变温度（T(g)）下的尺寸约为3纳米。作者在此扩展了一个最近提出的用于范德华液体玻璃化转变的模型。作者更详细地描述了此类液体中α弛豫的机制。这使得能够将范德华液体中的物理老化解释为密度涨落分布向平衡分布的演化。作者推导了宏观量（体积、柔量等）的表达式。将数值结果与简单热历史（淬火、退火）的实验数据（形状、达到平衡的时间）进行了比较。作者解释了“科瓦奇记忆效应”的存在以及向下跳跃和向上跳跃温度实验之间的时间不对称性，即使对于没有能垒的系统也是如此。他们的模型还允许计算老化过程中小探针扩散系数的演化。
