Kovacs效应的非平衡态热力学
Nonequilibrium Thermodynamics of the Kovacs Effect
摘要：
我们提出了一个热力学理论的Kovacs效应的基础上的想法，即玻璃形成材料的配置自由度被赶出与热浴不可逆的热收缩和膨胀的平衡。我们假设，缓慢变化的配置子系统，即由固有结构描述的系统的一部分，其特征在于有效温度，并包含体积相关的内部变量。我们研究的机制，快速，动力学振动自由度的不可逆动力学可以导致熵和有效温度的配置子系统在浴温度足够快的变化过程中增加。然后，我们使用这个理论来解释Mossa和Sciortino（MS）的数值模拟，他们观察到的Kovacs效应比实验室实验中的可行性更详细。我们的分析突出了两种机制的内部变量的平衡。在其中一种情况下，内部变量首先向由有效温度确定的准平衡状态松弛，然后随着有效温度向浴温缓慢松弛而接近真正的热力学平衡。在另一种机制中，内部变量在中间时间尺度上直接与浴温平衡，而在任何阶段都不与有效温度平衡。这两种机制对于理解MS结果似乎都是必不可少的。
英文摘要：
We present a thermodynamic theory of the Kovacs effect based on the idea that the configurational degrees of freedom of a glass-forming material are driven out of equilibrium with the heat bath by irreversible thermal contraction and expansion. We assume that the slowly varying configurational subsystem, i.e. the part of the system that is described by inherent structures, is characterized by an effective temperature, and contains a volume-related internal variable. We examine mechanisms by which irreversible dynamics of the fast, kinetic-vibrational degrees of freedom can cause the entropy and the effective temperature of the configurational subsystem to increase during sufficiently rapid changes in the bath temperature. We then use this theory to interpret the numerical simulations by Mossa and Sciortino (MS), who observe the Kovacs effect in more detail than is feasible in laboratory experiments. Our analysis highlights two mechanisms for the equilibration of internal variables. In one of these, an internal variable first relaxes toward a state of quasi-equilibrium determined by the effective temperature, and then approaches true thermodynamic equilibrium as the effective temperature slowly relaxes toward the bath temperature. In the other mechanism, an internal variable directly equilibrates with the bath temperature on intermediate timescales, without equilibrating with the effective temperature at any stage. Both mechanisms appear to be essential for understanding the MS results.
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