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arXiv 2402.01883cond-mat.dis-nn
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玻璃的动力学为何呈现超阿伦尼乌斯行为?

Why is the Dynamics of Glasses Super-Arrhenius?

Jean-Philippe Bouchaud

AI总结:

本文回顾了随机一阶相变理论与竞争理论在解释玻璃超阿伦尼乌斯弛豫行为上的共识与分歧,并提出通过老化阶段非线性磁化率的大规模数值模拟来揭示其机制。

摘要:

玻璃形成液体在冷却过程中弛豫时间的急剧增加,传统上被归因于即将到来的熵危机:既然系统“无处可去”,动力学必然趋于停滞。这一由 Adam 和 Gibbs 提出的经典论证,已因随机一阶相变(RFOT)理论的发展而得到支持与完善,该理论在重现过冷液体的大多数显著实验事实方面表现极为出色。RFOT 的所有静态预测,包括点对集长度(point-to-set length)的存在以及钉扎位点(pinning sites)的作用,均已通过详细的数值模拟得到证实。然而,对于解释玻璃化转变的基本机制是否就是 RFOT 所捕捉的机制,目前尚无共识。强烈的质疑源于以下观察:增加或移除动力学约束可以使弛豫时间改变数个数量级,而热力学性质保持不变。这与过量熵和弛豫时间之间存在一一对应关系的观点相矛盾。在 2023 年 10 月索尔维会议上发表的这篇讨论论文中,我们回顾了 RFOT 与其他竞争性理论提案之间达成共识和存在分歧的领域,并提出了(部分)调和这些分歧的可能路径。我们进一步论证,对玻璃的非线性磁化率进行大规模数值模拟,尤其是在老化阶段,应能为弛豫时间超阿伦尼乌斯行为起源的机制提供重要启示。无论如何,要最终解决玻璃为何不流动的问题,仍需要更多的想象力来提出实验、理论或数值方面的想法。

英文摘要:

The steep increase of the relaxation time of glass forming liquids upon cooling is traditionally ascribed to an impending entropy crisis: since the system has "nowhere to go", dynamics must come to a halt. This classic argument, due to Adam \& Gibbs, has been bolstered and refined by the development of the Random First Order Transition (RFOT) theory, which fares remarkably well at reproducing most salient experimental facts of super-cooled liquids. All static predictions of RFOT, including the existence of a point-to-set length and the role of pinning sites, have been vindicated by detailed numerical simulations. Yet, there is no consensus that the basic mechanism explaining the glass transition is the one captured by RFOT. Strong doubts have emerged following the observation that adding or removing kinetic constraints can change the relaxation time by orders of magnitude, while leaving thermodynamics unchanged. This is at odds with the idea of a one-to-one mapping between excess entropy and relaxation time. In the following discussion paper presented at the Solvay conference in October 2023, we review areas of consensus and dissent of RFOT with other competing theoretical proposals, and propose possible paths for (partial) reconciliation. We further argue that extensive numerical simulations of the non-linear susceptibility of glasses, in particular in the aging regime, should shed important light on the mechanism at the origin of the super-Arrhenius behaviour of the relaxation time. In any case, more imagination is still needed to come up with experimental, theoretical or numerical ideas that would allow to finally settle the question of why glasses do not flow.

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