Department of Fundamental Engineering, Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1, Meguro-ku, Tokyo 153-8505, Japan.
School of Mathematics, University of Bristol, Bristol BS8 1TW, UK.
Nat Commun. 2017 Jun 29;8:15954. doi: 10.1038/ncomms15954.
The glassy state is known to undergo slow structural relaxation, where the system progressively explores lower free-energy minima which are either amorphous (ageing) or crystalline (devitrification). Recently, there is growing interest in the unusual intermittent collective displacements of a large number of particles known as 'avalanches'. However, their structural origin and dynamics are yet to be fully addressed. Here, we study hard-sphere glasses which either crystallize or age depending on the degree of size polydispersity, and show that a small number of particles are thermodynamically driven to rearrange in regions of low density and bond orientational order. This causes a transient loss of mechanical equilibrium which facilitates a large cascade of motion. Combined with previously identified phenomenology, we have a complete kinetic pathway for structural change which is common to both ageing and crystallization. Furthermore, this suggests that transient force balance is what distinguishes glasses from supercooled liquids.
玻璃态已知会经历缓慢的结构弛豫，其中系统逐渐探索更低的自由能极小值，这些极小值可能是无定形的（老化）或结晶的（失透）。最近，人们对大量粒子的异常间歇集体位移（即“雪崩”）越来越感兴趣。然而，它们的结构起源和动力学仍有待充分解决。在这里，我们研究了硬球玻璃，根据粒径多分散性的程度，它们要么结晶，要么老化，并表明一小部分粒子在密度和键取向有序度低的区域被热力学驱动重新排列。这会导致暂时失去机械平衡，从而促进大量的运动级联。结合之前确定的现象学，我们得到了一个完整的结构变化动力学途径，这对于老化和结晶都是常见的。此外，这表明瞬态力平衡是区分玻璃和过冷液体的特征。
