Pastore Raffaele, Kikutsuji Takuma, Rusciano Francesco, Matubayasi Nobuyuki, Kim Kang, Greco Francesco
Department of Chemical, Materials and Production Engineering, University of Naples Federico II, P.le Tecchio 80, Napoli 80125, Italy.
Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
J Chem Phys. 2021 Sep 21;155(11):114503. doi: 10.1063/5.0059622.
The breakdown of the Stokes-Einstein relation in supercooled liquids, which is the increase in the ratio ττ between the two macroscopic times for structural relaxation and diffusion on decreasing the temperature, is commonly ascribed to dynamic heterogeneities, but a clear-cut microscopic interpretation is still lacking. Here, we tackle this issue exploiting the single-particle cage-jump framework to analyze molecular dynamics simulations of soft disk assemblies and supercooled water. We find that ττ∝⟨t⟩⟨t⟩, where ⟨t⟩ and ⟨t⟩ are the cage-jump times characterizing slow and fast particles, respectively. We further clarify that this scaling does not arise from a simple term-by-term proportionality; rather, the relations τ∝⟨t⟩⟨Δr ⟩ and τ∝⟨t⟩⟨Δr ⟩ effectively connect the macroscopic and microscopic timescales, with the mean square jump length ⟨Δr ⟩ shrinking on cooling. Our work provides a microscopic perspective on the Stokes-Einstein breakdown and generalizes previous results on lattice models to the case of more realistic glass-formers.
在过冷液体中，斯托克斯 - 爱因斯坦关系的失效，即随着温度降低，结构弛豫和扩散的两个宏观时间之比ττ增大，通常归因于动态不均匀性，但仍缺乏明确的微观解释。在此，我们利用单粒子笼跃框架来分析软磁盘组件和过冷水的分子动力学模拟，从而解决这个问题。我们发现ττ∝⟨t⟩⟨t⟩，其中⟨t⟩和⟨t⟩分别是表征慢粒子和快粒子的笼跃时间。我们进一步阐明，这种标度关系并非源于简单的逐项比例关系；相反，关系τ∝⟨t⟩⟨Δr ⟩和τ∝⟨t⟩⟨Δr ⟩有效地连接了宏观和微观时间尺度，随着冷却，均方跳跃长度⟨Δr ⟩减小。我们的工作为斯托克斯 - 爱因斯坦关系的失效提供了微观视角，并将先前晶格模型的结果推广到更现实的玻璃形成体的情况。
