Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
J Chem Phys. 2013 Mar 28;138(12):12A523. doi: 10.1063/1.4773321.
We examine dynamic heterogeneities in a model glass-forming fluid, a binary harmonic sphere mixture, above and below the mode-coupling temperature T(c). We calculate the ensemble independent susceptibility χ4(τ(α)) and the dynamic correlation length ξ4(τ(α)) at the α-relaxation time τ(α). We also examine in detail the temperature dependence of τ(α) and the diffusion coefficient D. For higher temperatures, we find that the standard Stokes-Einstein relationship, D∼τ(α)(-1), holds, but at lower temperatures a fractional Stokes-Einstein relationship, D∼τ(α)(-σ) with σ = 0.65, emerges. By examining the relationships between τ(α), D, χ4(τ(α)), and ξ4(τ(α)) we determine that the emergence of the fractional Stokes-Einstein relationship is accompanied by a dynamic crossover from τ(α)∼e(k2ξ4) at higher temperatures to τ(α)∼e(k1ξ4(3/2)) at lower temperatures.
我们研究了模型玻璃形成流体（二元调和球混合物）在模式耦合温度 T(c) 以上和以下的动态非均匀性。我们计算了在 α 松弛时间 τ(α)处的集合独立磁化率 χ4(τ(α))和动态相关长度 ξ4(τ(α))。我们还详细研究了 τ(α)和扩散系数 D 的温度依赖性。对于较高的温度，我们发现标准的 Stokes-Einstein 关系 D∼τ(α)(-1)成立，但在较低的温度下出现分数 Stokes-Einstein 关系 D∼τ(α)(-σ)，其中 σ = 0.65。通过检查 τ(α)、D、χ4(τ(α))和 ξ4(τ(α))之间的关系，我们确定分数 Stokes-Einstein 关系的出现伴随着从较高温度下的 τ(α)∼e(k2ξ4)到较低温度下的 τ(α)∼e(k1ξ4(3/2))的动态交叉。
