Li Yan-Wei, Zhu You-Liang, Sun Zhao-Yan
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
J Chem Phys. 2015 Mar 28;142(12):124507. doi: 10.1063/1.4916208.
We investigate numerically the relaxation and diffusion dynamics in three-dimensional Kob-Andersen glass-forming liquids in which part of the particles are randomly chosen and pinned permanently. We find that both the relaxation dynamics and diffusion dynamics slow down as increasing the pinning concentration (cpin) at fixed temperatures that we study. For higher temperature and lower cpin, the α relaxation time τ and the diffusion coefficient D have the scaling relationship D ∼ τ(-1). However, this coupling behavior breaks down if cpin is further increased, and the scaling relationship is replaced by D ∼ τ(-ν) with ν < 1. At temperatures around the onset temperature of the bulk system, a transition from ν ∼ 0.75 to ν ∼ 0.61 with increasing cpin is found. However, at lower temperatures, ν ∼ 0.67 holds in the whole studied cpin range. By fitting the relaxation time as a function of cpin with Vogel-Fulcher-Tamman equation, we find that the change of scaling exponent ν is accompanied with the change of fragility parameter K at higher temperatures. However, at lower temperatures, pinning particles have little effect on the system's qualitative properties. Moreover, we investigate three measures of heterogeneity of dynamics and find that the relaxation and the diffusion motion of particles show different responses to the pinned particles, which may lead to the slower relaxation than diffusion and the decoupling of relaxation and diffusion. The string-like motion is found to saturate at the mode-coupling theory (MCT) crossover point, which indicates that other relaxation modes may exist below the MCT transition point.
我们对三维Kob-Andersen玻璃形成液体中的弛豫和扩散动力学进行了数值研究，其中部分粒子被随机选择并永久固定。我们发现，在我们研究的固定温度下，随着固定浓度（cpin）的增加，弛豫动力学和扩散动力学都会减慢。对于较高温度和较低的cpin，α弛豫时间τ和扩散系数D具有标度关系D ∼ τ(-1)。然而，如果cpin进一步增加，这种耦合行为就会失效，标度关系将被D ∼ τ(-ν) 取代，其中ν < 1。在本体系统起始温度附近的温度下，发现随着cpin的增加，ν从约0.75转变为约0.61。然而，在较低温度下，在整个研究的cpin范围内ν约为0.67。通过用Vogel-Fulcher-Tamman方程将弛豫时间拟合为cpin的函数，我们发现在较高温度下，标度指数ν的变化伴随着脆性参数K的变化。然而，在较低温度下，固定粒子对系统的定性性质影响很小。此外，我们研究了动力学非均匀性的三种度量，发现粒子的弛豫和扩散运动对固定粒子表现出不同的响应，这可能导致弛豫比扩散更慢以及弛豫和扩散的解耦。发现串状运动在模式耦合理论（MCT）交叉点处饱和，这表明在MCT转变点以下可能存在其他弛豫模式。
