单层颗粒模型体系融化过程中的动力学和动力学异质性

Dynamics and dynamical heterogeneity in the melting of a single layer granular model system

在过去十几年中,人们对胶体和颗粒等软物质模型晶体的融化过程进行了广泛的研究.本文中选择了单层的颗粒体系作为软物质物理模型,利用摄像和粒子跟踪技术,在粒子尺度上定量地研究了体系的融化行为.与前人对融化研究的内容不同,他们大部分关注的都是融化的静态结构和序参量变化,而本文重点是研究融化过程中的动力学和动力学异质性.根据实验数据,计算了融化过程中表征动力学和动力学异质性的一系列物理量,包括散射函数、非高斯参数、极化率和动态构型.研究结果表明,单层的颗粒体系由晶体融化成为液体的过程中,不但动力学变快,而且动力学异质性出现独特的非单调变化,呈现为:晶体中是均匀的动力学,融化过程中动力学异质性增加,进入液体后又减小的变化过程.结合动态粒子运动的微观位型对这样独特的动力学和动力学异质性进行了讨论.

Over the past decade,melting of model soft matter systems, such as colloidal suspensions and granular materials,have received extensive studies. In this paper, we studied the melting behaviors of a single layer granular model system using video imaging and particle tracking technique. Unlike previous work, in which static structure and order parameters of the studied systems are the research attentions,we focus on dynamics and dynamical hetero- geneity during the melting process. By calculating a series of physical quantities such as intermediate scattering function,non-Gaussian parameter and susceptibility, we found, during the melting process, the dynamics speed up, and surprisingly,the dynamical heterogeneity exhibits a non-monotonic trend. The dynamical heterogeneity is small in the granular solid,and it reaches the maxim in the solid liquid coexistence regime,then it return to small value in the granular liquid state. We discussed these peculiar dynamical properties in terms of mobile particle configurations.