Dynamics and spatial correlation of voids in dense two dimensional colloids.
Dynamics and spatial correlation of voids in dense two dimensional colloids.
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DOI：
10.1063/1.4885035
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发表时间：
2014-07
期刊：
影响因子：
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通讯作者：
Jeongmin Kim;B. Sung
中科院分区：
文献类型：
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作者：
Jeongmin Kim;B. Sung
二维胶体表现出有趣的相和动力学行为。在二维中，在各向同性的液相和固相之间还有另一种中间相，称为六相。二维胶体在六相和固相中也表现出强烈的相关动力学行为。我们对二维胶体进行了分子动力学模拟，并说明了胶体在相变附近的局部结构和动力学如何反映在空隙的空间相关性和动力学中。胶体被建模为硬盘，而一个空洞被定义为与三个最近的硬盘相切的圆（一个孔）。孔径的变化代表了孔隙的无序程度，并且随着胶体的面积分数（φ）的增大而急剧减小，当胶体的六边形结构基序变得显著，并且在φ≈0.7处开始冻结转变。孔隙的空间相关函数捕捉到了相变附近胶体有序畴的生长过程。我们还研究了不同拓扑状态下胶体的拓扑跳跃概率和拓扑寿命，发现不同拓扑状态的稳定性可能与局部孔隙的大小变化有关：六重态的胶体被最有序、最小、拓扑寿命最长的孔隙所包围。六倍态的拓扑寿命增加约50倍的φ从液体到六相到固相增加。我们还比较了四个特征时间，以了解二维胶体的缓慢而独特的动力学：笼化时间（τ(c)），拓扑寿命（τ(top)），孔隙寿命（τ(p)）和平移弛豫时间（τ(α)）。
Two dimensional (2D) colloids show interesting phase and dynamic behaviors. In 2D, there is another intermediate phase, called hexatic, between isotropic liquid and solid phases. 2D colloids also show strongly correlated dynamic behaviors in hexatic and solid phases. We perform molecular dynamics simulations for 2D colloids and illustrate how the local structure and dynamics of colloids near phase transitions are reflected in the spatial correlations and dynamics of voids. Colloids are modeled as hard discs and a void is defined as a tangent circle (a pore) to three nearest hard discs. The variation in pore diameters represents the degree of disorder in voids and decreases sharply with the area fraction (ϕ) of colloids after a hexagonal structural motif of colloids becomes significant and the freezing transition begins at ϕ ≈ 0.7. The growth of ordered domains of colloids near the phase transition is captured in the spatial correlation functions of pores. We also investigate the topological hopping probability and the topological lifetime of colloids in different topological states, and find that the stability of different topological states should be related to the size variation of local pores: colloids in six-fold states are surrounded by the most ordered and smallest pores with the longest topological lifetime. The topological lifetime of six-fold states increases by about 50 times as ϕ increases from liquid to hexatic to solid phases. We also compare four characteristic times in order to understand the slow and unique dynamics of two dimensional colloids: a caging time (τ(c)), a topological lifetime (τ(top)), a pore lifetime (τ(p)), and a translational relaxation time (τ(α)).