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arXiv 1507.02533cond-mat.soft
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胶体哑铃悬浮液的平衡结构和涨落

Equilibrium structure and fluctuations of suspensions of colloidal dumbbells

Nils Heptner, Joachim Dzubiella

摘要:

我们研究的结构和平衡的线性响应动力学的悬浮液的硬胶体哑铃使用布朗动力学计算机模拟。重点在于稠密的流体和塑性晶体状态的胶体与调查的方面(伸长率直径)的比率从硬球极限变化到0.39,这大致是塑性晶体相的稳定极限。我们发现预期的结构变化与更大的伸长率相对于硬球参考的情况下,非常本地化的取向相关性,通常只是涉及下一个邻居的耦合。这些相对较弱的相关性也反映在只有轻微的影响的平移和旋转扩散系数为大多数的调查伸长率。然而,线性响应剪切粘度在超过约$L^* \simeq 0.15$的临界各向异性因子的高填充分数($ϕ\gtrsim 0.5$)下表现出显著增加,这是令人惊讶的,因为之前在胶体自动力学水平上发现了相对弱的变化。我们怀疑,即使是小的调查各向异性,新发生的,集体旋转平移耦合必须负责出现在塑料晶体中的缓慢的时间尺度。

英文摘要:

We investigate the structure and equilibrium linear-response dynamics of suspensions of hard colloidal dumbbells using Brownian Dynamics computer simulations. The focus lies on the dense fluid and plastic crystal states of the colloids with investigated aspect (elongation-to-diameter) ratios varying from the hard sphere limit up to 0.39, which is roughly the stability limit of the plastic crystal phase. We find expected structural changes with larger elongation with respect to the hard sphere reference case and very localized orientational correlations, typically just involving next-neighbor couplings. These relatively weak correlations are also reflected in only minor effects on the translational and rotational diffusion coefficients for most of the investigated elongations. However, the linear response shear viscosity exhibits a dramatic increase at high packing fractions ($ϕ\gtrsim 0.5$) beyond a critical anisotropy factor of about $L^* \simeq 0.15$ which is surprising in view of the relatively weak changes found before on the level of colloidal self-dynamics. We suspect that even for the small investigated anisotropies, newly occurring, collective rotational-translational couplings must be made responsible for the slow time scales appearing in the plastic crystal.

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