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arXiv 0709.3936cond-mat.soft
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棒状胶体悬浮液中耗尽诱导的各向同性-各向同性相分离

Depletion induced isotropic-isotropic phase separation in suspensions of rod-like colloids

S. Jungblut, R. Tuinier, K. Binder, T. Schilling

摘要:

当将非吸附性聚合物添加到棒状胶体的各向同性悬浮液中时,胶体通过耗尽力有效地彼此吸引。我们进行了蒙特卡罗模拟来研究这种棒状聚合物混合物的相图。胶体棒被建模为硬spherocylinders;聚合物被描述为与棒相同直径的球体。聚合物可以重叠而没有能量成本,而聚合物和棒的重叠是禁止的。大量的稀释剂导致混合物的相分离。我们估计的各向同性各向同性共存的相边界,在散装和禁闭。为了确定相边界,我们使用连续伞形采样应用巨正则系综[J. Chem. Phys. 120,10925(2004)],并且我们执行有限尺寸标度分析以估计临界点的位置。结果与Lekkerkerker和Stroobants [Nuovo Cimento D 16,949(1994)]提出的自由体积理论的预测进行了比较。我们还估计了共存的各向同性相之间的界面张力,并分析了其幂律行为的临界点的方法。

英文摘要:

When non-adsorbing polymers are added to an isotropic suspension of rod-like colloids, the colloids effectively attract each other via depletion forces. We performed Monte Carlo simulations to study the phase diagram of such rod-polymer mixture. The colloidal rods were modelled as hard spherocylinders; the polymers were described as spheres of the same diameter as the rods. The polymers may overlap with no energy cost, while overlap of polymers and rods is forbidden. Large amounts of depletant cause phase separation of the mixture. We estimated the phase boundaries of isotropic-isotropic coexistence both, in the bulk and in confinement. To determine the phase boundaries we applied the grand canonical ensemble using successive umbrella sampling [J. Chem. Phys. 120, 10925 (2004)], and we performed a finite-size scaling analysis to estimate the location of the critical point. The results are compared with predictions of the free volume theory developed by Lekkerkerker and Stroobants [Nuovo Cimento D 16, 949 (1994)]. We also give estimates for the interfacial tension between the coexisting isotropic phases and analyse its power-law behaviour on approach of the critical point.

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