arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2002.01880cond-mat.softphysics.flu-dyn
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球形约束下的形状诱导偏析和反常粒子输运

Shape induced segregation and anomalous particle transport under spherical confinement

Abhinendra Singh, Jiyuan Li, Xikai Jiang, Juan P. Hernández-Ortiz, Heinrich M. Jaeger, Juan J. de Pablo

摘要:

胶体或纳米粒子在约束下的流动性对广泛的物理和生物过程至关重要。在这里,我们介绍了一个极小模型的粒子在流体动力学连续研究如何粒子的形状和浓度影响的颗粒在球形约束的运输。具体而言,浸没边界一般几何Ewald的方法是通过模拟短和长范围波动的水动力相互作用的影响下,适当的非滑动条件下的限制壁的球体和圆柱体的动力学。一个有效的$\it{O(N)}$并行有限元算法的使用,从而允许在高浓度的模拟,而切比雪夫多项式近似实现,以满足波动耗散定理。悬浮颗粒的浓度依赖性的异常扩散观察。据发现,引入圆柱体的背景中的球体,即具有简单程度的各向异性的颗粒,具有显着的影响上的颗粒的结构和动力学。首先,增加圆柱体的分数引起颗粒分离效应,其中球体被推向壁并且圆柱体保持在腔的中心附近。相对于在相同体积分数下纯球体的系统中遇到的流动性,这种分离导致球体的流动性较低。第二,扩散到异常的过渡和异常的程度-量化的幂律指数的均方位移与时间的关系-都增加的气缸的分数变得更大。这些发现与细胞质中扩散的研究有关,在细胞质中,蛋白质表现出大小和形状的分布,可能导致在这里报告的模拟中确定的一些影响。

英文摘要:

Colloid or nanoparticle mobility under confinement is of central importance to a wide range of physical and biological processes. Here, we introduce a minimal model of particles in a hydrodynamic continuum to examine how particle shape and concentration affect the transport of particles in spherical confinement. Specifically, an immersed boundary-General geometry Ewald-like approach is adopted to simulate the dynamics of spheres and cylinders under the influence of short-and long-range fluctuating hydrodynamic interactions with appropriate non-slip conditions at the confining walls. An efficient $\it{O(N)}$ parallel finite element algorithm is used, thereby allowing simulations at high concentrations, while a Chebyshev polynomial approximation is implemented in order to satisfy the fluctuation-dissipation theorem. A concentration-dependent anomalous diffusion is observed for suspended particles. It is found that introducing cylinders in a background of spheres, i.e. particles with a simple degree of anisotropy, has a pronounced influence on the structure and dynamics of the particles. First, increasing the fraction of cylinders induces a particle segregation effect, where spheres are pushed towards the wall and cylinders remain near the center of the cavity. This segregation leads to lower mobility for the spheres relative to that encountered in a system of pure spheres at the same volume fraction. Second, the diffusive-to-anomalous transition and the degree of anomaly--quantified by the power-law exponent in the mean square displacement vs. time relation-both increase as the fraction of cylinders becomes larger. These findings are of relevance for studies of diffusion in the cytoplasm, where proteins exhibit a distribution of size and shapes that could lead to some of the effects identified in the simulations reported here.

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