通过中心势相互作用的纳米粒子的Langevin凝聚
Langevin agglomeration of nanoparticles interacting via a central potential
摘要：
通过求解连续体系中一组相互作用单体的朗之万运动方程，模拟了纳米颗粒在静止流体中的团聚。单体通过径向快速衰减的单体间势相互作用。通过分形维数$d_f$和团簇配位数分析了生成团簇的形貌。集群分形维数的时间演化与两个种群的动态，小（$k \le 15$）和大（$k>15$）集群。在早期，单体-团簇凝聚是主要的凝聚机制（$d_f = 2.25$），而在晚期，团簇-团簇凝聚占主导地位（$d_f = 1.56$）。簇被发现是紧凑的（平均配位数$\sim 5$），管状，细长。聚集体的局部紧凑结构归因于相互作用势的各向同性，其允许键合单体的重排，而大规模的管状结构归因于其相对短的吸引范围。集群平移扩散系数被确定为成反比的集群质量和（每单位质量）的摩擦系数的一个孤立的单体，一个后果的忽视在集群中的单体屏蔽。由非屏蔽朗之万方程产生的团簇被称为\textit{ideal clusters}，因为发现底层流体可接近的表面积是孤立单体可接近表面积的总和。类似地，理想的团簇平均而言没有优先取向。随着时间的推移和一些碰撞内核元素的集群的数量减少进行评估和分析表达式相比。
英文摘要：
Nanoparticle agglomeration in a quiescent fluid is simulated by solving the Langevin equations of motion of a set of interacting monomers in the continuum regime. Monomers interact via a radial, rapidly decaying intermonomer potential. The morphology of generated clusters is analyzed through their fractal dimension $d_f$ and the cluster coordination number. The time evolution of the cluster fractal dimension is linked to the dynamics of two populations, small ($k \le 15$) and large ($k>15$) clusters. At early times monomer-cluster agglomeration is the dominant agglomeration mechanism ($d_f = 2.25$), whereas at late times cluster-cluster agglomeration dominates ($d_f = 1.56$). Clusters are found to be compact (mean coordination number $\sim 5$), tubular, and elongated. The local, compact structure of the aggregates is attributed to the isotropy of the interaction potential, which allows rearrangement of bonded monomers, whereas the large-scale tubular structure is attributed to its relatively short attractive range. The cluster translational diffusion coefficient is determined to be inversely proportional to the cluster mass and the (per-unit-mass) friction coefficient of an isolated monomer, a consequence of the neglect of monomer shielding in a cluster. Clusters generated by unshielded Langevin equations are referred to as \textit{ideal clusters} because the surface area accessible to the underlying fluid is found to be the sum of the accessible surface areas of the isolated monomers. Similarly, ideal clusters do not have, on average, a preferential orientation. The decrease of the numbers of clusters with time and a few collision kernel elements are evaluated and compared to analytical expressions.
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