Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at Microscales, iChEM, University of Science and Technology of China, Hefei, Anhui 230026, China.
Soft Matter. 2019 Feb 27;15(9):2020-2031. doi: 10.1039/c8sm02292e.
The diffusion behavior of an active Brownian particle (ABP) in polymer solutions is studied using Langevin dynamics simulations. We find that the long time diffusion coefficient D can show a non-monotonic dependence on the particle size R if the active force Fa is large enough, wherein a bigger particle would diffuse faster than a smaller one which is quite counterintuitive. By analyzing the short time dynamics in comparison to the passive one, we find that such non-trivial dependence results from the competition between persistent motion of the ABP and the length-scale dependent effective viscosity that the particle experiences in the polymer solution. We have also introduced an effective viscosity ηeff experienced by the ABP phenomenologically. Such an active ηeff is found to be larger than a passive one and strongly depends on R and Fa. In addition, we find that the dependence of D on propelling force Fa presents a good power-law scaling at a fixed R and the scaling factor changes non-monotonically with R. Such results demonstrate that the active process plays rather subtle roles in the diffusion of nano-particles in complex solutions.
利用朗之万动力学模拟研究了活性布朗粒子（ABP）在聚合物溶液中的扩散行为。我们发现，如果活性力 Fa 足够大，长时间扩散系数 D 可能会表现出非单调依赖于粒子尺寸 R 的关系，其中较大的粒子比较小的粒子扩散得更快，这与直觉相悖。通过与被动情况相比分析短时间动力学，我们发现这种非平凡的依赖关系源自 ABP 的持续运动与粒子在聚合物溶液中经历的与长度相关的有效粘度之间的竞争。我们还从唯象的角度引入了 ABP 所经历的有效粘度 ηeff。发现这种活性 ηeff 大于被动 ηeff，并且强烈依赖于 R 和 Fa。此外，我们发现，在固定 R 的情况下，D 对推进力 Fa 的依赖性呈现出良好的幂律标度，而标度因子随 R 的变化是非单调的。这些结果表明，在复杂溶液中纳米粒子的扩散过程中，活性过程起着相当微妙的作用。
