Jose Francis, Anand Shalabh K, Singh Sunil P
Department of Physics, Indian Institute of Science Education and Research, Bhopal 462 066, Madhya Pradesh, India.
Soft Matter. 2021 Mar 21;17(11):3153-3161. doi: 10.1039/d0sm02131h. Epub 2021 Feb 22.
We present the Brownian dynamics simulation of an active colloidal suspension in two dimensions, where the self-propulsion speed of a colloid is regulated according to the local density sensed by it. The role of concentration-dependent motility in the phase-separation of colloids and their dynamics is investigated in detail. Interestingly, the system phase separates at a very low packing fraction (Φ≈ 0.125) at higher self-propulsion speeds (Pe), into a dense phase coexisting with a homogeneous phase and attains a long-range crystalline order beyond the transition point. The transition point is quantified here from the local density profiles and local and global-bond order parameters. We have shown that the characteristics of the phase diagram are qualitatively akin to the active Brownian particle (ABP) model. Moreover, our investigation reveals that the density-dependent motility amplifies the slow-down of the directed speed, which facilitates phase-separation even at low packing fractions. The effective diffusivity shows a crossover from quadratic rise to a power-law behavior of exponent 3/2 with Pe in the phase-separated regime. Furthermore, we have shown that the effective diffusion decreases exponentially with packing fraction in the phase-separated regime, while it shows a linear decrease in the single phase regime.
我们展示了二维活性胶体悬浮液的布朗动力学模拟，其中胶体的自推进速度根据其感知到的局部密度进行调节。详细研究了浓度依赖的运动性在胶体相分离及其动力学中的作用。有趣的是，在较高的自推进速度（Pe）下，系统在非常低的堆积分数（Φ≈0.125）时发生相分离，形成与均匀相共存的致密相，并在转变点之后达到长程晶体有序。在此，通过局部密度分布以及局部和全局键序参数对转变点进行了量化。我们已经表明，相图的特征在定性上类似于活性布朗粒子（ABP）模型。此外，我们的研究表明，密度依赖的运动性会放大定向速度的减慢，这甚至在低堆积分数下也有利于相分离。在相分离区域，有效扩散系数呈现出从二次方增长到指数为3/2的幂律行为的转变，且与Pe有关。此外，我们已经表明，在相分离区域，有效扩散随堆积分数呈指数下降，而在单相区域则呈线性下降。
