Department of Mechanical Engineering & Applied Mechanics, University of Pennsylvania, Philadelphia, PA 19104, USA.
Dept. of Physics, Syracuse University, Syracuse, NY 13244, USA.
Soft Matter. 2021 Apr 21;17(15):4151-4160. doi: 10.1039/d0sm02115f.
Sedimentation in active fluids has come into focus due to the ubiquity of swimming micro-organisms in natural and industrial processes. Here, we investigate sedimentation dynamics of passive particles in a fluid as a function of bacteria E. coli concentration. Results show that the presence of swimming bacteria significantly reduces the speed of the sedimentation front even in the dilute regime, in which the sedimentation speed is expected to be independent of particle concentration. Furthermore, bacteria increase the dispersion of the passive particles, which determines the width of the sedimentation front. For short times, particle sedimentation speed has a linear dependence on bacterial concentration. Mean square displacement data shows, however, that bacterial activity decays over long experimental (sedimentation) times. An advection-diffusion equation coupled to bacteria population dynamics seems to capture concentration profiles relatively well. A single parameter, the ratio of single particle speed to the bacteria flow speed can be used to predict front sedimentation speed.
由于游动微生物在自然和工业过程中的普遍存在，活性流体中的沉降问题引起了关注。在这里，我们研究了被动颗粒在细菌大肠杆菌浓度的作用下的沉降动力学。结果表明，即使在预期沉降速度与颗粒浓度无关的稀相区，游动细菌的存在也会显著降低沉降前沿的速度。此外，细菌会增加被动颗粒的分散度，从而决定了沉降前沿的宽度。在短时间内，颗粒的沉降速度与细菌浓度呈线性关系。然而，均方位移数据表明，细菌的活性在较长的实验（沉降）时间内会衰减。一个与细菌种群动力学相关的对流-扩散方程似乎可以很好地捕捉浓度分布。一个单一的参数，即单个颗粒的速度与细菌流动速度的比值，可以用来预测前沿的沉降速度。
