| dc.description.abstract | Self-propelled micro-swimmers are biological organisms or synthetic objects that propel themselves through the surrounding fluids. Examples are a fish in a school, traveling birds, various swimming bacteria such as Escherichia coli and the green alga Chlamydomonas reinhardtii, etc. In the microscale living system, various self-propelled bacteria mostly have the same pattern of motion, which is called run-and-tumble motion. The trajectory of its motion is linear in a short interval, then punctuated by sudden and rapid randomizations in direction. The above process is repeated continually. This dynamics has something similar with Brownian motion but also something different. In addition, these swimmers can be classified as having pusher or puller polarity, which means that they are driven from the rear or the front fluids, respectively.
In this study, dissipative particle dynamics (DPD) based on the mode of run-and-tumble motion is employed to simulate self-propelled nano-swimmers in bounded/unbounded system. For the unbounded system, it is found that the diffusion coefficient of nano-swimmers is higher than that of passive swimmers. The sedimentation length is increasing for nano-swimmers at sedimentation equilibrium state which is consistent with results from experiments. For the bounded system, the diffusion coefficient of nano-swimmers was obtained as well. It has a high probability for nano-swimmers to detain at the wall because of the motion mode of ballistic trajectory, which leads to the increment of friction and decrement of diffusion coefficient. Based on Buckingham Pi theorem, the expression of diffusion coefficient is obtained which is associated with the velocity, distance between the two walls, and rotation characteristic time. Furthermore, when the walls are designed with a funnel shape, owing to the existence of diffusion coefficient difference between two opposite sites, the nano-swimmers tend to move toward the site with higher diffusion coefficient. | en_US |