||Self-propelled micro-swimmers are biological organisms or synthetic objects that propel themselves through the surrounding fluids. Examples are swimming fish, flying birds, or various swimming bacteria such as Escherichia coli and the green alga Chlamydomonas reinhardtii, etc. In the microscale living system, most of self-propelled bacteria have the same pattern of motion, which they move along one direction with linear motion, after a period of time, they stop suddenly and turn to another direction, and then they repeat the same process. This motion mode 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. However, the motion of the particles will be affect by Brownian motion in microscopic study. The particle will change the direction of the movement because rotational Brownian motion. In other words, the particle won’t move straightly before it tumbles. |
In this study, dissipative particle dynamics (DPD) is employed to simulate the rod-like self-propelled nano-swimmers in bounded/unbounded system. For the unbounded system, it is found that the longer nano-rods have the lower rotational diffusivity (Dθ), and the lower translational diffusivity (D). It means, the longer nano-rods need more time to change the direction of the movement, and the rate of the diffusion is lower. Additionally, the nano-rods become the self-propelled nano-swimmers from the active force (FA). The rotational diffusivity of the nano-swimmers is the same as the nano-rods. Both the square of the amount of active force and the time of the nano-swimmers changing the direction of the movement are directly proportional to the diffusivity of the nano-swimmers. For the sedimentation equilibrium, it is found that the sedimentation length of the nano-swimmers is higher than the nano-rod. In addition, the nano-swimmers exhibit polar order under gravity. It means, the nano-swimmers proceed toward reverse direction of gravity.
|| M. Doi; S. F. Edwards, The Theory of Polymer Dynamics. |
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