Fachbereich Physik, Universität Konstanz, Konstanz, D-78457, Germany.
Phys Rev Lett. 2018 Aug 17;121(7):078003. doi: 10.1103/PhysRevLett.121.078003.
We experimentally study the motion of light-activated colloidal microswimmers in a viscoelastic fluid. We find that, in such a non-Newtonian environment, the active colloids undergo an unexpected transition from enhanced angular diffusion to persistent rotational motion above a critical propulsion speed, despite their spherical shape and stiffness. We observe that, in contrast to chiral asymmetric microswimmers, the resulting circular orbits can spontaneously reverse their sense of rotation and exhibit an angular velocity and a radius of curvature that nonlinearly depend on the propulsion speed. By means of a minimal non-Markovian Langevin model for active Brownian motion, we show that these nonequilibrium effects emerge from the delayed response of the fluid with respect to the self-propulsion of the particle without counterpart in Newtonian fluids.
我们通过实验研究了在粘弹性流体中光激活胶体微泳者的运动。我们发现，在这种非牛顿环境中，尽管活性胶体具有球形和刚性，但它们的角扩散会从增强转变为持续的旋转运动，超过临界推进速度。我们观察到，与手性不对称微泳者相反，所得的圆形轨道可以自发地反转其旋转方向，并表现出角速度和曲率半径，它们与推进速度呈非线性关系。通过用于活性布朗运动的最小非马尔可夫朗之万模型，我们表明这些非平衡效应源自于流体对粒子自推进的延迟响应，而在牛顿流体中没有对应的效应。
