Scottish Universities Physics Alliance (SUPA), School of Physics and Astronomy, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Mar 13;109(11):4052-7. doi: 10.1073/pnas.1116334109. Epub 2012 Mar 5.
Adding a nonadsorbing polymer to passive colloids induces an attraction between the particles via the "depletion" mechanism. High enough polymer concentrations lead to phase separation. We combine experiments, theory, and simulations to demonstrate that using active colloids (such as motile bacteria) dramatically changes the physics of such mixtures. First, significantly stronger interparticle attraction is needed to cause phase separation. Secondly, the finite size aggregates formed at lower interparticle attraction show unidirectional rotation. These micro-rotors demonstrate the self-assembly of functional structures using active particles. The angular speed of the rotating clusters scales approximately as the inverse of their size, which may be understood theoretically by assuming that the torques exerted by the outermost bacteria in a cluster add up randomly. Our simulations suggest that both the suppression of phase separation and the self-assembly of rotors are generic features of aggregating swimmers and should therefore occur in a variety of biological and synthetic active particle systems.
向无吸附聚合物中添加被动胶体通过“耗尽”机制在颗粒之间诱导吸引力。聚合物浓度足够高会导致相分离。我们结合实验、理论和模拟来证明，使用活性胶体（例如运动细菌）会极大地改变此类混合物的物理性质。首先，需要更强的颗粒间吸引力才能引起相分离。其次，在较低的颗粒间吸引力下形成的有限尺寸聚集体表现出单向旋转。这些微型转子展示了使用活性粒子自组装功能结构。旋转簇的角速度大致按其尺寸的倒数缩放，通过假设簇中最外层细菌施加的扭矩随机相加，可以从理论上理解这一点。我们的模拟表明，相分离的抑制和转子的自组装都是聚集游泳者的普遍特征，因此应该会出现在各种生物和合成活性粒子系统中。
