Soft Materials, Department of Materials, ETH Zürich, 8093, Zürich, Switzerland.
Faculty of Physics, University of Warsaw, 02-093, Warsaw, Poland.
Nat Commun. 2020 May 26;11(1):2628. doi: 10.1038/s41467-020-15764-1.
Active systems such as microorganisms and self-propelled particles show a plethora of collective phenomena, including swarming, clustering, and phase separation. Control over the propulsion direction and switchability of the interactions between the individual self-propelled units may open new avenues in designing of materials from within. Here, we present a self-propelled particle system, consisting of half-gold-coated titania (TiO) particles, in which we can quickly and on-demand reverse the propulsion direction, by exploiting the different photocatalytic activities on both sides. We demonstrate that the reversal in propulsion direction changes the nature of the hydrodynamic interaction from attractive to repulsive and can drive the particle assemblies to undergo both fusion and fission transitions. Moreover, we show these active colloids can act as nucleation sites, and switch rapidly the interactions between active and passive particles, leading to reconfigurable assembly and disassembly. Our experiments are qualitatively described by a minimal hydrodynamic model.
主动系统，如微生物和自行推进的粒子，表现出大量的集体现象，包括聚集、聚类和相分离。控制个体自推进单元之间的推进方向和相互作用的可切换性，可能会为从内部设计材料开辟新途径。在这里，我们提出了一个由半金包覆的二氧化钛（TiO）粒子组成的自推进粒子系统，通过利用两侧不同的光催化活性，我们可以快速且按需反转推进方向。我们证明，推进方向的反转改变了流体动力相互作用的性质，从吸引力变为排斥力，并可以驱动粒子组装体经历融合和裂变转变。此外，我们表明这些活性胶体可以作为成核位点，并快速切换活性和惰性粒子之间的相互作用，导致可重构的组装和拆卸。我们的实验由一个最小的流体动力学模型定性描述。
