Chemically Driven Collective Motion in Mixtures of Catalytic and Inert Particles

Abstract

Active matter often exhibits ordered collective motion, such as in bacterial colonies or swarms of fish and birds. Understanding the mechanisms underlying the complicated collective behaviors is significant to develop innovative chemical systems. We discovered that Pt catalytic particles with simpler structures exhibit a unique collective motion, that is, repetitive cluster formation and disintegration in an aqueous ethanol solution. In this study, the collective behavior of Pt particles is demonstrated in mixtures containing inert particles. Two distinct types of cluster formation were observed by varying the mixing ratio of the Pt and Au particles: Pt/Au mosaic-like clusters and Pt/Au core–shell clusters. In contrast, no Pt/silica cluster formation was observed in the silica particles mixed with Pt particles. In the Pt/Au core–shell clusters observed in this study, the thickness of the Au particle shell could be controlled by adjusting the concentration of the Au particle. This finding suggests that the spatial separation of Pt and Au particles can be realized under controlled conditions.