(9a) Light-Switchable Active Particles: From Pulling to Pushing, from Fusion to Fission

Active or self-propelled colloidal-particle systems are currently a subject of great interest in soft condensed matter science, owing to their ability to mimic the collective behavior of complex living systems, but also to serve as model systems to study intrinsically out-of-equilibrium systems. Self-propelled particles can exhibit rich collective behavior, such as clustering, segregation, and anomalous density fluctuations, by consuming internal energy or extracting energy from their local environment in order to generate their own motion. Control over the propulsion direction and tunable interactions between the individual self-propelled units may open new avenues in the design of materials from within,using their collective dynamics. In this talk, we present a unique self-propelled particle system consisting of Janus photocatalytic colloids,in which we can,on demand, reverse the particle’s propulsion direction by exploiting the different photocatalytic activities on bothsides [1]. The control over activity and the reversibility of direction by wavelength and intensity of light,combined with the interplay between attractions and repulsions of the individual units allows the colloid alassemblies to undergo both “fusion”and“fission” transitions, mimicking some aspects of multi-cellular behavior. Moreover, we demonstrate our active particles can act as seed particles in active passive mixtures, and conveniently drive the assembly and disassembly of passive particles by light-modulation. These results would open new possibilities to drive the arrested systems (e.g. gels, and glasses) by “stirring with light”.

References.

[1]. H.R. Vutukuri, M. Lisicki,E. Lauga,and J. Vermant, submitted.

Acknowledgments: H.R.V. is supported by a Marie Skłodowska-Curie Intra European Fellowship (G.A. No. 708349- SPCOLPS) within Horizon 2020.