Non-Equilibrium Assembly of Light-Activated Colloidal Mixtures

The collective phenomena exhibited by artificial active matter systems present novel routes to fabricating out-of-equilibrium microscale assemblies. Here, the crystallization of passive silica colloids into well-controlled 2D assemblies is shown, which is directed by a small number of self-propelled active colloids. The active colloids are titania–silica Janus particles that are propelled when illuminated by UV light. The strength of the attractive interaction and thus the extent of the assembled clusters can be regulated by the light intensity. A remarkably small number of the active colloids is sufficient to induce the assembly of the dynamic crystals. The approach produces rationally designed colloidal clusters and crystals with controllable sizes, shapes, and symmetries. This multicomponent active matter system offers the possibility of obtaining structures and assemblies that cannot be found in equilibrium systems.

Non-equilibrium assembly of mixtures of active and passive colloids is shown to form 2D structures. The active self-propelled colloids are light driven, so the clustering can be externally triggered and is completely reversible. The shape and size of individual small clusters, as well as the lattice symmetry and order of larger assemblies, can be changed easily by controlling the light intensity and size ratio of active to passive particles.

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