An active particle, often a colloid, or a nanoparticle, that propels itself through a fluid, often via some phoretic mechanism, or via some mechanical propulsion mechanism (the particles are then often called microswimmers). Generally, "active colloid" simply refers to a self-propelled colloid (and similarly with "active particle" in general).
"In the current miniaturization race towards small motors and engines, a rapidly expanding subdomain is the quest for autonomous swimmers, able to move in fluids which appear very viscous given the small length scales (low Reynolds number). Robotic microswimmers that generate surface distortions is an avenue (e.g. by mimicking sperms [1]), but it seems equally interesting to try to take advantage of physical phenomena that become predominant at small scales. Interfacial ‘phoretic’ effects (electrophoresis, thermophoresis, diffusiophoresis, [2]) by which the gradients of fields (electrostatic potential, temperature, concentration) drive the motion of colloid particles, are from this standpoint a natural avenue given the increased surface to volume ratio of smaller objects. "
Microscopic artificial swimmers
Designing phoretic micro- and nano-swimmers. A common design for phoretic swimmers is the Janus swimmer design
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Phoretic self-propulsion
Propulsion of a Molecular Machine by Asymmetric Distribution of Reaction Products See Self-diffusiophoresis
Designing phoretic micro- and nano-swimmers See more at Designing phoretic micro- and nano-swimmers
Single phoretic swimmer stochastic dynamics
Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk (experiment)
Anomalous Diffusion of Symmetric and Asymmetric Active Colloids
Stochastic dynamics of self-propelled colloids
Self-assembly of phoretic active colloids
Self-assembly of active colloidal molecules with dynamic function See Self-assembly of active colloids
Self-Assembly of Catalytically Active Colloidal Molecules: Tailoring Activity Through Surface Chemistry See Self-assembly of active colloids
Collective behaviour
Clusters, asters, and collective oscillations in chemotactic colloids See Collective behaviour of active colloids There is a lot of different regimes in their complicated mathematical models, and fuller understanding requires going through their models more carefully
Emergent Cometlike Swarming of Optically Driven Thermally Active Colloids
Collective Behavior of Thermally Active Colloids See Collective behaviour of thermally active colloids. Others
Electrokinetic effects in catalytic platinum-insulator Janus swimmers. See Catalytic conductor-insulator Janus swimmer, Electrokinetic effects in catalytic conductor-insulator Janus swimmers. See also: Locomotion of electrocatalytic nanomotors due to reaction induced charge autoelectrophoresis and Self-electrophoresis
Boundaries can steer active Janus spheres See Boundary effects on the motion of active colloids