Feedback-controlled active brownian colloids with space-dependent rotational dynamics

Abstract

The non-thermal nature of self-propelling colloids offers new insights into non-equilibrium physics. The central mathematical model to describe their trajectories is active Brownian motion, where a particle moves with a constant speed, while randomly changing direction due to rotational diffusion. While several feedback strategies exist to achieve position-dependent velocity, the possibility of spatial and temporal control over rotational diffusion, which is inherently dictated by thermal fluctuations, remains untapped. Here, we decouple rotational diffusion from thermal fluctuations. Using external magnetic fields and discrete-time feedback loops, we tune the rotational diffusivity of active colloids above and below its thermal value at will and explore a rich range of phenomena including anomalous diffusion, directed transport, and localization. These findings add a new dimension to the control of active matter, with implications for a broad range of disciplines, from optimal transport to smart materials.

Shaping the gradients driving phoretic micro-swimmers: influence of swimming speed, budget of carbonic acid and environment

“…Consequently, a slowdown of propulsion may result from fuel exhaustion or decomposition. More complicated modifications, like oscillatory propulsion, on-off switches, steering, cargo pickup and delivery, are conveniently realized employing oscillating chemical reactions [35,36], as well as via additional local or global magnetic or optical fields [37][38][39][40][41].…”

“…These are further increased in the case of collective behaviour like swarm formation and other dynamic phase transitions [32]. Several diffusio-phoretic selfpropulsion mechanisms and the corresponding swimming performance have been characterized in great detail [24][25][26][27][28][29][30][31][34][35][36][37][38][39][40][41]. However, experimental data on the shape and evolution of the relevant chemical concentration fields, as well as on their mutual phoretic and hydrodynamic couplings, are sparse.…”

Reconfigurable artificial microswimmers with internal feedback

“…Realizing artificial microswimmers with similar adaptation capabilities and autonomous behavior might substantially impact technologies ranging from optimal transport to sensing and microrobotics 3 . Focusing on adaptation, existing approaches at the colloidal scale mostly rely on external feedback, either to regulate motility via the spatiotemporal modulation of the propulsion velocity and direction [4][5][6][7][8] or to induce shape changes via the same magnetic or electric fields [9][10][11] , which are also driving the particles. On the contrary, endowing artificial microswimmers with an internal feedback mechanism, which regulates motility in response to stimuli that are decoupled from the source of propulsion, remains an elusive task.…”

Investigating Time‐Dependent Active Motion of Janus Micromotors using Dynamic Light Scattering

“…[ 34,50 ] At long decay times, Δ L 2 is constant indicating that this decay does not correspond to translational diffusion and thus describes rotational diffusion. [ 55 ]…”