20 research outputs found
Exact symmetries in the velocity fluctuations of a hot Brownian swimmer
Symmetries constrain dynamics. We test this fundamental physical principle,
experimentally and by molecular dynamics simulations, for a hot Janus swimmer
operating far from thermal equilibrium. Our results establish scalar and
vectorial steady-state fluctuation theorems and a thermodynamic uncertainty
relation that link the fluctuating particle current to its entropy production
at an effective temperature. A Markovian minimal model elucidates the
underlying non-equilbrium physics.Comment: 5 pages, 3 figure
Suppressing rotational diffusion of Janus particles by surface modifications for directed thermophoretic motion
Hot Brownian motion and photophoretic self-propulsion
We describe the motion of heated particles in a simple liquid, for which we can theoretically derive generalized fluctuation-dissipation relations that hold far from equilibrium, as we demonstrate both experimentally and via molecular-dynamics simulations. Due to persistent laser-light absorption, these particles excite a radially symmetric or asymmetric (Janus particles) temperature profile in the solvent, which affects their random (Brownian) and systematic (self-phoretic) motion. In case of a radially symmetric temperature profile, we show that the particles perform “hot Brownian motion” (HBM), with different effective temperatures pertaining to their various degrees of freedom. We moreover predict and experimentally observe a peculiar dependence of their diffusivity on the particle size. In case of an asymmetric temperature profile, we find a superimposed self-phoretic directed motion. To adjust the importance of this “active” motion relative to the random hot Brownian motion, the shape of the particle is modified by binding DNA molecules and DNA origami to Janus beads. The persistence of the directed transport can thereby greatly be enhanced
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Individually tunable micromachines driven by laser induced self propelled thermophoresis
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Stochastic Localization of Microswimmers by Photon Nudging
Force free trapping and steering of single photophoretically self-propelled Janus
type particles using a feedback mechanism is experimentally demonstrated. Realtime
information on particle position and orientation is used to switch the self-propulsion
mechanism of the particle optically. The orientational Brownian motion of the particle
thereby provides the reorientation mechanism for the microswimmer. The particle
size dependence of the photophoretic propulsion velocity reveals that photon nudging
provides an increased position accuracy for decreasing particle radius. The explored
steering mechanism is suitable for navigation in complex biological environments and
in depth studies of collective swimming effects