6 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
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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
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
Thermo-Osmotic Flow in Thin Films
We report on the first microscale observation of the velocity field imposed by a nonuniform heat content along the solid-liquid boundary.We determine both radial and vertical velocity components of this thermoosmotic flow field by tracking single tracer nanoparticles. The measured flow profiles are compared to an approximate analytical theory and to numerical calculations. From the measured slip velocity we deduce the thermo-osmotic coefficient for both bare glass and Pluronic F-127 covered surfaces. The value for Pluronic F-127 agrees well with Soret data for polyethylene glycol, whereas that for glass differs from literature values and indicates the complex boundary layer thermodynamics of glass-water interfaces
Single Molecules Trapped by Dynamic Inhomogeneous Temperature Fields
We demonstrate a single molecule
trapping concept that modulates the actual driving force of Brownian
motionthe temperature. By spatially and temporally varying
the temperature at a plasmonic nanostructure, thermodiffusive drifts
are induced that are used to trap single nano-objects. A feedback
controlled switching of local temperature fields allows us to confine
the motion of a single DNA molecule for minutes and tailoring complex
effective trapping potentials. This new type of thermophoretic microbeaker
even provides control over a well-defined number of single molecules
and is scalable to large arrays of trapping structures