Abstract
We study both experimentally and theoretically the dynamics of chemically self-propelled Janus colloids moving atop a two-dimensional crystalline surface. The surface is a hexagonally close-packed monolayer of colloidal particles of the same size as the mobile one. The dynamics of the self-propelled colloid reflects the competition between hindered diffusion due to the periodic surface and enhanced diffusion due to active motion. Which contribution dominates depends on the propulsion strength, which can be systematically tuned by changing the concentration of a chemical fuel. The mean-square displacements (MSDs) obtained from the experiment exhibit enhanced diffusion at long lag times. Our experimental data are consistent with a Langevin model for the effectively two-dimensional translational motion of an active Brownian particle in a periodic potential, combining the confining effects of gravity and the crystalline surface with the free rotational diffusion of the colloid. Approximate analytical predictions are made for the MSD describing the crossover from free Brownian motion at short times to active diffusion at long times. The results are in semi-quantitative agreement with numerical results of a refined Langevin model that treats translational and rotational degrees of freedom on the same footing.
Highlights
The non-equilibrium behavior of active and passive particles ranging from microorganisms such as bacteria and artificial microswimmers to passive colloidal particles is the focus of a large number of ongoing studies [1,2,3,4]
A scanning electron microscope (SEM) image of the monolayer can be seen in figure 1(b), and the actual topography of the surface is inferred from the atomic force microscope (AFM) image in figure 1(d)
We have studied the problem of propulsion of an active colloidal particle above a crystalline surface by a combination of experiment, theory, and numerical simulations
Summary
Udit Choudhury, Arthur V Straube, Peer Fischer, John G Gibbs and Felix Höfling. We study both experimentally and theoretically the dynamics of chemically self-propelled Janus author(s) and the title of the work, journal citation colloids moving atop a two-dimensional crystalline surface. The dynamics of the self-propelled colloid reflects the competition between hindered diffusion due to the periodic surface and enhanced diffusion due to active motion. Our experimental data are consistent with a Langevin model for the effectively two-dimensional translational motion of an active Brownian particle in a periodic potential, combining the confining effects of gravity and the crystalline surface with the free rotational diffusion of the colloid. The results are in semi-quantitative agreement with numerical results of a refined Langevin model that treats translational and rotational degrees of freedom on the same footing
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