Active motion of Janus colloids at the surface of water.
Résumé
Active motion of living or artificial systems (active colloids) may occur in strong confinement or in complex environments such membranes. In confinement, the propulsion mechanism and motion features may strongly differ from the ones observed in the bulk of a simple fluid. As a primary form of confinement, we consider a single interface. Recently, we show that the interface between a liquid and a fluid dramatically affects the lateral frictions of partially wetted colloidal particles [1]. In this contribution, the impact of partial wetting dynamics on the motion of active Janus colloids will be presented. Spherical catalytic Janus colloids have been prepared by coating half surface of silica particles with a thin platinum layer. Immersion depth of the Janus colloids as well as their orientation with respect to the water surface reveal complex and rich wetting properties of Janus particles at the liquid-gas interface [2]. Active motion of Janus colloids at the interface in the presence of various concentrations of hydrogen peroxide, H2O2, has been studied. The types of observed trajectories, directional and circular ones, revealed the effective force and torque induced by the catalytic decomposition of H2O2 fuel. At the water surface, the persistence of directional active motion is greatly enhanced when compared to the motion in bulk [3]. This result has been explained in terms of loss of one rotational degree of freedom at the interface and also to a new contribution to the rotational friction due to partial wetting [1].
[1] G. Boniello, C. Blanc, D. Fedorenko, M. Medfai, NB. Mbarek, M. In, M. Gross, A. Stocco, M. Nobili, Nature Materials 14, 908 (2015).
[2] X. Wang, M. In, C. Blanc, P. Malgaretti, M. Nobili, A. Stocco, Faraday Discussions 191, 305 (2016).
[3] X. Wang, M. In, C. Blanc, M. Nobili, A. Stocco, Soft Matter 11, 7376 (2015).