Abstract
The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning. While much progress has been made in the last 10 years on various mechanisms to generate self-propulsion, the ability to steer self-propelled colloidal devices has so far been much more limited. A critical barrier in increasing the impact of such motors is in directing their motion against the Brownian rotation, which randomizes particle orientations. In this context, here we report directed motion of a specific class of catalytic motors when moving in close proximity to solid surfaces. This is achieved through active quenching of their Brownian rotation by constraining it in a rotational well, caused not by equilibrium, but by hydrodynamic effects. We demonstrate how combining these geometric constraints can be utilized to steer these active colloids along arbitrary trajectories.
Highlights
The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning
We demonstrate directed motion of a special class of catalytic motors—the spherical Janus colloid with half-coating of platinum with variable thickness—when moving in close proximity to solid surfaces through active quenching of their Brownian rotation, which leads to constrained in-plane swimming along the wall
The polar angle, y, which probes how the polarity of a Janus particle is oriented with respect to the surface normal vector, and the corresponding in-plane orientation can be observed under fluorescence microscopy as ‘phases of the moon’[27], Fig. 1
Summary
The advent of autonomous self-propulsion has instigated research towards making colloidal machines that can deliver mechanical work in the form of transport, and other functions such as sensing and cleaning. We demonstrate directed motion of a special class of catalytic motors—the spherical Janus colloid with half-coating of platinum with variable thickness—when moving in close proximity to solid surfaces through active quenching of their Brownian rotation, which leads to constrained in-plane swimming along the wall. Such prolonged directed transport is not dependent on any external fields or potentials and continues for length scales much larger than previously reported[23]. We demonstrate how it is possible to reduce the number of degrees of freedom for these autonomously moving catalytic colloids
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