Realization of a motility-trap for active particles

Soudeh Jahanshahi,Hartmut Löwen,Celia Lozano,Benno Liebchen,Clemens Bechinger

doi:10.1038/s42005-020-0393-4

Abstract

Trapping of atomic and mesoscopic particles with optical fields is a practical technique employed in many research disciplines. Developing similar trapping methods for self-propelled, i.e. active, particles is, however, challenging due to the typical anisotropic material composition of Janus-type active particles. This renders their trapping with magneto-optical fields to be difficult. Here we present the realization of a motility-trap for active particles, which only exploits their self-propulsion properties. By combining experiments, numerical simulations, and theory, we show that, under appropriate conditions, a force-free rotation of the self-propulsion direction towards the trap's center can be achieved, which results in an exponential localization of active particles. Because this trapping mechanism can be applied to any propulsion scheme, we expect such motility-tweezers to be relevant for fundamental studies of self-driven objects as well as for their applications as autonomous microrobots.

Highlights

Trapping of atomic and mesoscopic particles with optical fields is a practical technique employed in many research disciplines
active particles (APs) are made from colloidal silica particles with a diameter σ = 3.25 μm, which are half-coated with a 50-nm carbon layer on one hemisphere and afterwards suspended in a critical mixture of water and 2,6-lutidine
Once the cap temperature exceeds, Tc, this results in a local demixing of the adjacent fluid

Summary

Introduction

Trapping of atomic and mesoscopic particles with optical fields is a practical technique employed in many research disciplines. Numerical simulations, and theory, we show that, under appropriate conditions, a force-free rotation of the self-propulsion direction towards the trap's center can be achieved, which results in an exponential localization of active particles. Because this trapping mechanism can be applied to any propulsion scheme, we expect such motility-tweezers to be relevant for fundamental studies of self-driven objects as well as for their applications as autonomous microrobots. Depending on whether the illumination intensity is below or above Ir, APs will

Methods

Results

Conclusion