Rational design and dynamics of self-propelled colloidal bead chains: from rotators to flagella

TL;DR

This paper demonstrates how simple self-propelled colloidal bead chains can be designed to exhibit complex swimming behaviors, including rotational and flagella-like motion, by controlling their structure and flexibility.

Contribution

It introduces a method to assemble self-propelled Janus spheres into flexible chains that display diverse motion patterns, supported by experimental and minimal model simulations.

Findings

Rigid chains show only rotational or spinning motion.

Flexible chains exhibit combined translational and rotational motion.

Experimental results are validated by hydrodynamic simulations.

Abstract

The quest for designing new self-propelled colloids is fuelled by the demand for simple experimental models to study the collective behaviour of their more complex natural counterparts. Most synthetic self-propelled particles move by converting the input energy into translational motion. In this work we address the question if simple self-propelled spheres can assemble into more complex structures that exhibit rotational motion, possibly coupled with translational motion as in flagella. We exploit a combination of induced dipolar interactions and a bonding step to create permanent linear bead chains, composed of self-propelled Janus spheres, with a well-controlled internal structure. Next, we study how flexibility between individual swimmers in a chain can affect its swimming behaviour. Permanent rigid chains showed only active rotational or spinning motion, whereas longer semi-flexible chains showed both translational and rotational motion resembling flagella like-motion, in the presence of the fuel. Moreover, we are able to reproduce our experimental results using numerical calculations with a minimal model, which includes full hydrodynamic interactions with the fluid. Our method is general and opens a new way to design novel self-propelled colloids with complex swimming behaviours, using different complex starting building blocks in combination with the flexibility between them.