Regulation of propulsion in assemblies of thermophoretic nanomotors

TL;DR

This paper demonstrates a new regulation mechanism for thermophoretic nanomotors using laser-induced heating, revealing concentration-dependent propulsion and enabling self-regulation of active fluids.

Contribution

It introduces a novel thermally regulated propulsion pathway for nanomotors, combining experimental and modeling approaches to control 3D active fluid behavior.

Findings

Nanomotors achieve velocities up to ~800 μm/s.

Propulsion depends strongly on nanomotor concentration.

Thermal effects and nonlinearities are key to self-regulation.

Abstract

Active particles locally transduce energy into motion, leading to unusual and emergent behaviors. However, current synthetic particles lack sensing and adaptation mechanisms. Here, we demonstrate a novel regulation pathway, through the combined use of thermophoretic propulsion and nanometric building blocks. We build an active fluid composed of artificial nanomotors and study its three-dimensional (3D) dynamics. We use laser-induced photo-thermal effect to actuate nanoparticles, and probe their self-propulsion within assemblies. Despite significant thermal fluctuations at the nanoscale, our results reveal a strong dependence of the thermophoretic propulsion on the concentration of nanomotors, leading to ultrafast velocities of up to ~ 800 um/s. This unique behavior originates from a strong coupling of the local concentration of nanomotors and the temperature field, which feeds back on the thermophoretic mobility of the nanoparticles. We rationalize our results from independent modeling of all thermal effects, accounting for nonlinearities of thermophoretic self-propulsion. Our results open novel routes for the design and self-regulation of 3D active fluids by thermal processes.