Chemistry in Motion: Tiny Synthetic Motors

TL;DR

This paper reviews how synthetic self-propelled motors, like Janus particles and sphere dimers, generate motion through self-diffusiophoresis driven by concentration gradients, highlighting their dynamics, environmental effects, and potential applications.

Contribution

It provides a detailed description of propulsion mechanisms for synthetic motors and presents simulation results illustrating their dynamic behavior and limitations.

Findings

Concentration gradients enable directed motion in synthetic motors.

Rotational Brownian motion limits the size and effectiveness of small motors.

Simulations show how geometry and environment influence motor propulsion.

Abstract

In this Account, we describe how synthetic motors that operate by self-diffusiophoresis make use of a self-generated concentration gradient to drive motor motion. A description of propulsion by self-diffusiophoresis is presented for Janus particle motors comprising catalytic and noncatalytic faces. The properties of the dynamics of chemically powered motors are illustrated by presenting the results of particle-based simulations of sphere-dimer motors constructed from linked catalytic and noncatalytic spheres. The geometries of both Janus and sphere-dimer motors with asymmetric catalytic activity support the formation of concentration gradients around the motors. Because directed motion can occur only when the system is not in equilibrium, the nature of the environment and the role it plays in motor dynamics are described. Rotational Brownian motion also acts to limit directed motion, and it has especially strong effects for very small motors. We address the following question: how small can motors be and still exhibit effects due to propulsion, even if only to enhance diffusion? Synthetic motors have the potential to transform the manner in which chemical dynamical processes are carried out for a wide range of applications.