Probing the spatiotemporal dynamics of catalytic Janus particles with single-particle tracking and differential dynamic microscopy

TL;DR

This paper combines differential dynamic microscopy and particle tracking to analyze the complex spatiotemporal behavior of active Janus colloids, providing a comprehensive understanding of their motion across different scales.

Contribution

It offers an analytical solution for the intermediate scattering function of active Brownian particles and applies it to experimental data, distinguishing different reorientation mechanisms.

Findings

Agreement between analytical ISF and experimental data across scales

Ability to extract diffusion coefficients and speed distribution parameters

Discrimination of active Brownian motion from other reorientation processes

Abstract

We demonstrate differential dynamic microscopy and particle tracking for the characterization of the spatiotemporal behavior of active Janus colloids in terms of the intermediate scattering function (ISF). We provide an analytical solution for the ISF of the paradigmatic active Brownian particle model and find striking agreement with experimental results from the smallest length scales, where translational diffusion and self-propulsion dominate, up to the largest ones, which probe effective diffusion due to rotational Brownian motion. At intermediate length scales, characteristic oscillations resolve the crossover between directed motion to orientational relaxation and allow us to discriminate active Brownian motion from other reorientation processes, e.g., run-and-tumble motion. A direct comparison to theoretical predictions reliably yields the rotational and translational diffusion coefficients of the particles, the mean and width of their speed distribution, and the temporal evolution of these parameters.