Differential Dynamic Microscopy: Probing wave vector dependent dynamics with a microscope

TL;DR

This paper introduces a method using standard microscopy and digital video analysis to measure the wave vector-dependent dynamics of colloidal particles, aligning well with theoretical Brownian motion predictions.

Contribution

It presents a novel application of ordinary microscopy combined with Fourier analysis to study particle dynamics across various wavevectors.

Findings

Accurately measures q-dependent particle dynamics.

Agrees with theoretical Brownian motion models.

Works with particles not individually resolvable.

Abstract

We demonstrate the use of an ordinary white-light microscope for the study of the q-dependent dynamics of colloidal dispersions. Time series of digital video images are acquired in bright field with a fast camera and image differences are Fourier-analyzed as a function of the time delay between them. This allows for the characterization of the particle dynamics independent on whether they can be resolved individually or not. The characteristic times are measured in a wide range of wavevectors and the results are found to be in good agreement with the theoretically expected values for Brownian motion in a viscous medium.