Particle dynamics in two-dimensional random energy landscapes - experiments and simulations

TL;DR

This study investigates how colloidal particles move in two-dimensional random energy landscapes, combining experiments and simulations to understand the effects of landscape roughness on particle dynamics.

Contribution

It provides a comprehensive analysis of particle dynamics in 2D random energy landscapes through experimental holography and Monte Carlo simulations, highlighting differences from 1D landscapes.

Findings

Long-time diffusion coefficient matches theoretical predictions.

Particles exhibit initial diffusion, sub-diffusion, then diffusion again.

Weaker localization and faster diffusion recovery compared to 1D landscapes.

Abstract

The dynamics of individual colloidal particles in random potential energy landscapes were investigated experimentally and by Monte Carlo simulations. The value of the potential at each point in the two-dimensional energy landscape follows a Gaussian distribution. The width of the distribution, and hence the degree of roughness of the energy landscape, was varied and its effect on the particle dynamics studied. This situation represents an example of Brownian dynamics in the presence of disorder. In the experiments, the energy landscapes were generated optically using a holographic set-up with a spatial light modulator, and the particle trajectories were followed by video microscopy. The dynamics are characterized using, e.g., the time-dependent diffusion coefficient, the mean squared displacement, the van Hove function and the non-Gaussian parameter. In both, experiments and simulations, the dynamics are initially diffusive, show an extended sub-diffusive regime at intermediate times before diffusive motion is recovered at very long times. The dependence of the long-time diffusion coefficient on the width of the Gaussian distribution agrees with theoretical predictions. Compared to the dynamics in a one-dimensional potential energy landscape, the localization at intermediate times is weaker and the diffusive regime at long times reached earlier, which is due to the possibility to avoid local maxima in two-dimensional energy landscapes.