Colloids in light fields: particle dynamics in random and periodic energy landscapes

TL;DR

This study experimentally investigates colloidal particle dynamics in light-induced potential landscapes, revealing diffusive and subdiffusive regimes influenced by landscape shape, roughness, and concentration, with implications for understanding glassy behavior.

Contribution

It provides the first experimental realization and analysis of colloidal dynamics in both random and periodic light-induced energy landscapes, comparing results with simulations and theory.

Findings

Dynamics show initial diffusion, intermediate subdiffusion, then diffusion again.

Landscape shape and roughness significantly affect particle motion.

Resembles dynamics near glass transition in concentrated systems.

Abstract

The dynamics of colloidal particles in potential energy landscapes have mainly been investigated theoretically. In contrast, here we discuss the experimental realization of potential energy landscapes with the help of light fields and the observation of the particle dynamics by video microscopy. The experimentally observed dynamics in periodic and random potentials are compared to simulation and theoretical results in terms of, e.g. the mean-squared displacement, the time-dependent diffusion coefficient or the non-Gaussian parameter. The dynamics are initially diffusive followed by intermediate subdiffusive behaviour which again becomes diffusive at long times. How pronounced and extended the different regimes are, depends on the specific conditions, in particular the shape of the potential as well as its roughness or amplitude but also the particle concentration. Here we focus on dilute systems, but the dynamics of interacting systems in external potentials, and thus the interplay between particle-particle and particle-potential interactions, is also mentioned briefly. Furthermore, the observed dynamics of dilute systems resemble the dynamics of concentrated systems close to their glass transition, with which it is compared. The effect of certain potential energy landscapes on the dynamics of individual particles appears similar to the effect of interparticle interactions in the absence of an external potential.