3D Brownian Diffusion of Submicron-Sized Particle Clusters

TL;DR

This study investigates the 3D translational and rotational diffusion of submicron-sized colloidal particle clusters with complex shapes using advanced light scattering techniques, providing experimental validation for hydrodynamic models.

Contribution

It introduces a method to measure 3D diffusion of complex-shaped colloidal clusters and validates hydrodynamic shell models against experimental data.

Findings

Excellent agreement between experimental DDLS data and hydrodynamic shell model predictions.

Demonstrated the ability to study true 3D diffusion of complex objects.

Provided detailed diffusion coefficients for various cluster geometries.

Abstract

We report on the translation and rotation of particle clusters made through the combination of spherical building blocks. These clusters present ideal model systems to study the motion of objects with complex shape. Because they could be separated into fractions of well-defined configurations on a sufficient scale and their overall dimensions were below 300 nm, the translational and rotational diffusion coefficients of particle duplets, triplets and tetrahedrons could be determined by a combination of polarized dynamic light scattering (DLS) and depolarized dynamic light scattering (DDLS). The use of colloidal clusters for DDLS experiments overcomes the limitation of earlier experiments on the diffusion of complex objects near surfaces because the true 3D diffusion can be studied. When the exact geometry of the complex assemblies is known, different hydrodynamic models for calculating the diffusion coefficient for objects with complex shapes could be applied. Because hydrodynamic friction must be restricted to the cluster surface the so-called shell model, in which the surface is represented as a shell of small friction elements, was most suitable to describe the dynamics. A quantitative comparison of the predictions from theoretical modeling with the results obtained by DDLS showed an excellent agreement between experiment and theory.