Abstract
If a colloidal particle is exposed to an external field, its Brownian motion is modified. In the case of an anisotropic particle, the external potential might not only affect its translation but also its rotation. We experimentally investigate the dynamics of a trimer, which consists of three spherical particles, within a random potential energy landscape. This energy landscape has energy values drawn from a Gamma distribution, a spatial correlation length similar to the particle size and is realised by a random light field, that is a laser speckle pattern. The particle translation and rotation are quantified by the mean squared (angular) displacement, the van Hove function and other observable quantities. The translation shows an intermediate subdiffusive regime and a long-time diffusion that slows down upon increasing the modulation of the potential. In contrast, the mean squared angular displacement exhibits only small deviations from a linear time dependence but a more detailed analysis reveals discrete angular jumps reflecting the symmetry of the trimer. A coupling between the translation and rotation is observed and found to depend on the length scale.
Highlights
The motion was modified by a random potential energy landscape whose values are drawn from a Gamma distribution with standard deviation ǫ and whose spatial correlation length is about the size of a spherical particle [34]
The translational and rotational dynamics of trimers subjected to a random potential energy landscape have been investigated
The translational center-of-mass motion is characterized by subdiffusion at intermediate times due to the confinement to the minima and diffusion at long times reflecting the random motion between minima
Summary
Colloidal particles in more complex situations, for example in the presence of interparticle interactions or external potentials, can show different behavior such as subdiffusion or superdiffusion. These imply mean squared displacements with time dependencies that are less than or greater than linear, respectively [1]. Such dynamics are frequently encountered in systems with biological or industrial relevance. Due to the analogy between the behaviors of colloidal particles and many different complex and experimentally less accessible systems, colloidal suspensions are frequently used as model systems to systematically and quantitatively study particle dynamics
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