Diffusion of Anisotropic Particles in Random Energy Landscapes—An Experimental Study

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 realized 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.

Non-Gaussian, transiently anomalous, and ergodic self-diffusion of flexible dumbbells in crowded two-dimensional environments: Coupled translational and rotational motions

“…Normal and anomalous diffusion in the crowded solutions of anisotropic and/or non-spherical-as well as of spherical but non-isotropically interacting 80,81molecules was examined in a number of studies , including some recent experimental investigations 96,99,104 . The diffusive properties of molecules of dumbbell-, ellipsoid-, and rod-like shape 82,96,97,100,101,[104][105][106][107][108][109] , protein molecules 110,111 , active and passive dimers with anisotropic mobility 89,102,106,[112][113][114] , self-propelled massive particles with time-dependent mass 109 , colloidal dimers and flexible multimers 115,116 , stiff self-propelled filaments in crowded solutions 117 , trimer-like tracers in 2D 93,95 and tetrahedral patchy particles in 3D 81,118 , as well as the dynamics of elongated particles with fluctuating and oscillating shapes [119][120][121] were studied recently as well.…”

Speckle Tweezers for Simultaneous Controlling of Low and High Refractive Index Micro-particles

“…Proper geometry of the fluidic channels and controlled speckle field engineering can be also combined toward the application of the method in endoscopic studies. It is remarkable that the hydrodynamic interactions between dispersed particles induced with the speckle field, cause the changes in their particle-particle distances and can hinder their diffusion 54 . However, this effect is common for either NP encapsulated or empty liposomes and can be disregarded in the presented experiment schemes.…”

First-passage statistics of colloids on fractals: Theory and experimental realization

“…Moreover, since the individual particles can be followed, any parameter can be determined, in particular first-passage times. The experiments may be extended to various other situations, for example, colloidal particles with other properties, such as a size different from the speckle size ( 52 ), a nonspherical shape ( 72 ), or activity ( 73 ), or also different objects, such as bacteria ( 74 ) or microorganisms ( 75 ). Furthermore, the speckle pattern can be modified ( 76 ) or made time dependent ( 77 ), or a directed flow can be superimposed ( 6 ).…”