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

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.

Enhanced diffusion with abnormal temperature dependence in underdamped space-periodic systems subject to time-periodic driving

“…It is likely that multidimensionality effects were crucial for TAD. Instead of having two, locked and running, populations in 1D accounting for (already sophisticated in this case) diffusion features, flows in higher dimensional problems are far more complex, known to result in further peculiarities in transport and diffusion [5,29].…”

“…The phenomena of diffusion and transport over a potential energy landscape play a key role in a number of processes in physics, chemistry and biology [1][2][3][4][5]. Josephson tunneling junctions, superionic conductors, phaselocked-loop frequency control systems, charge density waves are a few examples of systems in which these processes in periodic potential are important [6].…”

Shell formation in short like-charged polyelectrolytes in a harmonic trap

“…The objective of this work is to theoretically study the distribution of charged polymers in a trap potential to understand the underlying mechanisms of the structure formation in charged biomolecules. In many colloidal and plasma systems, the pattern formation is due to the presence of some short-ranged attractive forces in the system [35][36][37][38][39][40][41]. Here we show that the pattern formations can occur even in the absence of the attractive interactions, primarily due to the competing effects of the trap and the electrostatic repulsions.…”

Speckle optical tweezers: micromanipulation with random light fields

“…Moreover, one major challenge common to all these techniques is the light scattering occurring in optically complex media, such as biological tissues, turbid liquids and rough surfaces, which naturally gives rise to apparently random light fields known as speckles [20]. Earlier experimental works showed trapping of atoms and particles in a gas by high-intensity speckle light fields [21][22][23][24], while both static and timevarying speckle fields were related to the emergence of anomalous diffusion in colloids [25][26][27][28][29]. Recently, we derived a theory to describe the motion of a Brownian particle in a speckle light field which allowed us to demonstrate numerically how a speckle field can be used to control the motion a Brownian particle in the limit of particles much smaller than the light wavelength (dipole approximation) [29].…”