Structural transitions and long-time self-diffusion of interacting colloids confined by a parabolic potential

Abstract

We report on the ordering and dynamics of interacting colloidal particles confined by a parabolic potential. By means of Brownian dynamics simulations, we find that by varying the magnitude of the trap stiffness, it is possible to control the dimension of the system and, thus, explore both the structural transitions and the long-time self-diffusion coefficient as a function of the degree of confinement. We particularly study the structural ordering in the directions perpendicular and parallel to the confinement. Further analysis of the local distribution of the first-neighbors layer allows us to identify the different structural phases induced by the parabolic potential. These results are summarized in a structural state diagram that describes the way in which the colloidal suspension undergoes a structural re-ordering while increasing the confinement. To fully understand the particle dynamics, we take into account hydrodynamic interactions between colloids; the parabolic potential constricts the available space for the colloids, but it does not act on the solvent. Our findings show a non-linear behavior of the long-time self-diffusion coefficient that is associated to the structural transitions induced by the external field.

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

“…At strong trap strength we get sharp shells where the inter-shell transitions do not occur while the polymers inside each shell remain in a fluid phase as was concluded in Reference [36,37]. In most of these studies the presence of an attractive potential or multiple species causes the formation of additional structures.…”

“…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.…”

“…In recent years structural transitions in trapped colloids as well as plasmas have attracted the attention of experimentalists as well as theorists [35][36][37][38][39][40]. The colloidal and dusty plasmas have been found to form shell structures in 3D…”

“…In this work Γ measures the strength of the trap (as well as the Coulomb coupling) and thus our observations from for the polymers to move from one shell to another. Thus the system is effective frozen in the radial direction but is in a fluid phase within each shell as concluded in References [26,27,36]. At still higher Γ the system crystallizes and the liquid state theories are no longer valid.…”

“…In the experiments and simulations on trapped colloidal systems, the strength of the trap is the primary controlling parameter. Increasing the strength of the trap leads to the formation of sharper shells [26,36,37]. In this work Γ measures the strength of the trap (as well as the Coulomb coupling) and thus our observations from for the polymers to move from one shell to another.…”