Structure and dynamics of two-dimensional colloidal systems in circular cavities

Bubeck, Ralf; Leiderer, Paul; Bechinger, Clemens

doi:10.1007/3-540-45725-9_16

Cited by 7 publications

(10 citation statements)

References 14 publications

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“…Additionally, most observed clusters had a coupling parameter that would refer to the solid state of a corresponding extended crystal. 5 In this phase, the diffusion coefficient of a colloidal dipole crystal scales only weakly with G, whereas signicant differences between angular and radial diffusion were found for clusters in hard-wall pots at low G. 25,45 In Fig. 7(a), angular diffusion D para…”

Section: Transport Coefficient From Inmmentioning

confidence: 92%

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Effect of confinement on the mode dynamics of dipole clusters

et al. 2015

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Dynamical properties of colloidal clusters composed of paramagnetic beads are presented. The clusters were trapped either in a parabolic trough or in a hard-wall confinement. In order to access the dynamics of the ensembles, the instantaneous normal mode (INM) approach is utilized, which uses cluster configurations as an input. The peaks in the mode spectra weaken when the system size is increased and when the coupling strength is lowered. The short-time diffusive properties of the clusters are deduced using the INM technique. It is found that angular diffusion is always larger than radial diffusion regardless of the shape of the external trap. Further, short-time diffusion seems to be almost independent of the coupling strength in the solid regime, but decreases with increasing packing fraction and size of the ensembles. In general, it is found that diffusion is larger for parabolically confined than for hard-wall trapped clusters.

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Section: Transport Coefficient From Inmmentioning

confidence: 92%

“…Using the denition of r 0 as the equilibrium distance of two dipole -interacting particles in a parabolic trap, one gets u 0 ¼ 2.3 Â 10 3 s À1 for the parabolically trapped N ¼ 71 dipole cluster at B ¼ 25 mT. 13,45 …”

Section: Physical Properties Of Dipole Clustersmentioning

confidence: 99%

Effect of confinement on the mode dynamics of dipole clusters

et al. 2015

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“…the particles form a concentric shell structure. 8,9,16 The melting scenario of few-particle systems in circular cavities was also investigated by experiments 17,18 where an unexpected re-entrant melting was found. It has been experimentally demonstrated that at low effective temperatures the particles are arranged in a shell-like structure with high radial and angular order.…”

Section: Introductionmentioning

confidence: 99%

Binary colloidal systems in two-dimensional circular cavities: Structure and dynamics

Mangold

Birk

Leiderer

et al. 2004

Phys. Chem. Chem. Phys.

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We study the melting behavior of a binary system (R ¼ 4.5 mm, r ¼ 2.8 mm) of paramagnetic colloidal spheres in two-dimensional (2D) circular cavities. A repulsive interaction between the particles is caused by an external magnetic field B that induces magnetic dipole moments perpendicular to the sample plane. By means of video microscopy, we investigate the positions of the particles and their trajectories. For small interaction strengths, we observe a completely liquid phase where large and small particles diffuse across the entire system. With increasing B the larger particles become-due to their larger magnetic moment-localized and form a stable structure while the smaller particles behave still as a liquid. For even higher magnetic fields, the small particles also become increasingly localized and preferentially arrange as interstitial sites between the structures formed by the large particles. We present a systematic study of this rather complex multi-stage melting process which strongly depends on the particle numbers of large and small particles.

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“…As a result, the mean distance between adjacent shells increases with increasing Γ and thus counteracts the mechanism described above. As a result, a non-monotonic behavior in D Θ is absent in parabolic confinements [10,21].…”

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Fluctuation-induced order in two-dimensional colloidal clusters

Bubeck¹,

Leiderer²,

Bechinger³

2002

Europhys. Lett.

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PACS. 82.70.Dd -Colloids. PACS. 64.60.Cn -Order-disorder transformations; statistical mechanics of model systems. PACS. 83.10.Tv -Structural and phase changes.Abstract. -The behavior of a finite number (N = 29) of paramagnetic colloidal particles in 2D circular hard-wall cavities is investigated. By applying a magnetic field B, the interaction between the particles is varied. We demonstrate that the angular diffusion of the particles which are arranged in shells is highly anisotropic and shows a non-monotonic behavior as a function of B. When reducing radial particle fluctuations in one shell by a ring-shaped optical tweezer, the relative angular diffusion between adjacent shells increases again. This clearly demonstrates that radial particle fluctuations are responsible for an enhanced registration between adjacent shells.Thermal fluctuations are well known to have a strong influence on the phase behavior of two-dimensional (2D) systems compared to their three-dimensional counterparts [1]. The most striking evidence for such a difference is probably the melting transition which is, in 2D, predicted to occur via two sequential defect-driven continuous phase transitions as described by the KTHNY theory (see, e.g., [2]). Amongst conveniently accessible experimental systems for basic investigations of 2D melting colloidal particles have been established as model systems because they allow direct optical observation of topological defects and comparison to theoretical predictions [3][4][5]. However, while the KTHNY theory applies only for extended 2D systems, much less (both experimentally and theoretically) is known about the properties of 2D systems which are only comprised of a few particles (typically less than N = 100). Due to the finitness of such systems a different melting scenario compared to infinite systems is expected which may be important for the understanding of melting and freezing of, e.g., small 2D clusters or ions in radiofrequency traps [6]. It has been experimentally demonstrated that when super paramagnetic colloidal particles are confined to a circular hard-wall cavity, the particles at low effective temperatures T eff do not crystallize in a triangular lattice, but are rather arranged in a shell-like structure with both positional and orientational order. Upon increasing the temperature first orientational order between adjacent shells is lost which is typically refered to as intershell rotation. As the temperature is increased further, a "re-entrant" ordered phase is observed which is followed by complete melting of the cluster [7]. While intershell rotation is also observed in numerical studies of finite 2D systems of ions or electrons in circular cavities, the "re-entrant" ordered phase as found in the experiments, is still c EDP Sciences

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Structure and dynamics of two-dimensional colloidal systems in circular cavities

Cited by 7 publications

References 14 publications

Effect of confinement on the mode dynamics of dipole clusters

Effect of confinement on the mode dynamics of dipole clusters

Binary colloidal systems in two-dimensional circular cavities: Structure and dynamics

Fluctuation-induced order in two-dimensional colloidal clusters

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