Effect of confinement on the mode dynamics of dipole clusters

Abstract

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.

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

“…As shown in Fig. 5(b), the relative interparticle distance fluctuations u rel decrease with the increase of the external field, with an amplitude of order similar to that reported for microscopic particles 38 . Further, we observe a clear change in slope of u rel close to the second transition at high field where only intrashell motion occurs.…”

“…Increasing the applied field, leads to a stronger localization of nanoparticles in the trap and simultaneously strengthens the repulsion between them. In a related context, melting of confined few-body systems has been investigated in experiments 34,35 and numerical simulations [36][37][38] for dipolar particles under hard-wall confinements. However, in contrast to these works, our system is characterized by a nearly harmonic confining potential that can be controlled together with the pairwise interaction.…”

“…Further we average it at each time step over all particles. Following a previous work on optically trapped colloidal cluster 54 , to minimize artefacts from the curved frontier we calculate ψ 6 (t) = ψ 6,k , by considering only the particles not adjacent to the outer boundary. Finally, we perform a running-time average and obtain the measure Ψ 6 = ψ 6 (t) for an entire simulation, as shown in Fig.…”

Active particles in geometrically confined viscoelastic fluids

“…the width of the radial distribution function r R r ( )decreases appreciably due to the radial localization, see figure 10(c). Note that such an ordered arrangement of the APs within the circular pore resembles qualitatively the formation of crystalline clusters in confined paramagnetic colloidal systems [55,56]. In such cases, repulsive dipole-dipole interactions foster classical 2D atomic-like structures composed of concentric shells [57], where the applied magnetic field plays a role similar to the particle activity in our multi-AP system.…”

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

“…Increasing the applied field, leads to a stronger localization of nanoparticles in the trap and simultaneously strengthens the repulsion between them. In a related context, melting of confined few-body systems has been investigated in experiments 36 , 37 and numerical simulations 38 – 40 for dipolar particles under hard-wall confinements. However, in contrast to these works, our system is characterized by a nearly harmonic confining potential that can be controlled together with the pairwise interaction.…”