Nucleation, aggregation, annealing, and disintegration of granular clusters

Abstract

The processes of nucleation, aggregation, annealing, and disintegration of clusters of non-Brownian paramagnetic beads in a vibrofluidized system are experimentally investigated. The interaction among the beads is induced by a magnetic seed composed of two dipoles allocated outside the container cell. We observe a clearly differentiated nucleation stage, whose evolution (nucleation time versus acceleration strength) follows a power law. Thereafter, the beads aggregate forming 2D disordered clusters around the nucleus. Both processes (nucleation and aggregation) are determined by the competition between magnetic forces and the drag produced by a thermal bath created by glass particles. Once the agglomerates reach a final state (shape and length), they are annealed by increasing and decreasing the granular temperature. We found that the fractal dimension and the lacunarity index clearly describe the structural variations of the clusters. Our discussion on this phenomenon is addressed, making a rough analogy with the glass transition in a super-cooled liquid. Finally, we study the disintegration of the clusters as a function of time and the density of the surrounding gas. The question is not if, but how they disintegrate upon removing the external field; we find that the disintegration follows an exponential decay.

Deterministic aggregation kinetics of superparamagnetic colloidal particles

“…3,30,42,44 Another approach is to fit to a particular scaling law with the packing fraction dependence and field dependence as free fitting parameters. 45,46 However, in the approach we use here, we do not require a specific functional form for the cluster growth. Instead, we write that the mean cluster size, ⟨L⟩, grows as a monotonic scaling function f of unspecified form of the variable t * = φ α B β t, such that…”

Order-fractal transitions in abstract paintings

“…This measure of complexity has been employed to characterize the structural transition of rheological fluids [23,25,33], granular materials [26,34], magnetic wall domains in boracite [27] and other complex systems [35,36].…”

“…The multi-fractal spectrum has been used as a measure of all the local fractal dimensions coexisting in spatial structures of a wide variety of physical, chemical and biological systems. This measure of complexity has been employed to characterize the structural transition of rheological fluids [23,25,33], granular materials [26,34], magnetic wall domains in boracite [27] and other complex systems [35,36].…”

Active dipole clusters: From helical motion to fission

“…Clusters comprising N individual particles occur in widely different areas of physics ranging from the atomic world [1] to nanoparticles [2], colloids [3][4][5][6][7][8][9][10][11] and to macroscopic granulates [12]. In the simplest case, the particles interact via a pairwise potential, such as a Lennard-Jones potential [13] or a hard-sphere-dipole interaction [14][15][16][17][18][19][20][21][22], and the equilibrium groundstate structure of the cluster is obtained by minimization of the total potential energy.…”