Spreading of triboelectrically charged granular matter

Abstract

We report on the spreading of triboelectrically charged glass particles on an oppositely charged surface of a plastic cylindrical container in the presence of a constant mechanical agitation. The particles spread via sticking, as a monolayer on the cylinder's surface. Continued agitation initiates a sequence of instabilities of this monolayer, which first forms periodic wavy-stripe-shaped transverse density modulation in the monolayer and then ejects narrow and long particle-jets from the tips of these stripes. These jets finally coalesce laterally to form a homogeneous spreading front that is layered along the spreading direction. These remarkable growth patterns are related to a time evolving frictional drag between the moving charged glass particles and the countercharges on the plastic container. The results provide insight into the multiscale time-dependent tribolelectric processes and motivates further investigation into the microscopic causes of these macroscopic dynamical instabilities and spatial structures.

Active uniaxially ordered suspensions on disordered substrates

“…This includes the prediction of long range order in two dimensions for motile XY spins on a substrate [8][9][10][11], the generic destruction of apolar phases in infinite, momentum-conserved systems in any dimension [3,12,13] and the anomalous scaling of number fluctuations with the mean number N in orientationally ordered phases which, being larger than √ N , violates the law of large numbers [14,15]. These predictions have been confirmed in experiments [3,16] and have been shown to be responsible for various biological phenomena ranging from flocking of birds [17] to spatio-temporally chaotic flows in bacterial fluids [18] to crawling of cell-layers [19] to spontaneous rotation of the cellular nucleus [20].…”

“…Furthermore, many such experiments are conducted in systems which are confined between a substrate and a cover-slip. Boundary conditions fundamentally change the behaviours of active systems [20,21]. The theories of homogeneous active polar and apolar suspensions on substrates or in confined channels were considered in [22] and [23] respectively.…”

Oriented Active Solids

“…Biological systems and their artificial analogues are driven out of equilibrium by a direct and independent supply of free energy to the individual constituent units. The nontrivial coupling of the constituent particles to this power input [1,2] results in macroscopic stresses and currents in the system which have been shown to be responsible for diverse phenomena ranging from coherent intracellular flows [3][4][5], to defect turbulence in living liquid crystals [6], to flocking in animal groups [7]. Active hydrodynamics [8], which extends the traditional continuum dynamics of conserved and brokensymmetry variables by introducing terms that break only the time-reversal symmetry of the corresponding passive systems, offers a successful general framework to describe the macroscopic behaviour of such systems.…”

Spatio-temporal dynamics of an active, polar, viscoelastic ring

“…Another prediction is that actomyosin rings may spontaneously rotate, due to the occurrence of propagating waves in an active, polar, viscoelastic ring (see figures 2 and 4). As a consequence of mechanical coupling between the actin cytoskeleton and the cell nucleus, rotation of the actin ring may in turn entrain the rotation of the cell nucleus [25]. Another active, polar, viscoelastic ring is the contractile ring assembled during cytokinesis by eukaryotic cells [26]: it may also rotate thanks to the same mechanism.…”