Mechanisms of spontaneous chain formation and subsequent microstructural evolution in shear-driven strongly confined drop monolayers

Abstract

Experimentally observed drop-chain formation in sheared drop monolayers is explained in terms of Hele-Shaw quadrupolar interactions and swapping-trajectory repulsion.

Vorticity-Aligned Droplet Bands in Sheared Immiscible Polymer Blends Induced by Solid Particles

“…17 The spatial organization of droplets under flow in multiphase materials often results in the formation of a macroscopic anisotropic structure. For example, Migler et al 18,19 found that in sheared polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends, dispersed droplets could arrange into flow-aligned pearl necklace structures due to the confinement effect when their dimensions were comparable to the flow geometry. Caserta et al 20 found that biphase liquids of silicone oil in polybutene with a low viscosity ratio (0.1) formed vorticity-aligned droplet bands due to the reduction of viscous dissipation under slow confined flow.…”

Field-controlling patterns of sheared ferrofluid droplets

“…As a result, the droplets form a chain-like pattern as Ref. [23,28] [see Fig. 2(b)] when there is no magnetic field.…”

“…In a simple shear flow, the droplets will migrate towards the mid-plane of the channel (z = L z /2) due to the hydrodynamic interaction between the droplets and the walls [26,27]. Since droplets in the wall-bounded shear flow can generate quadrupole flow fields [23,24] (see Fig. 2(a)), they will attract and align in the flow direction (x direction) while they repel each other in the vorticity direction (y direction).…”

“…2(a)), they will attract and align in the flow direction (x direction) while they repel each other in the vorticity direction (y direction). The droplets have their stable inter-droplet distance due to the interplay with the flow field [23,24]. As a result, the droplets form a chain-like pattern as Ref.…”

“…A mixture of ferrofluid and non-magnetic fluid under confinements has been known to form various patterns such as labyrinthine [18] or crystal (hexagonal) pattern [19], which are tunable by magnetic field [1,20]; by increasing the strength of the magnetic field, the twophase fluids can change the organised pattern from the labyrinthine one to the crystal one when the magnetic dipolar interactions dominate over the surface energy [21,22]. Meanwhile, it has been known that flow field can also help to tune the organisation patterns of suspended non-magnetic particles; for example droplets [23] or red blood cells [24] under a wall-bounded shear can form 1D chain or 2D crystal, depending on the area fraction or the wall height. Thus, it is not trivial to answer how ferrofluid droplets can be organised when considering both the magnetic interactions and hydrodynamic interactions between the droplets, which is usually the case in microfluidic applications of ferrofluid droplets.…”