Stability of particle laden interfaces of drops flowing through a pore

TL;DR

This study investigates the stability of particle-laden drop interfaces during flow through a pore, identifying conditions under which particles are expelled based on surface pressure and geometrical constraints.

Contribution

It introduces a framework using three non-dimensional numbers to predict particle expulsion from Pickering drops in pore flow.

Findings

Particles are expelled when surface pressure builds up at the rear of the drop.

Surface pressure relaxation is hindered by geometrical constraints, leading to particle expulsion.

The behavior is characterized by capillary number, particle-to-pore size ratio, and drop-to-particle size ratio.

Abstract

When a drop laden with solid particles and suspended in a liquid passes through a narrow pore, its interface experiences strong shear and elongation, and the raft of particles may accumulate toward the back of the drop. Using well controlled formulations of Pickering drops driven at set pressure, we determine the two conditions for which solid particles are expelled from the oil-water interface after a Pickering drop passes a converging-diverging pore: (i) particles accumulation at the rear of the drop is such that surface pressure builds-up at the interface. (ii) Surface pressure relaxation by buckling is impaired by geometrical constraints. These two conditions are rationalized using three non dimensional numbers: the capillary number, the particle to pore size ratio, and the drop to particle size ratio, which allow to account for the viscous shear at the interface, the stability of the lubricating film between the pore wall and the drop, the drag on the raft of particles adsorbed at the interface, and its mechanical behaviour.