Particles under thin Liquid Film Confinement – ProLiFiC

Suspensions of solid non-brownian particles in a liquid are encountered in various geophysical, industrial or biological systems. Whereas most of the past studies have characterized the transport of particles in bulk flow or the rheology of suspensions, some situations, such as in liquid sheets or thin liquid films, where the thickness of the liquid layer becomes comparable to the particle size are less understood. For instance, various situations involve thin liquid films that form spontaneously behind a plug of liquid or during the spreading of self-suspended liquid sheets. Therefore, the particles deform the liquid interface, which leads to complex interactions modifying the transport of particles or the stability of the liquid films. Indeed, when a non-brownian particle is confined by the liquid layer, its displacement is controlled by the competition between capillary, drag and friction forces. As a result, some particles can remain trapped on the substrate or trigger an instability of liquid film. In typical thin-film flow conditions, non-Brownian particles can be deposited, which results in the contamination of the surface and the loss of transported material. Despite the consequences of the contamination process, there is no description of the mechanisms responsible for particle capture and removal. Indeed the couplings between particle and fluid dynamics render the fundamental understanding of these systems challenging. We will therefore first rely on controlled experiments to unravel the relevant scaling law.

The purpose of this ground breaking project is thus to characterize the influence of particles on thin film flows in model configurations. This proposal builds on extensive prior work on thin films of Newtonian fluids and recent studies on the fragmentation of particle-laden jets. This work advances our knowledge of suspension flows through a systematic characterization of the dynamics of particles confined in thin liquid films, including (1) the deposition on and (2) removal of particles from a surface and (3) the fragmentation of a liquid sheet in presence of particles. This challenging project aims at providing a fundamental physical understanding of the influence of particles on the flow of thin liquid film and at identifying the mechanisms that control the deposition of particles and the stability of liquid interfaces through an experimental approach.