Force measurements between particles and the air‐water interface: Implications for particle mobilization in unsaturated porous media

Abstract

[1] Capillary forces acting at the air-water interface play an important role in colloid fate and transport in subsurface porous media. We quantified capillary forces between different particles (sphere, cylinder, cube, disk, sheet, and natural mineral particles) and a moving air-water interface. The particles had different sizes and contact angles (ranging from 14°to 121°). Theoretical calculations using the Young-Laplace equation were used to support and generalize the experimental data. When the air-water interface moved over the particles, there were strong capillary forces acting on the particles in the direction of the moving interface. The measured maximum capillary forces were similar to those calculated by the Young-Laplace equation. The larger the contact angles and the larger the particle size, the stronger were the capillary forces. Particles with irregular shape and sharp edges experienced greater forces than smooth particles. Generalization of the results indicates that capillary forces exerted by a moving air-water interface can readily exceed attractive Derjaguin-Landau-Verwey-Overbeek (DLVO) and gravity forces for typical subsurface particles, and a moving air-water interface is therefore an effective mechanism for mobilization of particles in porous media. Particles in the colloidal size range are particularly susceptible for mobilization by a moving air-water interface.Citation: Shang, J., M. Flury, and Y. Deng (2009), Force measurements between particles and the air-water interface: Implications for particle mobilization in unsaturated porous media, Water Resour. Res., 45, W06420,

Indicator and Pathogen Removal by Low Impact Development Best Management Practices

“…Attachment also occurs at particle-air and air-water interfaces under unsaturated conditions when air, water, and solid phases are all present inside the biofilter. Microbes can attach to the air-water interface due to strong capillary forces, be pinned to media grains by the thinning water film, or be captured in water pockets between grains that are disconnected from the bulk flow [12,17].…”

Geological Disposal of Nuclear Waste: Fate and Transport of Radioactive Materials

“…These are interception of the particle, attachment or thinning of the liquid film in between the particle and the liquid-gas interface, and stabilization of the particle on the liquid-gas interface [22,30,67,70]. The total detachment probability (P det ) is defined as [22]:…”

“…For the transport and mobilization of radioactive materials in colloidal size or its attachment with colloidal particle, the balance among electrostatic, hydrodynamic, and capillary forces are responsible for attraction of particle towards the liquid-gas interface [29,67,68,70,72,79]. If capillary force dominates then the colloidal particles attracted towards the liquid-gas interface and if electrostatic dominates then the colloidal particles remain stay over the grain surface.…”

“…Shang et al [67] had recently studied the total force balance exerted on a particle passing through a liquid-gas interface. They considered different shape and size (1 to 6 µm) of particles of different surface properties to pass through a liquid-gas interface and measured the forces exerted on the particle over time using a tensiometer and compared with their theocratical force balance calculations.…”

“…They considered different shape and size (1 to 6 µm) of particles of different surface properties to pass through a liquid-gas interface and measured the forces exerted on the particle over time using a tensiometer and compared with their theocratical force balance calculations. It has been observed that the liquid-gas interface due to capillary force generates a strong repulsion of particles from the stationary surfaces when water film expands or move through the solid surfaces [67]. In order to detach a particle from the solid surfaces, a liquid film larger than the particle diameter must build up around the particle so that the repulsive capillary force can dominate and a lift can occur.…”