Jamming, two-fluid behavior, and "self-filtration" in concentrated particulate suspensions

Area of Science:

• Colloid and interface science
• Soft matter physics
• Granular materials science

Background:

• Colloidal suspensions at high volume fractions exhibit complex flow behaviors.
• Jamming and unjamming transitions are critical phenomena in dense particulate systems.
• Understanding flow in confined geometries is crucial for various industrial applications.

Purpose of the Study:

• To investigate the flow dynamics of hard-sphere colloidal suspensions through a constriction at high volume fractions.
• To characterize the jamming and unjamming transitions observed during flow.
• To elucidate the mechanism behind the observed reduction in colloid concentration downstream of the constriction.

Main Methods:

• Utilizing direct microscopic observations to monitor particle behavior during flow.
• Employing a pressure gradient to drive the colloidal suspensions through a constricted channel.
• Analyzing particle-size dependent jamming limits (Phi(0)) and downstream colloid concentration (Phi(x)).

Main Results:

• Jamming and unjamming transitions were observed above a critical volume fraction Phi(0) dependent on particle size.
• A significant reduction in colloid concentration (self-filtration) was measured downstream of the constriction.
• The self-filtration effect was attributed to the jamming of particles and the continued flow of the solvent through the jammed solid.

Conclusions:

• Jamming in colloidal suspensions under flow through constrictions leads to a self-filtration phenomenon.
• This process can be described by a two-fluid model, separating the flow of the solid (jammed particles) and liquid (solvent) phases.
• The findings connect jamming in colloidal systems with classical granular material behavior, referencing Reynolds' dilation experiments.