Soft granular particles sheared at a controlled volume: rate-dependent dynamics and the solid-fluid transition

Area of Science:

• Soft Matter Physics
• Rheology
• Granular Materials

Background:

• Understanding the flow of soft particle suspensions is crucial for materials science and engineering.
• Granular suspensions exhibit complex behaviors near the jamming transition, influenced by particle softness and interstitial fluid.

Purpose of the Study:

• To investigate the rheological response of fluid-immersed soft hydrogel spheres under shear.
• To characterize the transition from solid-like to fluid-like behavior in these suspensions.
• To explore the influence of particle softness and interstitial fluid on flow dynamics.

Main Methods:

• Controlled shearing of hydrogel spheres between rough cones.
• Sudden shear cessations coupled with internal imaging.
• Flow-curve measurements and stress residue analysis.
• Determination of yield stress and solid-fluid transition points.

Main Results:

• Distinct flow regimes identified: quasi-static yielding of networks vs. fluid-mediated particle sliding.
• A continuous transition in particle settling observed with changing shear rate at high volume fractions.
• Solid-fluid transition confirmed via stress extrapolation and particle settling dynamics.
• Verification of a power law relating characteristic stress to proximity from jamming.

Conclusions:

• Soft particle dynamics involve multiple relaxation timescales, challenging existing paradigms for dense systems.
• The interplay between particle softness, interstitial fluid, and shear rate dictates suspension behavior.
• Further research is needed to extend current models to account for active softness in dense flows.