Confinement controls the creep rate in soft granular packings

Area of Science:

• Soft Matter Physics
• Rheology
• Materials Science

Background:

• Flow in soft materials exhibits complex viscous, plastic, and elastic behaviors, posing challenges for microscopic modeling.
• Understanding and controlling creep flow in these materials is crucial for various applications.

Purpose of the Study:

• To investigate the impact of global confinement stress on creep flow in soft material packings.
• To identify and characterize different creep regimes under controlled external loading.

Main Methods:

• Falling ball viscometry was employed on packings of soft, frictionless hydrogel spheres.
• Controlled driving stress was applied to a sinking sphere, with an additional global confinement stress introduced via an external load.

Main Results:

• Two distinct creep regimes were identified based on the level of confinement stress.
• At low confinement, creep rate was independent of load; at higher confinement, creep rate scaled with the mechanical load, showing exponential dependence.
• A master curve was developed by rescaling, successfully capturing creep rates over five orders of magnitude.

Conclusions:

• Bulk creep phenomena in soft materials can be effectively controlled by external mechanical forces.
• The findings provide a new method for manipulating soft material flow through applied stress and confinement.