Rheology finds distinct glass and jamming transitions in emulsions

Area of Science:

• Rheology of complex fluids
• Colloid and interface science

Background:

• Dispersions exhibit liquid-solid transitions at a critical volume fraction (φc).
• Theoretical models predict distinct glass transitions for small thermal particles (φg ≈ 0.58) and jamming transitions for large athermal systems (φJ ≈ 0.64).
• Simulations suggest a crossover where both transitions may occur simultaneously.

Purpose of the Study:

• To experimentally investigate the rheological behavior of monodisperse and bidisperse emulsions.
• To determine the influence of droplet size on liquid-solid transitions (glass and jamming).
• To analyze rheological data using established models and assess data universality.

Main Methods:

• Shear rheometry was performed on four oil-in-water emulsions with varying droplet sizes (1-2 μm).
• Monodisperse and bidisperse systems were studied to compare their rheological responses.
• Data were fitted using the Herschel-Bulkley and three-component models.

Main Results:

• Smaller diameter droplets exhibited both glass and jamming transitions.
• Larger diameter droplets displayed only a jamming transition.
• The bidisperse sample showed behavior similar to the small droplet sample, with two observed transitions.
• Rheological data did not collapse onto a master curve based on fitting parameters.

Conclusions:

• Liquid-solid transitions in dispersions are size-dependent, not universal phenomena.
• Droplet size critically influences whether a system undergoes a single (jamming) or multiple (glass and jamming) transitions.
• The findings challenge universal theories and highlight the importance of particle size in dispersion rheology.