Rheological implications of embedded active matter in colloidal gels

Area of Science:

• Soft Matter Physics
• Materials Science
• Colloid Science

Background:

• Colloidal gels exhibit solid-like properties due to inter-particle interactions.
• Active colloids introduce autonomous dynamics into soft matter systems.
• Previous studies show active components can stiffen networks, unlike findings here.

Purpose of the Study:

• Investigate the impact of embedded active colloids on colloidal gel rheology.
• Understand the mechanism behind changes in gel elasticity.
• Characterize the violation of the fluctuation-dissipation theorem in active gels.

Main Methods:

• Fabrication of fractal cluster colloidal gels with embedded active Janus particles.
• Introduction of hydrogen peroxide to activate Janus particle motion.
• Measurement of linear viscoelastic moduli and microdynamics.

Main Results:

• Embedded active colloids decrease gel elasticity, contrary to some existing research.
• The decrease in modulus correlates with hydrogen peroxide concentration and active colloid density.
• A theoretical model explains softening via active motion-induced reduction of inter-particle attraction.
• Discrepancy observed between macroscopic rheology and microrheology, indicating fluctuation-dissipation theorem failure.

Conclusions:

• Active particle dynamics can be harnessed to tune gel mechanical properties.
• The findings offer a pathway to engineer reconfigurable gels with tunable, multi-state mechanical properties.
• Potential applications include paints, coatings, pharmaceuticals, self-healing materials, and soft robotics.