Probing a nonequilibrium einstein relation in an aging colloidal glass

Area of Science:

• Soft matter physics
• Colloidal science
• Non-equilibrium statistical mechanics

Background:

• Colloidal glasses are complex systems exhibiting aging phenomena.
• Understanding non-equilibrium dynamics is crucial for soft matter systems.
• The fluctuation-dissipation relation (FDR) typically describes equilibrium systems.

Purpose of the Study:

• To experimentally measure the effective temperature in aging colloidal laponite glass.
• To investigate the validity of the fluctuation-dissipation relation in this non-equilibrium system.
• To correlate effective temperature behavior with system aging and relaxation dynamics.

Main Methods:

• Utilized a micrometric bead as a thermometer for direct temperature measurement.
• Performed diffusion and mobility measurements of the embedded bead.
• Analyzed the bead's behavior within the aging colloidal glass.

Main Results:

• Observed a nonmonotonic behavior of the effective temperature during system aging.
• The effective temperature initially increased from bath temperature, peaked, then decreased.
• Deviations from the standard Einstein relation were quantified.

Conclusions:

• The effective temperature in colloidal glass is not constant and depends on aging.
• The observed deviations from the Einstein relation are linked to system relaxation times.
• This study provides direct experimental evidence for complex thermal behavior in aging soft matter.