Heterogeneous Activation, Local Structure, and Softness in Supercooled Colloidal Liquids

Area of Science:

• Soft Matter Physics
• Colloidal Science
• Nonlinear Dynamics

Background:

• Supercooled liquids exhibit complex dynamics, deviating from simple exponential relaxation.
• Heterogeneity in particle environments contributes to nonexponential relaxation.
• The concept of 'softness' offers a new way to characterize particle behavior in such systems.

Purpose of the Study:

• To experimentally investigate heterogeneous nonexponential relaxation in bidisperse supercooled colloidal liquids.
• To utilize the 'softness' concept to classify particles and understand their relaxation dynamics.
• To link particle local environments and neighbor interactions to relaxation behavior.

Main Methods:

• Experimental characterization of particle trajectories and structure in colloidal liquids.
• Classification of particles into subgroups based on their 'softness' and local environments.
• Determination of residence times between particle hops and application of Kramers' reaction rate model.

Main Results:

• Residence times within softness subgroups follow exponential distributions.
• Mean residence times and activation energy barriers are monotonic functions of softness.
• Particle softness is determined by combinations of large and small particle neighbors.
• Multiple exponential relaxation channels were identified, explaining the overall nonexponential liquid behavior.

Conclusions:

• The 'softness' parameter effectively characterizes heterogeneous relaxation in supercooled liquids.
• Particle-level dynamics, influenced by local environment, collectively lead to macroscopic nonexponential relaxation.
• This study provides a framework for understanding complex dynamics in disordered materials.