Structural origin of relaxation in dense colloidal suspensions.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Statistical Mechanics

Background:

• Amorphous solids undergo structural relaxation via molecular rearrangement, driven by thermal fluctuations or stress.
• Predicting these relaxations has relied on dynamic properties or complex computational models, lacking a simple structural indicator.
• A physically meaningful structural quantity for predicting relaxation in disordered systems has remained elusive.

Purpose of the Study:

• To introduce and validate a novel structural order parameter for predicting structural relaxations in amorphous solids.
• To establish a direct correlation between this parameter and experimentally observed relaxations.
• To demonstrate the parameter's utility in both quiescent and sheared amorphous systems.

Main Methods:

• Derivation of a structural order parameter from the mean-field caging potential experienced by particles.
• Utilizing density functional theory to compute the structural parameter.
• Experimental validation using dense colloidal suspensions under quiescent and sheared conditions.

Main Results:

• The introduced structural order parameter reliably predicts the occurrence of structural relaxations.
• A strong correlation was observed between the order parameter and experimental structural relaxations in colloidal suspensions.
• The parameter effectively identifies weak or defect-like regions susceptible to particle rearrangement.
• In sheared systems, the parameter accurately pinpoints shear transformation sites.

Conclusions:

• The developed structural order parameter offers a physically meaningful and predictive measure of relaxation in amorphous solids.
• This finding provides a new avenue for understanding and controlling the mechanical behavior of disordered materials.
• The approach is applicable to a broad range of amorphous solids, including suspensions and metallic glasses.