Kinetics of Shear-Induced Structural Ordering in Dense Colloids.

Area of Science:

• Colloid science
• Materials science
• Rheology

Background:

• Macroscopic rheological properties of colloidal solutions are linked to microscopic structural changes.
• Understanding these structure-property relationships is crucial for material design.

Purpose of the Study:

• To investigate the relationship between microscopic structure and macroscopic rheology in colloidal solutions.
• To explore the ordering-to-disordering transitions induced by oscillatory shear.
• To elucidate the kinetics and dynamics of structural changes under varying strain amplitudes.

Main Methods:

• Utilized in situ Rheo-Small-Angle X-ray Scattering (Rheo-SAXS) for high temporal resolution structural analysis.
• Applied oscillatory shear to induce controlled structural transitions.
• Analyzed time-dependent kinetics and dynamic equilibrium pathways.

Main Results:

• Demonstrated a strain-controlled ordering-to-disorder transition in colloidal solutions.
• Identified a novel shear-thickening mechanism distinct from hydrodynamic or frictional effects.
• Revealed complex, non-monotonic kinetics towards structural ordering, especially near critical strain values.
• Observed oscillation between two dynamic metastable states within a single cycle.

Conclusions:

• Macroscopic rheology is directly correlated with microscopic structural dynamics in colloidal systems.
• Oscillatory shear induces unique shear-thickening behavior via strain-controlled transitions.
• The colloidal system exhibits complex kinetics and metastable states during structural evolution under shear.