Emergence of Multiscale Dynamics in Colloidal Gels

Area of Science:

• Colloidal science
• Soft matter physics
• Materials science

Background:

• Colloidal gels are ubiquitous in nature and industry.
• Understanding their evolution, especially at low particle concentrations, is crucial.
• Nonergodicity marks a critical transition in gel dynamics.

Purpose of the Study:

• Investigate the kinetics of colloidal gel formation at low particle volume fractions (ϕ).
• Characterize particle aggregation, geometric percolation, and the transition to nonergodic dynamics.
• Uncover the multiscale dynamics associated with the onset of nonergodicity.

Main Methods:

• Differential dynamic microscopy (DDM) was employed.
• Analysis focused on particle aggregation and percolation.
• DDM enabled the study of dynamics across different length scales.

Main Results:

• Rich multiscale dynamics emerge upon reaching nonergodicity.
• Three distinct dynamic regimes were identified based on wave vector (q).
• High-q: ϕ-independent internal vibrations of fractal clusters.
• Intermediate-q: q-independent relaxation time (τ) due to density fluctuations.
• Low-q: τ scales as q⁻³ indicating homogeneous network behavior.

Conclusions:

• The onset of nonergodicity in colloidal gels is characterized by complex, multiscale dynamics.
• Distinct dynamic regimes (vibrations, density fluctuations, homogeneous scaling) are observed.
• Two characteristic length scales, separate from cluster size, emerge at regime transitions.