A Novel Physical Mechanism to Model Brownian Yet Non-Gaussian Diffusion: Theory and Application

Area of Science:

• Soft Matter Physics
• Biological Physics
• Colloidal Science

Background:

• Experiments report Brownian yet non-Gaussian diffusion, characterized by Laplacian displacement distributions.
• Existing models are either stochastic, introducing unknown random elements, or microscopic, limiting physical scenarios.
• A deeper understanding of media-particle interactions is needed to explain this diffusion behavior.

Purpose of the Study:

• To develop a comprehensive mathematical model for Brownian yet non-Gaussian diffusion.
• To incorporate weak molecular interactions into the diffusion model.
• To explain the observed Laplacian probability distribution in particle displacements.

Main Methods:

• Utilized De Gennes' interface theory and Langevin dynamics.
• Developed a mathematical model including weak molecular interactions.
• Analyzed long-range interactions in weakly interacting fluids.
• Investigated the role of phase separation in diffusion dynamics.

Main Results:

• The model predicts long-range interactions cause Laplacian radial displacement distributions at short timescales.
• Phase separation explains high diffusivity and the transition from Laplacian to Gaussian distributions over time.
• Model predictions align qualitatively and quantitatively with experimental data on colloidal beads.

Conclusions:

• The proposed model successfully explains Brownian yet non-Gaussian diffusion.
• Weak molecular interactions and phase separation are key factors in this diffusion phenomenon.
• The model provides a robust framework for understanding complex diffusion in soft matter systems.