Structural disorder and anomalous diffusion in random packing of spheres

Area of Science:

• Physics
• Material Science
• Biophysics
• Medicine

Background:

• Nuclear Magnetic Resonance diffusion (dNMR) is widely used for studying water in heterogeneous systems.
• Current methods analyzing the diffusion coefficient (D(t)) in the tortuosity limit struggle to characterize structural disorder and transitions.
• Complex systems require advanced methods for accurate microstructural analysis.

Purpose of the Study:

• To introduce and validate the dNMR measurable parameter α as a quantitative tool for characterizing structural disorder and transitions in heterogeneous systems.
• To demonstrate the utility of the continuous time random walk framework in interpreting dNMR data.
• To establish a correlation between experimental dNMR findings and simulation-based disorder parameters.

Main Methods:

• Experimental dNMR measurements of water diffusion in random packed monodisperse micro-spheres.
• Molecular Dynamics (MD) simulations of disordered porous media.
• 3D Monte Carlo simulations of particle diffusion in simulated porous systems.
• Analysis of the anomalous diffusion regime using the parameter α.

Main Results:

• The parameter α, derived from the continuous time random walk framework, effectively quantifies structural disorder.
• Experimental α measurements in micro-spheres align well with simulation results.
• Simulations successfully correlated α with established parameters characterizing disorder in porous media.

Conclusions:

• The dNMR parameter α provides a quantitative method for characterizing structural disorder and transitions in complex heterogeneous systems.
• This approach overcomes limitations of traditional diffusion coefficient analysis.
• The study validates the continuous time random walk framework for interpreting dNMR data in disordered media.