Fractionation by Spatially Heterogeneous Diffusion: Experiments and the Two-Component Random Walk Model.

Area of Science:

• Physical Chemistry
• Colloid and Surface Chemistry
• Statistical Mechanics

Background:

• Fractionation is a key process in separating mixtures.
• Understanding the driving forces behind particle fractionation is crucial for various scientific and industrial applications.
• The role of diffusion versus advection in particle fractionation across interfaces remains debated.

Purpose of the Study:

• To investigate whether diffusion alone or a combination of diffusion and advection drives particle fractionation.
• To experimentally determine the physical mechanisms governing particle fractionation at a solid-solid interface.

Main Methods:

• Experimentally observing time-sequential fractionation patterns of dye particles.
• Diffusing particles across a solid-solid interface with varying polyacrylamide gel densities.
• Analyzing experimental data using a two-component diffusion model and comparing it with single-component models (Fick, Wereide, Chapman).

Main Results:

• The two-component diffusion model accurately captured the observed fractionation dynamics.
• Single-component diffusion models failed to replicate the experimental results.
• Results indicate that diffusion alone is sufficient to explain the observed fractionation phenomenon.

Conclusions:

• Diffusion, not advection, is the primary mechanism responsible for particle fractionation in the studied heterogeneous environments.
• A two-component random walk model effectively describes the underlying physics of fractionation.
• This finding simplifies the understanding of particle transport and separation processes.