Transition from fractional to classical Stokes-Einstein behaviour in simple fluids.

Area of Science:

• Physical Chemistry
• Nanotechnology
• Materials Science

Background:

• The Stokes-Einstein relationship describes particle diffusion, but deviations occur for smaller particles.
• Molecular dynamics simulations predicted a transition in diffusion behavior based on particle size.

Purpose of the Study:

• To experimentally determine the particle diameter at which diffusion transitions from fractional to classical Stokes-Einstein behavior.
• To validate predictions from molecular dynamics simulations regarding this diffusion transition.

Main Methods:

• Utilized an optical technique for single-particle tracking.
• Evaluated particle diffusion behavior across a range of concentrations and viscosities.

Main Results:

• Confirmed the existence of a critical particle size for diffusion behavior transition.
• Observed an inverse dependence of transition diameter on concentration and viscosity.
• Found the transition diameter to be independent of particle density.
• Identified the transition occurring between 150-300 nm for tested concentrations (5 × 10⁻³ to 5 × 10⁻⁶ mg/ml) and viscosities (0.8 to 150 mPa·s).

Conclusions:

• Experimental results align with molecular dynamics predictions for particle diffusion transition.
• The findings provide a quantitative understanding of diffusion behavior changes with particle size.