Diffusion of organic solutes in squalane

Area of Science:

• Physical Chemistry
• Fluid Dynamics
• Thermodynamics

Background:

• The Stokes-Einstein relation predicts how fast particles move in a fluid.
• Understanding solute diffusion in liquids is crucial for various chemical and physical processes.
• Previous studies have explored diffusion in n-alkanes, but data across a wider viscosity range is needed.

Purpose of the Study:

• To measure translational diffusion constants (D) for 26 hydrocarbons in squalane at room temperature.
• To investigate deviations from the Stokes-Einstein relation across a 100-fold viscosity range.
• To analyze the relationship between solute size, viscosity, and diffusion behavior.

Main Methods:

• Utilized capillary flow techniques to determine diffusion constants.
• Collected data for 26 hydrocarbon solutes in squalane.
• Compared new data with existing diffusion data in n-alkanes (n-C(6)-n-C(16)).

Main Results:

• Measured diffusion constants for 26 hydrocarbons in squalane.
• Observed deviations from the Stokes-Einstein relation in both n-alkanes and squalane.
• Found that hydrodynamic radius (r) decreases with increasing viscosity.
• Smaller solutes exhibited larger deviations from the Stokes-Einstein relation.

Conclusions:

• The Stokes-Einstein relation is insufficient to describe solute diffusion across a wide range of viscosities.
• A modified Stokes-Einstein equation with an exponent p < 1 better fits the observed diffusion data.
• The relative sizes of solutes and the viscosity of the medium significantly impact diffusion behavior.