Comparing Rotational and Translational Diffusion to Evaluate Heterogeneity in Binary Solvent Systems

Area of Science:

• Physical Chemistry
• Chemical Physics
• Materials Science

Background:

• Understanding molecular diffusion is crucial for chemical processes.
• Hydrodynamic models predict molecular motion but may not fully capture complex solvent effects.

Purpose of the Study:

• To investigate rotational and translational diffusion of fluorescent probes in glycerol-water.
• To compare experimental data with hydrodynamic models and assess model utility.
• To determine solvent-solute frictional interactions.

Main Methods:

• Time-resolved fluorescence anisotropy (TRFA) for rotational diffusion.
• Fluorescence recovery after photobleaching (FRAP) for translational diffusion.
• Utilized cationic oxazine 118 and anionic resorufin probes.

Main Results:

• Experimental diffusion dynamics deviated from modified Debye-Stokes-Einstein (DSE) and Stokes-Einstein-Sutherland (SES) models.
• Deviations were attributed to local solvation differences and solvent heterogeneity.
• Empirical solvent-solute frictional factors were determined by comparing DSE and SES models.

Conclusions:

• Glycerol-water solvent system exhibits heterogeneity affecting molecular diffusion.
• Local solvation differences between cationic and anionic probes influence their dynamics.
• The study provides insights into the limitations of hydrodynamic models in complex fluids.