On the validity of Stokes-Einstein-Debye relations for rotational diffusion in colloidal suspensions

Area of Science:

• Colloid Science
• Physical Chemistry
• Soft Matter Physics

Background:

• The Stokes-Einstein-Debye (SED) relation predicts tracer diffusion coefficients based on solvent viscosity.
• Its applicability to complex colloidal suspensions with varying tracer-to-host size ratios and interactions is not fully understood.

Purpose of the Study:

• To investigate the generalization of the SED relation for tracer diffusion in neutral and charged colloidal host sphere suspensions.
• To analyze the impact of hydrodynamic interactions and particle shape on tracer diffusion dynamics.

Main Methods:

• Rotational diffusion coefficients were measured using dynamic light scattering and phosphorescence spectroscopy.
• Two- and three-particle hydrodynamic interactions were incorporated into theoretical calculations.

Main Results:

• Tracer rotational diffusion was consistently faster than SED predictions, except at large tracer/host size ratios.
• Deviations were rationalized by a slip boundary coefficient for neutral spheres and significantly larger for charged spheres due to hindered dynamics.
• Rod-shaped hosts exhibited much stronger hydrodynamic hindrance than spherical hosts.

Conclusions:

• The SED relation requires modification for accurate predictions in colloidal suspensions.
• Hydrodynamic interactions and particle geometry significantly influence tracer diffusion dynamics.
• Further research is needed to fully elucidate tracer diffusion in complex colloidal systems.