Electrophoresis of solid particles at large Peclet numbers

Area of Science:

• Physical Chemistry
• Colloid Science

Background:

• Concentration polarization of electrical double layers (DL) is crucial in understanding particle behavior under electric fields.
• Existing models often simplify the complex interplay of diffusion, convection, and electric fields, especially at high Peclet numbers.

Purpose of the Study:

• To develop a theory for concentration polarization of a thin electrical double layer (DL) on a spherical particle in the regime of large Peclet numbers.
• To investigate the influence of strong electric fields on the concentration field, DL polarization, and electrophoretic velocity.

Main Methods:

• Developed a theoretical framework for concentration polarization in thin electrical double layers (DL) on spherical particles.
• Estimated the concentration field considering diffusion and convection under large Peclet number conditions.
• Derived a nonlinear term for the Smoluchowski formula incorporating zeta-potential changes and secondary electroosmosis.

Main Results:

• At large Peclet numbers, DL polarization alters Stern potential, induces dipole moments, and creates long-range potentials.
• The diffuse layer deviates from spherical symmetry, with charge screening provided by both the diffuse atmosphere and an induced convective-diffusion layer charge.
• Secondary electroosmosis arises from the electric field's effect on induced charge, leading to additional electroosmotic slip.

Conclusions:

• The developed theory accurately describes concentration polarization effects in strong electric fields.
• The findings provide a more comprehensive understanding of electrophoretic velocity, including secondary electroosmosis.
• The theory shows considerable agreement with experimental results, validating its applicability.