Limiting electrophoretic mobility of a highly charged soft particle in an electrolyte solution: solidification effect

Area of Science:

• Colloid and Surface Science
• Electrochemistry
• Polymer Science

Background:

• Electrophoretic mobility of charged particles in electrolytes is crucial for understanding colloid behavior.
• Highly charged liquid drops and rigid spheres show a 'solidification effect' where mobility becomes constant at high potentials.
• Polyelectrolyte-coated (soft) particles present a unique case due to their ion-penetrable layer.

Purpose of the Study:

• To derive the electrophoretic mobility expression for highly charged spherical soft particles.
• To investigate the influence of the ion-penetrable layer on particle mobility.
• To compare the behavior of soft particles with rigid particles and liquid drops.

Main Methods:

• Theoretical derivation of electrophoretic mobility for a soft particle model.
• Analysis of the limiting mobility in conditions of large Debye-Hückel parameter (kappa*a) and large Dukhin number (Du).
• Mathematical formulation considering particle core radius (a), layer thickness (d), and electrolyte properties.

Main Results:

• A novel mobility expression for soft particles was derived under specific conditions (kappa*a >> 1, kappa*d >> 1).
• The scaled limiting mobility magnitude is given by |mu((infinity))|=2epsilon(r)epsilon(o)kT/3etaze x (1+a(3)/2b(3)) x 2 ln 2.
• The solidification effect, where mobility approaches a constant value, is observed for soft particles, similar to rigid spheres when a approaches b.

Conclusions:

• Soft particles, like rigid spheres and liquid drops, exhibit a solidification effect in their electrophoretic mobility at high zeta potentials.
• The derived mobility expression provides insights into the electrokinetic behavior of polyelectrolyte-coated particles.
• This study extends the understanding of electrokinetic phenomena in complex colloidal systems.