Electrophoresis of concentrated spherical particles with a charge-regulated surface

The electrophoretic behavior of spherical colloidal particles is modeled th eoretically. The classic analysis is extended to the case of a concentrated dispersion in which the double layer surrounding a particle can assume an arbitrary thickness, and the effect of double-layer polarization is taken i nto account. Also, the surface of a particle is charge regulated, which lea ds to a general mixed-type boundary condition, and simulates entities beari ng dissociable functional groups such as biological cells and particles wit h a membrane layer. We show that the absolute surface potential decreases w ith the increase in kappa a, kappa and a are, respectively, the reciprocal Debye length and the radius of a particle. The variation of the absolute el ectrophoretic mobility as a function of kappa a is found to have a local ma ximum. The higher the surface potential the more significant the effect of double-layer polarization, and it becomes insignificant if kappa a approach es infinity. (C) 2000 American Institute of Physics. [S0021-9606(00)70114-0 ].