ELECTROPHORETIC MOTION OF 2 SPHERICAL-PARTICLES WITH THICK DOUBLE-LAYERS

The electrophoretic mobilities of two interacting spheres are calculat ed numerically for arbitrary values of the double-layer thickness. A g eneral formula for the electrophoreric translational and angular veloc ities of N interacting particles is derived for low-zeta-potential con ditions. The present calculation complements the well-studied case of thin double layers. The results are compared with recent reflection ca lculations and are used to compute the O(empty set) contribution to th e electrophoretic mobility of a suspension. Particle interactions can be significant for values of the scaled particle radius kappa alpha le ss than or equal to 10. At kappa alpha = 1 the O(empty set) contributi on can increase by a factor of 2-3 over its thin-double-layer value. T he precise values depend on the strength of the double-layer repulsion s as determined by the particle size. Fluctuations in the electrophore tic velocity are also calculated but would appear to be limited to abo ut 10% of the mean velocity. The reflection results to order R-6, wher e R is the particle separation, are in good agreement with the numeric al results for the suspension mobility and fluctuations but higher ord er reflections produce worse results. Although the effects of pair int eractions are noticeable, the major result is that pair interactions e ven for quite thick double layers are not large. (C) 1997 Academic Pre ss.