Importance of Boundary on the Electrophoresis of a Soft Cylindrical Particle

We modeled the electrophoresis of a soft cylindrical particle comprising a rigid core and a polyelectrolyte layer along the axis of a long, cylindrical pore, and the applicability of the model proposed is verified by the experimental data available in the literature. Previous analysis is extended to the case where the effects of double-layer polarization (DLP) and electroosmotic flow (EOF) can be significant. We show that the interaction between the particle's double layer and the pore, the competition between the effective charge density and the local electric field strength, and the presence of EOF yield interesting and significant results. For example, if EOF is absent, the particle mobility as the bulk salt concentration varies depends highly on the amount of fixed charge of its polyelectrolyte layer: if that amount is small, the mobility decreases monotonically with increasing bulk salt concentration, and if that amount is large, then the mobility shows a local maximum. At a high bulk salt concentration, the longer the particle the larger is its mobility, that trend is reversed if it is low. That local minimum vanishes when the boundary effect is important. If the pore is positively charged, a positively charged particle can be driven to the direction opposite to that of the applied electric field. These provide necessary information for the design of electrophoresis devices.