Electrophoresis of a charge-regulated soft sphere: importance of effective membrane charge

The importance of the effective membrane charge on the electrophoretic behavior of a soft spherical particle comprising a rigid core and a charge-regulated membrane layer, mimicking both inorganic and biological colloids, is investigated. The mobility of the particle is simulated under various conditions by varying the double layer thickness, the bulk solution pH, and the charged conditions of the membrane layer. Several interesting electrophoretic behaviors that are of practical significance, are observed. For example, the particle mobility can be controlled by adjusting its properties such as the ratios of (acidic equilibrium constant/basic equilibrium constant) and (concentration of acidic functional groups/that of basic functional groups). Double layer polarization (DLP) is found to render the soft particle having behaviors different from those of the corresponding rigid particle. For instance, DLP can either be intensified or weakened, depending upon the strength of the hydrodynamic force and the electric force acting on the membrane layer. As the bulk electrolyte concentration increases in a certain range, because double layer shrinks into the membrane layer, its effective charge density increases, so is the particle mobility.