Diffusiophoresis of a Soft, Charge-Regulated Particle in a Solution Containing Multiple Ionic Species

   The diffusiophoresis of a soft, charged-regulated particle comprising a rigid core and a polyelectrolyte (PE) layer in an aqueous electrolyte solution containing multiple ionic species is modeled theoretically. We show that the diffusiophoretic behavior of such particle can be different appreciably from that of a rigid particle. For example, both the sign and the magnitude of the diffusiophoretic mobility of a soft particle can vary with the friction coefficient of its PE layer. In addition, if this coefficient is sufficient large, the particle always moves toward the opposite direction as that of the applied concentration gradient, regardless of the value of pH. The type of particle considered covers a wide class of colloids and the conditions assumed are more realistic than those made in previous studies, the results obtained provide valuable and necessary information for interpretation of experimental data and design diffusiophoresis devices.