Diffusiophoresis of a Charged Dielectric Fluid Droplet in a Cylindrical Pore in the Presence of Diffusion Potential

We conduct a theoretical analysis on the diffusiophoretic motion of a dielectric droplet in a cylindrical pore in the presence of an induced diffusion potential, such as in the NaCl electrolyte solution. The fundamental electrokinetic governing equations are solved using a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to handle the irregular solution domain. The impact of boundary confinement effect on droplet mobility is examined in detail. Interesting electrokinetic phenomena are found in this work, such as mobility reversal in narrow cylindrical pores with the droplet moving against the direction expected based on the classical Coulomb electrostatic law due to the strong boundary confinement effect. Two critical points of κa are found, where κ is the electrolyte strength and a is the droplet radius. The spinning orientation on the droplet surface changes each time past them. The profound boundary confinement effect, both electrostatically and hydrodynamically, is responsible for these peculiar phenomena. The results presented here has direct applications in microfluidic and nanofluidic operations as well as drug delivery applications.