Electrokinetic actuation of an uncharged polarizable dielectric droplet in charged hydrogel medium

Abstract

Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non‐homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst–Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free‐solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gel medium.

Gel Electrophoresis of a Hydrophobic Liquid Droplet with an Equipotential Slip Surface

“…Besides, Barman et al studied the GE electrophoresis of nonconducting charged liquid droplets embedded in a charged hydrogel medium. Recently, they further extended their numerical study on the induced charge electrophoresis of uncharged and nonconducting liquid droplets through the charged hydrogel medium . In a recent review, Liu et al address the most recent developments of the electric field response of the liquid droplet migrating through the free-electrolyte or quenched hydrogel medium.…”

“…Considering this point, we have further derived the approximate form of the mobility expressions under various electrohydrodynamic conditions and found them to be in excellent agreement with the exact results. The merit of this work is therefore the elaboration of an original analytical expression for the electrophoretic mobility of the liquid droplet embedded in a polymeric hydrogel, which can be used as an analytical tool for GE measurements, such as separation, characterization, and size distribution of nanoemulsions, , and to study the electric field response on the emulsion-filled hydrogel. − …”

“…Recently, they further extended their numerical study on the induced charge electrophoresis of uncharged and nonconducting liquid droplets through the charged hydrogel medium. 57 In a recent review, Liu et al 58 address the most recent developments of the electric field response of the liquid droplet migrating through the freeelectrolyte or quenched hydrogel medium. Besides the theoretical/numerical study on the gel electrophoresis of liquid droplets, Afuwape and Hill 59 made an extensive experimental study on the electrokinetics of nanoemulsion drops in polyacrylamide hydrogels under an oscillatory electric field.…”