Solvent‐mediated nonelectrostatic ion–ion interactions predicting anomalies in electrophoresis

Abstract

We study the effects of solvent-mediated nonelectrostatic ion-ion interactions on electrophoretic mobility of a charged spherical particle. To this end, we consider the case of low surface electrostatic potential resulting in the linearization of the governing equations, which enables us to deduce a closed-form analytical solution to the electrophoretic mobility. We subsequently compare our results to the standard model using Henry's approach and report the changes brought about by the nonelectrostatic potential. The classical approach to determine the electrophoretic mobility underpredicts the particle velocity when compared with experiments. We show that this issue can be resolved by taking into account nonelectrostatic interactions. Our analysis further reveals the phenomenon of electrophoretic mobility reversal that has been experimentally observed in numerous previous studies.

Electrophoretic motion of a non-uniformly charged particle in a viscoelastic medium in thin electrical double layer limit

“…The resulting balances are as follows (Anderson 1985; Ohshima 2006; Goswami et al. 2017): It is important to note here that the above ‘force-free’ conditions only remain valid in an unbounded medium, as previously noted by Yariv (2006). Presence of a wall sufficiently close to the particle may change the force balance on the same.…”

“…As such, the momentum equation at any order of may be expressed in terms of as follows (Leal 2007; Goswami et al. 2017): where (Leal 2007), ; and .…”

“…2013; Schnitzer & Yariv 2014; Goswami et al. 2017), which may or may not contain ions in the form of electrolytes (Saville 1977; Ohshima 2006). This phenomenon has been a prominent area of research over decades owing to its wide gamut of applications such as colloid science (Ohshima 2006; Khair, Posluszny & Walker 2012) and separation of particles (Ghosal 2006), DNA analysis (Khair & Squires 2009), gel electrophoresis (Babnigg & Giometti 2004), particle deposition (Besra & Liu 2007) among many others.…”

“…Electrophoresis is characterized as the motion of charged particles under the action of externally imposed electric fields in a liquid medium (Levich 1962;Saville 1977;Anderson 1985;Ohshima 1996;Yariv & Brenner 2003;Ohshima 2006;Khair & Squires 2009;Schnitzer et al 2013;Schnitzer & Yariv 2014;Goswami et al 2017), which may or may not contain ions in the form of electrolytes (Saville 1977;Ohshima 2006). This phenomenon has been a prominent area of research over decades owing to its wide gamut of applications such as colloid science (Ohshima 2006;Khair, Posluszny & Walker 2012) and separation of particles (Ghosal 2006), DNA analysis (Khair & Squires 2009), gel electrophoresis (Babnigg & Giometti 2004), particle deposition (Besra & Liu 2007) among many others.…”

The effect of the finite size of ions and Debye layer overspill on the screened Coulomb interactions between charged flat plates

“…There have been several refinements to the PB equation through the extension of the dilute solution theory to account for the excluded volume between ions using statistical mechanics or by minimization of entropic contribution of equal‐sized ions and solvent molecules to the free energy functional, based on continuum mean‐field theory and lattice‐gas approximation in recent years. Numerous studies in the literature have subsequently addressed such steric interactions in electrokinetic transport . Additionally, the inclusion of steric hindrance due to the finite‐size of ions can amplify the EDL charge expulsion beyond that caused by the end effects, especially for a strong EDL overlap.…”