Importance of Boundary on the Electrophoresis of a Soft Cylindrical Particle

Abstract

We modeled the electrophoresis of a soft cylindrical particle comprising a rigid core and a polyelectrolyte layer along the axis of a long, cylindrical pore, and the applicability of the model proposed is verified by the experimental data available in the literature. Previous analysis is extended to the case where the effects of double-layer polarization (DLP) and electroosmotic flow (EOF) can be significant. We show that the interaction between the particle's double layer and the pore, the competition between the effective charge density and the local electric field strength, and the presence of EOF yield interesting and significant results. For example, if EOF is absent, the particle mobility as the bulk salt concentration varies depends highly on the amount of fixed charge of its polyelectrolyte layer: if that amount is small, the mobility decreases monotonically with increasing bulk salt concentration, and if that amount is large, then the mobility shows a local maximum. At a high bulk salt concentration, the longer the particle the larger is its mobility, that trend is reversed if it is low. That local minimum vanishes when the boundary effect is important. If the pore is positively charged, a positively charged particle can be driven to the direction opposite to that of the applied electric field. These provide necessary information for the design of electrophoresis devices.

Electrophoresis of a soft sphere in a necked cylindrical nanopore

“…The liquid phase is an aqueous KCl solution, implying that z 1 = Àz 2 , a = 1, and Pe 1 = Pe 2 = 0.235. 50…”

“…This arises from the intensification of the local electric field near the particle. 50 Because this effect becomes most significant if the particle's charge density is high and the thickness of EDL is thick, m* increases with increasing ka for smaller ka, and decreases with increasing ka for larger ka. To further understand the effects of the EDL thickness and the surface charge density of a soft particle as it locates within the necked area of the pore, we plot the particle mobility at d/a = 0 versus ka for various values of s à a in Fig.…”

Electrokinetic motion of single nanoparticles in single PDMS nanochannels

“…These conditions can be divided into two branches, including the above-mentioned unbounded environment (Wiersema et al 1966;Ohshima et al 1983;Chen and Keh 1988) and the bonded domain which investigates the channel wall effects on the electrophoretic motion of particles. Particle motion near a flat plane (Keh and Anderson 1985;Keh and Chen 1988;Shugai and Carnie 1999), in rectangular channels (Movahed and Li 2012;Liu et al 2016), cylindrical channels (Keh and Chiou 1996;Hsu and Chen 2007) with the conditions of thick EDL limit (Ennis and Anderson 1997;Hsu et al 2004;Miloh and Boymelgreen 2014), thin EDL limit (O'Brien and Hunter 1981;Keh and Anderson 1985;Keh and Chen 1988;Hsu et al 2012a) and arbitrary EDL thickness (Keh and Hsieh 2008;Chen and Keh 2013;Liu et al 2014) has been studied. The thickness of EDL is dominated by the ionic concentration of the buffer solutions (Li 2004), however, pH values (Hsu et al 2012b;Wang et al 2013) and symmetry or asymmetry property of the ions (O'Brien and White 1978;Semenov et al 2013;Nedelcu and Sommer 2014;Liu et al 2016) also affect the electrophoretic behavior.…”

“…Besides the general low zeta potential assumption (Ennis and Anderson 1997;Shugai and Carnie 1999;Hsu et al 2004), particles with high zeta potential (Wiersema et al 1966;O'Brien and White 1978;Liu et al 2016), arbitrary zeta potential (Keh and Hsieh 2008) and particles with non-uniform zeta potential distribution (Qian et al 2008;Wang and Keh 2009) have also been studied. In addition, electrophoresis models involving neutral particles and dielectric particles (Shugai and Carnie 1999;Miloh and Boymelgreen 2014) and particles made of soft materials Ohshima 1995;Hsu et al 2012a;Chen and Keh 2013;Tseng et al 2013) , porous media (Huang et al 2012;Li and Keh 2016) as well as air bubbles (Schnitzer et al 2014) have been investigated. It is also a fact that in the practical applications, the shape of the particles is diverse.…”

“…It is also a fact that in the practical applications, the shape of the particles is diverse. As a result, modeling of electrophoresis of spherical (Wiersema et al 1966;Keh and Anderson 1985;Keh and Chiou 1996;Ennis and Anderson 1997;Shugai and Carnie 1999;Miloh and Boymelgreen 2014;Liu et al 2016), cylindrical (Hsu and Ku 2005;Hsu et al 2012a), rectangular (Li and Daghighi 2010;Movahed and Li 2012) or spheroidal (Yoon and Kim 1989) particles has been conducted.…”