Electrophoretic mobility of a spherical nanoparticle in a nanochannel

Abstract

Numerical simulation is used to calculate accurately the electrophoretic mobility of a charged spherical nanoparticle confined in a nanochannel, under a weakly applied electric field. Classic models for electrophoretic mobility are valid only in the linear regime of small particle zeta potential, and for an unbounded fluid domain. However, these models fail to predict the electrophoretic mobility measured experimentally in bounded nanochannels. We adopt asymptotically expanded formulations and solve the fully coupled equations on a 3D finite element domain. Factors affecting particle mobility include electrolyte concentration, channel size, and zeta potentials on both the particle surface and channel walls. Specifically, spherical particles are examined with diameters 2a = 10 and 50 nm, in a 100 nm high channel. The non-dimensional electric double layers were varied between 0.1 < κa < 100. The results indicate that the mobility of a particle located at the nanochannel centerline agrees to within 1% of the average mobility of a particle distributed transversely throughout the nanochannel. Furthermore, confinement by the nanochannel walls was found to affect greatly nanoparticle mobility. As a result, it is feasible to use nanochannels to separate two different size nanoparticles, even when the particles have equal zeta potentials. Finally, a new method is proposed to estimate accurately particle and wall zeta potentials by contrasting the observed differences in mobility between observed in two different height channels. C 2014 AIP Publishing LLC. [http://dx.

Electrophoretic mobility of spherical particles in bounded domain

“…Note that we consider the particle locates at the center plane of the channel, because the mobility calculated at the center plane is a good approximation to the average mobility of the particle at different locations [1]. The subscript "0" and "1" correspond to electrostatic and perturbed states, respectively.…”

“…The subscript "0" and "1" correspond to electrostatic and perturbed states, respectively. In this study we consider the particle locates at the center plane of the channel, because the mobility calculated at the center plane is a good approximation to the average mobility [1]. Note that we consider the particle locates at the center plane of the channel, because the mobility calculated at the center plane is a good approximation to the average mobility of the particle at different locations [1].…”

“…Therefore, the electro-osmotic background flow and the electrophoretic particle motion must be solved simultaneously to include the effect of EDL overlap [1]. Borate buffer solutions of pH = 9 with 5, 10 and 50 mM concentrations are used as electrolyte solutions, and the wall zeta potential was estimated by current monitoring.…”

“…Recently, we developed an improved numerical model to account for the effect of both bounded domains as well as high surface charge [1]. In experiments, the particle velocity is usually measured in a fluidic channel under an external applied electric field.…”

“…In the current study, we improve our steady-state model [1] to consider multiple nonsymmetric electrolytes. Next, we compare the measured particle mobility from the experimental work of Semenov et al [2], Napoli et al [3], and Wynne et al [4] to determine the corresponding particle zeta potential.…”