Characterization of the Nonlinear Electrophoretic Behavior of Colloidal Particles in a Microfluidic Channel

Abstract

Contemporary findings in the field of insulator-based electrokinetics have demonstrated that in systems under the influence of direct current (DC) fields, dielectrophoresis (DEP) is not the main electrokinetic mechanism responsible for particle manipulation but rather the sum of electroosmosis, linear and nonlinear electrophoresis. Recent microfluidic studies have brought forth a methodology capable of experimentally estimating the nonlinear electrophoretic mobility of colloidal particles. This methodology, however, is limited to particles that fit two conditions: (i) the particle charge has the same sign as the channel wall charge and (ii) the magnitude of the particle ζ-potential is lower than that of the channel wall. The present work aims to expand upon this methodology by including particles whose ζ-potential has a magnitude larger than that of the wall, referred to as “type 2” particles, as well as to report findings on particles that appear to still be under the influence of the linear electrophoretic regime even at extremely high electric fields (∼6000 V/cm), referred to as “type 3” particles. Our findings suggest that both particle size and charge are key parameters in the determination of nonlinear electrophoretic properties. Type 2 microparticles were all found to be small (diameter ∼ 1 μm) and highly charged, with ζ-potentials above −60 mV; in contrast, type 3 microparticles were all large with ζ-potentials between −40 and −50 mV. However, it was also hypothesized that other nonconsidered parameters could be influencing the results, especially at higher electric fields (>3000 V/cm). The present work also aims to identify the current limitations in the experimental determination of μEP,NL and propose a framework for future work to address the current gaps in the evolving topic of nonlinear electrophoresis of colloidal particles.

Capillary Electrophoresis as a Complementary Analytical Tool for the Separation and Detection of Nanoplastic Particles

“…It is important to note that there are two distinct regimes of nonlinear electrophoretic migration; the particles in this study followed the cubic regime, as described in eq . v normale , nl = μ normale , nl E 3 where μ e,nl is the mobility of the nonlinear electrophoresis velocity, which has been recently characterized for biological and synthetic particles, including viruses. ,,,− The detailed explanation on how the appropriate regime for nonlinear electrophoretic migration was determined is included in the supporting material (eqs S1–S6 and e ). ,,, CE experiments at higher electric field strengths (Table ) were performed to ensure the presence of nonlinear electrophoresis, as this phenomenon is significant only at higher electric fields . The process for characterizing both the velocity ( v e,nl ) and mobility (μ e,nl ) of the particles under nonlinear electrophoresis is described below ,,, v normale , nl = v CE − v eof − v normale , normall μ normale , nl = v e , nl E 3 where v CE is the particle velocity from the CE experiments at high electric fields (see Table ). The mobility of the nonlinear electrophoretic velocity experienced by the particles is reported in Table for eight of the particles included in this study.…”

Manipulating the insulating post arrangement in DC-biased AC-iEK devices to improve microparticle separations

“…The values of ζ P , μ EP,L and μ (3) EP,NL were experimentally assessed for each particle type using PTV experiments (Table 1) employing a channel with a constant cross section. 25,28–30,38 A three-step EK injection process was used to introduce a defined volume of the microparticle mixture into the iEK device. 39…”

“…Furthermore, the recent reports on the importance of nonlinear electrophoresis (EP NL ) in iEK systems, 25–31 have enabled the design of new separation strategies, employing both DC potentials 14,32 and low-frequency AC potentials. 24 Inclusion of EP NL effects is crucial for designing effective iEK separation strategies, as neglecting these effects results in inaccurate predictions of separation performance.…”

Zeta potential characterization using commercial microfluidic chips

“…17 The electrophoretic component of the velocity has a linear component (proportional to E) and non-linear component (proportional to E 3 or E 3/2 ). [25][26][27] The nonlinear component can be ignored if the Peclet number is smaller or equal to 1 and the Dukhin number is much smaller than 0.1. 28,29 The Peclet number corresponds to the ratio of the convective to the diffusive movement of the ions located close to the surface of the particle, while the Dukhin number refers to the ratio of the surface conductivity to the bulk conductivity of the medium.…”