Polarization behavior of polystyrene particles under direct current and low‐frequency (<1 kHz) electric fields in dielectrophoretic systems

Abstract

The relative polarization behavior of micron and submicron polystyrene particles was investigated under direct current and very low frequency (<1 kHz) alternating current electric fields. Relative polarization of particles with respect to the suspending medium is expressed in terms of the Clausius-Mossotti factor, a parameter of crucial importance in dielectrophoretic-based operations. Particle relative polarization was studied by employing insulator-based dielectrophoretic (iDEP) devices. The effects of particle size, medium conductivity, and frequency (10-1000 Hz) of the applied electric potential on particle response were assessed through experiments and mathematical modeling with COMSOL Multiphysics(®). Particles of different sizes (100-1000 nm diameters) were introduced into iDEP devices fabricated from polydimethylsiloxane (PDMS) and their dielectrophoretic responses under direct and alternating current electric fields were recorded and analyzed in the form of images and videos. The results illustrated that particle polarizability and dielectrophoretic response depend greatly on particle size and the frequency of the electric field. Small particles tend to exhibit positive DEP at higher frequencies (200-1000 Hz), while large particles exhibit negative DEP at lower frequencies (20-200 Hz). These differences in relative polarization can be used for the design of iDEP-based separations and analysis of particle mixtures.

Assessment of Sub-Micron Particles by Exploiting Charge Differences with Dielectrophoresis

“…In contrast, for the larger particles utilized in this study (500 nm and 1 μm in diameter), electrophoretic effects are not as significant since λ D ≤ 0.1. This is in agreement with previous results by our group, where particles with diameter ≤200 nm exhibited positive dielectrophoretic behavior and particles with diameter ≥500 nm showed negative DEP [ 23 ]. However, in that previous report [ 23 ], all particles had a high surface charge.…”

“…A particle that is more polarizable than the suspending medium will migrate towards the regions of higher electric field gradient under positive DEP; while particles with lower polarizability than the medium would migrate away from these regions due to negative DEP [ 22 ]. Particle polarization is a complex phenomenon; many groups have studied the polarization of submicron particles and its relation to particle dielectrophoretic behavior [ 7 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Differences in dielectric properties, such as surface charge, can be exploited to achieve effective particle separation.…”

“…However, the behavior of these particles at low frequencies (<1000 Hz) is still an unexplored area. Insulator-based DEP (iDEP), a dielectrophoretic mode where insulating structures are employed to create non-uniform electric fields [ 31 , 32 ]; usually employs low frequency AC and DC electric potentials to achieve particle manipulation [ 15 , 23 , 33 , 34 , 35 , 36 ]. In iDEP microsystems, particles are exposed to several forces simultaneously (EOF, EP, and DEP), and the resulting particle motion is the net migration caused by the combination of all present forces [ 37 , 38 ].…”

Electrokinetic device design and constraints for use in high conductance solutions

“…Multiphysics simulations on particles are not shown due to insufficient characterization of the dielectric properties of various particles, especially when accounting for their local environment, e.g. double layer effects, although models are being developed to do so . Instead, the simulations are to show the major factors in different device architectures while acknowledging that devices must ultimately be characterized empirically.…”

Self-assembly of micro-particles by electric fields towards optical materials

“…When < 0 or < , DEP is negative, and particles move in the opposite direction of the positive DEP (Figure 2.6 (b)). The velocity exerted on the spherical particle by DEP force is formulated as[76]:…”