Extended Abstracts of the Second Asian Conference on Thermal Sciences, 2nd ACTS
October 3-7, 2021, Online
ACTS- 1057

PARTICLES SEPARATION AND ALIGNMENT TECHNIQUE IN
MICROCHANNEL FLOW USING DIELECTROPHORETIC FORCE
Kazuya Tatsumi*, Renato Honma, Reiko Kuriyama, Kazuyoshi Nakabe
Kyoto University, Kyotodaigaku-katsura, Nishikyo-ku, Kyoto 615-8540, Japan

KEY WORDS: Particle alignment, dielectrophoretic force, microchannel, Timing control. Particle separation
1. INTRODUCTION
Controlling the position of the particles, the interval (space) between the particles, and the timing when they
pass the specific location in the microchannel is an important technique to perform the sensing, sorting, andencapsulation accurately in microfluidic devices [1-3]. We developed a technique which can control theinterval (space), velocity and timing of the particles in microchannel flow by exerting dielectrophoretic force
on the particles periodically over time and space using the boxcar-type electrode. Regions ofdielectrophoretic force accelerating and decelerating the particles were formed periodically in the streamwise
direction. The force was activated periodically over time by turning the applied voltage on and off. We
showed that the combination of these two schemes could align the particles and Jurket cells with equal space
and intervals [4, 5]. In this paper, we will demonstrate the performance of the proposed technique using
boxcar-electrodes: especially, separation of the two particles located within one periodic region of theboxcar-electrode will be discussed. Numerical simulations and measurements for 12μm polystyrene particles
flowing in the boxcar electrode region are conducted to visualize the particle separation effect of twoparticles located in the same periodic region of the boxcar electrode, analyze the particle motion during
separation, and evaluate the particle alignment performance [6].

2. METHODS
Figure 1 show the schematic and dimensions of the microchannel and electrodes. The rail-electrodes andboxcar-electrodes were patterned on the bottom wall, and the ground electrode covered the top wall of themain channel. The particles supplied from the center inlet of the sheath-type flow focus on the centerline in
the rail-electrode region by the dielectrophoretic force FDEP, and flow in to the boxcar-electrodes.
The flow rate was 3.9 L/min, giving an average flow velocity of 6.4 mm/s. The Reynolds number based on
the channel hydraulic diameter and particle size of 12 m in this case, were 0.37 and 0.055, respectively.
We applied an alternating current to the boxcar-electrode using a function generator with a peak-to-peakvoltage of Vp-p = 16.8 V and frequency of fV = 10 MHz. This voltage was turned on and off periodically witha frequency of fon-off = 125 Hz. The duty rate of the applied voltage was fixed at 50%.
Polystyrene microparticles with diameters of 12 m (Thermoscientific Co., 4212A) were used in themeasurements. The particles were mixed in Milli-Q water at a concentration of 0.2 %. Sodium lauryl sulfate

Fig. 1 Photograph and schematic of the microchannel and boxcar-type electrodes.
*Corresponding Author: tatsumi@me.kyoto-u.ac.jp

ACTS-1057

Fig. 2: (a) Photograph of particles at inelet of the boxcar-electrode region. (b) Snapshots of the two particles locatedin the same periodic area separating and align in the downstream region. Numbers shown over the boxes show thesame spatial box. (c) Particles at outlet (aligned). (d) Motion trajectory of the two particles initially located in thesame periodic region (computation). (e) Probability density function of the number of particles located in the same
periodic region (period).

was added to the solution at a concentration of 0.1 wt% to prevent the adhesion of particles to the wall.
In the computation, the equation of motion of the particles was solved considering the effects of the FDEP andthe hydrodynamic forces exerted on the particles [4, 5]. The multipole method using a third-order Clausius–
Mossotti (CM) function was applied to calculate the FDEP distribution from the electric field gradients. The
hydrodynamic forces were based on the Stokes force for spheres, to which the models considering the effectsof the velocity gradient and the wall were applied.

3. RESULTS AND DISCUSSION
Figures 2 (a)-(c) show the photographs of the particles entering the boxcar-electrode region, the motion of
two particles located in a periodic region of the boxcar-electrode, and particles at the outlet. The particles
randomly are aligned by the boxcar-electrodes and flows over the outlet region with even space. In Fig. 2 (b),the two particles approach, contact, and separate having the particle initially located in downstream side
move to the upstream periodic region. The computation gave the same results as shown in Fig. 2 (d): theupstream particle is accelerated while the downstream particle reduces its speed due to the FDEP, and theupstream particle pass over the other particle. The downstream particle is strongly decelerated and remains inthe same spatial periodic region which makes it changing its period to the next cycle. The particle will follow
the same pattern until it reaches a vacant one. Thus, each particle is located in different periodic region, andall particles align with even space equal to the streamwise pitch of the boxcar-electrode. The accuracy of thealignment can be confirmed by the probability density function shown in Fig. 2 (e).

4. CONCLUSIONSThe particles with random space entering the boxcar-electrode region could be aligned in the downstream ateven space. The boxcar-electrode could separate two particles located in the same periodic region, anddisperse them over the boxcar-electrode leading to the accurate alignment of 100% yield.

ACKNOWLEDGMENT
This work was supported by the JSPS KAKENHI Grant Number 17K18841.

REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]

Abate, A. R., Chen, C-H., Agresti, J. J., Weitz, D. A., “Beating Poisson encapsulation statistics using close-packed ordering”,
Lab Chip., 9, pp. 2628-2631, (2009).
Edd, J. F., Di Carlo, D., Humphry, K. J., Köster, S., Irimia, D., Weitzb, D. A., Toner, M., “Controlled encapsulation of singlecells into monodisperse picolitre drops”, Lab Chip., 8, pp. 1262-1264, (2008).
Chen, T., Wu, T.-H., Kung, Y.-C., Teitell, M. A., Chiou, P.-Y., “3D pulsed laser-triggered high-speed microfluidic
fluorescence-activated cell sorter”, Analyst, 24, pp. 7308-7315, (2013).
Tatsumi, K., Kawano, K., Shintani, H., Nakabe, K., “Particle timing control and alignment in microchannel flow by applying
periodic force control using dielectrophoretic force”, Analytical Chemistry, 91, pp. 6462-6470, (2019).
Tatsumi, K., Noma, A., Honma, R., Kuriyama, R., Nakabe, K., “Timing and Spacing Control in Microchannel Flow by
Applying Periodic Force over Space and Time”, Microfluidics and Nanofluidics, 25, p. 15, (2021).
Honma, R., Tatsumi, R., Kuriyama, R., Nakabe, K., “Particle separation and alignment technique in microchannel flow bydielectrophoretic force using boxcar-type electrode”, Trans. JSME, 86 (890), 20-00117, (2020).