(505a) Colloidal Dielectric Forces within an Electric Curtain

The electric curtain is a platform first developed by Masuda [1] to lift and transport charged particles, typically in air, and relevant forces have typically been associated with the interaction of the applied electric field with charged particles. However, recent work by our group has demonstrated, contrary to traditional electric curtain theory, that dielectric phenomena is significant for particle manipulation. Preliminary results demonstrate that the magnitude and direction of a manipulated particle is a function of the applied AC frequency.

An electric curtain consists of a series of parallel coplanar electrodes that generate a standing wave (SW) or travelling wave (TW) AC electric field to lift particles from the platform surface and, for the TW case, simultaneously translate them away. This multiphysical system is rich in electrokinetic and mechanical physics; particle motion is governed by particle electrokinetic properties, particle mass, field properties, and medium properties [2-5]. The assumed operation was the manipulation of charged particles via Coulombic forces; particles are either inherently charged or they obtain a net charge via tribocharging or absorption of gaseous ions. However, dielectric phenomena are typically overlooked.

Our simple electric curtain system consists of a printed circuit board (ExpressPCB) with four sets of repeating interdigitated electrodes (0.020 inch width and spacing) where a SW (0^o-180^o-0^o-180^o) or TW (0^o-90^o-180^o-270^o) AC signal was applied with a custom four-channel step-up amplifier. The electrodes were covered with a dielectric of polypropylene tape (ε_r = 2.2-2.36). For preliminary tests Martian dust simulant (JSC MARS-1A, Orbital Technologies Corp.) was used with a particle diameter of 1 mm or smaller with over 50% of the particles (by weight) had diameters greater than 0.25 mm.

The electrokinetic-induced deflection of a suspended AFM cantilever functionalized with a 20 µm diameter borosilicate glass sphere was measured. The cantilever was suspended 34 µm away from the surface and aligned parallel with the electrodes. Its sinusoidal deflection oscillated at twice the applied AC frequency, typical of a dielectric response.

A sample of solid soda lime glass beads (180-212 µm, SLGMS-2.5, Cospheric) coated the surface of the electric curtain platform prior to the activation of a SW or TW field. A high speed camera acquired images showing the interactions and positions of particles relative to the electrode. At 50 Hz particles were repelled for both SW and TW fields. For both scenarios particles experienced either low velocity oscillatory â??rollingâ? and/or rapid projectile motion. Additional experiments showed that the repelled directionality of the particles is a function of the applied AC signal and particle type.

Further understanding of related dielectric phenomena is needed to bridge the disconnect between experimental observations and electrokinetic theory. Future results will advance applications based on such discoveries, including air-based dielectrophoresis systems for selective particle sorting or macroscale â??smart filterâ? applications for particle detection.

References:

1.  â??Confinement and transportation of charged aerosol clouds via electric curtain,â? S. Masuda, K. Fujibayashi, K. Ishida, H. Inada, Electrical Engineering in Japan, 92, 43 (1972).
2. â??Study of dust removal by standing-wave electric curtain for application to solar cells on Mars,â? P. Atten, H.L. Pang, J.-L. Reboud, IEEE Transactions on Industry Applications, 45, 75 (2009).
3. â??Nonlinear dynamics of particles excited by an electric curtain,â? O.D. Myers, J. Wu, J.S. Marshall, Journal of Applied Physics, 114, 154907, (2013)
4. â??Electrodynamic dust shields on the international space station: exposure to the space environment,â? C.I. Calle, P.J. Mackey, M.D. Hogue, M.R. Johansen, H. Yim, P.D. Delaune, J.S. Clements, Journal of Electrostatics, 71, 257 (2013).
5. â??Some techniques on electrostatic separation of particle size utilizing electrostatic traveling-wave field,â? H. Kawamoto, Journal of Electrostatics, 66, 220 (2008).