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Numerical calculation of the dielectrophoretic force on a slender body
Department of Process Technology, SINTEF Materials and Chemistry.
Department of Mechanical Engineering, The University of Tokyo.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-3336-1462
2009 (English)In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 30, no 5, 831-838 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, a model is proposed to numerically calculate the dielectrophoretic (DEP) force acting on a straight slender body in a non-uniform electric field. The induced charges are assumed to be located along the centerline of the slender body. By enforcing the boundary conditions at the interfaces of the two dielectrics, an integral equations system is obtained with the induced charge densities as unknowns. Based on the calculated induced charge densities, expressions to calculate the DEP force and torque are obtained. The calculated induced charge density of a prolate ellipsoid under a uniform electric field is compared with the analytic solution and an excellent agreement is achieved. The smaller the slenderness (the ratio of maximum radius to length of the slender body), the smaller the error is. The DEP force that a prolate ellipsoid experiences in a general electric field is numerically calculated and compared with the results obtained by the commonly accepted effective dipole moment method. The current model is expected to possess higher accuracy than the effective dipole moment method and to demand less calculation work than the Maxwell stress tensor method.

Place, publisher, year, edition, pages
2009. Vol. 30, no 5, 831-838 p.
Keyword [en]
Carbon nanotube, Dielectrophoretic force, Induced charge density, Slender body, walled carbon nanotubes, stokes flow, separation, particles
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-18280DOI: 10.1002/elps.200800599ISI: 000264471900012ScopusID: 2-s2.0-65949088589OAI: diva2:336326
QC 20100525. Tidigare titel: Numerically calculate dielectrophoretic force of slender bodyAvailable from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-01-12Bibliographically approved
In thesis
1. Modeling of dielectrophoresis in micro and nano systems
Open this publication in new window or tab >>Modeling of dielectrophoresis in micro and nano systems
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents models and simulations of dielectrophoretic separation of micro and nano particles. The fluid dynamics involved and the dielectric properties of water inside single-walled carbon nanotube are studied as well.

Based on the effective dipole moment method, the particle dynamic model focuses on the translational motions of micro particles. The hydrodynamic force between the particles and the particle-particle electrostatic interactions are considered as well. By comparing the dimensionless parameters, the dominating force can be determined. Based on a simplified version of the particle dynamic model, two numerical simulations are carried out to predict the efficiency of dielectrophoretic separation of micro size particles. The first calculation suggests a strategy to improve the trapping efficiency of E.coli bacteria by applying superimposed AC electric fields. The second calculation discusses the concept of mobility and improves the separation rate of particles by a multi-step trapping-releasing dielectrophoresis strategy.

The model is extended down scale to calculate the separation of metallic and semiconducting single-walled carbon nanotubes by the modified effective dipole moment method for prolate ellipsoids. The steeply changed gradient of electric field results in the local joule heating therefore creates gradient of dielectric properties in the solution. As a result, certain pattern of fluid flow with a considerable strength is created and affects the motion of carbon nanotubes especially close to the electrode gap, which indicates that the so-called electrothermal flow should be considered in designing the experiment to separate single-walled carbon canotubes.

When the length scale of particles is comparable to that of the electrodes, the calculation of dielectrophoretic force by the effective dipole moment is considered not to be accurate since only the electric field in the center point is taken into account. Hence in the thesis a new method based on distributed induced charge is suggested. By approximating a straight slender body as a prolate ellipsoid, the electric field of multiple points along the centerline are all considered in the calculation and the interaction between particles could be concurrently taken care. This method is expected to be an improved method to calculate the dielectrophoretic force of rod-like virus, DNA, nanowires and carbon nanotubes.

The dielectric property of water confined in carbon nanotubes is expected to be dramatically different from that of bulk water. The thesis also contains a molecular dynamics study to reveal the difference also a dependence on the diameter of carbon nanotubes. The results show that along the axial direction, both the static permittivity and the relaxation time are larger than the isotropic bulk water, and in the cross-section plane it is opposite. When the radius of the carbon nanotubes increases, the properties of water inside become closer to the bulk water.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. vii, 46 p.
Trita-MEK, ISSN 0348-467X ; 2008:05
Dielectrophoresis, micro particle, molecular dynamics, single-walled carbon nanotubes, hydrodynamics, particle-particle interaction, superimposed, multi-step
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-4784 (URN)978-91-7415-008-7 (ISBN)
Public defence
2008-06-11, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 10:00
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-08-20Bibliographically approved

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