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Modeling of dielectrophoresis in micro and nano systems
KTH, School of Engineering Sciences (SCI), Mechanics.
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.
Series
Trita-MEK, ISSN 0348-467X ; 2008:05
Keyword [en]
Dielectrophoresis, micro particle, molecular dynamics, single-walled carbon nanotubes, hydrodynamics, particle-particle interaction, superimposed, multi-step
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-4784ISBN: 978-91-7415-008-7 (print)OAI: oai:DiVA.org:kth-4784DiVA: diva2:13943
Public defence
2008-06-11, Sal D2, KTH, Lindstedtsvägen 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-08-20Bibliographically approved
List of papers
1. Superpositioned dielectrophoresis for enhanced trapping efficiency
Open this publication in new window or tab >>Superpositioned dielectrophoresis for enhanced trapping efficiency
2005 (English)In: Electrophoresis, ISSN 0173-0835, E-ISSN 1522-2683, Vol. 26, no 22, 4252-4259 p.Article in journal (Refereed) Published
Abstract [en]

One of the major applications for dielectrophoresis is selective trapping and fractionation of particles. If the surrounding medium is of low conductivity, the trapping force is high, but if the conductivity increases, the attraction decreases and may even become negative. However, high-conductivity media are essential when working with biological material such as living cells. In this paper, some basic calculations have been performed, and a model has been developed which employs both positive and negative dielectrophoresis in a channel with interdigitated electrodes. The finite element method was utilized to predict the trajectories of Escherichia coli bacteria in the superpositioned electrical fields. It is shown that a drastic improvement of trapping efficiency can be obtained in this way, when a high conductivity medium is employed.

Keyword
alternating current electrokinetics; dielectrophoresis; Escherichia coli; field superposition; trajectory analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5516 (URN)10.1002/elps.200500068 (DOI)000233740900003 ()2-s2.0-28244475356 (Scopus ID)
Note
QC 20100820Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2017-11-21Bibliographically approved
2. Multi-step dielectrophoresis for separation of particles
Open this publication in new window or tab >>Multi-step dielectrophoresis for separation of particles
2006 (English)In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1131, no 1-2, 261-266 p.Article in journal (Refereed) Published
Abstract [en]

A new concept for separation of particles based on repetitive dielectrophoretic trapping and release in a flow system is proposed. Calculations using the finite element method have been performed to envision the particle behavior and the separation effectiveness of the proposed method. As a model system, polystyrene beads in deionized water and a micro-flow channel with arrays of interdigited electrodes have been used. Results show that the resolution increases as a direct function of the number of trap-and-release steps, and that a difference in size will have a larger influence on the separation than a difference in other dielectrophoretic properties. About 200 trap-and-release steps would be required to separate particles with a size difference of 0.2%. The enhanced separation power of dielectrophoresis with multiple steps could be of great importance, not only for fractionation of particles with small differences in size, but also for measuring changes in surface conductivity, or for separations based on combinations of difference in size and dielectric properties.

Keyword
dielectrophoresis; dielectrophoretic mobility; resolution; selectivity; particle separation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8578 (URN)10.1016/j.chroma.2006.07.022 (DOI)000241429000027 ()2-s2.0-33749267590 (Scopus ID)
Note
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-11-08Bibliographically approved
3. Simulation of dielectrophoretic motion of microparticles using a molecular dynamics approach
Open this publication in new window or tab >>Simulation of dielectrophoretic motion of microparticles using a molecular dynamics approach
2006 (English)In: 4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006, 2006, 1-10 p.Conference paper, Published paper (Refereed)
Abstract [en]

We model and simulate dielectrophoresis of microscale particles using the finite element method. A soft sphere system molecular dynamics model is presented, which solves a set of equations for the motion of every particle. The model couples most of the significant forces, i.e. the dielectrophoresis (DEP) forces, the particle-particle electrostatic forces, particle-particle interfacial repulsive forces, particle-wall repulsive forces and the hydrodynamic forces in Stokes flow. Since the system of equations is stiff, an implicit scheme is used. To obtain the particle trajectories, a constant time-step is applied. We present some numerical tests computing hydrodynamic force, electrostatic force and DEP force using our model, including simulated trapping of particles in a micro channel by dielectrophoresis. The results are in agreement with the theories and the experimental observations.

Keyword
Computer simulation; Electrostatics; Equations of motion; Finite element method; Mathematical models; Particles (particulate matter); Dielectrophoresis (DEP) forces; Electrostatic forces; Interfacial repulsive forces; Stokes flows
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-5518 (URN)000249885500001 ()2-s2.0-33847006942 (Scopus ID)978-0-7918-4760-2 (ISBN)
Conference
4th International Conference on Nanochannels, Microchannels and Minichannels, ICNMM2006; Limerick; Ireland
Note

QC 20100820

Available from: 2006-03-22 Created: 2006-03-22 Last updated: 2014-11-18Bibliographically approved
4. Electrothermal flow in dielectrophoresis of single-walled carbon nanotubes
Open this publication in new window or tab >>Electrothermal flow in dielectrophoresis of single-walled carbon nanotubes
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 76, no 4, 045419-1-045419-5 p.Article in journal (Refereed) Published
Abstract [en]

We theoretically investigate the impact of the electrothermal flow on the dielectrophoretic separation of single-walled carbon nanotubes (SWNTs). The electrothermal flow is observed to control the motions of semiconducting SWNTs in a sizable domain near the electrodes under typical experimental conditions, therefore helping the dielectrophoretic force to attract semiconducting SWNTs in a broader range. Moreover, with the increase of the surfactant concentration, the electrothermal flow effect is enhanced, and with the change of frequency, the pattern of the electrothermal flow changes. It is shown that under some typical experimental conditions of dielectrophoretic separation of SWNTs, the electrothermal flow is a dominating factor in determining the motion of SWNTs.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8580 (URN)10.1103/PhysRevB.76.045419 (DOI)000248540000113 ()2-s2.0-34547111313 (Scopus ID)
Note
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-08-20Bibliographically approved
5. Numerical calculation of the dielectrophoretic force on a slender body
Open this publication in new window or tab >>Numerical calculation of the dielectrophoretic force on a slender body
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.

Keyword
Carbon nanotube, Dielectrophoretic force, Induced charge density, Slender body, walled carbon nanotubes, stokes flow, separation, particles
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-18280 (URN)10.1002/elps.200800599 (DOI)000264471900012 ()2-s2.0-65949088589 (Scopus ID)
Note
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
6. Dielectric properties of water inside single-walled carbon nanotubes
Open this publication in new window or tab >>Dielectric properties of water inside single-walled carbon nanotubes
(English)Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8582 (URN)
Note
QC 20100820Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-08-20Bibliographically approved

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