Joule heating effects on electrokinetic flows with conductivity gradients

Song, Lei; Yu, Liandong; Brumme, Christian; Shaw, Ryan; Zhang, Cheng; Xuan, Xiangchun

doi:10.1002/elps.202000264

Cited by 12 publications

(11 citation statements)

References 55 publications

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“…It becomes even more complicated if one or all of the fluids become complex fluids. The author's group [189] has recently studied the effects of Joule heating on electrokinetic flows of Newtonian fluids with electric conductivity gradients, where the induced temperature rise was found to suppress the electrokinetic instability [190]. In another study, the author's group ob-served elastic instabilities in the DC electroosmotic flow of two identical non-Newtonian fluids through a microchannel T-junction [191].…”

Section: Current Idep Microdevices Have Been Limited To Workmentioning

confidence: 99%

Review of nonlinear electrokinetic flows in insulator‐based dielectrophoresis: From induced charge to Joule heating effects

Xuan

2021

Electrophoresis

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Insulator‐based dielectrophoresis (iDEP) has been increasingly used for particle manipulation in various microfluidic applications. It exploits insulating structures to constrict and/or curve electric field lines to generate field gradients for particle dielectrophoresis. However, the presence of these insulators, especially those with sharp edges, causes two nonlinear electrokinetic flows, which, if sufficiently strong, may disturb the otherwise linear electrokinetic motion of particles and affect the iDEP performance. One is induced charge electroosmotic (ICEO) flow because of the polarization of the insulators, and the other is electrothermal flow because of the amplified Joule heating in the fluid around the insulators. Both flows vary nonlinearly with the applied electric field (either DC or AC) and exhibit in the form of fluid vortices, which have been utilized to promote some applications while being suppressed in others. The effectiveness of iDEP benefits from a comprehensive understanding of the nonlinear electrokinetic flows, which is complicated by the involvement of the entire iDEP device into electric polarization and thermal diffusion. This article is aimed to review the works on both the fundamentals and applications of ICEO and electrothermal flows in iDEP microdevices. A personal perspective of some future research directions in the field is also given.

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Section: Current Idep Microdevices Have Been Limited To Workmentioning

confidence: 99%

Review of nonlinear electrokinetic flows in insulator‐based dielectrophoresis: From induced charge to Joule heating effects

Xuan

2021

Electrophoresis

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“…S1 in the supporting information shows the FEM element size and meshing around the electrode edges. Three modules were coupled with each other and simulated simultaneously under specific boundary conditions using the Multiphysics software COMSOL [33]. The first module was the electric current module which was used to solve Poisson's equation to obtain the electric field distribution.…”

Section: Simulation Modelmentioning

confidence: 99%

Assembly of long carbon nanotube bridges across transparent electrodes using novel thickness‐controlled dielectrophoresis

et al. 2021

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The assembly of carbon nanotubes (CNTs) across planner electrodes using dielectrophoresis (DEP) is one of the standard methods used to fabricate CNT-based devices such as sensors. The medium drag velocity caused by electrokinetic phenomena such as electrothermal and electroosmotic might drive CNTs away from the deposition area. This problem becomes critical at large-scale electrode structures due to the high attenuation of the DEP force. Herein, we simulated and experimentally validated a novel DEP setup that uses a top glass cover to minimize the medium drag velocity. The simulation results showed that the drag velocity can be reduced by 2-3 orders of magnitude compared with the basic DEP setup. The simulation also showed that the optimum channel height to result in a significant drag velocity reduction was between 100 μm and 240 μm. We experimentally report, for the first time, the assembly and alignment of CNT bridges across indium tin oxide (ITO) electrodes with spacing up to 125 μm. We also derived an equation to optimize the CNT's concentration in suspensions based on the electrode gap width and channel height. The deposition of long CNTs across ITO electrodes has potential use in transparent electronics and microfluidic systems.

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“…Controlling the electrical conductivity of CNT solutions by adjusting the surfactant concentration is one of the current challenges to avoid the occurrences of electrothermal phenomena in DEP systems, such as the joule heating effect and medium circulation due to the heat convection . Furthermore, solutions with high electrical conductivity allow more carriers to pass through the circuit, which might damage the microelectrodes at low frequencies or break the CNT connections across the electrode gaps .…”

Section: Introductionmentioning

confidence: 99%

Optimization of Surfactant Concentration in Carbon Nanotube Solutions for Dielectrophoretic Ceiling Assembly and Alignment: Implications for Transparent Electronics

et al. 2022

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Surfactants such as sodium dodecyl sulfate (SDS) are used to improve the dispersity of carbon nanotubes (CNTs) in aqueous solutions. The surfactant concentration in CNT solutions is a critical factor in the dielectrophoretic (DEP) manipulation of CNTs. A high surfactant concentration causes a rapid increase in the solution conductivity, while a low concentration results in undesirably large CNT bundles within the solution. The increase in the solution conductivity causes drag velocity that obstructs the CNT manipulation process due to the electrothermal forces induced by the electric field. The presence of large CNT bundles is undesirable since they degrade the device performance. In this work, mathematical modeling and experimental work were used to optimize the concentration of the SDS surfactant in multiwalled carbon nanotube (MWCNT) solutions. The solutions were characterized using dynamic light scattering (DLS) and ultraviolet− visible spectroscopy (UV−Vis) analysis. We found that the optimum SDS concentration in MWCNT solutions for the successful DEP manipulation of MWCNTs was between 0.1 and 0.01 wt %. A novel DEP configuration was then used to assemble MWCNTs across transparent electrodes. The configuration was based on ceiling deposition, where the electrodes were on top of a droplet. The newly proposed configuration reduced the drag velocity and prevented the assembly of large MWCNT bundles. MWCNTs were successfully assembled and aligned across interdigitated electrodes (IDEs). The assembly of MWCNTs from aqueous solutions across transparent electrodes has potential use in future transparent electronics and sensor devices.

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Joule heating effects on electrokinetic flows with conductivity gradients

Cited by 12 publications

References 55 publications

Review of nonlinear electrokinetic flows in insulator‐based dielectrophoresis: From induced charge to Joule heating effects

Review of nonlinear electrokinetic flows in insulator‐based dielectrophoresis: From induced charge to Joule heating effects

Assembly of long carbon nanotube bridges across transparent electrodes using novel thickness‐controlled dielectrophoresis

Optimization of Surfactant Concentration in Carbon Nanotube Solutions for Dielectrophoretic Ceiling Assembly and Alignment: Implications for Transparent Electronics

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