Dr. Chehung Wei Profile

Dr. Chehung Wei

Assistant Professor at Tatung Univ

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Publications (3)

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Proceedings Article | 9 September 2008 Paper

The effect of chamber size on collection efficiency and pattern in 3D electroosmosis chip

Chehung Wei, You-Zong Shih, Ching-Chieh Wang

Proceedings Volume 7039, 70391H (2008) https://doi.org/10.1117/12.795735

KEYWORDS: Particles, Electrodes, Ions, Latex, Optical lithography, Dielectrophoresis, Microfluidics, Solids, Chromium, Numerical simulations

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The advantages of using electric fields to manipulate and assemble samples are the ability to control the force exerted on particles and the simplicity of fabrication. Electroosmosis, an electrokinetic effect from the interaction between ions in the electrical double layer and the electric field, has less dependency on material property compared to dielectrophoresis. The critical parameters in electroosmosis are electrical double layer, the strength of electrical field and the flow velocity field. In an attempt to find the correlation among these parameters, a 3D electroosmosis chip is fabricated with different collection chamber size. The chamber size varying from 100 to 1000 μm was defined via photolithography and the size effect on the accumulation efficiency and collection pattern were studied by numerical simulations and experiments. The amine-modified polystyrene fluorescent particles whose average size is 1μm were used for experiments. The results show that the collection efficiency is a combined effect of the strength of the tangential electric field and the flow velocity gradient. As the chamber size decreases, the strength of the tangential field decreases and then increases, but the gradient of flow velocity intensifies. For small chamber size, the tangential electrical field induces greater flow velocity and results in more high velocity region. This explains why the smaller chamber size has better collection efficiency than the larger chamber size. For electroosmosis collection, the size of the chamber is a critical parameter for efficiency consideration.

Proceedings Article | 4 September 2008 Paper

The application of dielectrophoresis on the characterization of electric property in multi-walled carbon nanotubes

Chehung Wei, Cheng-Hou Liang, Ting-You Wei

Proceedings Volume 7037, 703708 (2008) https://doi.org/10.1117/12.795623

KEYWORDS: Dielectrophoresis, Particles, Electrodes, Carbon nanotubes, Curium, Dielectrics, Raman spectroscopy, Numerical simulations, Polarizability, Microfluidics

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Carbon nanotubes have been extensively studied due to their unique property and potential application like field emission. For successful implementation, it is essential to know the properties of carbon nanotubes. In this work, we propose a simple method to estimate the electric property of multi walled carbon nanotubes (MWCNTs) by ac dielectrophoresis. Dielectrophoresis is a phenomenon resulted from the inhomogeneous electric field and has been used to sort out colloids with different dielectric properties. When applied ac dielectrophoresis, the movement of the colloids depends on the polarizability of the colloids relative to the medium as well as the applied frequency. In certain frequency, the direction of dielectrophoresis force will change and this crossover frequency is related to the electric property of colloids. Since the crossover frequency is a function of the particle's dielectric property, as a result, if the crossover frequency can be obtained, then the electric property of MWCNTs can be estimated. In a preliminary experiment, NanoAmor MWCNTs (95+%, core diameter: 5-10 nm, outside diameter 20-40 nm, length 5-15 μm) mixed with alcohol, DI water and the surfactant was injected onto a dielectrophoresis microfluidic chip to measure the crossover frequency. These MWCNTs were under negative dielectrophoresis (repelled from high electric field) for frequencies over 12 KHz, and were under positive dielectrophoresis (attracted to the high electric field) for frequencies under 1 KHz. These results were compared with the CM factor frequency spectrum with known electric properties. The results show that for positive dielectrophoresis in low frequency and negative dielectrophoresis in high frequency is a characteristic of conducting materials which indicates that these MWCNTs are conducting in nature. One application of this technique is the characterization of electric property of SWCNT which is currently under investigation.

Proceedings Article | 11 September 2007 Paper

The role of electro-osmosis and dielectrophoresis in collection of micro/nano size particles in low frequency AC electric field

Chehung Wei, Che-Wei Hsu, Ching-Chieh Wang

Proceedings Volume 6645, 664528 (2007) https://doi.org/10.1117/12.735185

KEYWORDS: Particles, Dielectrophoresis, Electrodes, Dielectrics, Latex, Curium, Glasses, Chromium, Solids, Photoresist materials

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The collecting and sorting micro size particles by electric force is easy to integrate with other bioassays. There are many forms of electric forces such as electrophoresis, dielectrophoresis and electroosmosis which can be used to manipulate particles. In an attempt to understand the role of electroosmosis and dielectrophoresis in the collection of micro size particles, a small device made of two parallel plates is used to study the particle movement under AC electric field. The device is fabricated by a top electrode and a bottom electrode separated by a spacer. The top electrode is made from an ITO glass where the bottom electrode is made of Corning 1737 glass sputtered with chromium. A dielectric layer is fabricated by spin coating a thin photo-resist (0.5~1μm) on the bottom electrode and a spacer made of curing PDMS is utilized to separate these electrodes. A 900μm × 900μm collecting chamber is fabricated on the bottom electrode via photolithography. The amine-modified polystyrene fluorescent particles whose average size is 1 μm were used for collection experiments. Different frequency and power were applied to generate the non-uniform electric field. It was found that frequency is the critical factor for electroosmotic velocity. There seems to be an optimum frequency that leads to largest particle velocity. The underlying mechanism is believed to the competing forces among dielectrophoresis and electroosmosis. This device demonstrates that the electroosmosis force is suitable for collecting bio-particles in AC electric field.

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