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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.
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