The separation of different conducting multi-walled carbon nanotubes by AC dielectrophoresis

A microfluidic device was fabricated to separate different conducting parts of multi-walled carbon nanotubes (MWCNTs). The device consists of a curing PDMS fluidic-flow chamber covered on electrode coated glass. The electrode was designed to generate non-uniform electric field by patterning via lithography. A range of frequencies with low applied voltage was utilized to induce different sign of dielectrophoresis force. Two different separation schemes based on positive and negative dielectrophoresis were employed to separate different conducting parts in unsorted MWCNTs. From Raman spectroscopy, conducting MWCNTs collected by positive dielectrophoresis showed little variation in the intensities of D-band and G-band ratio while the less conducting MWCNTs collected by negative dielectrophoresis showed decreasing intensities in these positions. The ID/IG ratio in the samples collected by both separation schemes is decreasing compared to the unsorted samples. The electric properties of the samples were characterized by a dielectrophoresis frequency spectra method. The conductance in positive dielectrophoresis collected sample is the greatest while the conductance in negative dielectrophoresis collected sample is the smallest. The trend in the conductance in unsorted and sorted samples is confirmed by current-voltage measurements.