2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Electrostatic Printing of CNT Liquid Toners

R. Detig, D. Eberlein and M. Finzi
Electrox corp., US

Keywords:
CNT toners, CNT self assembly

Abstract:
Using techniques developed from the electrostatics industry and liquid toner techniques from the copier/laser printer industry, we will describe techniques for the patterning and manipulation of carbon nano-tubes. We will also describe a self assembly process for the patterning of virgin carbon nanotubes from dispersions of them in naptha like liquids. By virgin nanotubes we mean SWNT’s with no surface functionality per se; no wetting agents and surfactants are employed, nor are there any poly-electrolytes (charge directors) added to the liquid. The naptha like liquids are from the Isopar series of Exxon/Mobil which are linear, aliphatic hydrocarbons that are synthesized from gaseous materials and are very, very pure. They are a close approximation to the odorless mineral spirits used to thin alkyd paints by the home owner. The virgin nanotubes are an obvious requirement for the manufacture of chemical/biological sensors. The CNT toners, on the other hand, have either an acidic or basic functionality imparted to their surfaces. This is usually done by a thin resin coating. Dispersed in the diluent with a polyelectrolyte, an ionization reaction occurs which produces an electrochemical charge, either negative or positive, on the nanotube which allows one to move the particles under the action of an electric field. The sensor/transistor assemblies are created between two electrodes on a dielectric surface with gaps between electrodes (called the channel) that ranging form 0.1 mm to 2 mm. Much smaller gaps are easily produced. The channel widths extend to the 6 to 10 mm range. The dielectric surfaces include glass/epoxy semi-rigid boards (PWB’s), aramid fiber reinforced Teflon (high frequency board), and soda lime glass. . We will discuss the theory behind the operation of this fiber self assembly process and show samples of typical parts. Hopefully a video of the assembly process can be shown. In typical sensor applications, functional surface coatings are added after the fact of assembly; and there may be as many as two dozen of them for a single family of sensors. Beyond the obvious application of building sensors, the process can also assemble the channel of a high performance, field effect transistor; useful for phased array radars and backplanes for flat panel displays. The functionalized CNT’s are made into a liquid toner, with a pos. or neg. charge, which allow them to be patterned or coated broadly over a surface. We will show samples of CNT’s imaged on a printing plate capable of features in the 10 micron region, with even very small features possible in the future. Alternately the toners can be uniformly coated on electrically conductive surfaces. Basically all of the technology of digital printing is available to patterning these CNT toners.

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