Effect of Source, Surfactant, and Deposition Process on Electronic Properties of Nanotube Arrays

The electronic properties of arrays of carbon nanotubes from several different sources differing in the manufacturing process used with a variety of average properties such as length, diameter, and chirality are studied. We used several common surfactants to disperse each of these nanotubes and then deposited them on Si wafers from their aqueous solutions using dielectrophoresis. Transport measurements were performed to compare and determine the effect of different surfactants, deposition processes, and synthesis processes on nanotubes synthesized using CVD, CoMoCAT, laser ablation, and HiPCO

Synthesis and characterization of new nitrile -containing acetylenic monomers and polymers.

An efficient synthesis of 1-methyl-2-ethynyl-4,5-dicyanoimidazole via Sonogashira coupling is described for the first time. Synthetic optimizations are described in detail. Our optimized method generates 1-methyl-2-ethynyl-4,5-dicyano-imidazole in almost 80% yield from 1-methyl-2-bromo-4,5-dicyanoimidazole. Synthesis of the ethyl, propyl, and p-methoxybenzyl derivatives of 2-ethynyl-4,5-dicyanoimidazole are discussed along with the improved synthesis of 4-cyanophenylacetylene. The polymerization of 1-methyl-2-ethynyl-4,5-dicyanoimidazole and 4-cyano-phenylacetylene with transition metal catalysts and triethylamine are described. The transition metal catalyst, [Rh(nbd)Cl]2, proved to be the most effective catalyst for the polymerization of both monomers. Triethylamine led to the oligomerization of 1-methyl-2-ethynyl-4,5-dicyanoimidazole but did not affect 4-cyanophenylacetylene. Variation of catalyst concentration, reaction time and temperature is also described for the polymerization of both monomers. Increasing the amount of catalyst increases the yield, molecular weight and polydispersity of the product. Extending the reaction time and increasing the temperature increases the product yield. For the first time, a more complete mechanistic picture of acetylene polymerizations, especially those with electron-withdrawing substituents, is presented. An insertion mechanism is proposed for the [Rh(nbd)Cl] 2 catalyzed polymerization of both monomers. Termination is most likely via chain transfer to monomer or solvent. A possible end group is the rhodium-norbornadiene moiety. Electron paramagnetic resonance (EPR) revealed the presence of unpaired electrons in solid samples of both 1-methyl-2-ethynyl-4,5-dicyanoimidazole oligomers and poly(4-cyanophenylacetylene). Quantitation of unpaired electrons relative to copper(II)acetylacetonate is described. In the oligomer samples, we found that for every unpaired electron, there are approximately 10 3 repeat units or 102 oligomer chains. For the polymer samples, we found that for every unpaired electron, 106 repeat units or 102 polymer chains. We conclude that unpaired electrons are generated from carbon-carbon double bond twisting. The relationship between EPR signal, chain length and temperature is also discussed. In short chain oligomers, the unpaired electrons are likely to recombine with increasing temperature. Thus, a decrease in EPR signal is observed. In long chain polymers, the unpaired electrons are not likely to recombine with increasing temperature. Thus, an increase in EPR signal is observed. These new nitrile-containing acetylenic polymers, 1-methyl-2-ethynyl-4,5-dicyanoimidazole oligomers and poly(4-cyanophenylacetylene), gave low values of conductivity and low photocurrent generation in their pristine form.Ph.D.Applied SciencesOrganic chemistryPlasticsPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123821/2/3106045.pd

Effect of Source, Surfactant, and Deposition Process on Electronic Properties of Nanotube Arrays

The electronic properties of arrays of carbon nanotubes from several different sources differing in the manufacturing process used with a variety of average properties such as length, diameter, and chirality are studied. We used several common surfactants to disperse each of these nanotubes and then deposited them on Si wafers from their aqueous solutions using dielectrophoresis. Transport measurements were performed to compare and determine the effect of different surfactants, deposition processes, and synthesis processes on nanotubes synthesized using CVD, CoMoCAT, laser ablation, and HiPCO