William W. Limburg

Hole transport in solid solutions of substituted triarylmethanes in bisphenol-A-polycarbonate

The time-of-flight and xerographic discharge techniques have been used to study electronic transport in films of dialkylamine-substituted triarylmethanes in bisphenol-A-polycarbonate binder. The hole mobility has been measured as a function of applied electric field, concentration of the molecules, and temperature. The results indicate that charge transport occurs by hopping among localized states associated with the molecule. In chemical terms, the hole transport involves a series of one-electron oxidation-reduction steps involving the organic molecules. The influence of some substituent groups on the electronic transport in these aromatic diamines has also been studied.

Electrical properties of a series of carbazole polymers

The electrical transport properties of three vinyl carbazole polymers have been examined to determine if the observed variations in NMR chemical shifts resulting from inter−ring shielding effects could be correlated with carrier mobilities in the polymers. Drift mobilities were measured in films of the polymers overcoated with thin layers of amorphous Se using a xerographic discharge technique. Under the conditions for observing trap free space charge limited currents the hole mobilities were calculated from Child’s law. The three polymers exhibited mobilities varying as the square of the electric field over the range of fields examined. P2VK which showed the overall largest upfield shift of the aromatic protons exhibited a mobility of 1.4×10−6 cm2/V⋅sec at a field of 4×105 V/cm. PVK which exhibit an intermediate degree of shielding had a mobility of 1.4×10−7 cm2/V⋅sec and P3VK which exhibits the smallest shielding effect had a mobility of 2.4×10−8 cm2/V⋅sec both at equivalent fields. Although P2VK showed...

Generation of electron accepting surface sites in carbon blacks by peracetic acid oxidation

Abstract Surface oxidation of three different carbon blacks was carried out using peracetic acid. An electron spin resonance investigation of these oxidized blacks revealed that a significant number of surface sites were generated. These surface sites were in equilibrium with the bulk conduction electrons as evidenced by the large deviation from the Curie Law. Electrochemical reduction of these blacks also resulted in electron transfer to these surface sites as evidenced by ESR. The ESR results on the reduced and oxidized carbon blacks correlated with the measured contact potentials. This is consistent with a mechanism of electron acceptance by surface sites during contact electrification in a xerographic developer system.

Comparison of Hole Hopping Diffusion and Migration in a Triarylamine Containing Polymer

Abstract Electron hopping charge transport rates in a triarylamine containing polymer were investigated electrochemically in the presence of a contacting electrolyte and in the solid state (absence of liquid electrolyte). Electron hopping diffusion coefficients were measured by steady state voltammetry in thin polymer films on Au microelectrode interdigitated arrays. In addition, zero-field extrapolated electron hopping mobilities and zero-field mobility activation energies are obtained from time-of-flight (TOF) measurements. Electron hopping diffusion coefficients (Dh, cm2/s) and diffusion activation energies obtained in solid state electrochemical experiments can be correlated with zero-field hole mobilities (cm2/V-s) and activation energies via the Einstein relationship.

Structural effects on the electrochemisty and charge distribution of mono-, di-, and tri-cyanovinyl aromatic compounds

The effect on electrochemical behaviour and electronic charge distribution was examined for a series of 12 vinyl aromatic compounds having the following structural variations : (a) number of cyano-groups attached to the vinyl double bond, (b) substitution para to the vinyl group, and (c) separation between para-substituent and the vinyl group. The radical anion formed in the first one-electron reduction step can either accept a second electron or undergo an irreversible dimerization. Oxidation waves were seen only with those compounds having an amino nitrogen atom para to the vinyl group. Trends in half-wave potentials caused by variation in structure are correlated by means of the Hammett–Zuman and molecular orbital approaches. Due to the strong electron-withdrawing power of the cyano-substituted vinyl group, considerable intramolecular donor–acceptor interaction occurs between the ends of the molecules. This is seen in the measured molecular dipole moments and reflected in the nitrile stretching frequencies and proton chemical shifts. Finally, the efficiences for generation of charge carriers in the compounds as measured by xerographic discharge are related to their solution reduction potentials.