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91 results on '"Zawodzinski, T. A."'

5. Basic Research Needs for the Hydrogen Economy. Report of the Basic Energy Sciences Workshop on Hydrogen Production, Storage and Use, May 13-15, 2003

Author

Dresselhaus, M, primary, Crabtree, G, additional, Buchanan, M, additional, Mallouk, T, additional, Mets, L, additional, Taylor, K, additional, Jena, P, additional, DiSalvo, F, additional, Zawodzinski, T, additional, Kung, H, additional, Anderson, I S, additional, Britt, P, additional, Curtiss, L, additional, Keller, J, additional, Kumar, R, additional, Kwok, W, additional, Taylor, J, additional, Allgood, J, additional, Campbell, B, additional, and Talamini, K, additional

Published
2004
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6. Dielectric relaxation and underlying dynamics of acetonitrile and 1-ethyl-3-methylimidazolium triflate mixtures using THz transmission spectroscopy.

Author

Asaki, M. L. T., Redondo, A., Zawodzinski, T. A., and Taylor, A. J.

Subjects
DIELECTRICS, ACETONITRILE, DIELECTRIC relaxation
Abstract

We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric functions for pure acetonitrile, pure 1-ethyl-3-methylimidazolium triflate (emim triflate, a room temperature molten salt), and mixtures of the two liquids. The behavior of the pure liquids is modeled with either two (acetonitrile) or three (emim triflate) Debye relaxations. We then discuss the interactions of the molten salt and solvent based on the modified Debye relaxations evident in the mixtures. We determine that at low molten salt concentrations, the mixtures behave like electrolyte solutions of a crystalline salt dissolved in a solvent. At higher molten salt concentrations, the behavior is that of a mixture of two liquids. [ABSTRACT FROM AUTHOR]

Published
2002
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7. Dielectric relaxation of electrolyte solutions using terahertz transmission spectroscopy.

Author

Asaki, M. L. T., Redondo, A., Zawodzinski, T. A., and Taylor, A. J.

Subjects
LIQUID dielectrics, SPECTRUM analysis, WATER, METHANOL, PROPYLENE carbonate
Abstract

We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric constants of water, methanol, and propylene carbonate, and solutions of lithium salts in these solvents. The behavior of the pure solvents is modeled with either two (water) or three (methanol and propylene carbonate) Debye relaxations. We discuss the effects of ionic solvation on the relaxation behavior of the solvents in terms of modifications to the values of the Debye parameters of the pure solvents. In this way we obtain estimates for numbers of irrotationally bound solvent molecules, the numbers of bonds broken or formed, and the effects of ions on the higher-frequency relaxations. [ABSTRACT FROM AUTHOR]

Published
2002
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46. Multilayer Self-Assembly of Amphiphilic Cyclodextrin Hosts on Bare and Modified Gold Substrates:  Controlling Aggregation via Surface Modification

Author

Godinez, L. A., Lin, J., Munoz, M., Coleman, A. W., Rubin, S., Parikh, A., Zawodzinski, T. A., Jr., Loveday, D., Ferraris, J. P., and Kaifer, A. E.

Abstract

Self-assembled multilayers of the three modified cyclodextrins (hexakis(2,3-O-hexyl-6-deoxy-6-amino)-α-cyclodextrin (1), heptakis(2,3-O-hexyl-6-deoxy-6-amino)-β-cyclodextrin (2), and octakis(2,3-O-hexyl-6-deoxy-6-amino)-γ-cyclodextrin (3)) on bare gold, as well as on gold surfaces modified with mercaptopropionic (4) and mercaptooctanoic (5) acid, were investigated by cyclic voltammetric, contact angle, FT-IR, and quartz crystal microbalance measurements in neutral aqueous media. The level of organization of the aggregates formed by the three CD derivatives (1−3) on the negatively charged surface of the mercaptopropionic and mercaptooctanoic acid modified gold electrodes proved to be substantially better than that on bare gold electrodes. This finding suggests that although the amphiphilic character of compounds 1−3 can induce aggregation on a gold surface, the electrostatic interaction between the carboxylic acid groups and the positively charged cyclodextrins is the primary force leading to the formation of well-organized aggregates.

Published
1998

47. Dendrimer-Modified Silicon Oxide Surfaces as Platforms for the Deposition of Gold and Silver Colloid Monolayers:  Preparation Method, Characterization, and Correlation between Microstructure and Optical Properties

Author

Bar, G., Rubin, S., Cutts, R. W., Taylor, T. N., and Zawodzinski, T. A., Jr.

Abstract

We describe a novel approach for Au and Ag colloid monolayer formation on different silicon oxide surfaces such as glass, silicon, and ITO. The preparation method is simple and yields monolayers with easily controlled spacing within the monolayer without aggregation of metal particles. The colloid monolayers are prepared in two steps:  (1) modification of the substrates with starburst dendrimers and (2) noble metal colloid deposition onto the dendrimer layer. Different Au and Ag colloids, ranging from 15 to 80 nm in particle diameter, have been deposited onto the dendrimer-modified surfaces. The structure and properties of the resulting particle arrays have been studied by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV−vis spectroscopy, and surface-enhanced Raman scattering (SERS). XPS data show that the dendrimers spontaneously adsorb to various silicon oxide surfaces. The thickness of the dendrimer overlayer has been calculated and lies in the d = 14−25 Å range. SEM and AFM data show that the colloids spontaneously form continuous films on the dendrimer-modified surfaces. The noble metal particles are well isolated and confined to a single layer, and aggregation does not occur on the surface. The interparticle spacing (74−829 nm) and surface coverage can be controlled over a wide range by colloid size, colloid concentration, and immersion time. UV−vis spectroscopic data show that the microstructure directly controls the optical properties of the layer. Finally, we demonstrate that the prepared substrates provide a useful platform for SERS studies of materials adsorbed on the metal particles.

Published
1996

48. Electrical Communication between Components of Self-Assembled Mixed Monolayers

Author

Rubin, S., Chow, J. T., Ferraris, J. P., and Zawodzinski, T. A., Jr.

Abstract

The use of an alkanethiol-based self-assembled mixed monolayer as an electronic relay system effecting mediated electron transfer between immobilized glucose oxidase (GOx) and a gold electrode is reported. We compare the behavior of mixed monolayers of various compositions of 16-ferrocenylhexadecanethiol (16FAT) and aminoethanethiol, to which GOx is attached, as biosensors for glucose. The amperometric response of such electrodes in the presence of glucose in solution depends on the mole ratio between the 16FAT molecules and the attached protein molecules. The most sensitive system is a mixed monolayer that contains 7% 16FAT. For higher 16FAT concentrations, both a catalytic response and a wave corresponding to reversible 16FAT voltammetry are observed in the presence of glucose. This suggests that there are separate domains of 16FAT and of aminoethanethiol in such a mixed monolayer. When the mixed monolayer contains more than 7% 16FAT, a portion of the 16FAT molecules cannot “feel” the GOx and does not function as relays. The existence of these domains was also characterized by studying the solution voltammetry of Ru(NH3)63+ at electrodes with various proportions of 16FAT and aminoethanethiol.

Published
1996

49. Variation of the Dissociation Constant of Triflic Acid with Hydration

Author

Paddison, S. J., Pratt, L. R., and Zawodzinski, T. A., Jr.

Abstract

The variation of the acid dissociation equilibrium of trifluoromethane sulfonic acid in dilute aqueous solution along the liquid−vapor dissociation curve is treated by a dielectric hydration model. The computational results indicate that the dissociation equilibrium becomes unfavorable from the point of view of the free energy change as temperature is increased above 500 K where the solvent density is less than 85% of the triple-point density. These results give additional perspective for the view that insufficient hydration can result in incomplete proton dissociation from sulfonic acid headgroups in Nafion membranes.

Published
2001

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