Andrea Labouriau

Characterization of reaction intermediate aggregates in aniline oxidative polymerization at low proton concentration.

Aggregates of reaction intermediates form during the early stages of aniline oxidative polymerization whenever the initial mole ratio of proton concentration to aniline monomer concentration is low ([H(+)](0)/[An](0) <or= 1.0). Detailed characterization is carried out on those aggregates. The intermediate aggregates show a UV-Vis absorption peak at around 410 nm when dispersed in aqueous solution, whereas the peak is centered on 370 nm when dissolved in an organic solvent such as N-methylpyrrolidone. The electronic band gap decreases when the intermediates aggregate to form a solid, and thus, the absorption peak is red-shifted. Gel permeation chromatography (GPC) shows the aggregates contain a major low molecular weight peak with a long tail. The oligoanilines with low molecular weights consistently show a UV-Vis absorption peak at around 370 nm. Mass spectrometry confirms that the intermediate aggregates contain mainly a component with mass number 363 (M + H(+)), likely a tetramer. UV-Vis, GPC, mass spectrometry, NMR, FTIR, and XRD characterization results are presented and chemical structures for the tetramer are proposed. The major components of the intermediate aggregates are likely highly symmetric phenazine- and dihydrophenazine-containing structures. These particular organic compounds have not been identified before as intermediates. The aggregation and precipitation of the tetramers apparently stabilizes these intermediates. The aggregates are highly crystalline, as evidenced by powder X-ray diffraction. A new reaction mechanism for the formation of these intermediates is proposed.

Titanium solid-state NMR in anatase, brookite and rutile

We report 47Ti and 49Ti NMR spectra of powdered samples of the three common phases of titania, TiO2. The linewidths are dominated by the electric quadrupole interaction. The relative linewidths of the three samples cannot be explained in terms of simple structural symmetry using point charges. This indicates that a significant amount of the TiO interaction is covalent in nature.

A 19F NUCLEAR MAGNETIC RESONANCE STUDY OF NATURAL CLAYS

A series of natural clays, including 1:1 layer silicates (serpentines, kaolin minerals), smectites, vermiculite, micas, talc, pyrophyllite, sepiolite, and palygorskite, were studied by “F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The “F chemical shift in these layer silicates is characteristic of the structure, in particular, to the local octahedral cation occupancy. Fluoride ions bonded to three Mg octahedral cations have a chemical shift of about −177 ppm and those bonded to two Al cations and a vacancy have a chemical shift of about −134 parts per million (ppm). The shift at −182.8 ppm in hectorite is apparently associated with fluoride bonded to two Al cations and a Li cation. Surprisingly, the difference in chemical shift of the interlayer and inner fluoride in 1:1 layer silicates is insufficient to distinguish these sites. Based on trends in chemical shift, it appears that fluoride substitution for inner hydroxyls in clays with octahedral substitution is not random. Fluoride is apparently preferentially associated with Mg rather than Al in the octahedral sheet as no resonance due to a fluoride bonded to two Al cations and a vacancy is observed in clays such as SAz-1.

Synthesis of dealuminated zeolites NaY and MOR and characterization by diverse methodologies: 27Al and 29Si MAS NMR, XRD, and temperature dependent 129Xe NMR

Zeolites NaY and mordenite have been dealuminated by SiCl4 and steaming methods and carefully characterized during and after the various synthetic stages by 27Al and 29Si magic angle spinning nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) to ensure sample quality. 129Xe NMR spectra for xenon adsorbed in NaX, siliceous Y, mordenite, and dealuminated mordenite have been obtained for very low xenon loadings and as a function of temperature. Data obtained for faujasites indicate that 129Xe NMR chemical shifts are very sensitive to the Si/Al ratio reflecting the presence or absence of strong adsorption sites. 129Xe NMR chemical shift data for the mordenite samples show that Xe dwells preferentially in the side pockets which do not seem to be affected by the dealumination process. In addition, the 129Xe NMR data clearly reveal information not available from 29Si and 27Al NMR or XRD regarding structural integrity of the zeolites. The findings presented here point to the need for characterization of siliceous zeolites by several techniques before conclusions regarding zeolite structural integrity can be drawn.

Damage of Rubber Foams During Large Cyclic Compression

Polymeric foams are employed as cushions in many applications to prevent components from experiencing large dynamic stresses in service. While the performance of foam cushions may be quantified through certain mechanical variables, the strength and damage behavior of these materials remains poorly understood. The present work examined the deformation response of a rubbery Room Temperature Vulcanizing (RTV) foam under large cyclic compressions, subjected to a large dose of gamma radiation. Reduction in load carrying capacity occurred for all cases, attributable to some combination of material changes (Mullins effect) and permanent plasticity and damage to the microscopic ligaments surrounding pores in the material. Irradiation dose correlated to changes in the rate of nonlinear cyclic degradation, potentially pointing to a radiation aging effect.