Ann Marie Straccia

The Formation of Reactive Oxygen Species Catalyzed by Neutral, Aqueous Extracts of NIST Ambient Particulate Matter and Diesel Engine Particles

ABSTRACT It is important to characterize the chemical properties of particulate matter in order to understand how low doses, inhaled by a susceptible population, might cause human health effects. The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of two ambient par-ticulate samples, National Institute of Standards & Technology (NIST) Standard Reference Materials (SRM) 1648 and 1649, and two diesel particulate samples, NIST SRM 1650 and SRM 2975, were measured. The formation of reactive oxygen species was estimated by measuring the formation of malondialdehyde from 2-deoxyribose in the presence of ascorbic acid; H2O2 was not added to this assay. SRM 1649, ambient particulate matter collected from Washington, DC, generated the most malondialdehyde, while SRM 2975, diesel particulate matter collected from a forklift, yielded the least amount. Desferrioxamine inhibited the formation of malondialdehyde from the par-ticulate samples providing additional data to support the observation that transition metals were involved in the generation of reactive oxygen species. Six transition metal sulfates (iron sulfate, copper sulfate, vanadyl sulfate, cobalt sulfate, nickel sulfate, and zinc sulfate) were assayed

High Frequency Rheometry of Viscoelastic Coatings with the Quartz Crystal Microbalance

We describe a quantitative method for using the quartz crystal microbalance (QCM) to characterize the high frequency viscoelastic response of glassy polymer coatings with thicknesses in the 5-10 μm regime. By measuring the frequency and dissipation at the fundamental resonant frequency (5 MHz) and at the third harmonic (15 MHz), we obtain three independent quantities. For coatings with a predominantly elastic response, characterized by relatively low phase angles, these quantities are the mass per unit area of the coating, the density-shear modulus product, and the phase angle itself. The approach was demonstrated with a model polyurethane coating, where the evolution of these properties as a function of cure time was investigated. For fully cured films, data obtained from the QCM are in good agreement with results obtained from traditional dynamic mechanical analysis.

Chemistry of surface modification with UV/ozone for improved intercoat adhesion in multilayered coating systems

Surface modification using UV/ozone was explored as an approach towards ensuring robust intercoat adhesion in multilayered automotive coating systems. This study was directed toward reducing the variability in adhesion performance associated with changes in coating surface chemistry that can result from the surface migration of formulation additives. The evaluated coating system included a melamine-cross-linked polyester layer applied over a commercially available epoxy layer, which is known to become surface-enriched by a polyether-based crater-control additive (CCA) in its formulation. X-ray photoelectron spectroscopy established that UV/ozone treatment oxidizes the epoxy CCA overlayer and forms carboxyl species. Contact angle measurements identified a concomitant increase in surface wettability. Epoxy-to-polyester adhesion improved slightly after exposure to ozone alone and dramatically after exposure to UV/ozone. X-ray photoelectron spectroscopy of interfacial epoxy surfaces, exposed by delamination of the polyester coating, disclosed that bond-line fracture occurs within a CCA-enriched region, with a trend of decreasing CCA concentrations in proportion to the UV/ozone exposure time initially received by the epoxy. Copyright