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Two long (> 40 m) continuous push cores of sediments from the Mississippi Delta Plain, one at a northern freshwater site and one at a southern marine-influenced site, have provided samples of individual concretions and homogenized bulk samples for a study of early diagenesis. Early ( pyrite > calcite dolomite > vivianite hematite. Siderite formed postburial and contains bands of clastic minerals and accessory diagenetic calcite and dolomite, as well as Ca, Mg, and Mn substituted in the lattice. Values for 13C increase with increasing depth to +11o/oo (PDB) at a depth of 40 m, reflecting the increasing role of methanogenesis with depth. From analyses of bulk samples, pyrite concentrations are higher in organic-rich horizons, do not vary appreciably with depth below one meter when adjusted for organic-carbon control, and are generally higher in the marine-influenced core than at the freshwater site. Conversely, concentrations of siderite are higher in fine-grained siliciclastic horizons, increase with depth to about 20 m, and do not vary with the extent of marine influence in these cores. To a first approximation, distributions of pyrite appear to be controlled by variations in organic carbon concentration in sulfate-sufficient systems that formed through marine incursion into organic-rich layers that cap sediment packages in the deltaic system. Residual pyritic S is sulfate-controlled and lower in the northern, more freshwater organic-rich sediments. Siderite formation appears to be focused in sulfate-deficient systems that formed when siliciclastic wedges that constitute the central parts of sediment packages prograded into lacustrine or bay environments. Low sulfate levels in these horizons in both cores facilitated similar levels of siderite. A juxtaposition of marine versus freshwater diagenetic mineral suites in adjacent horizons resulted from these interactions between physical and geochemical processes.

The viscoelastic properties of a series of carboxylated styrene/butadiene latexes were determined using dynamic mechanical spectroscopy. The viscoelastic properties of the latex films were found to depend on the pH of the latex and the type of neutralization ions present in the latex. This change in the viscoelastic properties is explained by the change in the ionomeric characteristics of the latex and a change of morphology of the latex film as determined using transmission electron microscopy. At low pH, the low-Tg (glass-transition temperature) essentially noncarboxylated bulk polymer phase is often the continuous phase with the high-Tg carboxylated interfacial polymer as the dispersed phase. As the mobility of the interfacial polymer decreases with increasing ionomeric characteristic with increasing pH, the morphology changes to one in which the high-Tg carboxylated interfacial polymer is the continuous phase.

Modern polymer blends are frequently composed of domains and interfacial phases having submicron dimensions. Previously, die characterization of specific unknown submicron polymer phases has been limited to selective staining methods that help to classify the phase but rarely lead to chemical identification. The present procedure uses parallel detection electron energy loss spectroscopy (PEELS) to perform submicron molecular microanalysis on beam sensitive materials. Polymer domains are first differentiated by their elemental composition and then by their characteristic carbon core loss edge structure. These spectra are compared to spectra recorded from polymers of known composition.A polymer film composed of alternating 0.5 μm layers of polycarbonate (PC) and polymethylmethacrylate (PMMA) was used as a test specimen (Fig. 1). Ultra-thin sections (

The interpretation of, and information available from a transmission electron photomicrograph, frequently depend upon specimen preparation. A major consideration in the selection of a preparation method is the potential for preparation artifacts. The goal of this work is to illustrate some sectioning and staining artifacts found in the preparation of a variety of polymer specimens. The following artifacts, in addition to several others, will be presented during the poster session.