Mark E. Curtis

Microstructural investigation of gas shales in two and three dimensions using nanometer-scale resolution imaging

The microstructure of gas shale samples from nine different formations has been investigated using a combination of focused ion beam (FIB) milling and scanning electron microscopy (SEM). Backscattered electron (BSE) images of FIB cross sectioned shale surfaces show a complex microstructure with variations observed among the formations. Energy dispersive spectroscopy of the shale cross sections indicates that clay, carbonate, quartz, pyrite, and kerogen are the most prevalent components. In the BSE images, areas of kerogen are observed interspersed with the inorganic grains. Pores are observed in both the kerogen and inorganic matrix with the size, shape, and number of pores varying among the shale samples. By using FIB milling and SEM imaging sequentially and repetitively, three-dimensional (3-D) data sets of SEM images have been generated for each of the shale samples. Three-dimensional volumes of the shales are reconstructed from these images. By setting thresholds on the gray scale, the kerogen and pore networks are segmented out and visualized in the reconstructed shale volumes. Estimates of kerogen and pore volume percentages of the reconstructed shale volumes have been made and range from 0 to 90.0% for the kerogen and 0.2 to 2.3% for pores. Estimates of pore-size distributions suggest that although pores with radii of approximately 3 nm dominate in number, they do not necessarily dominate in total volumetric contribution. Scanning electron microscopy images and 3-D reconstructions reinforce the facts that shales are quite different and that their microstructures are highly variable and complex.

Spatially resolved probing of Preisach density in polycrystalline ferroelectric thin films

Applications of the ferroelectric materials for the information storage necessitate the understanding of local switching behavior on the level of individual grains and microstructural elements. In particular, implementation of multilevel neuromorphic elements requires the understanding of history-dependent polarization responses. Here, we introduce the spatially resolved approach for mapping local Preisach densities in polycrystalline ferroelectrics based on first-order reversal curve (FORC) measurements over spatially resolved grid by piezoresponse force spectroscopy using tip-electrode. The band excitation approach allowed effective use of cantilever resonances to amplify weak piezoelectric signal and also provided insight in position-, voltage-, and voltage history-dependent mechanical properties of the tip-surface contact. Several approaches for visualization and comparison of the multidimensional data sets formed by FORC families or Preisach densities at each point are introduced and compared. The relationship between switching behavior and microstructure is analyzed.

The role of fibrinogen spacing and patch size on platelet adhesion under flow

Platelet adhesion to the vessel wall during vascular injury is mediated by platelet glycoproteins binding to their respective ligands on the vascular wall. In this study we investigated the roles that ligand patch spacing and size play in regulating platelet interactions with fibrinogen under hemodynamic flow conditions. To regulate the size and distance between patches of fibrinogen we developed a photolithography-based technique to fabricate patterns of proteins surrounded by a protein-repellant layer of poly(ethylene glycol). We demonstrate that when mepacrine labeled whole blood is perfused at a shear rate of 100 s ⁻¹ over substrates patterned with micron-sized wide lines of fibrinogen, platelets selectively adhere to the areas of patterned fibrinogen. Using fluorescent and scanning electron microscopy we demonstrate that the degree of platelet coverage (3-35%) and the ability of platelet aggregates to grow laterally are dependent upon the distance (6-30 μm) between parallel lines of fibrinogen. We also report on the effects of fibrinogen patch size on platelet adhesion by varying the size of the protein patch (2-20 μm) available for adhesion, demonstrating that the downstream length of the ligand patch is a critical parameter in platelet adhesion under flow. We expect that these results and protein patterning surfaces will be useful in understanding the spatial and temporal dynamics of platelet adhesion under physiologic flow, and in the development of novel platelet adhesion assays.

Investigation of the Microstructure of Shales in the Oil Window

Summary We present the results of a microstructural study of oil window organic shales, with samples from the Avalon, Bakken, and Woodford shale plays. The results of this study are placed within the framework of an overview of shale microstructure in both the oil and gas windows. Results show shales in the oil window possess a significantly different microstructure than those in the gas window with a general lack of porosity in the organic matter of oil window shales. While this fits the current idea of porosity development in the organic matter occurring during the generation of gas, several deviations to this rule of thumb are observed. Some oil window Avalon samples exhibit porosity in the organic matter. Other Avalon samples exhibit fractures contained solely within the organic matter that have the appearance of hydraulic fracturing possible due to oil generation within the organic matter. In addition, several of the gas window Woodford samples exhibit a mixture of porous and non-porous regions of organic matter within microns of each other. From this two important observations are made: