Organization of Asphaltenes in a Vacuum Residue: A Small-Angle X-ray Scattering (SAXS)–Viscosity Approach at High Temperatures

Temperature-dependent rheological behavior of heavy oils and bitumen is usually modeled with a colloidal approach, taking into account a temperature-dependent solvation effect (Storm, D. A.; Barresi, R. J.; Sheu, E. Y. Rheological study of Ratawi vacuum residue in the 298–673 K temperature range. Energy Fuels 1995, 9, 168−176). In addition to viscosity measurements for vacuum residue at various asphaltene contents, in the present study, we make use of small-angle X-ray scattering (SAXS) data on the 80–240 °C temperature range to propose an interpretation on asphaltene aggregation, consistent with both approaches. The radius of gyration <i>R</i>_g and molecular weight <i>M</i>_W of asphaltenes in a vacuum residue are measured and are of the same magnitude as asphaltenes in toluene. Dimensions and masses decrease with the temperature, while the small length scale remains unchanged, reinforcing the hierarchical aggregation scheme previously described in toluene. These findings enrich the viscosity data interpretation. A solvation factor has to be accounted for, as noticed in previous works. Its signification is made clear by SAXS data: lose asphaltene clusters in maltenes dissociate with temperature, decreasing their solvation

Rivecourt_water-desorption

This file corresponds to an image sequence of neutron transmission images of a fossil wood during drying. The wood comes from Rivecourt (Parisian Basin, Oise, Paleogene

Rivecourt_water-sorption

This file corresponds to a sequence of neutron transmission images recorded during humidification of a fossil wood sample coming from Rivecourt (Parisian Basin, France, paleogene

Angeac_water-desorption

This file corresponds to a sequence of neutron transmission images recorded on a fossil wood during drying. The wood comes from Angeac (Aquitanian basin, Cretaceous:Paleocene

Angeac_water-sorption

This file corresponds to a sequence of neutron transmission images recorded during humidification of a fossil wood sample coming from Angeac (Aquitanian Basin, France, cretaceous:paleocene

Mesoscale Organization in a Physically Separated Vacuum Residue: Comparison to Asphaltenes in a Simple Solvent

Physical separation of heavy oils and bitumen is of particular interest because it improves the description of the chemical and structural organization in these industrial and challenging fluids (Zhao, B.; Shaw, J. M. Composition and size distribution of coherent nanostructures in Athabasca bitumen and Maya crude oil. Energy Fuels 2007, 21, 2795−2804). In this study, permeates and retentates, differing in aggregate concentrations and sizes, were obtained from nanofiltration of a vacuum residue at 200 °C with membranes of varying pore size. Elemental composition and density extrapolations show that aggregates are best represented as <i>n</i>-pentane asphaltenes, while the dispersing phase corresponds to <i>n</i>-pentane maltenes. Small-angle X-ray scattering (SAXS) measurements are processed, on this basis, to calculate the size and mass of the aggregates. Aggregates in the vacuum residue are similar in size and mass to asphaltenes in toluene, and temperature elevation decreases the size of the aggregates. Wide-angle X-ray scattering (WAXS) highlights a coherent domain observed for fluids containing aggregates, corresponding to aromatic stacking described for dry asphaltenes. The scattered signal in this region, not observed in maltenes, grows as aggregate content increases, and the signal persists up to 300 °C. A generic behavior of aggregation in the vacuum residue is depicted, from nanoaggregates to large fractal clusters with high aggregation numbers, that is similar to the organization in toluene

High-Resolution Cellular MRI: Gadolinium and Iron Oxide Nanoparticles for in-Depth Dual-Cell Imaging of Engineered Tissue Constructs

Recent advances in cell therapy and tissue engineering opened new windows for regenerative medicine, but still necessitate innovative noninvasive imaging technologies. We demonstrate that high-resolution magnetic resonance imaging (MRI) allows combining cellular-scale resolution with the ability to detect two cell types simultaneously at any tissue depth. Two contrast agents, based on iron oxide and gadolinium oxide rigid nanoplatforms, were used to “tattoo” endothelial cells and stem cells, respectively, with no impact on cell functions, including their capacity for differentiation. The labeled cells’ contrast properties were optimized for simultaneous MRI detection: endothelial cells and stem cells seeded together in a polysaccharide-based scaffold material for tissue engineering appeared respectively in black and white and could be tracked, at the cellular level, both <i>in vitro</i> and <i>in vivo</i>. In addition, endothelial cells labeled with iron oxide nanoparticles could be remotely manipulated by applying a magnetic field, allowing the creation of vessel substitutes with in-depth detection of individual cellular components