Small-Angle and Ultrasmall-Angle Neutron Scattering (SANS/USANS) Study of New Albany Shale: A Treatise on Microporosity

Small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) techniques were applied to study the microstructure of several New Albany shales of different maturity. It has been established that the total porosity decreases with maturity and increases somewhat for post-mature samples. A new method of SANS data analysis was developed, which allows the extraction of information about the size range and number density of micropores from the relatively flat scattering intensity observed in the limit of the large scattering vector <i>Q</i>. Macropores and significant number of mesopores are surface fractals, and their structure can be described in terms of the polydisperse spheres (PDSP) model. The model-independent Porod invariant method was employed to estimate total porosity, and the results were compared with the PDSP model results. It has been demonstrated that independent evaluation of incoherent background is crucial for accurate interpretation of the scattering data in the limit of large <i>Q</i>-values. Pore volumes estimated by the N₂ and CO₂ adsorption, as well as via the mercury intrusion technique, have been compared with those measured by SANS/USANS, and possible reasons for the observed discrepancies are discussed

Mechanism of Spontaneous Blebbing Motion of an Oil–Water Interface: Elastic Stress Generated by a Lamellar–Lamellar Transition

A quaternary system composed of surfactant, cosurfactant, oil, and water showing spontaneous motion of the oil–water interface under far-from-equilibrium condition is studied in order to understand nanometer-scale structures and their roles in spontaneous motion. The interfacial motion is characterized by the repetitive extension and retraction of spherical protrusions at the interface, i.e, blebbing motion. During the blebbing motion, elastic aggregates are accumulated, which were characterized as surfactant lamellar structures with mean repeat distances <i>d</i> of 25 to 40 nm. Still unclear is the relationship between the structure formation and the dynamics of the interfacial motion. In the present study, we find that a new lamellar structure with <i>d</i> larger than 80 nm is formed at the blebbing oil–water interface, while the resultant elastic aggregates, which are the one reported before, have a lamellar structure with smaller <i>d</i> (25 to 40 nm). Such transition of lamellar structures from the larger <i>d</i> to smaller <i>d</i> is induced by a penetration of surfactants from an aqueous phase into the aggregates. We propose a model in which elastic stress generated by the transition drives the blebbing motion at the interface. The present results explain the link between nanometer-scale transition of lamellar structure and millimeter-scale dynamics at an oil–water interface

Thermo-Induced Limited Aggregation of Responsive Star Polyelectrolytes

Poly­(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate) (PDMAEMA) star polyelectrolytes with dual thermo- and pH-responsive properties have been studied by <i>in situ</i> small-angle neutron scattering at different temperatures and pH conditions in order to reveal their conformational changes in semidilute solution. At pH values close to the p<i>K</i>_a, all PDMAEMA stars studied here are partially charged and show a core–shell quasi-micellar morphology caused by microphase separation with a collapsed core region with high monomer density and a hydrated loosely packed shell region. Upon increasing the temperature, the PDMAEMA star polyelectrolytes first experience a contraction in the shell region while the core size remains almost unchanged, and then start to form limited intermolecular aggregates. With decreasing pH values, the transition temperature increases and the size of the aggregates decreases (average aggregation number changes from 10 to 3). We suggest that these changes are triggered by the decrease in solvent quality with increasing temperature, which leads to the transition from an electrostatically dominated regime to a regime dominated by hydrophobic interactions. The observed phenomenon is in striking contrast to the phase behavior of linear PDMAEMA polyelectrolytes, which show macrophase separation with increasing temperature under the same conditions

Effect of Ionic Liquid Treatment on the Structures of Lignins in Solutions: Molecular Subunits Released from Lignin

The solution structures of three types of isolated ligninorganosolv (OS), Kraft (K), and low sulfonate (LS)before and after treatment with 1-ethyl-3-methylimidazolium acetate were studied using small-angle neutron scattering (SANS) and dynamic light scattering (DLS) over a concentration range of 0.3–2.4 wt %. The results indicate that each of these lignins is comprised of aggregates of well-defined basal subunits, the shapes and sizes of which, in D₂O and DMSO-<i>d</i>₆, are revealed using these techniques. LS lignin contains a substantial amount of nanometer-scale individual subunits. In aqueous solution these subunits have a well-defined elongated shape described well by ellipsoidal and cylindrical models. At low concentration the subunits are highly expanded in alkaline solution, and the effect is screened with increasing concentration. OS lignin dissolved in DMSO was found to consist of a narrow distribution of aggregates with average radius 200 ± 30 nm. K lignin in DMSO consists of aggregates with a very broad size distribution. After ionic liquid (IL) treatment, LS lignin subunits in alkaline solution maintained the elongated shape but were reduced in size. IL treatment of OS and K lignins led to the release of nanometer-scale subunits with well-defined size and shape

Polymer Chain Behavior in Polymer Nanocomposites with Attractive Interactions

Chain behavior has been determined in polymer nanocomposites (PNCs) comprised of well-dispersed 12 nm diameter silica nanoparticles (NPs) in poly­(methyl methacrylate) (PMMA) matrices by Small-Angle Neutron Scattering (SANS) measurements under the Zero Average Contrast (ZAC) condition. In particular, we directly characterize the bound polymer layer surrounding the NPs, revealing the bound layer profile. The SANS spectra in the high-<i>q</i> region also show no significant change in the bulk polymer radius of gyration on the addition of the NPs. We thus suggest that the bulk polymer conformation in PNCs should generally be determined using the high <i>q</i> region of SANS data

Role of Liquid vs Vapor Water in the Hydrothermal Degradation of SBA-15

The hydrothermal stability of mesoporous silica is critical for applications including catalytic processing of biofuels due to the presence of significant amounts of water. We have combined neutron diffraction intensity analysis with NLDFT analysis of nitrogen sorption isotherms to characterize the spatial distribution of the secondary pore network in SBA-15 following postcalcination hydrothermal treatment in both liquid and vapor phase water at temperatures from 115 to 155 °C under autogenous pressure. The results are consistent with a degradation mechanism in which silica dissolves from regions of small positive curvature, e.g., near the entrance to the secondary pores, and is redeposited deeper into the framework. Pore volumes decrease fastest for the micropores and more slowly for larger secondary mesopores. Under water treatment at 115 °C, the mesopore diameter increases and the intrawall void fraction decreases significantly. The behavior is similar for steam treatment but occurs more slowly. Differences in the chemical environment and transport limitations are discussed. At higher temperatures of 155 °C, pores in the region surrounding the mesopore are nearly eliminated, trapping water deeper in the matrix, which can be seen with neutron scattering but is inaccessible to nitrogen isotherm measurements