Domain Wall Patterning and Giant Response Functions in Ferrimagnetic Spinels.

The manipulation of mesoscale domain wall phenomena has emerged as a powerful strategy for designing ferroelectric responses in functional devices, but its full potential is not yet realized in the field of magnetism. This work shows a direct connection between magnetic response functions in mechanically strained samples of Mn3 O4 and MnV2 O4 and stripe-like patternings of the bulk magnetization which appear below known magnetostructural transitions. Building off previous magnetic force microscopy data, a small-angle neutron scattering is used to show that these patterns represent distinctive magnetic phenomena which extend throughout the bulk of two separate materials, and further are controllable via applied magnetic field and mechanical stress. These results are unambiguously connected to the anomalously large magnetoelastic and magnetodielectric response functions reported for these materials, by performing susceptibility measurements on the same crystals and directly correlating local and macroscopic data.

Nanoscale Interfacial Smoothing and Dissolution during Unconventional Reservoir Stimulation: Implications for Hydrocarbon Mobilization and Transport.

Hydraulic fracturing of low-permeability rocks significantly enhances hydrocarbon production from unconventional reservoirs. However, fluid transport through low-permeability rocks and the influence of geochemical transformations on pore networks are poorly constrained. Mineral reactivity during interactions with injected water may alter the physical nature of the rock, which may affect hydrocarbon mobility. To assess alterations to the rock, we have previously conducted a hydrothermal experiment that reacted cubed rock samples (1 cm3) with synthetic hydraulic fracturing fluid (HFF) to simulate physicochemical reactivity during hydraulic fracturing. Here, we analyze unreacted and reacted rocks by small-angle neutron scattering and high-pressure mercury intrusion to determine how the pore networks of unconventional reservoir rocks are influenced by the reaction with hydraulic fracturing injectates. Our results suggest that fluid-rock interactions exhibit a two-fold influence on hydrocarbon recovery, promoting both hydrocarbon mobilization and transport. Pore-matrix interfaces smooth via the removal of clay mineral surface asperities, reducing the available surface area for hydrocarbon adsorption by 12-75%. Additionally, HFF-induced dissolution creates new pores with diameters ranging from 800-1400 nm, increasing the permeability of the rocks by a factor of 5-10. These two consequences of mineral dissolution likely act in concert to release hydrocarbons from the host rock and facilitate transport through the rock during unconventional reservoir production.

Effects of soil particles and convective transport on dispersion and aggregation of nanoplastics via small-angle neutron scattering (SANS) and ultra SANS (USANS).

Terrestrial nanoplastics (NPs) pose a serious threat to agricultural food production systems due to the potential harm of soil-born micro- and macroorganisms that promote soil fertility and ability of NPs to adsorb onto and penetrate into vegetables and other crops. Very little is known about the dispersion, fate and transport of NPs in soils. This is because of the challenges of analyzing terrestrial NPs by conventional microscopic techniques due to the low concentrations of NPs and absence of optical transparency in these systems. Herein, we investigate the potential utility of small-angle neutron scattering (SANS) and Ultra SANS (USANS) to probe the agglomeration behavior of NPs prepared from polybutyrate adipate terephthalate, a prominent biodegradable plastic used in agricultural mulching, in the presence of vermiculite, an artificial soil. SANS with the contrast matching technique was used to study the aggregation of NPs co-dispersed with vermiculite in aqueous media. We determined the contrast match point for vermiculite was 66% D2O / 33% H2O. At this condition, the signal for vermiculite was ~50-100%-fold lower that obtained using neat H2O or D2O as solvent. According to SANS and USANS, smaller-sized NPs (50 nm) remained dispersed in water and did not undergo size reduction or self-agglomeration, nor formed agglomerates with vermiculite. Larger-sized NPs (300-1000 nm) formed self-agglomerates and agglomerates with vermiculite, demonstrating their significant adhesion with soil. However, employment of convective transport (simulated by ex situ stirring of the slurries prior to SANS and USANS analyses) reduced the self-agglomeration, demonstrating weak NP-NP interactions. Convective transport also led to size reduction of the larger-sized NPs. Therefore, this study demonstrates the potential utility of SANS and USANS with contrast matching technique for investigating behavior of terrestrial NPs in complex soil systems.

Fractionation of Lignin for Selective Shape Memory Effects at Elevated Temperatures.

We report a facile approach to control the shape memory effects and thermomechanical characteristics of a lignin-based multiphase polymer. Solvent fractionation of a syringylpropane-rich technical organosolv lignin resulted in selective lignin structures having excellent thermal stability coupled with high stiffness and melt-flow resistance. The fractionated lignins were reacted with rubber in melt-phase to form partially networked elastomer enabling selective programmability of the material shape either at 70 °C, a temperature that is high enough for rubbery matrix materials, or at an extremely high temperature, 150 °C. Utilizing appropriate functionalities in fractionated lignins, tunable shape fixity with high strain and stress recovery, particularly high-stress tolerance were maintained. Detailed studies of lignin structures and chemistries were correlated to molecular rigidity, morphology, and stress relaxation, as well as shape memory effects of the materials. The fractionation of lignin enabled enrichment of specific lignin properties for efficient shape memory effects that broaden the materials' application window. Electron microscopy, melt-rheology, dynamic mechanical analysis and ultra-small angle neutron scattering were conducted to establish morphology of acrylonitrile butadiene rubber (NBR)-lignin elastomers from solvent fractionated lignins.

Crystallization Mechanism in Spark Plasma Sintered Bulk Metallic Glass Analyzed using Small Angle Neutron Scattering.

Understanding the thermal stability of metallic glasses is critical to determining their safe temperatures of service. In this paper, the crystallization mechanism in spark plasma sintered Fe48Cr15Mo14Y2C15B6 metallic glass is established by analyzing the crystal size distribution using x-ray diffraction, transmission electron microscopy and in-situ small angle neutron scattering. Isothermal annealing at 700 °C and 725 °C for 100 min resulted in the formation of (Fe,Cr)23C6 crystals, measured from transmission electron micrographs, to be from 10 to 30 nm. The small angle neutron scattering intensity measured in-situ, over a Q-range of 0.02 to 0.3 Å-1, during isothermal annealing of the sintered samples, confirmed the presence of (Fe,Cr)23C6 crystals. The measured scattering intensity, fitted by the maximum entropy model, over the Q-range of 0.02 to 0.06 Å-1, revealed that the crystals had radii ranging from 3 to 18 nm. The total volume fraction of crystals were estimated to be 0.13 and 0.22 upon isothermal annealing at 700 °C and 725 °C for 100 min respectively. The mechanism of crystallization in this spark plasma sintered iron based metallic glass was established to be from pre-existing nuclei as confirmed by Avrami exponents of 0.25 ± 0.01 and 0.39 ± 0.01 at the aforesaid temperatures.

A path for lignin valorization via additive manufacturing of high-performance sustainable composites with enhanced 3D printability.

We report the manufacture of printable, sustainable polymer systems to address global challenges associated with high-volume utilization of lignin, an industrial waste from biomass feedstock. By analyzing a common three-dimensional printing process-fused-deposition modeling-and correlating the printing-process features to properties of materials such as acrylonitrile-butadiene-styrene (ABS) and nylon, we devised a first-of-its-kind, high-performance class of printable renewable composites containing 40 to 60 weight % (wt %) lignin. An ABS analog made by integrating lignin into nitrile-butadiene rubber needs the presence of a styrenic polymer to avoid filament buckling during printing. However, lignin-modified nylon composites containing 40 to 60 wt % sinapyl alcohol-rich, melt-stable lignin exhibit enhanced stiffness and tensile strength at room temperature, while-unexpectedly-demonstrating a reduced viscosity in the melt. Further, incorporation of 4 to 16 wt % discontinuous carbon fibers enhances mechanical stiffness and printing speed, as the thermal conductivity of the carbon fibers facilitates heat transfer and thinning of the melt. We found that the presence of lignin and carbon fibers retards nylon crystallization, leading to low-melting imperfect crystals that allow good printability at lower temperatures without lignin degradation.

Liquid worm-like and proto-micelles: water solubilization in amphiphile-oil solutions.

Noncovalent interactions determine the structure-property relationship of materials. Self-assembly originating from weak noncovalent interactions represents a broad variety of solution-based transformations spanning micellization and crystallization, which, nevertheless, conforms to neither colloid nor solution sciences. Here, we investigate the weak self-assembly in water-amphiphile-oil solutions to understand the connection between the amphiphilic molecular structure and water solubilization in oil. X-ray and neutron scattering, converged with large-scale atomistic molecular dynamics simulations, support the fact that the amphiphiles assemble into liquid worm-like micelles and loose inverted proto-micelles. The inverted proto-micelles are energetically ready to accommodate a higher amount of water. These structures arise from a balance of intermolecular interactions controlled by the amphiphile tail-group structures. Thus, by linking the aggregate morphology to the molecular structure, this work provides insights on the molecular design for control of water solubility and dispersion in oil.

Characterization of colloidal structures during intestinal lipolysis using small-angle neutron scattering.

HYPOTHESIS: Bile micelles are thought to mediate intestinal absorption, in part by providing a phase into which compounds can partition. Solubilizing capacity of bile micelles is enhanced during the digestion of fat rich food. We hypothesized that the intestinal digestion of triglycerides causes an increase in volume of micelles that can be quantitatively monitored over the course of digestion using small-angle neutron scattering (SANS), and that SANS can enable evaluation of the contribution of each of the components present during digestion to the size of micelles. EXPERIMENTS: SANS was used to characterize the size and shape of micelles present prior to and during the in vitro simulated intestinal digestion of a model food-associated lipid, triolein. FINDINGS: Pre-lipolysis mixtures of a bile salt and phospholipid simulating bile concentrations in fed conditions were organized in micelles with an average volume of 40 nm3. During lipolysis, the micelle volume increased 2.5-fold over a 2-h digestion period due to growth in one direction as a result of insertion of monoglycerides and fatty acids. These efforts represent a basis for quantitative mechanistic understanding of changes in solubilizing capacity of the intestinal milieu upon ingestion of a fat-rich meal.

Nanoscopic Structural Investigation of Physically Cross-Linked Nanogels Formed from Self-Associating Polymers.

The detailed structure of a nanogel formed by self-association of cholesterol-bearing pullulans (CHPs) was determined by contrast variation small-angle neutron scattering. The decomposition of scattering intensities into partial scattering functions of each CHP nanogel component, i.e., pullulan, cholesterol, and the cross-term between the pullulan and the cholesterol, allows us to investigate the internal structure of the nanogel. The effective spherical radius of the skeleton formed by pullulan chains was found to be 8.1 ± 0.3 nm. In the CHP nanogel, there are about 19 cross-linking points where a cross-linking point is formed by aggregation of trimer cholesterol molecules, and the spatially inhomogeneous distribution of the cross-linking points in the nanogel can be represented by the mass fractal dimension of 2.6. The average radius of gyration of the partial chains can also be determined to be 1.7 ± 0.1 nm by analyzing the extracted cross-correlation between the cross-linker and the tethered polymer chain quantitatively, and the size agrees with the value assuming random distribution of the cross-linkers on the chains. As the result, the complex structure of the nanogels is coherently revealed at the nanoscopic level.

SANS study on the solvated structure and molecular interactions of a thermo-responsive polymer in a room temperature ionic liquid.

We have utilized small-angle neutron scattering (SANS) to quantitatively characterize the LCST-type phase behavior of the poly(benzyl methacrylate) (PBnMA) derivative poly(2-phenylethyl methacrylate) (PPhEtMA) in the deuterated ionic liquid (IL) d8-1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (d8-[C2mIm(+)][TFSA(-)]). The SANS curves showed a discontinuous change from those characteristics of dispersed polymer chains to those of large aggregates of PPhEtMA chains suspended in the IL solution, indicating that phase separation occurs discontinuously at Tc. Furthermore, we evaluated the enthalpic and entropic contributions to the effective interaction parameter χeff of PPhEtMA in [C2mIm(+)][TFSA(-)] and compared them with those of PBnMA. The absolute value of the enthalpic contribution observed for PPhEtMA was smaller than that for PBnMA. This difference in the enthalpic term can be attributed to the unfavorable interaction between the IL and the alkyl group in the side chain of PPhEtMA. In addition, the temperature dependence of χeff was smaller than the previously reported value for a thermo-responsive polymer in an aqueous system. It was found out that the strong dependence of Tc on the chemical structure in IL systems originated from the relatively smaller temperature dependence of χeff.

Formation of kinetically trapped nanoscopic unilamellar vesicles from metastable nanodiscs.

Zwitterionic long-chain lipids (e.g., dimyristoyl phosphatidylcholine, DMPC) spontaneously form onion-like, thermodynamically stable structures in aqueous solutions (commonly known as multilamellar vesicles, or MLVs). It has also been reported that the addition of zwitterionic short-chain (i.e., dihexanoyl phosphatidylcholine, DHPC) and charged long-chain (i.e., dimyristoyl phosphatidylglycerol, DMPG) lipids to zwitterionic long-chain lipid solutions results in the formation of unilamellar vesicles (ULVs). Here, we report a kinetic study on lipid mixtures composed of DMPC, DHPC, and DMPG. Two membrane charge densities (i.e., [DMPG]/[DMPC] = 0.01 and 0.001) and two solution salinities (i.e., [NaCl] = 0 and 0.2 M) are investigated. Upon dilution of the high-concentration samples at 50 °C, thermodynamically stable MLVs are formed, in the case of both weakly charged and high salinity solution mixtures, implying that the electrostatic interactions between bilayers are insufficient to cause MLVs to unbind. Importantly, in the case of these samples small angle neutron scattering (SANS) data show that, initially, nanodiscs (also known as bicelles) or bilayered ribbons form at low temperatures (i.e., 10 °C), but transform into uniform size, nanoscopic ULVs after incubation at 10 °C for 20 h, indicating that the nanodisc is a metastable structure. The instability of nanodiscs may be attributed to low membrane rigidity due to a reduced charge density and high salinity. Moreover, the uniform-sized ULVs persist even after being heated to 50 °C, where thermodynamically stable MLVs are observed. This result clearly demonstrates that these ULVs are kinetically trapped, and that the mechanical properties (e.g., bending rigidity) of 10 °C nanodiscs favor the formation of nanoscopic ULVs over that of MLVs. From a practical point of view, this method of forming uniform-sized ULVs may lend itself to their mass production, thus making them economically feasible for medical applications that depend on monodisperse lipid-based systems for therapeutic and diagnostic purposes.

Small-angle neutron scattering for molecular biology: basics and instrumentation.

As researchers strive to understand the interplay between the complex molecular systems that make up living cells, tools for characterizing the interactions between the various players involved have developed. Small-angle neutron scattering (SANS) plays an important role in building a molecular-level understanding of the structures of macromolecular systems that make up cells. SANS is widely applicable to the study of biological structures including, but by no means limited to, protein-protein or protein-nucleic acid complexes, lipid membranes, cellular scaffolding, and amyloid plaques. Here, we present a brief description of the technique as it is commonly applied to the study of biological systems and an overview instrumentation that is available at the various facilities around the world.

Absence of the density minimum of supercooled water in hydrophobic confinement.

The surface effect on the peculiar dynamic and thermodynamic properties of supercooled water, such as the density, has been puzzling the scientific community for years. Recently, using the small angle neutron scattering method, we were able to measure the density of H(2)O confined in the hydrophobic mesoporous material CMK-1-14 from room temperature down to the deeply supercooled temperature 130 K at ambient pressure. We found that the well-known density maximum of water is shifted 17 K lower and, more interestingly, that the previously observed density minimum in hydrophilic confinement disappears. Furthermore, the deduced thermal expansion coefficient shows a much broader peak spanning from 240 to 180 K in comparison with the sharp peak at 230 K in hydrophilic confinement. These present results may help in the understanding of the effect of hydrophobic/hydrophilic interfaces on the properties of supercooled confined water.

Structural studies of bleached melanin by synchrotron small-angle X-ray scattering.

Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 angstroms with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 angstroms at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules.