KWS-3: Very small angle scattering diffractometer with focusing mirror

KWS-3, which is operated by JCNS, Forschungszentrum Jülich, is a very small angle neutron scattering (VSANS) instrument running on the focussing mirror principle. KWS-3 is designed to bridge the gap between Bonse-Hart and pinhole cameras. Owing to its extended Q range, optimized flux, and good wavelength resolution, KWS-3 has shown good performance and has become scientifically productive to the user community

Tunable viscosity modification with diluted particles: When particles decrease the viscosity of complex fluids

While spherical particles are the most studied viscosity modifiers, they are well known only to increase viscosities, in particular at low concentrations. Extended studies and theories on non-spherical particles find a more complicated behavior, but still a steady increase. Involving platelets in combination with complex fluids displays an even more complex scenario that we analyze experimentally and theoretically as a function of platelet diameter, to find the underlying concepts. Using a broad toolbox of different techniques we were able to decrease the viscosity of crude oils although solid particles were added. This apparent contradiction could lead to a wider range of applications.Comment: 13+7 pages, 6+7 figure

Validating reactive transport models of CO2-brine-rock reactions in caprocks using observations from a natural CO2 reservoir

Storage of anthropogenic CO2 in geological formations relies on impermeable caprocks as the primary seal preventing buoyant super-critical CO2 escaping. Although natural CO2 reservoirs demonstrate that CO2 may be stored safely for millions of years, uncertainty remains in predicting how caprocks will react with acid CO2-bearing brines. This uncertainty poses a challenge to the assessment of carbon capture and storage schemes. Prediction of caprock behaviour is based primarily on theoretical modelling and laboratory experiments. However, the reactive transport phenomena cannot be reproduced in laboratory experiments over sufficient timescales, theoretical models need calibration against observational data and existing studies on natural caprocks have not resolved mineral reactions. Here we report a detailed description of a stacked sequence of CO2 reservoir-caprock systems exposed to CO2-rich fluids over ∼ 105 years, a time-scale comparable with that needed for effective geological carbon storage. Fluid-mineral reactions in the base of multiple caprocks is driven by diffusion of CO2 and minor H2S from the underlying reservoirs. The reactions include dissolution of hematite, dolomite and K-feldspar and precipitation of Fe-bearing dolomite, gypsum, pyrite and illite over centimetre length-scales. The mineral dissolution reactions generate transient increases in porosity, as determined by neutron scattering measurements, but the propagation of mineral reaction fronts is retarded by the reaction stoichiometry and mineral precipitation. Modelling of the mineral reaction fronts shows that the alteration is sluggish, developing over a >104 year period. The results attest to the significance of transport-limited reactions to the long-term integrity of sealing behaviour in caprocks exposed to CO2

Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach

The preparation of poly(N-isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e., from core–shell-like to a more homogeneous one. The internal structure and dynamics of these microgels with low and medium crosslinker concentrations are studied with dynamic light scattering and small-angle neutron scattering in a wide q-range below and above the volume phase transition temperature. The influence of the preparation method, and crosslinker and initiator concentration on the internal structure of the microgels is investigated. In contrast to the classical conception where polymer microgels possess a core–shell structure with the averaged internal polymer density distribution within the core part, a detailed view of the internal inhomogeneities of the PNIPAM microgels and the presence of internal domains even above the volume phase transition temperature, when polymer microgels are in the deswollen state, are presented. The correlation between initiator concentration and the size of internal domains that appear inside the microgel with temperature increase is demonstrated. Moreover, the influence of internal inhomogeneities on the dynamics of the batch- and feeding-microgels studied with neutron spin-echo spectroscopy is reported.TU Berlin, Open-Access-Mittel - 201

The Low-Resolution Structure of Nascent High Density Lipoprotein Reconstituted with DMPC With and Without Cholesterol Reveals A Mechanism for Particle Expansion

High density lipoproteins (HDL) are athero-protective particles under investigation as potential therapeutic agents for cardiovascular disease. We applied small angle neutron scattering (SANS) with contrast variation to obtain the low resolution structure of nascent HDL (nHDL) reconstituted with dimyristoyl phosphatidyl choline (DMPC), apoA1:DMPC (1:80, mol:mol). The overall shape of the entire particle is discoidal, with low resolution architecture of apoA1 visualized as an open, contorted, and slightly out of plane structure with three arms, while the low resolution shape of the lipid phase is an oblate ellipsoid that fits well within the protein shape. Modeling studies incorporating the SANS data indicate that apoA1 within the lipoprotein is folded onto itself, making a hairpin, which was also confirmed independently by both cross-linking mass spectrometry and hydrogen-deuterium exchange mass spectrometry analyses. The open conformation of apoA1 observed coupled with the lipid shape indicate that the lipid is predominantly a bilayer with a small micelle domain between the open apoA1 arms. Collectively, these studies demonstrate that full length apoA1 retains an open architecture that is dictated by its lipid cargo. This configuration may help accommodate potential changing lipid cargo content of the particle by quantized expansion of hairpin structures in apoA

Beyond structural models for the mode of action:How natural antimicrobial peptides affect lipid transport

Hypothesis: Most textbook models for antimicrobial peptides (AMP) mode of action are focused on structural effects and pore formation in lipid membranes, while these deformations have been shown to require high concentrations of peptide bound to the membrane. Even insertion of low amounts of peptides in the membrane is hypothesized to affect the transmembrane transport of lipids, which may play a key role in the peptide effect on membranes. Experiments: Here we combine state-of-the-art small angle X-ray/neutron scattering (SAXS/SANS) techniques to systematically study the effect of a broad selection of natural AMPs on lipid membranes. Our approach enables us to relate the structural interactions, effects on lipid exchange processes, and thermodynamic parameters, directly in the same model system. Findings: The studied peptides, indolicidin, aurein 1.2, magainin II, cecropin A and LL-37 all cause a general acceleration of essential lipid transport processes, without necessarily altering the overall structure of the lipid membranes or creating organized pore-like structures. We observe rapid scrambling of the lipid composition associated with enhanced lipid transport which may trigger lethal signaling processes and enhance ion transport. The reported membrane effects provide a plausible canonical mechanism of AMP-membrane interaction and can reconcile many of the previously observed effects of AMPs on bacterial membranes

Aqueous Solutions of Poly(ethylene oxide): Crossover from Ordinary to Tricritical Behavior

The aqueous associating solution poly(ethylene oxide) (PEO) of molar mass between 0.45 and 280 kDa was studied with small-angle neutron scattering (SANS) near their critical concentration in a temperature interval from 11.8 to 95.7 °C. SANS measures thermal concentration fluctuations whose susceptibility and correlation length identified mean-field, 3D-Ising, and tricritical Θ-point critical behavior. Scaling laws of the critical amplitudes of susceptibility and correlation length were observed for the samples obeying 3D-Ising and tricritical Θ-point behavior in agreement with the predicted ones for nonassociating semidilute solutions. On the other hand, chain conformation is different for both classes of criticality and is attributed to the concentrated and semidilute regime of the phase diagram. In the concentrated regime the chains are slightly more compacted than Gaussian coils. However, all PEO solutions approach ideal chain conformation at the Θ-temperature. A small amount of PEO of the order of 10–5 is forming compact PEO aggregates

Densification of Supercritical Carbon Dioxide Accompanied by Droplet Formation When Passing the Widom Line

Thermal density fluctuations of supercritical CO2 were explored using small-angle neutron scattering (SANS), whose amplitude (susceptibility) and correlation length show the expected maximum at the Widom line. At low pressure, the susceptibility is in excellent agreement with the evaluated values on the basis of mass density measurements. At about 20 bar beyond the Widom line, SANS shows the formation of droplets accompanied by an enhanced number density of the supercritical fluid. The corresponding borderline is interpreted as a Frenkel line separating gas- and liquidlike regimes