Shear thickening, temporal shear oscillations, and degradation of dilute equimolar CTAB/NaSal wormlike solutions

The rheological characterization of dilute and semi-dilute equimolar cetyltrimethylammonium bromide and sodium salicylate solutions is reported, including their linear and nonlinear responses. Start-up experiments and direct birefringence measurements suggest that even at a concentration of as low as 1.0 mM, temporal shear oscillations occur at low shear rates. At concentrations above 10 mM, those low-stress structures vanish and give way to shear-thickening and shear-banding behaviors as seen for other semi-dilute surfactant solutions. Also, the degradation of these solutions after exposure to rubber pump tubing is covere

Evolution of iron carbides during tempering of low-alloy tool steel studied with polarized small angle neutron scattering, electron microscopy and atom probe

The magnetic scattering of iron carbides in low-alloy tool steel was investigated ex-situ by polarized small angle neutron scattering measurements after tempering the steel at 550 \ub0C and 600 \ub0C. Magnetic features could be detected in the as-quenched sample resulting in a negative interference term, believed to be either θ-Fe3C, η-Fe2C, or ε-Fe2-3C. During tempering the evolution of cementite could be studied by the variation of the interference term and in γ-ratio, which is the ratio of the magnetic to nuclear scattering length density contrast. From scanning transmission electron microscopy (STEM) and atom probe tomography, it is evident that cementite (θ-Fe3C) is present directly when reaching the tempering temperature of either 550 \ub0C or 600 \ub0C. At longer tempering times, cementite gets enriched with substitutional elements like chromium and manganese, forming an enriched shell on the cementite particles. STEM and energy dispersive x-ray spectrometry show that the chemical composition of small cementite particles approaches that of Cr-rich M7C3 carbides after 24 h at 600 \ub0C. It is also seen that small non-magnetic particles precipitate during tempering and these correspond well with molybdenum and vanadium-rich carbides

The salt curve revisited - Electrostatic charges govern the viscoelastic properties of micellar solutions

In ionic surfactant micelles, interactions among surfactant monomers, their counterion, and additives are fundamental to tune molecular self-assembly and thus the rheological properties (see Figure 1). Here we propose a combination of 1H-NMR, integrated small-angle neutron scattering (SANS) and small-angle X-ray scattering, and rheology to probe the molecular arrangements of the individual molecules within the micelle and the resulting flow properties [1, 2]. Shifts in the 1H-NMR signal show the penetration of counterions and additives into the micellar surfactant structure while SANS and SAXS determine specific intramicellar length scales and intermicellar interactions. SANS signals are sensitive to the contrast between the solvent (deuterium) and the hydrocarbonic tails in the micellar core (hydrogen) and SAXS access the inner structure of the polar shell because the headgroups, counterions, and penetrated salt have higher electron densities compared to the solvent and to the micellar core. Please click Additional Files below to see the full abstract

Carbide Precipitation during Processing of Two Low-Alloyed Martensitic Tool Steels with 0.11 and 0.17 V/Mo Ratios Studied by Neutron Scattering, Electron Microscopy and Atom Probe

Two industrially processed low-alloyed martensitic tool steel alloys with compositions Fe-0.3C-1.1Si-0.81Mn-1.5Cr-1.4Ni-1.1Mo-0.13V and Fe-0.3C-1.1Si-0.81Mn-1.4Cr-0.7Ni-0.8Mo-0.14V (wt.%) were characterized using small-angle neutron scattering (SANS), scanning electron microscopy (SEM), Scanning transmission electron microscopy (STEM), and atom probe tomography (APT). The combination of methods enables an understanding of the complex precipitation sequences that occur in these materials during the processing. Nb-rich primary carbides form at hot working, while Fe-rich auto-tempering carbides precipitate upon quenching, and cementite carbides grow during tempering when Mo-rich secondary carbides also nucleate and grow. The number density of Mo-rich carbides increases with tempering time, and after 24 h, it is two to three orders of magnitude higher than the Fe-rich carbides. A high number density of Mo-rich carbides is important to strengthen these low-alloyed tool steels through precipitation hardening. The results indicate that the Mo-rich secondary carbide precipitates are initially of MC character, whilst later they start to appear as M2C. This change of the secondary carbides is diffusion driven and is therefore mainly seen for longer tempering times at the higher tempering temperature of 600◦C

The Connection between Biaxial Orientation and Shear Thinning for Quasi-Ideal Rods

The complete orientational ordering tensor of quasi-ideal colloidal rods is obtainedas a function of shear rate by performing rheo-SANS (rheology with small angle neutronscattering) measurements on isotropic fd-virus suspensions in the two relevant scatteringplanes, the flow-gradient (1-2) and the flow-vorticity (1-3) plane. Microscopic ordering canbe identified as the origin of the observed shear thinning. A qualitative description of therheological response by Smoluchowski, as well as Doi–Edwards–Kuzuu theory is possible,as we obtain a master curve for different concentrations, scaling the shear rate with theapparent collective rotational diffusion coefficient. However, the observation suggests that theinterdependence of ordering and shear thinning at small shear rates is stronger than predicted.The extracted zero-shear viscosity matches the concentration dependence of the self-diffusion ofrods in semi-dilute solutions, while the director tilts close towards the flow direction already atvery low shear rates. In contrast, we observe a smaller dependence on the shear rate in the overallordering at high shear rates, as well as an ever-increasing biaxiality

Size-dependent reversal of grains in perpendicular magnetic recording media measured by small-angle polarized neutron scattering

Polarized small-angle neutron scattering has been used to measure the magnetic structure of a CoCrPt–SiOx thin-film data storage layer, contained within a writable perpendicular recording media, at granular (<10 nm) length scales. The magnetic contribution to the scattering is measured as the magnetization is reversed by an external field, providing unique spatial information on the switching process. A simple model of noninteracting nanomagnetic grains provides a good description of the data and an analysis of the grain-size dependent reversal provides strong evidence for an increase in magnetic anisotropy with grain diameter

Magnetic diffuse scattering in artificial kagome spin ice

This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.93.224413The study of magnetic correlations in dipolar-coupled nanomagnet systems with synchrotron x-ray scattering provides a means to uncover emergent phenomena and exotic phases, in particular in systems with thermally active magnetic moments. From the diffuse signal of soft x-ray resonant magnetic scattering, we have measured magnetic correlations in a highly dynamic artificial kagome spin ice with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering patterns with Monte Carlo simulations based on a needle-dipole model, we conclude that kagome ice I phase correlations exist in our experimental system even in the presence of moment fluctuations, which is analogous to bulk spin ice and spin liquid behavior. In addition, we describe the emergence of quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I phase. These quasi-pinch-points bear similarities to the fully developed pinch points with singularities of a magnetic Coulomb phase, and continually evolve into the latter on lowering the temperature. The possibility to measure magnetic diffuse scattering with soft x rays opens the way to study magnetic correlations in a variety of nanomagnetic systems.Seventh Framework Programme (Grant ID: 290605