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Perfect Crystal Diffractometer for Ultra Small-Angle Neutron Scattering

Nanoscale Structure of Cement

C-S-H representationFor the first time, the composition and solid density of the principal binding reaction product of cement hydration, calcium–silicate–hydrate (C-S-H) gel, one of the most complex of all gels, has been measured without recourse to drying.
C-S-H representationUltra small-angle neutron scattering measurements enabled the critical distinction to be made between the C-S-H gel microstructure and that of the other main hydration product, calcium hydroxide. Then, by combining small-angle neutron and X-ray scattering data, and by exploiting the hydrogen-deuterium neutron isotope effect both in water and methanol, the group from NIST and Northwestern University determined the mean formula and mass density of the nanoscale C–S–H gel particles in hydrating cement.

A.J. Allen, et. al. Nature Materials, 6(4), 311 (2007) (PDF)

Concentrated Emulsions

I versus Q graph of concentrated emulsions Concentrated oil-in-water emulsions were prepared with polydispersities ranging from about 0.5 to 1 at drop volume fractions between 0.1 and 0.5. The drop size distributions were obtained from electroacoustic measurements, and from USANS via both Porod limit scattering and modeling of the scattering data as polydisperse hard spheres.
In these systems, the drop size distribution was found not to change with dilution on the experimental time scale, which was up to several days. The consistency between the mean radii calculated from fitting the USANS data with those derived from electroacoustics confirms the validity of using electroacoustic models which include the effects of stagnant layer conduction when analyzing the electrokinetic behavior of dispersions.
USANS provides both a confirmation of the results from electroacoustics and demonstrates its use for in situ determination of drop size distributions in concentrated emulsions where other Single walled carbon nanotubes (SWNTs) dispersed in a poly(ethylene oxide) (PEO) matrix with aid techniques require alteration of the sample by dilution.

C.P. Whitby, et. al. Langmuir, 23(4), 1694 (2007)

Fractal Networks in Nanotube-Polymer Networks

0.4wt% SWNT/PEO Single walled carbon nanotubes (SWNTs) dispersed in a poly(ethylene oxide) (PEO) matrix with aid of an anionic surfactant (lithium dodecyl sulfate (LDS)) have been studied by USANS and SANS.
At concentrations well beyond the percolation threshold the nanotubes form a self-similar fractal network which gives rise to ‘time-temperature-composition’ superposition of rheological properties. Analysis of the combined SANS/USANS data using a two level Beaucage model shows that while the mesh size (correspondig to the smaller length scale of the network) decreases (power law decay with exponent -0.4) with increasing concentration, the floc size (correspond to the bigger length scale of the network) remains over the concentration window studied (3.0 ? p/pc ? 15.0).
The concentration dependencies of the elastic modulus of the network and the onset-strain for shear-thinning are consistent with the short-range nature of the interactions that dominate these dispersions. The strain dependence of the damping behavior for the nanocomposites shows concentration invariance when represented against the local strain experienced by the network element, with the onset occurring at a local strain value of 0.1, similar to other nanocomposite systems dominated by short range interactions.

T. Chatterjee, et. al. Physical Review E, 75(5), 050403 (2007)

Water Vapor Sorption on the Nanoscale Structure of NAFION

Schematics of possible NAFION structures Several poly(perfluorosulfonic acid) membranes (NAFION, EW = 1100) with the same sulfonic acid content were systematically investigated with SANS under in-situ water vapor sorption and/or with bulk water to quantify the effects of relative humidity (RH), membrane processing (melt-extruded and solution-casting), prehistory (pretreated at 80 C and as-received), and thickness on the nanoscale structure at room temperature. The sorption isotherm (water uptake vs RH) of the membranes showed a strong correlation between the interionic domain distance (Lion) and RH. The melt-extruded membranes showed evidence of partial alignment of better organized ionic domains than those solution-cast. Pretreating the membranes resulted in a larger Lion and a broader scattering over the entire range of RH. The ionic peak of the melt-extruded membranes (as-received and pretreated) became more symmetric and narrower with sorption time. Diffusion coefficients of water vapor, based on structural evolution and Fick's second law, are in the range of 1 × 10-7-3 × 10-7 cm2/s for both extruded (pretreated and as-received) membranes. A thickness-dependent crystalline feature around Q 0.03 Å-1 was also observed.

M.-H. Kim, et. al. Macromolecules, 39(14), 4775 (2006) (PDF)


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