Design and performance of a thermal-neutron double-crystal diffractometer for USANS at NIST

Barker, J. G.; Glinka, C. J.; Moyer, J. J.; Kim, M. H.; Drews, A. R.; Agamalian, M.

doi:10.1107/s0021889805032103

Cited by 209 publications

(182 citation statements)

References 31 publications

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“…Because the low pH coacervate with PDADMAC was prepared with high-molecular-weight polymer (M n ) 460 kDa vs 140 kDa for others) the difference in their two PDADMAC curves in Figure 4 might be related to either pH or molecular weight. Previous DLS and rheology data show no effect of molecular weight on coacervate structure in regard to DLS modes or modulus 31 but strong effects of pH and ionic strength, so the influence of molecular weight in Figure 4 is secondary to the effect of pH, and these two SANS curves will be considered below in terms of the different interaction strengths and not molecular weights. The most striking difference in the SANS profiles between the two systems is a 10-fold increase in scattering intensity for the chitosan coacervate at q < 0.006 Å -1 , corresponding to length scales greater than 100 nm.…”

Section: Resultsmentioning

confidence: 99%

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Effect of Polyelectrolyte Structure on Protein−Polyelectrolyte Coacervates: Coacervates of Bovine Serum Albumin with Poly(diallyldimethylammonium chloride) versus Chitosan

et al. 2007

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Electrostatic interactions between synthetic polyelectrolytes and proteins can lead to the formation of dense, macroion-rich liquid phases, with equilibrium microheterogeneities on length scales up to hundreds of nanometers. The effects of pH and ionic strength on the rheological and optical properties of these coacervates indicate microstructures sensitive to protein-polyelectrolyte interactions. We report here on the properties of coacervates obtained for bovine serum albumin (BSA) with the biopolyelectrolyte chitosan and find remarkable differences relative to coacervates obtained for BSA with poly(diallyldimethylammonium chloride) (PDADMAC). Coacervation with chitosan occurs more readily than with PDADMAC. Viscosities of coacervates obtained with chitosan are more than an order of magnitude larger and, unlike those with PDADMAC, show temperature and shear rate dependence. For the coacervates with chitosan, a fast relaxation time in dynamic light scattering, attributable to relatively unrestricted protein diffusion in both systems, is diminished in intensity by a factor of 3-4, and the consequent dominance by slow modes is accompanied by a more heterogeneous array of slow apparent diffusivities. In place of a small-angle neutron scattering Guinier region in the vicinity of 0.004 Å -1 , a 10-fold increase in scattering intensity is observed at lower q. Taken together, these results confirm the presence of dense domains on length scales of hundreds of nanometers to micrometers, which in coacervates prepared with chitosan are less solidlike, more interconnected, and occupy a larger volume fraction. The differences in properties are thus correlated with differences in mesophase structure.

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Section: Resultsmentioning

confidence: 99%

“…All SANS fits were performed by the use of interactive procedures of Igor (Wavemetrics, Inc., Portland, OR) data analysis software. 30 Ultra-small-angle scattering (USANS) experiments were performed at the Bonse-Hart-type instrument 31 on beam port BT-5 at NIST. Coacervate samples were loaded into demountable titanium cells with 5 /8 in.…”

Section: Methodsmentioning

confidence: 99%

Effect of Polyelectrolyte Structure on Protein−Polyelectrolyte Coacervates: Coacervates of Bovine Serum Albumin with Poly(diallyldimethylammonium chloride) versus Chitosan

et al. 2007

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“…The USANS measurement was performed using a Bonse-Hart-type instrument (at BT5 of NCNR) that uses a pair of triple-bounce channel-cut perfect silicon (220) crystals as monochromator and analyzer, and λ n ) 2.4 Å. 47 Neutron Transmission Measurement. Neutron transmission of the pretreated membranes decreases by about 5% in a semiparabolic manner from the ∼96% for the dry to ∼92% for the membrane equilibrated at 95% RH ( Figure 2).…”

Section: Methodsmentioning

confidence: 99%

SANS Study of the Effects of Water Vapor Sorption on the Nanoscale Structure of Perfluorinated Sulfonic Acid (NAFION) Membranes

et al. 2006

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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 (L ion ) 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 L ion 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 cm 2 /s for both extruded (pretreated and as-received) membranes. A thickness-dependent crystalline feature around Q ≈ 0.03 Å -1 was also observed.

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“…USANS measurements were performed on the BT5 instrument at the Center for Neutron Research at the National Institute of Standards and Technology (Barker et al, 2005), with wavelength = 8.09 Å and wavelength spread Δλ/λ = 0.11, and Q vectors ranging from 2.8 × 10 −5 to 2.5 × 10 −3 Å −1 . As the scattering vector Q increases, the size of the objects that contribute to the scattering signal decreases, according to Bragg's law: | Q| = 2πd = 4π sinθ/λ, where d is the distance between scattering surfaces, θis the scattering angle, and λ is the neutron wavelength.…”

Section: Sans/usansmentioning

confidence: 99%

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

Beckingham

Steefel

Swift

et al. 2017

Geochimica et Cosmochimica Acta

121

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The rates of mineral dissolution reactions in porous media are difficult to predict, in part because of a lack of understanding of mineral reactive surface area in natural porous media. Common estimates of mineral reactive surface area used in reactive transport models for porous media are typically ad hoc and often based on average grain size, increased to account for surface roughness or decreased by several orders of magnitude to account for reduced surface reactivity of field as opposed to laboratory samples. In this study, accessible mineral surface areas are determined for a sample from the reservoir formation at the Nagaoka pilot CO2 injection site (Japan) using a multi-scale image analysis based on synchrotron Xray microCT, SEMQEMSCAN, XRD, SANS, and FIB-SEM. This analysis not only accounts for accessibility of mineral surfaces to macro-pores, but also accessibility through connected micro-pores in smectite, the most abundant clay mineral in this sample. While the imaging analysis reveals that most of the micro-and macro-pores are well connected, some pore regions are unconnected and thus inaccessible to fluid flow and diffusion. To evaluate whether mineral accessible surface area accurately reflects reactive surface area a flow-through core experiment is performed and modeled at the continuum scale. The core experiment is performed under conditions replicating the pilot site and the evolution of effluent solutes in the aqueous phase is tracked.Various reactive surface area models are evaluated for their ability to capture the observed effluent chemistry, beginning with parameter values determined as a best fit to a disaggregated sediment experiment (Beckingham et al., 2016) described previously.Simulations that assume that all mineral surfaces are accessible (as in the disaggregated sediment experiment) over-predict the observed mineral reaction rates, suggesting that a reduction of RSA by a factor of 10-20 is required to match the core flood experimental data. While the fit of the effluent chemistry (and inferred mineral dissolution rates) greatly improve when the pore-accessible mineral surface areas are used, it was also necessary to include highly reactive glass phases to match the experimental observations, in agreement with conclusions from the disaggregated sediment experiment. It is hypothesized here that the 10-20 reduction in reactive surface areas based on the limited pore accessibility of reactive phases in core flood experiment may be reasonable for poorly sorted and cemented sediments like those at the Nagaoka site, although this reflects pore rather than larger scale heterogeneity.

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Design and performance of a thermal-neutron double-crystal diffractometer for USANS at NIST

Cited by 209 publications

References 31 publications

Effect of Polyelectrolyte Structure on Protein−Polyelectrolyte Coacervates: Coacervates of Bovine Serum Albumin with Poly(diallyldimethylammonium chloride) versus Chitosan

Effect of Polyelectrolyte Structure on Protein−Polyelectrolyte Coacervates: Coacervates of Bovine Serum Albumin with Poly(diallyldimethylammonium chloride) versus Chitosan

SANS Study of the Effects of Water Vapor Sorption on the Nanoscale Structure of Perfluorinated Sulfonic Acid (NAFION) Membranes

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

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