A study of carbon black Corax N330 with small-angle scattering of neutrons and X-rays

Carbon black Corax N330 (hereinafter called CB) is used as a filler in elastomers. The properties of the surface are important for the binding of the elastomer to the carbon black particles. Porod's law requires the intensity to satisfy I(q) approximately q(-alpha) with alpha = 4 for large q. Rieker et al. observed alpha = 3.7 +/- 0.1 for small-angle X-ray scattering (SAXS) data and concluded that the particle surface is fractally rough. Ruland critized this and suggested that the observed deviation is due to fluctuations of the spacing of the graphitic layer planes ("graphenes") which contribute a component I(q)fluc = 1Cflucq(-2) to the intensity component satisfying Porod's law. We studied CB by nitrogen adsorption, high-resolution transmission electron microscopy, synchroton SAXS, and small-angle neutron scattering (SANS). Our SAXS experiments with samples of high transmission (Tr = 0.96) confirmed the form of the scattering curves published by Rieker et al., but the correction for I(q)fluc restored Porod's law. SANS experiments were performed with a sample of low transmission in order to analyze the high q-range for scattering from voids and isolated graphenes. We found I(q) approximately q(-beta) with beta approximately 2 at q > 2.5 nm(-1) and will show that this intensity component requires graphenes consisting of about 12 benzene rings. The contrast matching technique revealed the presence of inaccessible voids. The SANS data for a sample with Tr = 0.363 satisfy Porods law, in contrast to the SAXS data for the high transmission samples. The latter discrepancy is likely due to the lower resolution of the SANS measurements because of wavelength smearing and multiple scattering. A SANS sample with Tr = 0.97 shows a minor deviation from Porod's law only (alpha = 3.9). The original SANS data and the SAXS data corrected for the fluctuation component indicate that the CB surface is essentially smooth.     

Application of off-specular scattering of X-rays and neutrons to the study of soft matter

Recent applications of the use of off-specular reflection of neutrons and X-rays in the study of soft matter are reviewed after a brief introduction to the status of the current theoretical treatment of such data. The review is intended to highlight the range of systems that may now be studied with off-specular reflection and recent progress in understanding the results that are observed. A few specific experimental cases are discussed as well as recent technical developments that may enable further more sophisticated treatments of off-specular scattering to be investigated.     

Mixed spherical and wormlike micelles: a contrast-matching study by small-angle neutron scattering

Small-angle neutron scattering studies were used to investigate the effect of adding an alcohol ethoxylate nonionic surfactant (d-C12E20) to aqueous solutions of a cationic surfactant, erucyl bis(hydroxyethyl) methylammonium chloride (EHAC), with and without salt (KCl). The systematic use of contrast-matching, by alternately highlighting or hiding one of the surfactants, confirms that mixed micelles are formed. In salt-free solutions, mixed spherical micelles are formed and a core-shell model combined with a Hayter-Penfold potential was used to describe the data. The core radius is dominated by the EHAC tails and the outer radius determined by the ethoxylate headgroups of the nonionic surfactant. Addition of KCl promotes micellar growth; however, results of varying the solvent contrast revealed that when the nonionic surfactant is incorporated into the wormlike structure micellar breaking is promoted. Thus, mixed wormlike micelles with shorter contour lengths compared to the pure EHAC worms are formed.     

Preferential hydration of lysozyme in water/glycerol mixtures: a small-angle neutron scattering study

In solution small-angle neutron scattering has been used to study the solvation properties of lysozyme dissolved in water/glycerol mixtures. To detect the characteristics of the protein-solvent interface, 35 different experimental conditions (i.e., protein concentration, water/glycerol fraction in the solvent, content of deuterated compounds) have been considered and a suitable software has been developed to fit simultaneously the whole set of scattering data. The average composition of the solvent in the close vicinity of the protein surface at each experimental condition has been derived. In all the investigated conditions, glycerol resulted especially excluded from the protein surface, confirming that lysozyme is preferentially hydrated. By considering a thermodynamic hydration model based on an equilibrium exchange between water and glycerol from the solvation layer to the bulk, the preferential binding coefficient and the excess solvation number have been estimated. Results were compared with data previously derived for ribonuclease A in the same mixed solvent: even if the investigated solvent compositions were very different, the agreement between data is noticeable, suggesting that a unique mechanism presides over the preferential hydration process. Moreover, the curve describing the excess solvation number as a function of the solvent composition shows the occurrence of a region of maximal hydration, which probably accounts for the changes in protein stability detected in the presence of cosolvents.     

Density measurement of 1-d confined water by small angle neutron scattering method: pore size and hydration level dependences

Small angle neutron scattering (SANS) is used to measure the absolute density of water contained in 1-D cylindrical pores of a silica material MCM-41-S with pore diameters of 19 and 15 A. By being able to suppress the homogeneous nucleation process inside the narrow pore, one can keep water in the liquid state down to at least 160 K. From a combined analysis of SANS data from both H(2)O and D(2)O hydrated samples, we determined the absolute value of the density of 1-D confined water. We found that the average density of water inside the fully hydrated 19 A pore is 8% higher than that of the bulk water at room temperature. The temperature derivative of the density shows a pronounced peak at T(L) = 235 K signaling the crossing of the Widom line at ambient pressure and confirming the existence of a liquid-liquid phase transition at an elevated pressure. Pore size and hydration level dependences of the density are also studied.     

Neutron scattering study of water confined in periodic mesoporous organosilicas

A series of quasi-elastic neutron scattering measurements were performed using IN6 at the Institute Laue Langevin for a mesoporous organosilica material with phenyl functions, called phenyltriethoxysilane (PTES). The aim of the experiment was to study the diffusion dynamics of nano-scale water clusters inside the hydrophobic pores as a function of temperature and hydration. By fitting the Debye-Waller factor, the data show clearly the different behavior between water, both inside and outside the hydrophobic pores, which resembles bulk water. The mean thermal displacement 〈u²〉 of the external water increases with T almost linearly up to 353 K, while the internal water quickly reaches the maximum at T∼323 K, indicating the confinement by an averaged pore diameter of the porous organosilica.     

A small-angle x-ray scattering study of starch gelatinization in excess and limiting water

The architecture of the starch granule, and its subsequent disruption due to the application of heat and water, known as gelatinization, is of wide interest. Small-angle x-ray scattering (SAXS) techniques have been used to study gelatinization in limiting and excess water. SAXS allows the absorption of water into the differing regions of the starch granule to be monitored. In excess water, a process of cooperative melting can be seen. In limiting water, the crystalline order melts at a higher temperature. These features have been studied, and observed features of the gelatinization related to those known from other techniques. © 1993 John Wiley & Sons, Inc.     

Experimental and theoretical studies of small-angle electron scattering by the water molecule

The total (elastic plus inelastic) intensities of 51 keV electrons scattered by water molecules have been measured over a range of 1 ≦ K = (4π/λ) sin(θ/2) ≦ 12 Å^?1. A computer program, ELIC, has been written for calculating the total intensities of electrons scattered by free molecules. The intensities can be calculated with self-consistent field and configuration interaction wavefunctions. The theoretical intensities based on a CI wavefunction are in good agreement with the observed intensities.     

Investigating the adhesion of water droplets at low temperatures

Adhesion of droplets to solid surfaces at low temperatures is crucial for antifogging and antifreezing, etc. So far, most reports on adhesion measurements have been carried out in air-liquid-solid systems, but it remains difficult to precisely investigate the adhesion at low temperatures due to the uncontrollable condensation. On the basis of the liquid-liquid-solid system, a new method to measure the adhesion of water droplets at low temperatures was developed and employed. Moreover, the reported method could be viable in other liquid-liquid-solid systems with wider temperature window; thus, it will find applications in broad fields such as crude oil recovery, ore-dressing, and transfer printing.     

Structural behaviour of mixed cationic surfactant micelles: a small-angle neutron scattering study

Self-assembly in mixtures of two single-chain cationic surfactants, with different tail lengths (CTAB and DTAB) as well as of a single-chain (DTAB) and a double-chain (DDAB) cationic surfactant, with identical tail lengths, have been investigated with small-angle neutron scattering (SANS) and rationalised in terms of bending elasticity properties. The growth behaviour of micelles with respect to surfactant composition appears completely different in the two surfactant mixtures. DTAB form small oblate spheroidal micelles in presence of [NaBr] = 0.1 M that transform into prolate spheroidal mixed CTAB/DTAB micelles upon adding moderate amounts of CTAB, so as to give a mole fraction y = 0.20 in solution. Most unexpectedly, upon further addition of CTAB the mixed CTAB/DTAB micelles grow with an almost equal rate in both length and width directions to form tablets. In contrast to this behaviour, mixed DDAB/DTAB micelles grow virtually exclusively in the length direction, in presence of [NaBr] = 0.1 M, to form elongated ellipsoidal (tablet-shaped) and subsequently long wormlike micelles as the fraction of DDAB in the micelles increases. Mixed DDAB/DTAB micelles grow to become as long as 2000 Å before an abrupt transition to large bilayer structures occurs. This means that the micelles are much longer at the micelle-to-bilayer transition as compared to the same mixture in absence of added salt. It is found that the point of transition from micelles to bilayers is significantly shifted towards higher fractions of aggregated DTAB as an appreciable amount of salt is added to DDAB/DTAB mixtures, indicating a considerable reduction of the spontaneous curvature with an increasing [NaBr]. By means of deducing the various bending elasticity constants from our experimental results, according to a novel approach by ours, we are able to conclude that the different growth behaviours appear as a consequence of a considerably lower bending rigidity, as well as higher saddle-splay constant, for DDAB/DTAB surfactant mixtures in presence of [NaBr] = 0.1 M, as compared to mixtures of CTAB/DTAB in [NaBr] = 0.1 M and DDAB/DTAB in absence of added salt.     

Interaction of blockcopolymer micelles as probed by small-angle neutron and by small-angle X-ray scattering

 The analysis of the interaction of micelles formed by a blockcopolymer is given by means of small-angle X-ray (SAXS) and small-angle neutron scattering (SANS). The blockcopolymer consists of poly(styrene) and poly(ethylene oxide) (molecular weight of each block: 1000 g/mol) and forms well-defined micelles (weight-association number: 400, weight-average diameter: 15.4 nm) in water. The internal structure has been studied previously (Macromolecules 29:4006 (1996)) by SAXS. There it has been shown that the micelles are spherical objects. The structure factor S(q) as a function of the scattering vector q (q=(4π/λ) sin (θ/2); λ: wavelength of the radiation in the medium; θ: scattering angle) can be extracted from both sets of small-angle scattering data (SANS: q≤0.4 nm^-1; SAXS: q≤0.6 nm^-1). It is shown that particle interaction in the present system can be described by assuming soft interaction which is modeled by a square-step potential. Received: 12 May 1997 Accepted: 9 July 1997     

Structural coarsening of aspen wood by hydrothermal pretreatment monitored by small- and wide-angle scattering of X-rays and neutrons on oriented specimens

Structural changes across multiple length scales associated with hydrothermal pretreatments of biomass were investigated by using small- and wide-angle X-ray and neutron scattering on oriented specimens. Isotropic and anisotropic scattering components were numerically separated and then interpreted as contributions from matrix and cellulose components, respectively. Equatorial diffraction peaks present in the isotropic component became sharper after hydrothermal treatments or ammonia treatment. Before pretreatment the wet cell wall was found to be homogeneous in the 10–100 nm range and scattering below Q = 0.5 (nm^?1) was dominated by surface scattering from the lumen. After pretreatment with acid or steam at 160 or 180 °C, density fluctuation developed in the cell wall at length scales above 10 nm, most likely due to lateral coalescence of microfibrils that partially co-crystallize to give larger apparent crystal sizes. A density fluctuation up to about 100 nm appeared in the isotropic component after acid and steam pretreatments due to morphological changes in the hemicellulose and lignin matrix.     

The study of liposomes,lamellae and membranes using neutrons and X-rays

Advances in colloid and interface science have stimulated a renewed interest in the study of lipid–water systems. In recent years, much progress has been achieved in the domains of sample preparation and sample environments, offering the unique possibility of studying these systems under physiologically relevant conditions. In the case of neutron reflectometry, new experimental protocols allow for the unique structural determination of one-dimensional membrane profiles, while the advantages offered by synchrotron radiation (e.g., high flux and spatial resolution) make X-rays an excellent tool for addressing questions pertaining to membrane interactions. Most recently, holographic techniques are evolving so that one day they may be able to resolve, to atomic resolution, the structure of poorly crystallized membrane associated proteins.     

Monitoring coalescence behavior of soft colloidal particles in water by small-angle light scattering

The fractal dimension (D _f) of the clusters formed during the aggregation of colloidal systems reflects correctly the coalescence extent among the particles (Gauer et al., Macromolecules 42:9103, 2009). In this work, we propose to use the fast small-angle light scattering (SALS) technique to determine the D _f value during the aggregation. It is found that in the diffusion-limited aggregation regime, the D _f value can be correctly determined from both the power law regime of the average structure factor of the clusters and the scaling of the zero angle intensity versus the average radius of gyration. The obtained D _f value is equal to that estimated from the technique proposed in the above work, based on dynamic light scattering (DLS). In the reaction-limited aggregation (RLCA) regime, due to contamination of small clusters and primary particles, the power law regime of the average structure factor cannot be properly defined for the D _f estimation. However, the scaling of the zero angle intensity versus the average radius of gyration is still well defined, thus allowing one to estimate the D _f value, i.e., the coalescence extent. Therefore, when the DLS-based technique cannot be applied in the RLCA regime, one can apply the SALS technique to monitor the coalescence extent. Applicability and reliability of the technique have been assessed by applying it to an acrylate copolymer colloid.     

On the interpretation of small-angle X-ray scattering during water adsorption by carbon adsorbents

Two models accounting for the changes of shape of the small-angle X-ray scattering (SAXS) curves during water adsorption by carbon adsorbents are discussed. The first model is based on the assumption of partial filling of the pore space; the second one presumes micropore swelling during water adsorption. Analysis of the results allows one to conclude that the first model is valid. This conclusion is in agreement with adsorption investigation data.Deseased 1993.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1220–1223, July, 1993.     

Amphiphilic networks based on cross-linked star polymers: a small-angle neutron scattering study

Four different polymer model networks of identical molecular architecture based on cross-linked stars (CLSs) were investigated by small-angle neutron scattering (SANS). One of the model networks was a hydrophilic homopolymer CLS of 2-(dimethylamino)ethyl methacrylate (DMAEMA), and the other three were amphiphilic copolymer CLS co-networks of DMAEMA and hydrophobic methyl methacrylate (MMA): one based on a star with random copolymer arms and the other two based on heteroarm star copolymers. For the homopolymer and random copolymer star networks, the scattering curves show shoulders at low values of the scattering vector, indicating very small compacted domains with radii of 1.0-1.3 nm, with the random copolymer star co-network having somewhat larger domains. For the heteroarm star co-networks, pronounced peak maxima are observed because of a much higher degree of microphase structuring than for the other two co-networks. The scattering patterns are described by the presence of well-defined hydrophobic domains with radii of 7.1 and 10.3 nm in the two heteroarm star co-networks, respectively, thereby proving pronounced microphase separation in these systems.