Small-angle neutron scattering study of the effect of n -alkanols on interacting micelles

Small-angle neutron scattering cross-section distributions of sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DTAB), each 0·3 M in D₂O were obtained in the absence and presence of 0·1 M 1-pentanol, 1-hexanol, and 1-octanol at 25°C. The Hayter-Penfold type analysis was adopted. An ellipsoidal model with semiminor axis (a=16·5 ?) and semimajor axes (b=40·7 ? and 29·8 ?) for pure SDS and DTAB micelles has produced best fits. On increasing alkanol chain lengths an increase inb values was found. Micellar parameters like effective radius (R), (a, b), fraction of counterions per micelle, and intermicellar distances were obtained. Surfactant aggregation number, additive aggregation number intermicellar interaction potentials and values of Debye screening length were obtained for SDS and DTAB in the presence of alkanols. Implications of partitioning effect, surfactant ionicity and intermicellar potentials on the microstructures are rationalised.     

Small-angle neutron scattering study of sodium cholate and sodium deoxycholate interacting micelles in aqueous medium

Small angle neutron scattering (SANS) measurements of D₂O solutions (0.1 M) of sodium cholate (NaC) and sodium deoxycholate (NaDC) were carried out atT= 298 K. Under compositions very much above the critical micelle concentration (CMC), the bile salt micelle size growths were monitored by adopting Hayter-Penfold type analysis of the scattering data. NaC and NaDC solutions show presence of correlation peaks atQ = 0.12 and 0.1 ?_-1 respectively. Monodisperse ellipsoids of the micelles produce best fits. For NaC and NaDC systems, aggregation number (9.0, 16.0), fraction of the free counterions per micelle (0.79, 0.62), semi-minor (8.0 ?) and semi-major axes (18.4, 31.7 ?) values for the micelles were deduced. Extent of micellar growth was studied using ESR correlation time measurements on a suitable probe incorporating NaC and NaDC micelles. The growth parameter (axial ratio) values were found to be 2.3 and 4.0 for NaC and NaDC systems respectively. The values agree with those of SANS.     

Micelle formation in sodium hexadecyl sulfate surfactant solutions studied by small-angle neutron scattering

Micelle formation in aqueous sodium hexadecyl sulfate solutions is studied by small-angle neutron scattering. Measurements are carried out at different concentrations (1.1, 2.2, 3.2, 5.4, 10.9 and 32.8 mM/dm³) and at different temperatures (40°, 50°, and 60°C). The monotonous evolution of interparticle correlation can be observed on the measured scattering patterns. At high concentrations (10.9 and 32.8 mM/dm³) scattering patterns are described by interacting ellipsoids, but at low concentrations by non-interacting ellipsoids. Computation of the distance distribution function proved the ellipsoidal shape at 10.9 and 32.8 mM/dm³, but showed an unexpectedly large particle dimension and elongation of the micelles at lower concentrations.     

Small-angle neutron scattering from a hexagonal phase under shear

Summary The shear orientation of a micellar hexagonal liquid crystalline phase was investigated by small-angle neutron scattering. The hexagonal phase in the quiescent state showed a symmetrical scattering pattern typical of a polydomain structure. Enhanced scattering along the flow direction was observed during shear and the anisotropy of scattering intensity became stronger with increasing shear rate. The anisotropic scattering pattern corresponds to an orientation perpendicular to the flow direction and can be interpreted as a log-rolling state. The oriented sample did not relax after cessation of shear. The results from small-angle neutron scattering confirm data obtained previously from rheo-small angle light scattering measurements and are discussed in comparison to shear alignment of lyotropic liquid crystalline polymer solutions.     

Small-angle neutron scattering from Al-Zn and AI-Zn-Mg alloys during Guinier-Preston zone formation

Summary Small-angle neutron scattering from A1-6.8 at % Zn and Al-6.8 at % Zn-0.1 at % Mg alloys during Guinier-Preston zone formation have been measured at KUR (Kyoto University Reactor). The samples were quenched from 300 °C into brine at -20 °C and kept at 77 K. They were aged at 40 °C for various periods ranging from 0 up to 1000 minutes each with subsequent neutron measurement at 77 K. The observed temporal evolution of the cross section can be interpreted qualitatively in terms of Saito's formula which consists of two distinct parts due to the incoherent anomalous fluctuation and to the coherent ordered structure of the concentration.

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Zusammenfassung Die Kleinwinkelstreuung der Neutronen von A1-6.8 at % Zn und Al-6.8 at % Zn- 0.1 at % Mg-Legierungen während der Guinier-Preston-Zonen-Bildung wurde am KUR (Kyoto Universität Reaktor) gemessen. Die Proben wurden aus 300 °C in Salzwasser von — 20 °C abgeschreckt und bei 77 K gehalten. Sie wurden bei 40 °C während der verschiedenen Zeitdauer von 0 bis 1000 Minuten mit der nachfolgenden Neutronenmessung bei 77 K gealtert. Die gemessene zeitliche Entwicklung des Streuquerschnittes kann qualitativ erklärt werden in übereinstimmung mit Saitos Formel, die aus zwei verschiedenen Teilen besteht, die der inkohärenten anomalen Schwankung und der kohärenten geordneten Struktur der Konzentration entsprechen.

     

Determination of the chain conformation of polypropylene in the crystalline state by neutron scattering

Summary Wide and small angle neutron scattering from melt-crystallised isotactic polypropylene mixtures of deuterated and protonated molecules were measured in aQ range of 0.003 Å^–1 to 0,8 Å^–1. The scattering curves between 0.1 Å^–1 and 0.8 Å^–1 are very sensitive to the amount of folding of the chains within a lamella. Different annealing conditions which influence the degree of crystallinit between 0.39 and 0.67 and the long spacing between 125 Å and 245 Å had an insignificant influence on the scattering in this range. For various arrangements of crystalline sequences scattering functions were calculated. Best agreement with the experimental scattering curves was obtained for a mixture of single and double crystalline sequences of equal proportion. An adjacent reentry folding model for the molecular conformation is not consistent with the experimental data.The neutron scattering experiments have been performed at the Institute Laue-Langevin in Grenoble/France and at the Kernforschungsanlage Jülich/Germany.     

Viscosity reduction in polymer nanocomposites: Insights from dynamic neutron and X-ray scattering

The addition of nanoparticles to a polymer matrix can in certain cases induce a reduction in viscosity, with respect to the pure matrix, in the resulting composites. This counterintuitive phenomenon cannot be explained using the most common rheological models. For this reason, it has been chosen as a good example in this paper to demonstrate the value and methods of dynamic X-ray and neutron scattering techniques for the investigation of polymer nanocomposites. An overview of the main results on this topic is presented together with an introduction to the basic concepts relating to X-ray photon correlation spectroscopy, neutron backscattering, and neutron spin echo measurements.     

A scattering study on intermicellar interactions and structures of polymeric micelles

The micellar structure is usually considered to be composed of a hard sphere (liquid) core and a heavily solvated corona. Therefore, the correction for intermicellar interactions at finite concentrations can be relatively complicated. In this article, small-angle neutron scattering of a copolymer, known as Pluronic L64 (PEO₁₃PPO₃₀PEO₁₃), in o-xylene in the presence of D₂O is used to demonstrate that, based on the hard sphere approximation, intermicellar interactions can be corrected by representing the micellar size as having an equivalent hard sphere radius. The procedure remains valid even if the micellar shape becomes asymmetric, with axial ratios of 3 ? 4. For the present system, the equivalent hard sphere radius corresponds to the micellar core radius plus one-half of the micellar shell thickness. With the equivalent hard sphere approach, the scattering behavior of the micelle could be described by using a core-shell structure. © 1994 John Wiley & Sons, Inc.     

Structure of casein micelles I. Small angle neutron scattering and light scattering fromβ- andχ-casein

Casein is the main protein component of milk and is of remarkable colloidal stability. Under the influence of milk clotting enzymes casein shows the striking behaviour of coagulation. This clotting process has already been studied by other groups, neglecting the fact that casein is not a homogeneous protein. The purpose of the present study is focused, in this first stage, on the determination of the structure of the various casein components. In cooperation with other laboratories we have been able to obtain the well separated individual proteins. Studies have been performed so far with- and-casein. For detailed structural information we carried out small angle neutron scattering and combined static and dynamic light scattering measurements and determined the molecular weight,M _w, the radius of gyration, S ² the hydrodynamic radius,R _H, the-value and the particle scattering factor, P_z(q). The two caseins show a strikingly different behaviour. For the-casein we found a star-like structure, i. e. an aggregation pattern that is expected for a common micelle. The micelle consists of about 38 monomer chains. The aggregates of-casein appear to be composed of star-like submicelles, where each submicelle contains nine-casein chains and the total degree of aggregation is about 140.     

Neutron scattering studies on micelles of dodecylhexaoxyethylene glycol monoether

Small angle neutron scattering studies have been made on solutions of dodecylhexaoxyethylene glycol in D₂O above the critical micelle concentration and as a function of temperature. It was possible to fit the experimental data at low values of scattering vector using a cylindrical model for the micelle shape.     

Small angle neutron scattering and its application in battery systems

Small angle neutron scattering is a powerful, non-destructive technique that can provide both structural and compositional information. Recently, it has been applied to the field of battery research and has helped elucidate some of the phenomena that are traditionally difficult to probe, including lithiation mechanisms, solid electrolyte interface formation/composition, and electrode microstructure. Specific components of interest can be selectively probed through the application of targeted experiments, contrast variation, and specific composition/structural models gained from complementary data from other analytical techniques.     

Small-angle neutron-scattering study of concentrated nonionic-amphiphile solutions

The structure of aqueous solutions of two polyoxyethylene non-ionic amphiphiles, C₁₀E₅ and C₈E₄, is studied by small-angle neutron-scattering along isothermal paths crossing the isotropic single-phase region from 0% to 100% amphiphile volume fractions. The scattered intensityI(k) shows a peak at a valuek _m , which grows monotonically as the amphiphile volume fraction increases. The interpretation of the scattering data lead to the following conclusion: as increases the micellar structure becomes less and less sharp, but some orientational correlations between neighboring amphiphile molecules are preserved even in the pure amphiphile phase.     

Structural and dynamic single chain behaviour in a binary blend of low molecular mass poly(siloxanes) as studied by small angle neutron scattering and neutron spin echo spectroscopy

Elastic and quasi elastic neutron scattering investigations, using the small angle neutron scattering (SANS) and neutron spin echo (NSE) techniques, respectively, were performed in order to study the static and dynamic single chain behaviour in a binary blend of low molecular mass deuterated poly(dimethylsiloxane) (d-PDMS) and protonated poly(ethylmethylsiloxane) (p-PEMS) at the critical composition _c. Since the single chain observation requires that only a small amount of one of both components is labelled, the d-PDMS/p-PEMS system was modified in such a way that the major part of the protonated PEMS component was replaced by the corresponding deuterated material. Although the de-mixing of the PEMS isotopes occurs far below the de-mixing of the PDMS/PEMS system the resulting chemically binary d-PDMS/d-PEMS/p-PEMS blend with the volume composition 0.5/0.425/0.075 is strictly speaking a ternary system. This complication had to be taken into account, in particular with respect to the correct evaluation of the SANS data.The careful analysis of the SANS curves allows one to determine all three thermodynamic interaction parameters with reasonable reliability and gives evidence that the radii of gyration agree with those, which were determined in corresponding isotopic PDMS and PEMS blends. This is in contrast to the observation on real binary PDMS/PEMS blends at _c, where the collective conformational properties exhibit a considerable chain expansion. The NSE data of the ternary system follow completely the predictions of the Rouse model, which describes the dynamics of a dense low molecular mass polymeric system in a single chain approximation. The experimental observations are also in contrast to the results of former NSE measurements on binary PDMS/PEMS blends, where a transition from Rouse behaviour at short times to a much weaker relaxation at longer times became obvious.The results of the static and dynamic single chain behaviour presented here confirm the results of a computer simulation on a low molecular mass binary blend at the critical concentration, where explicitly the pure single chain behaviour was probed and no indications for chain expansion and deviations from the Rouse dynamics were found.Dedicated to Prof. Dr. Erhard W. Fischer on the occasion of the 75th anniversary of his birthday.     

Small angle neutron scattering study of alkyl polyoxyethylene sulfate micelles. Sodium dodecyl-(oxyethylene)2 sulfate in D2O-H2O mixtures at 25°C

SANS data have been obtained for C₁₂H₂₅ (OC₂H₄)₂SO₄ Na. Results have been obtained for i) a series of solutions of variable concentration of the surfactant, ii) an approximately 0.07 M surfactant concentration to which variable amounts of NaCl were added, iii) a series of solutions 0.058M in surfactant but in different D₂O-H₂O mixtures. The SANS data can be described in terms of a model of monodispersed hard spheres interacting via a screened Coulombic potential. The micelles seem to be able to tolerate substantial amounts of salt without changing the internal structure.     

Light scattering study of solubilization of organic molecules by block copolymer micelles in aqueous media

Block copolymers, when dissolved in a selective solvent, form spherical micelles. These micelles can selectively solubilize organic molecules otherwise insoluble in the pure solvent. In this study, we report solubilization of organic molecules by styrene-methacrylic acid block copolymer micelles in aqueous buffers. A light scattering technique was developed to determine the extent of micellar solubilization. Our results indicate that the extent of micellar solubilization depends on the chemical nature of organic molecules, specifically, on the interactions between the organic compound and polystyrene. A thermodynamic model has been developed to describe micellar solubilization. The theoretical calculation agrees reasonably well with the experimental results for two micellar samples examined. ©1995 John Wiley & Sons, Inc.     

Attractive interactions in critical scattering from non-ionic micelles

We have studied the temperature-dependent critical scattering of both light and neutrons from aqueous solutions ofn-octyl pentaoxyethylene glycol monoether (C₈E₅). We show that the assumption of a short-ranged temperature-dependent attractive pair potential between approximately spherical micelles of constant size permits a quantitative analysis of the neutron scattering data. The analysis, which is undertaken using current liquid-state theory and is in analytic form, contains only one free parameter, the depth of the attractive potential. We find that a potential with a range of only a fraction of a nm is sufficient to generate spatial correlations over tens of nm as the attractive potential deepens on approaching the critical temperature. The analysis also provides a semi-quantitative understanding of the light scattering data as a function of concentration and temperature, and leads to a qualitative prediction of the form of the phase diagram. Numerical values obtained are consistent with the hypothesis that the primary effect of raising the temperature is to lower the degree of structure of water near the micelle surface, allowing increased van der Waals attraction due to closer contact.     

Dielectric RheoSANS: a mutual electrical and rheological characterization technique using small-angle neutron scattering

Dielectric RheoSANS is a new measurement technique that combines in situ electrical, mechanical, and scattering capabilities to probe the structure and dynamics of soft materials at equilibrium and under flow. This review summarizes the technique and presents data from model systems including conductive polymers, colloidal suspensions, and viscoelastic surfactant solutions. Finally, we identify several areas within soft matter that have historically combined dielectric, rheological, and structural characterization methods and discuss the outlook for studying those systems with dielectric RheoSANS.     

Small-angle neutron scattering from mixtures of sodium dodecyl sulfate and a cationic, bolaform surfactant containing azobenzene

This paper reports on the microstructures formed in aqueous solutions containing mixtures of sodium dodecyl sulfate (SDS) and a photosensitive, bolaform surfactant, bis(trimethylammoniumhexyloxy)azobenzene dibromide (BTHA). By using quasi-elastic light scattering and small-angle neutron scattering, we determined that aqueous solutions containing SDS and the trans isomer of BTHA (0.1 wt % total surfactant, 15 mol % BTHA, 85 mol % SDS) form vesicles with average hydrodynamic diameters of 1350 +/- 50 angstroms and bilayer thicknesses of 35 +/- 2 angstroms. The measured bilayer thickness is consistent with a model of the vesicle bilayer in which the trans isomer of BTHA spans the bilayer. Upon illumination with UV light, the BTHA underwent photoisomerization to produce a cis-rich photostationary state (80% cis isomer). We measured this photoisomerization to drive the reorganization of vesicles into cylindrical aggregates with cross-sectional radii of 19 +/- 3 angstroms and average hydrodynamic diameters of 240 +/- 50 angstroms. Equilibration of the cis-rich solution in the dark at 25 degrees C for 12 h or illumination of the solution with visible light leads to the recovery of the trans-rich photostationary state of the solution and the reformation of vesicles, thus demonstrating the potential utility of this system as the basis of a tunable fluid.     

Effects of temperature on neutron scattering from aqueous solutions of hydrophobically modified poly(ethylene oxide)

The effect of temperature on the structure of aqueous dispersions of hydrophobically end-capped poly(ethylene oxide) (PEOM) was investigated by small angle neutron scattering (SANS). Polymers with hydrogenated or deuterated n-octadecyl end-groups were studied in heavy water or in a mixture heavy water / water, respectively. In the latter case the PEO chains were selectively matched. In all the cases, the scattering curves were characterised by a main peak which revealed organisation of polymers into micelles consisting of hydrophobic cores surrounded by repulsive PEO coronae. Measurements were performed in the semi-dilute regime where micelles coronae overlap. At constant polymer concentration, an increase in temperature leads to decreasing solvent strength of water for the PEO chains and decreasing repulsion between the PEO coronae. As a result, the intensity of the peak in a mixture of water /heavy water decreases with temperature On the contrary, in heavy water, the peak of the scattered intensity increases with increasing temperature. This scattering behaviour is interpreted on the basis of a scaling theory of the semi-dilute solutions of star-like polymer micelles.     

Small-angle neutron scattering from surfactant-assisted aqueous dispersions of carbon nanotubes

The mechanism of surfactant-assisted dispersion of single-walled carbon nanotubes in water is studied by small-angle neutron scattering. The previously hypothesized formation of cylindrical micelles with the nanotubes forming the core of cylinders is inconsistent with the data presented. The scattering data favor a random structureless adsorption model for the dispersion of the nanotubes.