Spin-echo Small-angle Neutron Scattering Research Articles

Magnetised foils as white beam π/2 flippers for polarised neutrons

Magnetic foils as white beam π/2 flippers for polarised neutrons will be discussed. Their main advantage is the application for Larmor precession in strongly inclined precession regions as used in Larmor diffraction and especial in Spin Echo Small Angle Neutron Scattering (SESANS). Inclination angles of a few degrees in fields from mT up to hundreds of mT are achievable that are not possible with present conventional coils. The application in Larmor diffraction will be discussed and the application in SESANS will be explained in detail and supported by a simulated experiment.

Nanoparticles decorated with proteolytic enzymes, a promising strategy to overcome the mucus barrier

The intestinal mucus gel layer represents a stumbling block for drug adsorption. This study is aimed to formulate a nanoparticulate system able to overcome this barrier by cleaving locally the glycoprotein substructures of the mucus. Mucolytic enzymes such as papain (PAP) and bromelain (BRO) were covalently conjugated to poly(acrylic acid) (PAA). Nanoparticles (NPs) were then formulated via ionic gelation method and characterized by particle size, zeta potential, enzyme content and enzymatic activity. The NPs permeation quantified by rotating tube studies was correlated with changes in the mucus gel layer structure determined by pulsed-gradient-spin-echo NMR (PGSE-NMR), small-angle neutron scattering (SANS) and spin-echo SANS (SESANS). PAP and BRO functionalized NPs had an average size in the range of 250 and 285nm and a zeta potential that ranged between −6 and −5mV. The enzyme content was 242μgenzyme/mg for PAP modified NPs and 253μgenzyme/mg for BRO modified NPs. The maintained enzymatic activity was 43% for PAP decorated NPs and 76% for BRO decorated NPs. The rotating tube technique revealed a better performance of BRO decorated NPs compared to PAA decorated NPs, with a 4.8-fold higher concentration of NPs in the inner slice of mucus. Addition of 0.5wt% of enzyme functionalized NPs to 5wt% intestinal mucin led to c.a. 2-fold increase in the mobility of the mucin as measured by PGSE-NMR indicative of a significant break-up of the structure of the mucin. SANS and SESANS measurements further revealed a change in structure of the intestinal mucus induced by the incorporation of the functionalized NPs mostly occurring at a length scale longer than 0.5μm. Accordingly, BRO decorated NPs show higher potential than PAP functionalized NPs as mucus permeating drug delivery systems.

Spin echo small angle neutron scattering using a continuously pumped (3)He neutron polarisation analyser.

We present a new instrument for spin echo small angle neutron scattering (SESANS) developed at the Low Energy Neutron Source at Indiana University. A description of the various instrument components is given along with the performance of these components. At the heart of the instrument are a series of resistive coils to encode the neutron trajectory into the neutron polarisation. These are shown to work well over a broad range of neutron wavelengths. Neutron polarisation analysis is accomplished using a continuously operating neutron spin filter polarised by Rb spin-exchange optical pumping of (3)He. We describe the performance of the analyser along with a study of the (3)He polarisation stability and its implications for SESANS measurements. Scattering from silica Stöber particles is investigated and agrees with samples run on similar instruments.

Non-uniform transmission of supermirror devices for neutron polarization

Polarizing supermirrors have been widely used in neutron scattering facilities where they have been employed as neutron spin filters to polarize neutron beams as well as analyze their polarization. In the past, the performance of polarizing supermirrors has been limited by their small acceptance angle, which made them less suitable for use at short wavelengths or with highly divergent beams. Recent advances in supermirror coatings have led to an array of devices designed to, at least partially, overcome this limitation. V-polarizers and multi-channel polarizers have been employed in several different types of neutron scattering instruments. However, our observations in the field where these types of polarizers are in use have raised concerns about their performance. In this paper, we report on detailed Monte-Carlo simulations performed on a multi-channel polarizer used on a prototype Spin-Echo Small Angle Neutron Scattering (SESANS) instrument to better understand its performance. Our results show that careful simulations of polarizers based on mirror reflection are needed to determine whether a particular design is suitable for SESANS applications.

Present status and prospects for Spin-Echo Small-Angle Neutron Scattering (SESANS) at PIK neutron source

We discuss the present status and the prospects of Spin-Echo Small-Angle Neutron Scattering (SESANS) against the background of the available expertise and the neutron source PIK at PNPI (Gatchina). Two options for SESANS instruments are reviewed: (1) monochromatic with π-flipping permalloy foils and (2) with adiabatic radio frequency spin flippers in a white beam, combined with time-of-flight data collection. A software tool for quantitative prediction of the technical properties of option (2) is developed. For both options, we show that a SESANS instrument which can compete with instruments elsewhere, is realistic. For option (2), we suggest a perspective of spin-echo-length range such that neutron interference experiments become feasible.

A new approach for probing matter in periodic nanoconfinements using neutron scattering

The efficacy of spin-echo small-angle neutron scattering (SESANS) combined with an exact dynamical theory (DT) model in resolving the arrangement of spherical colloidal particles in planar confinements, such as the channels of a rectangular diffraction grating, is reported. SESANS data obtained with a suspension of charge-stabilized 180 nm silica particles in contact with a silicon diffraction grating, with ∼650 nm-wide channels, show clear deviations from the signal expected from a homogenous distribution of the suspension. DT fits to the data indicate that the colloidal particles are almost twice as concentrated in the channels as they are in the neighboring bulk suspension, consistent with a structure in which the particles are arranged in close-packed sheets parallel to the walls of the confining channels.

Direct comparison of SESANS and SAXS to measure colloidal interactions

We present a systematic comparison of conventional small-angle X-ray scattering (SAXS) with the relatively new real-space technique, spin-echo small-angle neutron scattering (SESANS). We apply both techniques to colloidal suspensions where the particles interact as hard spheres, with electrostatic repulsions, or with polymer-induced depletion attractions. We successfully model the data sets with the appropriate colloid-colloid interaction potentials to determine the colloid radius, effective volume fraction, and surface charge, while illustrating the different representations of colloid structuring related to both techniques.

Small Angle X-Ray and Neutron Scattering from Solutions of Biological Macromolecules. By Dmitri I. Svergun, Michel H. J. Koch, Peter A. Timmins and Roland P. May. IUCr Texts on Crystallography, No. 19. Oxford University Press, 2013. Pp. 358. Price (hardback) £49.99. ISBN: 978-0-19-963953-3.

<b>Small Angle X-Ray and Neutron Scattering from Solutions of Biological Macromolecules</b>. By Dmitri I. Svergun, Michel H. J. Koch, Peter A. Timmins and Roland P. May. IUCr Texts on Crystallography, No. 19. Oxford University Press, 2013. Pp. 358. Price (hardback) £49.99. ISBN: 978-0-19-963953-3.

Inter-particle correlations in a hard-sphere colloidal suspension with polymer additives investigated by Spin Echo Small Angle Neutron Scattering (SESANS)

Using a neutron scattering technique that measures a statistically-averaged density correlation function in real space rather than the conventional reciprocal-space structure factor, we have measured correlations between poly(methyl-methacrylate) (PMMA) colloidal particles of several sizes suspended in decalin. The new method, called Spin Echo Small Angle Neutron Scattering (SESANS) provides accurate information about particle composition, including the degree of solvent penetration into the polymer brush grafted on to the PMMA spheres to prevent aggregation. It confirms for particles, between 85 nm and 150 nm in radius that inter-particle correlations closely follow the Percus-Yevick hard-sphere model when the colloidal volume-fraction is between 30% and 50% provided the volume-fraction is used as a fitted parameter. No particle aggregation occurs in these systems. When small amounts of polystyrene are added as a depletant to a concentrated suspension of PMMA particles, short-range clustering of the particles occurs and there is an increase in the frequency of near-neighbor contacts. Within a small range of depletant concentration, near-neighbor correlations saturate and large aggregates with power law density correlations are formed. SESANS clearly separates the short- and long-range correlations and shows that, in this case, the power-law correlations are visible for inter-particle distances larger than roughly two particle diameters. In some cases, aggregate sizes are within our measurement window, which can extend out to 16 microns in favorable cases. We discuss the advantages of SESANS for measurements of the structure of concentrated colloidal systems and conclude that the method offers several important advantages.

On characterization of anisotropic plant protein structures.

In this paper, a set of complementary techniques was used to characterize surface and bulk structures of an anisotropic Soy Protein Isolate (SPI)-vital wheat gluten blend after it was subjected to heat and simple shear flow in a Couette Cell. The structured biopolymer blend can form a basis for a meat replacer. Light microscopy and scanning electron microscopy provided a detailed view of structure formation over the visible surfaces of the SPI-gluten blend. Protein orientation in the direction of the flow was evident and fibrous formation appeared to exist on the macro- and micro-scale. Furthermore, according to texture analysis, the structured biopolymer obtained from the Couette Cell after processing at 95 °C and 30 RPM for 15 min has high tensile stress and strain anisotropy indices (∼2 and ∼1.8, respectively), comparable to those of raw meat (beef). The novel element in this work is the use of the neutron refraction method, utilizing spin-echo small angle neutron scattering (SESANS), to provide a look inside the anisotropic biopolymer blend complementing the characterization provided by the standard techniques above. With SESANS, it is possible to quantify the number of fibre layers and the orientation distribution of fibres. For a specimen thickness of 5 mm, the obtained number of fibre layers was 36 ± 4 and the standard deviation of the orientation distribution was 0.66 ± 0.04 radians. The calculated thickness of one layer of fibres was 138 μm, in line with SEM inspection.

Present Status and Prospects for Spin-Echo Small-Angle Neutron Scattering (SESANS) at PIK Neutron Source

Present Status and Prospects for Spin-Echo Small-Angle Neutron Scattering (SESANS) at PIK Neutron Source

Spin-echo small-angle neutron scattering device: Test experiment using SiO2 colloidal particles

The results of the first experiments with a spin-echo small-angle neutron scattering (SESANS) device built at the VVR-M reactor at the St. Petersburg Institute of Nuclear Physics (Gatchina) are presented. SESANS utilizes the possibilities of the spin-echo method for determining the structural characteristics of materials in real space with on the 10–104-nm length scale. Validation measurements are conducted using SiO2 colloidal particles. Samples of SiO2 spheres with a diameter determined through scanning electron microscopy and synchrotron-radiation ultra-small-angle scattering are used for calibration of the device. Approximation of the data obtained with the SESANS device was conducted using the autocorrelation function for dilute monodisperse spheres. The sizes of the spheres determined via SESANS are in agreement with those determined by other methods within the experimental error.

DCD USANS and SESANS: a comparison of two neutron scattering techniques applicable for the study of large-scale structures

This paper provides a comparison of the capabilities of two techniques for extending the range of conventional small-angle neutron scattering (SANS) towards the micrometre length scale, namely the double-crystal diffraction ultra-small-angle neutron scattering (DCD USANS) technique, which uses perfect silicon crystals in Bragg reflection, and spin-echo SANS (SESANS), a method that uses the spin precessions of a polarized neutron beam. Both methods encode the scattering angle to very high precision. Based on round-robin test measurements, the strengths and weaknesses of the two techniques are discussed with respect to the measurement of the particle size of monodisperse scatterers, and potential performance gains for state-of-the-art DCD USANS and SESANS instruments are investigated.

Elucidation of spin echo small angle neutron scattering correlation functions through model studies

Several single-modal Debye correlation functions to approximate part of the overall Debey correlation function of liquids are closely examined for elucidating their behavior in the corresponding spin echo small angle neutron scattering (SESANS) correlation functions. We find that the maximum length scale of a Debye correlation function is identical to that of its SESANS correlation function. For discrete Debye correlation functions, the peak of SESANS correlation function emerges at their first discrete point, whereas for continuous Debye correlation functions with greater width, the peak position shifts to a greater value. In both cases, the intensity and shape of the peak of the SESANS correlation function are determined by the width of the Debye correlation functions. Furthermore, we mimic the intramolecular and intermolecular Debye correlation functions of liquids composed of interacting particles based on a simple model to elucidate their competition in the SESANS correlation function. Our calculations show that the first local minimum of a SESANS correlation function can be negative and positive. By adjusting the spatial distribution of the intermolecular Debye function in the model, the calculated SESANS spectra exhibit the profile consistent with that of hard-sphere and sticky-hard-sphere liquids predicted by more sophisticated liquid state theory and computer simulation.

Contrast variation in spin-echo small angle neutron scattering

The use of contrast variation in spin-echo small angle neutron scattering (SESANS) experiments is discussed for the case of colloidal structural investigation. On the basis of calculations for several model systems, we find that the contrast variation SESANS technique, in terms of the measured SESANS correlation function G(z), is not sensitive to the structural characteristics of colloidal suspensions consisting of particles with uniform scattering length density profiles. However, its ability to resolve structural heterogeneity, at both intra-colloidal and inter-colloidal length scales, is clearly demonstrated. The prospect of using this new technique to investigate structural information that is difficult to probe in other ways is also explored.

Prospect for characterizing interacting soft colloidal structures using spin-echo small angle neutron scattering

Spin-echo small angle neutron scattering (SESANS) provides a new experimental tool for structural investigation. Due to the action of spin-echo encoding, SESANS measures a spatial correlation function in real space, as opposed to the structure factor S(Q), I(Q), in momentum (Q) space measured by conventional small angle neutron scattering. To establish the usefulness of SESANS in structural characterization, particularly for interacting colloidal suspensions, we have previously conducted a theoretical study of the SESANS correlation functions for model systems consisting of particles with uniform density profiles [X. Li, C.-Y. Shew, Y. Liu, R. Pynn, E. Liu, K. W. Herwig, G. S. Smith, J. L. Robertson, and W.-R. Chen J. Chem. Phys. 132, 174509 (2010)]. Within the same framework, we explore in the present paper the prospect of using SESANS to investigate the structural characteristics of colloidal systems consisting of particles with nonuniform intraparticle mass distribution. As an example, a Gaussian model of interacting soft colloids is used to investigate the manifestation of structural softness in a SESANS measurement. The exploration shows a characteristically different SESANS correlation function for interacting soft colloids, in comparison to that of a uniform hard sphere system. The difference arises from the Abel transform imbedded in the mathematical formalism bridging the SESANS spectra and the spatial autocorrelation function.

Offspec, the ISIS spin-echo reflectometer

OffSpec has been purposely built as a low background, polarised neutron reflectometer with spin-echo for Larmor labeling. The instrument received first neutrons in December 2008 and five of the intended seven modes of operation have now been tested and operated with peer reviewed user experiments. The technical performance of the instrument will be reviewed in each of the modes and future scientific possibilities discussed. Particular attention will be paid to results from spin-echo SANS (SESANS) and spin-echo resolved grazing incidence scattering (SERGIS), where the largest number of measurements have been performed.

Spin-echo small-angle neutron scattering (SESANS) measurements of needle-like crystallites of gelator compounds

From dibenzoyl cystine, a low molecular weight gelator, we have prepared needle shaped crystals at relatively high concentrations. For the first time SESANS measurements are performed on objects with this geometry. From the measurements the average diameter can be seen directly. From a more careful analysis the width distribution is determined. The gel phase itself prepared at lower concentrations did not show any signal, in contrast to what one observes with conventional SANS. This shows the complementarity of SESANS and SANS.

Spin-Echo Small Angle Neutron Scattering analysis of liposomes and bacteria

Two types of liposomes, commonly used in drug delivery studies, and E. coli bacteria, all prepared in H2O, were resuspended in D2O and measured with Small Angle Spin-Echo Neutron Scattering (SESANS). Modeling was performed using correlation functions for solid spheres and hollow spheres. The signal strength and curve shape were more indicative of hollow particles, indicating that the H2O-D2O exchange occurred too fast to be observed with the available time resolution. Fitting the particle diameter and membrane thickness of the hollow sphere model to the data, gave results which were in good agreement with Dynamic Light Scattering (DLS) data and literature, showing as a proof-of-principle that SESANS is able to investigate such systems.SESANS may become a good alternative to conventional tritium studies or a tool with which to study intracellular vesicle transport phenomena, with possible in vivo applications. Calculations show that a substantial change in numbers of a mixed system of small and large biological particles should be observable. A possible application is the destruction by external means of great numbers of liposomes in the presence of tumor cells for triggered drug release in cancer treatment. Since SESANS is both non-invasive and non-destructive and can handle relatively thick samples, it could be a useful addition to more conventional techniques.

Theoretical studies on the structure of interacting colloidal suspensions by spin-echo small angle neutron scattering

The application of the spin-echo small angle neutron scattering (SESANS) technique for structural characterization of interacting colloidal suspensions is considered in this work. The framework to calculate the theoretical SESANS correlation function is briefly laid out. A general discussion regarding the features of the SESANS correlation functions obtained from different model systems is presented. In comparison with conventional elastic scattering tools operating at the same length scale, our mean-field calculations, based on a monodisperse spherical colloidal system, show that the real-space measurement provided by SESANS presents a powerful probe for studying the intercolloid potential. The reason of this sensitivity is discussed from the standpoint of way, in which how the spatial correlations are manifested in different neutron scattering implementations. This study leads to a better understanding regarding the distinction between SANS and SESANS.