Science case

Posted on 03/11/2011 by Jeroen Plomp

Advances in technology can only be made if materials are available that perform according to the requirements. In modern technology, these requirements become more and more stringent. The maximum operating temperature for gas turbines limits their efficiency and is determined by the temperature resistance of materials. The energy content, maximum power, and recyclability of a battery are limited by the performance of its electrodes and electrolyte. The administration of medicines could be more efficient by smart drug-delivery systems.

These are just a few examples of materials limiting the scope of technology. The performance of a material is determined by its composition, structure, and dynamics on the nano- and microscale. In order to further improve the performance of materials, fundamental understanding is needed of both the relation between structure and performance, and between processing conditions and structure.

Such fundamental understanding will even become more crucial in the coming decades, when the availability of several important elements will become an issue, like it is already the case for rare-earth elements. Environmental and health requirements ask for different compositions of paint, detergent, and food products. Physical modelling in these fields must be supported by microscopic analytical techniques as proposed in this project. Bulk observations, detecting also light elements, on the nano- and microscale form an important extension of the present scope of analysis and therefore the present initiative is of great importance to strengthen materials development in order to enable progress in technology. Only via this route great breakthroughs in the development of new materials may be expected. Although all foreseen research, listed in the sections “Research field and research plans” and “Relation to other research groups/centers” have a clear link to applications, the research is generally focused on the fundamental aspects. The foreseen research therefore will lead to new materials, which will be commercially available on a time scale of about 10 years.

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Material science

Posted on 03/11/2011 by Jeroen Plomp

Hybrid organically linked silica is a highly promising class of materials for the application in energy-efficient molecular separation membranes. The materials consist of an amorphous silica matrix in which part of the Si-O-Si bond are replaced by Si-R-Si, where R is an organic group. These materials are extremely stability allowing operation under aggressive working conditions. Depending on R, the pore size may vary from ~ 1 to several 10s of nanometers. Jelassi et al. studied, using SANS, the structure of water in mesoporous silicas depending on the affinity of the pores with respect to water. The versatility of the bridging group offers an extensive
toolbox to tune the nano structure and the affinity of hybrid silica membranes and by doing so to optimize the performance towards specific separation challenges. This provides excellent prospects for industrial applications such as carbon capture and bio fuel production.

The group from Van ‘t Hoff Institute for Molecular Science of the University of Amsterdam will use LARMOR to study the structure and the transport of molecules, such as H2O, H2
and CO2, in these materials as a function of pore size and affinity.

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Magnetism

Posted on 03/11/2011 by Jeroen Plomp

In some cases multiferroics can exhibit structural inhomogeneity in the form of domains with subtly different
structures. For example, when the prototypical spin-spiral multiferroic TbMnO3 is doped on the Tb-site by a few percent of Ca, the ferroelectricity is gradually suppressed via an intermediate state that resembles a relaxor ferroelectric. It is thought that so-called polar nanoregions (PNR) are formed in a non-ferroelectric matrix, the difference in structures of the two regions being too small to resolve using standard diffraction methods.

The higher resolution of Larmor diffraction should allow the structure of the PNR to be distinguished from that of the bulk. Two distinct phases would be observed if the PNR are coherent over “large” length scales, and a wider distribution of lattice parameters would be observed if the PNR are on the nanometre scale, associated with the strain arising from a high density of domain walls. Similar phenomena are present in other magnetic materials. For example, in the alkali metal superoxide RbO1.72 an orbital ordering transition occurs on cooling and domains with both antiferromagnetic and ferromagnetic ordering appear to coexist. The magnetic exchange is most likely determined by the type of orbital ordering, which in turn seems to be highly dependent on the cooling rate; domains with different types of orbital ordering or different oxygen contents should be manifested by differences in structure. The air sensitivity of these samples precludes investigation by microscopy techniques, but Larmor diffraction would enable the domain structure to be probed as a function of cooling rate in an inert atmosphere. In all cases where there is structural inhomogeneity and domain structures on the nanoscale, the SANS and SESANS modes of LARMOR will provide complementary information by probing the structure on the 1 nm – 1 µm length scale.

Most of this experimental work will be done and co-ordinated by the Zernicke Institute for Advanced Materials.

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Soft matter application

Posted on 03/11/2011 by Jeroen Plomp

The strength of neutrons in soft matter investigations lies in the direct sensitivity to the relevant time and length scales as well as in the ability to distinguish between hydrogen and deuterium, the so-called contrast variation method. The SANS, SESANS, NRSE and MISANS modes situate LARMOR in the most relevant parameter space for soft matter studies. Moreover, Dutch soft matter science with its strong position in polymers, membranes, colloids and biology will benefit from LARMOR. In the following we will discuss the impact LARMOR will have on three important fields of soft-matter research relevant to Dutch scientists: colloids, complex molecular systems, and food materials.

The fundamental physical chemical research on interactions between nanoparticles in solution, such as colloidal suspensions and micro emulsions, form the basis for many industrial applications ranging from water-based paint to ink for ink-jet printers or oil-water systems for oil recovery. It is also a starting point for the description of complex molecular systems and food materials. The stability, structure and phase behavior of these suspensions depends on the balance between the different interactions such as excluded volume, electrostatic, hydrophobic or depletion and this equilibrium. By tuning the interactions, through proper choice of colloids, salt concentration, pH or by adding polymers, and investigating the resulting structures by light, X-Ray or neutron scattering, it is possible to have a targeted design of colloidal structures. In this field contrast variation can be exploited to studying e.g. depletion, which when adding non-adsorbing polysaccharide to the solution, may result in long-range attraction between proteins. SESANS was used to investigate a suspension of sterically stabilised 300-nm-diameter silica particles in cyclohexane, showing that the hard-sphere theory (Percus-Yevick with Henderson-Grundke correction) describes the data for the high-density phase. These studies will be pursued on LARMOR by the groups of Eindhoven University of Technology, Wageningen University and DSM.

Complex molecular systems

This field comprises supra molecular chemistry description, analysis, and synthesis of complexes of several (macro) molecules and their properties, such as self-assembly and phase behavior and is narrowly linked to nanotechnology. The resulting man-made assemblies have a wide variety of applications from sensors, light harvesting materials to drug delivery systems. Micelles formed by electrostatically driven assembly of oppositely charged components are relatively novel self-assembling systems. The resulting particles are termed complex coacervate core micelles (C3Ms) and SANS is a useful tool to investigate their structure.

In addition virus protein-based assemblies find increasing applications in the formation of (functional) nanostructures. In this emerging field, sometimes referred to as chemical virology, spherical viruses are used as containers to direct or confine mineralization or as nanoreactors when enzymes are encapsulated and SANS is a
unique tool for determining the structures.

This sub-section also includes photonic single crystals the spatial and magnetic structure of which will be studied by the polarised SANS and SESANS modes of LARMOR shows  microradian X-ray diffraction from these systems, which recently were also assembled in a magnetic version, in a so-called magnonic crystal. On LARMOR these studies will be pursued by the groups of Eindhoven University of Technology, Radboud University, University of Twente and Utrecht University.

Food materials

Food research plays a prominent role in the top sector ‘Life science and health’. One of the aims is to produce
healthier food, e.g. with ingredients that will decrease human cholesterol levels, lower the risk of cancer, or even
have therapeutical effects. Furthermore, new low-fat products, such as cream cheese and margarines are developed that should be stable under frequently varying temperatures. Wageningen University, Unilever and NIZO plan to use LARMOR. More industries and university labs showed their interest through the Top Institute for Food and Nutrition.

The structure of casein micelles in milk have been extensively studied using small-angle neutron. Using both light
scattering and SANS Huppertz et al. studied the stability of internally cross-linked casein micelles. This may offer potential applications for the use of crosslinked casein micelles as biocompatible protein micro-gel particles. SESANS showed the aggregation mechanism of these casein micelles during yoghurt formation. The effect of processing conditions of microgels (model system for fresh cheese) was measured with SESANS. Neutron scattering combined with H/D substitution has been applied to determine the hydrogen bond structure in glassy and liquid glucose. A Future project that will make optimum use of LARMOR is the determination of a new type
of margarine, a water/oil emulsion stabilised by supramolucular fibres. Then, all relevant length scales will be probed.

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The Instrument

Posted on 03/11/2011 by Jeroen Plomp

LARMOR is one of the four “phase 2” instruments planned to be built at the Second Target Station of the UK spallation source ISIS. The go ahead for these instruments came March 2011, with the allocation of 21M£. LARMOR will view a fully coupled solid-methane/hydrogen moderator, which is kept at 26 K to generate an intense, long-wavelength neutron flux. The pulses have a full width at half maximum of 300 microseconds and a repetition rate of 10 Hz. The distance from neutron target to detector will be approximately 28 metres, which in combination with the low repetition rate gives a wavelength band of Δλ = λmax-λmin ~ 14 Å. The pulse width gives the wavelength uncertainty of Δλ ~ 0.04 Å, which at the lowest wavelength of 2 Å gives Δλ/λ ~ 2% FWHM and a Q-resolution already an order of magnitude better than the typical monochromatisation of reactor based Neutron Spin Echo instruments. The beam delivery system includes a polarising neutron guide, which will polarise the beam and at the same time guide it from the target/moderator assembly to the actual instrument. Half way this guide a chopper system will shape the neutron pulse by cutting down unwanted wavelengths avoiding frame overlap.

With the allocated funds ISIS will build LARMOR as a medium resolution high flux Small Angle Neutron Scattering (SANS) instrument, with a high brilliance neutron extraction system and a highly performing position sensitive detector. The detector system covers 600×600 mm2 and has a resolution of ~8×8 mm2. It consists of 75 position sensitive 3He tubes with a diameter of 8mm. Each tube is capable of a maximum count rate of 250 kHz and along the tube length the resolution may vary between 5 and 8 mm.

This NWO grant will realise all polarized neutron and Larmor labelling extensions. The goal is to have a most performing and multipurpose setup by fully exploiting the capabilities offered by polarized neutrons and Larmor labelling and this can be done without compromising the performance of the instrument.

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Why do we want to use neutrons

Posted on 03/11/2011 by Jeroen Plomp

Atoms or groups of atoms (molecules) build our world including ourselves. If we want to use the materials around us: liquids, solids, magnets, polymers, proteins, we must know why they behave the way they do, we must understand the way they work at the microscopic scale, both in production and in use. Knowing where atoms are in materials and how they interact is the key to understanding their properties. This is particularly true when it comes to developing new materials – once we know the microscopic mechanisms we are able to tailor them according to our needs.

Tailored materials are behind all recent developments, which revolutionize our everyday life: drug delivery substances, magnets for smaller and more reliable computer hard drives, materials for better energy storage, conductors of electricity with very low resistivity, smart materials for airplanes or human bone implants. Targeted materials development is based on an extensive knowledge of microscopic mechanisms and needs a microscopic probe that interacts with all kinds of materials, penetrates deeply in the matter and is soft enough not to destroy even the frail biological substances. Neutron beams constitute this powerful microscopic and non-destructive probe. Free neutrons are unstable but their life-time of 15 minutes is long enough to allow complex beam manipulations required for their use in experiments on materials. Neutrons are electrically neutral particles and for this reason they interact weakly with matter and have a high penetration power. So-called “thermal” neutrons are uniquely suited for materials research, since they have wavelengths comparable to the distances between atoms and energies comparable to the interaction energies in solids and liquids. Unlike X-rays, neutrons can readily evade a material’s electrons to interact directly with atomic nuclei. These “scattered
neutrons” have different directions and speeds than the incoming ones. The changes in direction depend on the interatomic distances and resolve the microscopic structure. The changes in speed arise from energy exchange with the atoms and provide information on the atomic and molecular motions.

Neutron scattering is a technique, which unravels the microscopic behaviour of the investigated material by determining the direction and energy of scattered neutrons. The universality of the interaction of neutrons with matter leads to a number of variations of the technique and to a wide range of applications, from physics to engineering, chemistry and biology. Neutrons, like all sub-atomic particles, obey the laws of quantum mechanics and even though they are massive particles they also behave like waves. Consequently when they interact with a crystal, where atoms or molecules build a regular array, they are reflected, or scattered. Neutrons reflected from similarly oriented planes of atoms in the crystal interfere and re-inforce each other periodically to produce a characteristic diffraction pattern.

Elastic neutron scattering or neutron diffraction techniques record these patterns in the optimum way to provide information about the atomic configurations, i.e. the crystal lattice. Inelastic neutron scattering or neutron spectroscopy determines the characteristic energies and motions in a material from the energy analysis of the scattered neutrons.

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MISANS

Posted on 25/10/2011 by Jeroen Plomp

The Modulated Intensity Small Angle Neutron Scattering option. We modulate the polarization as function of time upstream of the sample.

MISANS uses only the resonant flippers in front of the sample, driven at different frequencies, which leads to a high-frequency intensity modulation at a specific position behind the sample. As in NSE, any change of the neutron beam due to inelastic scattering at the sample leads to a decrease of the amplitude of these oscillations, which is readily detected. The technique should cover approximately the same dynamical range as NRSE with the advantage that no components are needed between sample and detector, which minimizes the background. However, this performance has not been reached yet, because the existing neutron detectors do not reach the resolution in space and time required by MISANS. In the frame of this project new detector concepts will be developed and tested, which would reach the performance required for a competitive MISANS setup.

 

 

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TOFLAR

Posted on 25/10/2011 by Jeroen Plomp

The Time Of Flight Amplitude Regulation option. An increased resolution can be measured via a Fourier  transform.

TOFLAR uses only the Larmor labelling elements in front of the sample to modulate the beam as shown in the figure. In this configuration a precession magnetic coil and an analyser modulate the neutron beam in front of the sample. The combination of this modulation with the total time-of-flight information can be used to directly determine the quasi-elastic scattering while using the full intensity advantage of a polychromatic incoming neutron beam. Similarly to Neutron Spin Echo, TOFLAR measures the intermediate scattering function I(Q,t).

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N(R)SE

Posted on 25/10/2011 by Jeroen Plomp

The Neutron Resonance Spin-Echo option with magnets moved to 90 degree angle.  The accepted scattered beam divergence is low.

 

 

 

By replacing the RF magnet systems by a combination of RF flippers and large coils we can increase the  scattered beam divergence significantly and improve statistics.

N(R)SE uses the same magnetic field configuration and resonant flippers as SESANS and Larmor diffraction but without inclined field boundaries shown in the figure. In this case the echo probes the dynamics of the sample with a highest Fourier time of about 20 nanoseconds. This configuration will be pushed to the limits. The goal would be to reach the highest possible Fourier times, possibly by adopting the longitudinal NRSE configuration and incorporating correction elements.

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High reslolution Larmor diffraction

Posted on 25/10/2011 by Jeroen Plomp

High resolution Larmor diffraction will use the same components as SESANS but at wide-angle diffraction configuration and with the two precession fields in the same direction, shown in the figure, measuring lattice  spacings Δd/d with accuracies as high as high as 10‑6. When the fields are anti parallel, the setup is in “SESANS configuration” and measures with very high accuracy the broadening of the Bragg peaks. In this configuration, by having the detector at one scattering angle and when examining a polycrystalline sample more Bragg peaks can be measured simultaneously due to the time-of-flight technique and the broad wavelength band of LARMOR. This technique can also determine local strains and yield information about the size and size distribution of nano crystallites in nano structured materials.

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