Neutron scattering at high temperature and levitation techniques

Studies of the liquid state present an obvious fundamental interest and are also important for technological applications since the molten state is an essential stage in various industrial processes (e.g. glass making, single crystal growing, iron and steel making). Most of the physical properties of a high-temperature liquid are related to its atomic structure. Thus it is important to develop devices to probe the local environment of the atoms in the sample. At very high temperature, it is difficult to use conventional furnaces, which present several problems. In particular, physical contact with the container can contaminate the sample and/or modify its structural properties. Such problems encouraged the development of containerless techniques, which are powerful tools to study high-temperature melts. By eliminating completely any contact between sample and container, it is possible to study the sample with a very high degree of control and to access very high temperatures. An additional advantage of levitation methods is that it is possible to supercool hot liquids down to several hundred of degrees below their equilibrium freezing point, since heterogeneous nucleation processes are suppressed

Mapping Microstructural Dynamics up to the Nanosecond of the Conjugated Polymer P3HT in the Solid State

We present a detailed study of the structure-dynamics relationship of regio-regular and regio-random PEHT using different neutron scattering techniques. Deuteration is employed to modulate the coherent and incoherent cross-sections, allowing particularly to access both self-motions and collective dynamics of the materials. The measurements are underpinned by extensive quantitative calculations using classical MD, as well as first principles quantum chemistry. MD reproduced well the main structural features and slow motions, and shed light on differences in collective dynamics between Q-values linked with the $\pi-\pi$ stacking and the lamellar stacking, with the crystalline phase being the most impacted. On the other hand MD led to a limited description of molecular vibrations. In this context, first principles molecular calculations described well the high-energy vibrational features ( $>$ 900 cm$^{-1}$ ), while periodic calculations allowed to better describe the low- and mid-energy vibrational ranges ( 200-900 cm$^{-1}$ ). The mid-energy range is predominantly associated with both intra-molecular and inter-molecular mode coupling, which encloses information about both the polymer conformation and the polymer packing at short range. One of the outcomes of this study is the validation of the common assumption made that RRa-P3HT is a good approximation for the amorphous phase of RR-P3HT at the macroscopic level. The present work helps to clarify unambiguously the latter point which has been largely overlooked in the literature. We highlight the importance to complement optical spectroscopy techniques with inelastic neutron scattering. The latter offering the advantage of being insensitive to the delocalized $\pi$-electron system, and thus enabling to infer relevant quantities like conjugation lengths, for instance, impacting properties of conjugated polymer.Comment: Featured as ACS Editors' Choice. Featured on the Cover of the December 10, 2019 issue of Chemistry of Material

Probing the dynamics of quasicrystal growth using synchrotron live imaging

The dynamics of quasicrystal growth remains an unsolved problem in condensed matter. By means of synchrotron live imaging, facetted growth proceeding by the tangential motion of ledges at the solid-melt interface is clearly evidenced all along the solidification of icosahedral AlPdMn quasicrystals. The effect of interface kinetics is significant so that nucleation and free growth of new facetted grains occur in the melt when the solidification rate is increased. The evolution of these grains is explained in details, which reveals the crucial role of aluminum rejection, both in the poisoning of grain growth and driving fluid flow

Demonstration of Gd-GEM detector design for neutron macromolecular crystallography applications

The European Spallation Source (ESS) in Lund, Sweden will become the world's most powerful thermal neutron source. The Macromolecular Diffractometer (NMX) at the ESS requires three 51.2 x 51.2~cm$^{2}$ detectors with reasonable detection efficiency, sub-mm spatial resolution, a narrow point spread function (PSF) and good time resolution. This work presents measurements with the improved version of the NMX detector prototype consisting of a Triple-GEM detector with natural Gd converter and a low material budget readout. The detector was successfully tested at the neutron reactor of the Budapest Neutron Centre (BNC) and at the D16 instrument at the Institut Laue-Langevin (ILL) in Grenoble. The measurements with Cadmium and Gadolinium masks in Budapest demonstrate that the point spread function of the detector lacks long tails that could impede the measurement of diffraction spot intensities. On the D16 instrument at ILL, diffraction spots from Triose phosphate isomerase w/ 2-phosphoglycolate (PGA) inhibitor were measured both in the D16 Helium-3 detector and the Gd-GEM. The comparison between the two detectors show a similar point spread function in both detectors, and the expected efficiency ratio compared to the Helium-3 detector. Both measurements together thus give good indications that the Gd-GEM detector fits the requirements for the NMX instrument at ESS

The H5 guide system - the latest innovative guide system at the ILL

The H5 program with the complete rebuild of the guide system and the upgrade or renovation of all instruments leads to a tremendous increase of the instrument performances. The improvement was obtained both in terms of more useful flux and upgrade of the different instruments (e.g. higher field density for IN15). In addition, the industrial application instrument D50 offers an addition to the ILL instrument suite (see p. 27 in this issue). With the commissioning of the new spin echo spectrometer WASP in 2016, the H5 program will be completed and a considerable improvement for the ILL instrument park will be finalized

Structure factor of liquid n-butanol at room temperature

4 pags., 3 figs., 1 tab. -- 6th Meeting of the Spanish Neutron Scattering Association (SETN2012) 24–27 June 2012, Segovia, Spain)The structure factor of deuterated liquid n-butanol (C4D10O) has been investigated by neutron diffraction with the aim of exploring the physical nature of the observed prepeak. The experiment was conducted using two neutron diffractometers: D16 to get a detailed structure factor in the low-Q range, and D4 for a high precision structure factor and proper normalization. In this way a total structure factor was determined covering an extended Q-range from 0.04 to 23.4 Å−1. A molecular dynamics simulation using the general all-atom ab initio force field COMPASS was also carried out. The agreement between experimental and simulated data is very good, giving a plausible interpretation of the origin of the pre-peak observed at 0.6 Å−1 as coming from the intermolecular ordering in the liquid

Influence of the Surfactant Tail Length on the Viscosity of Oppositely Charged Polyelectrolyte/Surfactant Complexes

Aqueous mixtures of polyelectrolytes and oppositely charged surfactants form clear and homogeneous solutions if either the polyelectrolyte or the surfactant is present in excess. Around charge equilibrium, macroscopic precipitates are formed. Near the phase boundary on the polyelectrolyte rich side, nanometric polyelectrolyte surfactant complexes can greatly increase the viscosity of aqueous solutions. This behavior is governed by the composition and chemical nature of the polyelectrolyte and surfactant. Here, we investigate complexes consisting of the polycation JR 400 and two different surfactants, namely, sodium octyl sulfate SOS and sodium tetradecyl sulfate STS , which only differ in the length of their alkyl tail. Using small angle neutron scattering and neutron spin echo spectroscopy, we find that STS forms mixed aggregates with JR 400 which results in a pronounced increase in viscosity. Such an increase is not observed for SOS where no mixed aggregates are formed. Comparison with atomistic molecular dynamics simulations shows good qualitative agreemen

Quantification of Buckminsterfullerene (C60) in non-graphitizing carbon and a microstructural comparison of graphitizing and non-graphitizing carbon via Small Angle Neutron Scattering

In this article we present the first experimental evidence confirming a global presence of Buckminsterfullerene (C60) in non-graphitizing polymeric carbon, along with its volume fraction calculations. Partially stacked carbon fragments featuring weak or strong curvatures constitute the structural units in non-graphitizing carbons. It has been proposed that a certain fraction of completely closed spherical fullerenes, such as C60, is also present in these materials. Strongly curved structures are not expected to exist in graphitizing carbons. We report on a Small Angle Neutron Scattering (SANS) investigation conducted at the Institut Laue-Langevin, Grenoble, France, that enables us to (i) quantify C60 in a non-graphitizing carbon, (ii) investigate the evolution patterns of graphitizing and non-graphitizing carbons, and (iii) perform a detailed SANS analysis of pure crystalline C60 in dry powder form. We also revisit the formation patterns of slightly larger structures (3–5 nm) such as graphitic crystallites and voids in both classes of polymeric carbon. These results provide a strong evidence in support of the fullerene-like microstructural models of non-graphitizing carbon, adding that the curved structural units are not just “fullerene-like”, but also spherical fullerenes, C60 in particular

Local structure of liquid CaAl2O4 from ab initio molecular dynamics simulations

International audienc