L'IRAMIS et les Grands Instruments

$Elucidating Individual Magnetic Contributions in Bi-Magnetic Fe3O4/Mn3O4 Core/Shell Nanoparticles by Polarized Powder Neutron Diffraction$

Elucidating Individual Magnetic Contributions in Bi-Magnetic Fe3O4/Mn3O4 Core/Shell Nanoparticles by Polarized Powder Neutron Diffraction

I. V. Golosovsky, I. A. Kibalin, A. Gukasov, A. G. Roca, A. López-Ortega, M. Estrader, M. Vasilakaki, K. N. Trohidou, T. C. Hansen, I. Puente-Orench, E. Lelièvre-Berna, J. Nogués

Heterogeneous bi-magnetic nanostructured systems have had a sustained interest during the last decades owing to their unique magnetic properties and the wide range of derived potential applications. However, elucidating the details of their magnetic properties can be rather complex. Here, a comprehensive study of Fe3O4/Mn3O4 core/shell nanoparticles using polarized neutron powder diffraction, which allows disentangling the magnetic contributions of each of the components, is presented. The results show that while at low fields the Fe3O4 and Mn3O4 magnetic moments averaged over the unit cell are antiferromagnetically coupled, at high fields, they orient parallel to each other. This magnetic reorientation of the Mn3O4 shell moments is associated with a gradual evolution with the applied field of the local magnetic susceptibility from anisotropic to isotropic. Additionally, the magnetic coherence length of the Fe3O4 cores shows some unusual field dependence due to the competition between the antiferromagnetic interface interaction and the Zeeman energies. The results demonstrate the great potential of the quantitative analysis of polarized neutron powder diffraction for the study of complex multiphase magnetic materials.

https://doi.org/10.1002/smtd.202201725

Hybrid systems combining liposomes and entangled hyaluronic acid chains: Influence of liposome surface and drug encapsulation on the microstructure

Céline JAUDOIN, Isabelle GRILLO, Fabrice COUSIN, Maria GEHRKE, Malika OULDALI, Ana-Andreea ARTENI, Luc PICTON, Christophe RIHOUEY, Fanny SIMELIERE, Amélie BOCHOT, Florence AGNELY

Mixtures of hyaluronic acid (HA) with liposomes lead to hybrid colloid–polymer systems with a great interest in drug delivery. However, little is known about their microstructure. Small angle neutron scattering (SANS) is a valuable tool to characterize these systems in the semi-dilute entangled regime (1.5% HA) at high liposome concentration (80 mM lipids). The objective was to elucidate the influence of liposome surface (neutral, cationic, anionic or anionic PEGylated), drug encapsulation and HA concentration in a buffer mimicking biological fluids (37 °C). First, liposomes were characterized by SANS, cryo-electron microscopy, and dynamic light scattering and HA by SANS, size exclusion chromatography, and rheology. Secondly, HA-liposome mixtures were studied by SANS. In HA, liposomes kept their integrity. Anionic and PEGylated liposomes were in close contact within dense clusters with an amorphous organization. The center-to-center distance between liposomes corresponded to twice their diameter. A depletion mechanism could explain these findings. Encapsulation of a corticoid did not modify this organization. Cationic liposomes formed less dense aggregates and were better dispersed due to their complexation with HA. Liposome surface governed the interactions and microstructure of these hybrid systems.

https://doi.org/10.1016/j.jcis.2022.07.146

Hybrid systems combining liposomes and entangled hyaluronic acid chains: Influence of liposome surface and drug encapsulation on the microstructure

Disentangling water, ion and polymer dynamics in an anion exchange membrane

Fabrizia Foglia, Quentin Berrod, Adam J. Clancy, Keenan Smith, Gérard Gebel, Victoria García Sakai, Markus Appel, Jean-Marc Zanotti, Madhusudan Tyagi, Najet Mahmoudi, Thomas S. Miller, John R. Varcoe, Arun Prakash Periasamy, Daniel J. L. Brett, Paul R. Shearing, Sandrine Lyonnard and Paul F. McMillan

Semipermeable polymeric anion exchange membranes are essential for separation, filtration and energy conversion technologies including reverse electrodialysis systems that produce energy from salinity gradients, fuel cells to generate electrical power from the electrochemical reaction between hydrogen and oxygen, and water electrolyser systems that provide H2 fuel. Anion exchange membrane fuel cells and anion exchange membrane water electrolysers rely on the membrane to transport OH− ions between the cathode and anode in a process that involves cooperative interactions with H2O molecules and polymer dynamics. Understanding and controlling the interactions between the relaxation and diffusional processes pose a main scientific and critical membrane design challenge. Here quasi-elastic neutron scattering is applied over a wide range of timescales (100–103 ps) to disentangle the water, polymer relaxation and OH− diffusional dynamics in commercially available anion exchange membranes (Fumatech FAD-55) designed for selective anion transport across different technology platforms, using the concept of serial decoupling of relaxation and diffusional processes to analyse the data. Preliminary data are also reported for a laboratory-prepared anion exchange membrane especially designed for fuel cell applications.

https://doi.org/10.1038/s41563-022-01197-2

Heterogeneous Microscopic Dynamics of Intruded Water in a Superhydrophobic Nanoconfinement: Neutron Scattering and Molecular Modeling

J. Wolanin, L. Michel, D. Tabacchioni, J. M. Zanotti, J. Peters, I. Imaz, B. Coasne, M. Plazanet, and C. Picard

With their strong confining porosity and versatile surface chemistry, zeolitic imidazolate frameworks—including the prototypical ZIF-8—display exceptional properties for various applications. In particular, the forced intrusion of water at high pressure (∼25 MPa) into ZIF-8 nanopores is of interest for energy storage. Such a system reveals also ideal to study experimentally water dynamics and thermodynamics in an ultrahydrophobic confinement. Here, we report on neutron scattering experiments to probe the molecular dynamics of water within ZIF-8 nanopores under high pressure up to 38 MPa. In addition to an overall confinement-induced slowing down, we provide evidence for strong dynamical heterogeneities with different underlying molecular dynamics. Using complementary molecular simulations, these heterogeneities are found to correspond to different microscopic mechanisms inherent to vicinal molecules located in strongly adsorbing sites (ligands) and other molecules nanoconfined in the cavity center. These findings unveil a complex microscopic dynamics, which results from the combination of surface residence times and exchanges between the cavity surface and center.

https://doi.org/10.1021/acs.jpcb.1c06791

Heterogeneous Microscopic Dynamics of Intruded Water in a Superhydrophobic Nanoconfinement: Neutron Scattering and Molecular Modeling

Thermodiffusion anisotropy under a magnetic field in ionic liquid-based ferrofluids

T. Fiuza, M. Sarkar, J. C. Riedl, A. Cebers, F. Cousin, G. Demouchy, J. Depeyrot, E. Dubois, F. Gelebart, G. Meriguet, R. Perzynski and V. Peyre

Ferrofluids based on maghemite nanoparticles (NPs), typically 10 nm in diameter, are dispersed in an ionic liquid (1-ethyl 3-methylimidazolium bistriflimide – EMIM-TFSI). The average interparticle interaction is found to be repulsive by small angle scattering of X-rays and of neutrons, with a second virial coefficient A2 = 7.3. A moderately concentrated sample at F = 5.95 vol% is probed by forced Rayleigh scattering under an applied magnetic field (up to H = 100 kA m1 ) from room temperature up to T = 460 K. Irrespective of the values of H and T, the NPs in this study are always found to migrate towards the cold region. The in-field anisotropy of the mass diffusion coefficient Dm and that of the (always positive) Soret coefficient ST are well described by the presented model in the whole range of H and T. The main origin of anisotropy is the spatial inhomogeneities of concentration in the ferrofluid along the direction of the applied field. Since this effect originates from the magnetic dipolar interparticle interaction, the anisotropy of thermodiffusion progressively vanishes when temperature and thermal motion increase.

https://doi.org/10.1039/d0sm02190c

Chain Conformation and Aggregation Structure Formation of a High Charge Mobility DPP-Based Donor–Acceptor Conjugated Polymer

Chang Liu, Wenxian Hu, Hanqiu Jiang, Guoming Liu*, Charles C. Han, Henning Sirringhaus, François Boué, and Dujin Wang

The determination of intrinsic chain stiffness of conjugated polymers is challenging, in particular, for scattering techniques because of their strong light absorption and structural instability due to the complicated intra-/intermolecular interactions. In this work, the chain conformation and aggregation formation of a high charge mobility donor–acceptor polymer (DPPDTT) are systematically investigated by using small-angle neutron scattering (SANS) and static/dynamic light scattering (SLS/DLS). On the one hand, chloroform was chosen as a good solvent, in which SANS reveals a rod-like geometry with a radius of ∼15 Å. Once the absorption effect is properly accounted for, SLS shows a power law of 1 between the radius of gyration (R_g) and molecular weight (M_w) and a negative second virial coefficient (A₂). On the other hand, 1,2-dichlorobenzene was chosen as a poor solvent, in which SANS, SLS/DLS, and atomic force microscopy (AFM) reveal a strong temperature-/concentration-dependent assembling behavior. The results provide a general picture of the multiscale assembly process of conjugated polymers.

https://doi.org/10.1021/acs.macromol.0c01646

Chain Conformation and Aggregation Structure Formation of a High Charge Mobility DPP-Based Donor–Acceptor Conjugated Polymer

Direct evidence of weakly dispersed and strongly anharmonic optical phonons in hybrid perovskites

A. C. Ferreira, S. Paofai, A. Létoublon, J. Ollivier, S. Raymond, B. Hehlen, B. Rufflé, S. Cordier, C. Katan, J. Even & P. Bourges

Hybrid organolead perovskites (HOP) have started to establish themselves in the field of photovoltaics, mainly due to their great optoelectronic properties and steadily improving solar cell efficiency. Study of the lattice dynamics is key in understanding the electron-phonon interactions at play, responsible for such properties. Here, we investigate, via neutron and Raman spectroscopies, the optical phonon spectrum of four different HOP single crystals: MAPbBr₃, FAPbBr₃, MAPbI₃, and α-FAPbI₃. Low temperature spectra reveal weakly dispersive optical phonons, at energies as low as 2-5 meV, which seem to be the origin of the limit of the charge carriers mobilities in these materials. The temperature dependence of our neutron spectra shows as well a significant anharmonic behaviour, resulting in optical phonon overdamping at temperatures as low as 80 K, questionning the validity of the quasi-particle picture for the low energy optical modes at room temperature where the solar cells operate.

https://www.nature.com/articles/s42005-020-0313-7

Neutrons et froid quantique

La physique de la matière condensée repose sur quelques concepts fondateurs, comme le paradigme de Néel (avec sa description des ordres magnétiques classiques), la théorie des liquides de Fermi (avec le concept de quasi-particule), et la théorie de Landau des transitions de phases (mettant en exergue le concept de brisure spontanée de symétrie). Toutefois, de nouvelles découvertes bouleversent ces dogmes, mettant en lumière le rôle des fortes corrélations entre quasi-particules, la découverte de transitions de phase topologiques, ou l’observation de nouveaux états de la matière.

Ce sont par exemple les liquides ou glaces de spin, les états de boucle de courant dans certains oxydes, ou la description de nouvelles transitions de phase, sans symétrie brisée, mettant en jeu le confinement/déconfinement d’objets topologiques comme les vortex. Ceci suscite et motive toujours plus avant l’étude de la matière et des "matériaux quantiques", pour acquérir de nouvelles connaissances fondamentales et en tirer le meilleur parti pour des applications diverses. Ces nouveaux états de la matière se rencontrent dans des conditions ultimes et notamment aux très basses températures, dans la gamme du milliKelvin (mK).

Dans cette optique, et pour accompagner cette recherche, notre équipe du LLB responsable de l’opération du diffractomètre de neutrons G4-1 (LLB-Orphée) a fait l’acquisition d’un nouvel appareil permettant de réaliser des mesures de diffraction des neutrons jusqu’à des températures ultra-basses (40 mK).

A high pressure cell using metallic windows to investigate the structure of molecular solutions up to 600 MPa by small-angle neutron scattering

B. Annighöfer , A. Hélary, A. Brulet, A. Colas de la Noue, C. Loupiac and S. Combet
Review of Scientific Instruments 90 (2019) 025106

Abstract :

We report on a high pressure (HP) cell designed for the determination of the structure of molecular solutions by small-angle neutron scattering (SANS). The HP cell is fitted up with two thick metallic windows that make the device very resistant under hydrostatic pressures up to 600 MPa (or 6 kbar). The metallic windows are removable, offering the possibility to adapt the HP cell to a given study with the pressure desired on an appropriate spatial range to study the structure of various molecular solutions by SANS. In this context, we report the absorption, transmission, and scattering properties of different metallic windows. Finally, we describe, as a proof of principle, the solution structure changes of myoglobin, a small globular protein.

https://doi.org/10.1063/1.5051765

Cationic thermoresponsive poly(n-vinylcaprolactam) microgels synthesized by emulsion polymerization using a reactive cationic macro-raft agent

Cationic thermoresponsive poly(n-vinylcaprolactam) microgels synthesized by emulsion polymerization using a reactive cationic macro-raft agent
L. Etchenausia, E. Deniau, A. Brûlet, J. Forcada and M. Save, Macromolecules (2018) sous presse.

Abstract :

A series of reactive poly([2-(acryloyloxy)ethyl]trimethylammonium chloride) (P(AETAC)) cationic polymers with varying degrees of polymerization were synthesized by RAFT/MADIX polymerization and investigated as stabilizers for the emulsion polymerization of N-vinylcaprolactam (PVCL) in the presence of a cross-linker. It was demonstrated that the xanthate chain end of the cationic P(AETAC-X) polymers played a crucial role to produce stable cationic PVCL-based microgels at higher initial solids content (5–10 wt %) than usually reported for the synthesis of PVCL microgels. The thermoresponsive PVCL microgels with cationic shell undergo a reversible volume shrinkage upon heating in the absence of any hysteresis in accordance with the narrow particle size distribution.

The values of the volume phase transition temperature ranged between 28 and 30 °C for the microgels synthesized using 4 and 8 wt % of P(AETAC-X) based on VCL. The presence of a cationic outer shell onto the microgels was evidenced by the positive values of the electrophoretic mobility. The swelling behavior of the thermoresponsive microgel particles can be tuned by playing on two synthesis variables which are the initial solids content and the content of P(AETAC-X) macro-RAFT stabilizer. Furthermore, the inner structure of the synthesized microgels was probed by transverse relaxation nuclear magnetic resonance (T₂ NMR) and small-angle neutron scattering (SANS) measurements. The fit of T₂ NMR data confirmed a core–shell morphology with different cross-linking density in PVCL microgels. Through the determination of the network mesh size, SANS was suitable to explain the increase of the values of the PVCL microgel swelling ratios by increasing the initial solids content of their synthesis.

Cationic thermoresponsive poly(n-vinylcaprolactam) microgels synthesized by emulsion polymerization using a reactive cationic macro-raft agent

Neutrons provide a novel picture of thermal conductivity in complex materials.

Neutron experiments conducted by the Institut Laue-Langevin (ILL) and CNRS researchers, and performed on the neutron time-of-flight spectrometer (IN5@ILL) and 2T triple axis spectrometer at the Laboratoire Léon Brillouin (LLB), provide a direct quantitative measurement of phonon lifetimes in polymeric cage molecules, giving a novel picture of thermal conductivity in complex materials.

This study highlights the importance of neutron techniques in overcoming the challenging task of accessing and therefore successfully measuring phonon lifetimes.

Hemoglobin diffusion and the dynamics of oxygen capture by red blood cells

Stehane Longeville et Laura-Roxana Stingaciu

Translational diffusion of macromolecules in cell is generally assumed to be anomalous due high macromolecular crowding of the milieu. Red blood cells are a special case of cells filled quasi exclusively (95% of the dry weight of the cell) with an almost spherical protein: hemoglobin. Hemoglobin diffusion has since a long time been recognized as facilitating the rate of oxygen diffusion through a solution. We address in this paper the question on how hemoglobin diffusion in the red blood cells can help the oxygen capture at the cell level and hence to improve oxygen transport. We report a measurement by neutron spin echo spectroscopy of the diffusion of hemoglobin in solutions with increasing protein concentration. We show that hemoglobin diffusion in solution can be described as Brownian motion up to physiological concentration and that hemoglobin diffusion in the red blood cells and in solutions at similar concentration are the same. Finally, using a simple model and the concentration dependence of the diffusion of the protein reported here, we show that hemoglobin concentration observed in human red blood cells (≃≃330 g.L⁻¹) corresponds to an optimum for oxygen transport for individuals under strong activity.

Hemoglobin diffusion and the dynamics of oxygen capture by red blood cells

Matériaux à base de nanofils magnétiques pour aimants permanents renforcés

Au quotidien, les aimants permanents sont partout présents dans les dispositifs technologiques qui nous entourent. Aujourd’hui, il y en a 4 types principaux sur le marché mondial : NdFeB, ferrite, SmCo et AlNiCo, dont 65% contiennent des terres rares, essentiellement du néodyme. Depuis 2008, la Chine a établi un monopole de production des terres rares avec près de 95 % de la production mondiale, ce qui a entrainé une forte augmentation des prix ces dernières années. Suite aux restrictions de la Chine sur ses exportations, ce problème d’approvisionnement en terres rares est là pour durer.

Il y a donc un fort enjeu économique à trouver des alternatives à l'emploi des terres rares dans les aimants permanents. Une des voies, sur laquelle les équipes du LLB, de l’INSA de Toulouse et de l'ITODYS travaillent en collaboration, est d’utiliser l’anisotropie de forme pour augmenter la coercivité des matériaux. Il s’agit d’une idée ancienne, déjà utilisée en autre dans les aimants AlNiCo. Les progrès récents dans la synthèse de nano-objets magnétiques ont permis de revisiter l’idée et de l’appliquer à des métaux simples. Il a ainsi été possible de concevoir des matériaux à base de cobalt, ayant des propriétés intrinsèques équivalentes à celles des meilleurs aimants SmCo.