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Ce cours porte plus particulièrement sur les spectromètres de type "temps de vol" construits en France auprès de sources de neutrons continues, c'est à dire au réacteur Orphée (Saclay) et à l'Institut Laue-Langevin (Grenoble).

Lipo-fullerenes are lipophilic C60 derivatives (six pairs of alkyl chains symmetrically grafted to the C60 cage) that intercalate in phospholipid bilayers by the formation of rodlike structures of nanoscopic dimensions. Proton NMR measurements in the fringe field of a superconducting magnet (SFF-NMR) were employed to measure the long-range self-diffusion of lipo-fullerenes intercalated in oriented multilayers of dipalmitoylphosphatidylcholine (DPPC) between 27 and 70 °C. The lipo-fullerene diffusion was found to be an order of magnitude slower than that of the DPPC in the host bilayer. The lipo-fullerene diffusion continued largely unaffected even under conditions when the host bilayer assumed a solidlike gel state, indicating a decoupling of lipo-fullerene and DPPC motion. Quasi-elastic neutron scattering (QENS) was used to study the molecular dynamics of the lipo-fullerenes within the bilayer at four energy resolutions of the spectrometer (1, 19, 62, and 500 μeV), covering selectively the gighertz to terahertz frequency range of molecular motion. We find that the molecular dynamics in this frequency range is dominated by the motion of the 12 alkyl chains attached to each C60. At 25 °C where both the DPPC and the lipo-fullerenes are in a solidlike state, the dynamics of the latter is dominated by kink defects of the alkyl chains at high frequency (terahertz range) and alkyl chain jumps at lower frequency gighertz range). At 75 °C where both components are fluid, the lipo-fullerene dynamics can be described by a superposition of segmental rotational motion of chains and a spatially restricted diffusion of the chain inside a spherical volume. The radii of the volumes were found to scale linearly with the distance of the chain segment from the fullerene cage.

Quasielastic neutron scattering (QENS) measurements were employed to study changes in high-frequency dynamics of dipalmitoyl-phosphatidyl-choline (DPPC) bilayers induced by small amounts of nonionic surfactants (tetra-ethyleneglycol-mono-n-dodecyl ether, C12E4). The experiments were performed at three energy resolutions probing different frequency domains (GHz to lower THz range) of molecular motion and at two temperatures, corresponding to the crystal-like gel phase (T = 20 °C) and the fluid phase (T = 50 °C) of the bilayer. Two orientations of the bilayer stack were studied to obtain information about the anisotropy of the dynamics with respect to the in-plane and the out-of-plane lipid motion. At 5 mol % surfactant in a fluid DPPC bilayer, we observed drastic changes of lipid dynamics in the frequency domain which is dominated by diffusive motions of the whole molecule. The presence of surfactant increased the lipid in-plane diffusion constant by 50% and the spatial extension of this motion by 25%. In contrast, the out-of-plane lipid motion showed a reduction of the diffusion constant by 60% and its spatial extension was reduced by 40%. Solid-state deuterium NMR of fluid DPPC bilayers showed that the surfactant caused a reduction of the order parameter of the lipid chains and changed the shape of the order parameter profile. In the high-frequency domain where kink motions of the lipid chains dominate the dynamics, no surfactant effects were observed. In a time averaged picture, the results suggest a surfactant-induced spread of the lipid chains in the bilayer plane and a concomitant reduction of bilayer thickness. For gel phase bilayers, no surfactant- induced alterations of lipid dynamics were detected.

Magnetic ordering was investigated by neutron scattering in an YBa2Cu3O6+xsingle crystal. We observed antiferromagnetic ordering (AFI) (TN= 410 K for x= 0.1 and TN= 368 K for x= 0.18), but found no evidence for a reordering down to 2 K (AFII). The magnetic structure factors are presented to emphasize the anisotropic character of the form factor.

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