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Neutron spin echo (NSE) method at a pulsed neutron source presents new challenges to the data reduction and analysis as compared to the instruments installed at reactor sources. The main advantage of the pulsed source NSE is the ability to resolve the neutron wavelength and collect neutrons over a wider bandwidth. This allows us to more precisely determine the symmetry phase and measure the data for several Q-values at the same time. Based on the experience gained at the SNS NSE – the first, and to date the only one, NSE instrument installed at a pulsed spallation source, we propose a novel and unified approach to the NSE data processing.

Le revetement electrochimique de metaux sur des polymeres est frequemment realise dans de nombreuses applications industrielles. La surface du polymere doit pour cela subir un traitement d'activation. Dans une premiere etape, une fine couche de colloides palladium-etain est deposee sur le polymere; elle est suivie d'une etape d'echange qui consiste a echanger des atomes d'etain par des atomes de cuivre pour accroitre la conductivite de surface et rendre alors possible l'electrodeposition d'un metal comme le cuivre par exemple. Les colloides deposes sont produits dans une suspension acide. Leur taille est voisine de 2 nm et ils sont supposes avoir un coeur constitue d'un alliage Pd-Sn entoure d'une peau riche en etain. Le but de notre etude est d'approfondir la nature physico-chimique des suspensions colloidales et des couches adsorbees en surface d'un polymere en combinant plusieurs techniques de caracterisation microstructurales fines comme la diffusion centrale de rayons X (SAXS), la cryomicroscopie electronique, la spectroscopie de rayons X (EDX) et de photoelectrons (XPS), la retrodiffusion (RBS) et la spectroscopie de pertes d'energie des electrons transmis (EELS).

We report the dynamics of amplified spontaneous emission (ASE) in thin organic films of tris-(8-hydroxyquinoline)-aluminum (Alq3) doped with small amounts of the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The energy transfer from the initially photoexcited Alq3 to the DCM molecules affects the high excitation density dynamics significantly. The time delay between pulsed photoexcitation and the ASE burst depends on the pumping level. For higher pumping levels the competition between depopulation by ASE and refilling of the DCM states via energy transfer leads to an oscillatory emission with a fundamental frequency of up to 0.2 THz.

Elastic properties of surfactant membranes can be described in terms of the bending rigidity κ and the saddle splay modulus . Phase diagram measurements and neutron scattering experiments allowed the determination of these parameters. Recent simulations showed that the bending rigidity, which is deduced from the characteristic length scales in the microemulsion, is a mixture of and κ. By combining neutron spin echo (NSE) spectroscopy, small angle neutron scattering (SANS) and phase diagram measurements, we show that also experimentally the different contributions can be separated. For supercritical CO2 microemulsions and bicontinuous microemulsions with additives, the prefactors of the and κ contributions are determined and compared to those from simulations.

We studied unentangled poly(ethylene-alt-propylene) (PEP) in a composite with hydrophobic silica particles as a function of the filler concentration. Our neutron spin echo (NSE) experiments cover both the internal dynamics as well as the center of mass diffusion beyond the Rouse time. The key experimental results are (i) all of the chains are equally mobile, (ii) the basic segmental (Rouse) relaxation rate is unaffected even at highest filler concentrations, and (iii) apparently the obstacles reduce significantly the translational center of mass motion. This happens, even in the case when the particles do not significantly confine the polymer. (iv) A transition from regular to anomalous diffusion in the Rouse regime at the highest particle fractions is clearly evidenced. In order to understand the microscopic mechanisms underlying the experimental observations, we performed coarse grained simulations. We demonstrate that the geometrical confinement only affects the dynamics at a long time scale outside the experimental window and therefore it is not able to explain the results found in the NSE experiments. The consideration of inter-chain interactions, however, results in a significant influence even at shorter times and a quantitative agreement between the experiments and simulations was found. The simulations clearly demonstrate that the interfaces cause a deceleration of the chains in their close vicinity. Then the inter-chain interactions carry this slowing down to the other chains at a time-scale of the Rouse relaxation time. Hence, in the experimental datasets an overall slowing down is observed.

Neutron spin echo (NSE) spectroscopy is, due to its high energy resolution, a well-suited method for studying slow dynamics, such as the dynamics of soft matter systems (glasses, polymers and complex liquids), or paramagnetic properties of, e.g., spin glasses. The Julich NSE spectrometer has been in operation at the Julich research reactor FRJ-2 since 1996. It has been transferred now to the new research reactor FRM II of the TU Munchen, where it just started to continue operation. In the context of the transfer, parts of the spectrometer have been renewed and improved, leading to a significantly larger energy resolution and a larger dynamic range. Amongst other things, new correction coils have been designed and manufactured, allowing us to use higher currents in the main precession coils. The neutron guide system of the J-NSE allows the variation of the wavelength between about 4.5 to 16 A. A larger neutron guide exit of 60 × 60 mm2, the higher neutron flux, the possibility of varying the wavelength over a broad range and the better correction elements push the performance of the instrument to Fourier times τ = 1 ps to about 350 ns, with a q-range of q = 0.02–1.5 A−1. We describe here the technical changes and improvements of the J-NSE and show the first spin echoes measured with the reinstalled spectrometer.

The properties of bicontinuous microemulsions, consisting of water, oil, and a surfactant, can be modified by the addition of diblock copolymers (boosting effect) and homopolymers (inverse boosting effect) or a combination of both. Here, the influence of the addition of homopolymers (PEP(X) and PEO(X), X=5k or 10k molecular weight) on the dynamics of the surfactant layer is studied with neutron spin echo spectroscopy (NSE). Combining the results with the previous findings for diblock copolymers allows for a better separation of viscosity and bending modulus effects. With the addition of homopolymers, a significant increase of the relaxation rate compared to the pure microemulsion has been observed. The influence on the bending rigidity kappa is measured with NSE experiments. Homopolymer addition reduces kappa by up to Deltakappa approximately -0.5k(B)T, whereas the diblock copolymer yields an increase of kappa by approximately 0.3k(B)T. Comparison of the bending moduli that are obtained by analysis of the dynamics to those obtained from small angle neutron scattering (SANS) sheds light on the different renormalization length scales for NSE and SANS. Variation of the surfactant concentration at otherwise constant conditions of homopolymer or diblock-copolymer concentration shows that NSE results are leading to the pure bending rigidity, while the renormalized one is measured with SANS.