Spin-echo neutron scattering

Spin-echo neutron scattering measurements on molten poly (tetrahydrofuran) led Higgins et al. [53] to report that they found evidence for Rouse-like chain motion. The experiment was concerned with A > 0.3 nm". However, such k does not satisfy the condition l/dt > k, since dt for molten poly (tetrahydrofuran) is estimated to be 3 nm [53]. Hence, it is doubtful if the finding of Higgins et al. can rule out the possibility of reptation. 

In addition to the above techniques, inverse gas chromatography, swelling experiments, tensile tests, mechanical analyses, and small-angle neutron scattering have been used to determine the cross-link density of cured networks (240—245). Si soHd-state nmr and chemical degradation methods have been used to characterize cured networks stmcturaHy (246). H- and H-nmr and spin echo experiments have been used to study the dynamics of cured sihcone networks (247—250). 

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

In this review we consider large-scale polymer motions which naturally occur on mesoscopic time scales. In order to access such times by neutron scattering a very high resolution technique is needed in order to obtain times of several tens of nanoseconds. Such a technique is neutron spin echo (NSE), which can directly measure energy changes in the neutron during scattering [32,33]. 

In this review we will present the outcome of NSE studies on polymer systems covering results beyond those reported in an earlier review in Advances in Polymer Science [5] eight years ago. Table 1.1 shows the chemical structure and information on the chain dimensions of the systems considered here. In Chap. 2 we will commence with a brief description of neutron scattering principles and a discussion of the two different ways neutron spin echo may be implemented - the traditional NSE approach with precession coils and the neu-... 

The application of neutron spin-echo spectroscopy to the analysis of the slow dynamics of biomolecules is still in its infancy, but developing fast. The few published investigations either pertain to the diffusion of globular proteins in solution [332-334] or focus on the internal subnanosecond dynamics on the length scale, <10 A as measured on wet powders [335,336]. The latter regime overlaps with other quasi-elastic neutron scattering methods as backscattering and TOE spectrometry [337-339]. 

Anticipating further discussions on micro-emulsions, planned for volume V, it is noted that k, or k, or the combination (2kj -i- k ) can also be obtained using scattering techniques or, preferably, combinations thereof. For instance, neutron spin echo spectroscopy (NSES) can be combined with small-angle neutron scattering (SANS) or with dynamic light scattering. Alternatively, 2k + k can be obtained from the polydispersity of the micro-emulsion and then a second type of... 

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