Neutron Spin Echo in Polymer Systems -/-
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eutron Spin Echo in Polymer Systems D. Richter1 · M. Monkenbusch1 · A. Arbe 2 · J. Colmenero 2, 3 1
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Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich, Germany [email protected], [email protected] Unidad Física de Materiales (CSIC-UPV/EHU),Apartado 1072, 20080 San Sebastián, Spain [email protected], [email protected] Departmento de Física de Materiales (UPV/EHU) and Donostia International Physics Center, Apartado 1072, 20080 San Sebastián, Spain
Abstract Neutron spin echo spectroscopy (NSE) provides the unique opportunity to unravel the molecular dynamics of polymer chains in space and time, covering most of the relevant length and time scales. This article reviews in a comprehensive form recent advances in the application of NSE to problems in polymer physics and describes in terms of examples expected future trends. The review commences with a description of NSE covering both the generic longitudinal field set-up as well as the resonance technique. Then, NSE results for homopolymers chains are presented, covering all length scales from the very local secondary b-relaxation to large scale reptation. This overview is the core of the review. Thereafter the dynamics of more complex systems is addressed. Starting from polymer blends, diblock copolymers, gels, micelles, stars and dendrimers, rubbery electrolytes and biological macromolecules are discussed.Wherever possible the review relates the NSE findings to the results of other techniques, in particular emphasizing computer simulations. Keywords Neutron spin echo spectroscopy · Polymer dynamics · Reptation · Glassy relaxation
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D. Richter · M. Monkenbusch · A. Arbe · J. Colmenero
1 Introduction Among the experimental techniques for studying the structure and dynamics of polymers, neutron scattering plays a unique role for several reasons: i. The suitability of the length and time scales. These are accessed in particular by small angle neutron scattering (SANS) and neutron spin echo (NSE) and allow the exploration of large scale properties – for instance the conformation of a large macromolecule, its diffusion in the embedding medium and its entropy driven dynamics – as well as features characteristic for more local scales, e.g. the inter- and intrachain correlations in a glass-forming polymer and their time evolution, the rotational motion of methyl groups, the vibrations and so on. ii. By variation of the contrast between the structural units or molecular groups, complex systems may be selectively studied. In particular, the large contrast achieved by isotopic substitution of hydrogen – one of the main components of polymers – by deuterium constitutes the most powerful tool for deciphering complex structures and dynamic processes in these materials. iii. Neutron reflectometry constitutes a unique technique for the investigation of surfaces and interfaces in polymeric systems. iv. The high penetration of neutrons in matter allows the study of the influence of external fields, e.g. shear or pressure or the evolutio
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