Polymer blend dynamics neutron scattering

Compared to binary mixtures of low molecular fluids, the critical behavior of polymer blends has been much less explored so far. However, a number of interesting static and dynamic critical phenomena in polymer blends attract increasing attention [4, 5], Neutron, X-ray, and static light scattering experiments belong to the major techniques for characterizing the static properties of polymer blends. Photon correlation spectroscopy (PCS) has traditionally been the method of choice for the investigation of the dynamics of critical [6-9] and noncritical [10-12] polymer blends. 

Her current research interests include studies of miscibility and physical aging in blends, nanophase separation in polymers with long side-chains, polymer dynamics, liquid crystalline polymers, composites, and systems containing nanoparticles. A common feature of these studies is the use of scattering techniques, especially neutron scattering, to study the local structure, conformation, and dynamics in polymers. She has written various reviews and book chapters in this area and has served on selection panels to allocate beam time at neutron facilities. 

The Coupling Model is consistent with all the properties and has fundamental support from quasielastic neutron scattering and simulations. However, the emphasis of the entire section is on the many properties of component dynamics in HAPB that deserve attention and alternative explanation by researchers in glass transition and polymer chain dynamics and viscoelasticity. This is because the new physics found in the segmental and chain dynamics of components in highly asymmetric polymer blends could possibly revolutionize the current understanding of polymer dynamics and viscoelasticity. 

Similar results have been also reported by Adachi et al. (Urakawa et al. 2002) for PVME/PS, for the blend PMMA/PEO (Maranas 2007), or for blends of PVDF/ PMMA (Sy and Mijovic 2000). Besides dielectric spectroscopy quasielastic neutron scattering is found to be quite useful to investigate the molecular dynamics of dynamic asymmetric polymer blends because spatial information is provided by this technique (see, for instance, Tyagi et al. 2006, 2007). For a more detailed discussion, the reader is referred to the literature (Colmenero and Arbe 2007). 

Even given these limitations, neutron scattering is a unique and very powerful technique that can provide information on the microscopic structure and dynamics of a polymeric material that is not obtainable by any other method. For instance, no other method provides a direct measure of the size of a polymer chain in the melt that is available by measuring the scattered intensity of neutrons from a blend of deuterated and protonated versions of the same polymer. Similarly, the shape and thermodynamic interactions of polymers in concentrated mixtures are most effectively monitored by carefully designed neutron-scattering experiments, some of which will be described in detail later in the article. 

Neuutn scattering is often perftrmed as a function cf particle concentration to determine specific interactions between components. Blends cf metallocene synthesized polyolefins (32) and efi ds cf solvent on dendrima- size (33) have been studied using SANS. Interface widths between two polymer blend components in the melt have been studied by neuu-on reflectivity (34). Dynamic studies have been undertaken on bimodal melts (35) using neutron spin echo techniques. Some of these recent developments will be reported in ttie following chrqiters. 

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