Comparison with small-angle neutron scattering

Comparison of Small-Angle Neutron Scattering with Light Scattering... 

Whitmore and Noolandi (1985b) developed the self-consistent field theory to examine micellization in AB diblocks in a blend of AB diblock and A homopolymer solvent . The model was applied specifically to the case of PS-PB diblocks in PB homopolymer for comparison with the results of small-angle neutron scattering (SANS) experiment by Selb et al. (1983). This model is discussed in more detail in Section 3.4.2. 

Relatively few small angle neutron scattering studies have been performed on block copolymers in comparison to those on homopolymers, the majority of the published work is concerned with the solid state with little work reported on block copolymer solutions. Results on isotopic block copolymers, e.g. polystyrene molecules with... 

Such definitive forecasts do not result from the theories of Leibler or Hong and Noolandi. However, the latter theory describes in detail the phase diagram for copolymer — homopolymer mixtures and is therefore pertinent to the X-ray work of Roe Similarly, Leibler s theory provides a detailed description of a microphase separation mechanism and thus is of value in the interpretation of experiments investigating this phenomenon. Small angle neutron scattering data reported to date has been maitily concerned with pure styrene-diene block copolymers which are fully microphase separated and thus examined D, dj, and interfadal layer thickness as a function of molecular weight and composition and therefore comparison has usually been made with the MIA theory of Helfand. 

In polymer blends, the radius of gyration of a polymer molecule in a matrix of another polymer can be compared with the radius of gyration of in a matrix of molecules of the same composition. In order to achieve these comparisons, tagged molecules (deuterium) are usually required to achieve resolution and thus small angle neutron scattering employs the above noted procedure to assess the level of miscibility of polymer blends. 

The most important elasticity result of this type is obtained by small-angle neutron scattering. In particular, such studies yield information on how the radius of gyration of the network chains transforms with elongation (13). Preliminary comparisons between theory and experiment are quite encouraging (262), but many issues remain unresolved in this relatively new approach to characterizing elastomeric behavior. 

This paper consists of four major sections. In the first section are described some of the recent synthesis methods allowing the preparation of calibrated networks with labelled chains. The second section deals with the microscopic structure of networks. The recent small-angle neutron scattering results are reviewed and the deformation mechanisms in gels discussed. In the third section, scaling relations derived for the elastic moduli of networks swollen at equilibrium are compared with the existing experimental data. Finally, in the fourth section a comparison between the dynamic properties of networks swollen at equilibrium and semi-dilute solution is made within the framework of a scaling approach. 

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