Applications of small-angle neutron scattering

An exhaustive survey of the uses for SANS in polymer science would be too long for the space available here. Attention is focused on three aspects. Polymer blends provide an example of the application of the random-phase approximation and have also enabled a better appreciation to be obtained of the thermodynamic changes consequent on deuteration. Block copolymers in the homogeneous state are also analysable by using the random-phase approximation, and the theory of the segregation in these systems has progressed rapidly in recent years. Lastly, liquid-crystal polymers are the most recent class of polymers to be examined by SANS. They 

1 Polymer blends. Although it is well known that the mean-field Flory-Huggins theory of the thermodynamics of polymer systems is not a rigorously accurate description, especially for polymer blends, it is sufficiently valid that its use does not incur serious errors. Furthermore, de Gennes [16] used the mean-field random-phase approximation to obtain the scattering law for a binary polymer blend as  

Values of P// obtained ranged from 19 K to 57 K for the two types of mixtures concerned, and the error quoted on these values was 20%. 

In addition to the isotope effects discussed above, the miscibility of polymers will depend on the stereochemical micro structure and the tacticity of the constituent polymers. The influence of microstructure on the thermodynamics 

X for this system was essentially negligible however, at higher temperatures X became negative. This was attributed to the copolymer effect rather than the existence of specific interactions. The poly butadienes were treated as random copolymers of 1,4- and 1,2-addition units, and there are deuterated and hydrogenous homologues in the mixture, i.e. there are four different types of monomer segment. A, B,C and D. Using the copolymer theory of ten Brinke et al. [30], then % can be written as  

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Developments in the Application of Small-angle Neutron Scattering to Food Systems... 

The distribution of segments in loops and tails, p(z), which extend in several layers from the surface. p(z) is usually diflBcult to obtain experimentally, although recently the application of small-angle neutron scattering has been used to obtain such information. An alternative and useful parameter for assessing steric stabilisation is the hydrodynamic thickness, Sf, (the thickness of the adsorbed or grafted polymer layer plus any contribution from the hydration layer). Several methods can be applied to measure 5, as will be discussed below. 

APPLICATION OF SMALL ANGLE NEUTRON SCATTERING TO RNA-PROTEIN COMPLEXES... 

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of PEEK) supplied by Victrex, which may be better suited to PEMFC fabrication applications. In March 2002, U.S. Patent 6,359,019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluorovinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The strucmres of BAM membranes have been studied by way of small-angle neutron scattering (SANS) [97]. The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nalion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the membrane s mechanical and transport properties. 

Attention will be focused here on the use of small-angle neutron scattering (SANS) in polymer systems and the application of neutron reflectometry (NR) to polymer surfaces and interfaces. SANS has been used to investigate mole-... 

Higgins JS, Stein RS. Recent developments in polymer applications of small-angle neutron, X-ray and light scattering. J Appl Crystallogr 1978 11 346. 

The use of small angle scattering techniques for studying porous solids is well established, but it is only in recent years that their full potential has been appreciated. Several papers in the present symposium illustrate the application of small angle neutron (SANS) and X-ray (SAXS) scattering. 

Melnichenko, Y.B. and Wignall, G.D. (2007) Small-angle neutron scattering in materials science recent practical applications. Journal of Applied Physics, 102 (2), 021101. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

The use of neutron scattering techniques, both small angle neutron scattering (SANS) and neutron reflectometry, have been central to the development of our understanding of polymers at a microscopic level in bulk (solutions and melts), and at interfaces and in thin films. The power of these techniques and their extensive application stems primarily from the vastly different scattering powers of hydrogen and deuterium. Through this difference, H/D isotopic substitution provides a selectivity and sensitivity at an atomic scale resolution, which is more difficult to obtain with other techniques. 

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