Neutron Scattering Contrast

Another possibility is to adjust the coherent scattering lengths of two chemically different polymers in order to make them indistinguishable for SANS studies. In this way individual polymer chains in more complex mixtures can be explored. An example may be polystyrene PS and polybutadiene 

PB which are indistinguishable for neutrons if a fully deuterated PS is mixed with a partially deuterated PB consisting statistically of 4.4% protonated and 95.6% deuterated monomers. 

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When molecules are adsorbed in the nanopores, the neutron scattering contrast of the carbon decreases from its value in the dry state (i.e., in air) to... 

Compere, A. L., Griffith, W. L., Johnson, J. S., Caponetti, E., Chillura-Martino, D., and Triolo, R. (1997). Alcohol partition in a water-in-oil microemulsion Small-angle neutron-scattering contrast measurements. J. Phys. Chem. B, 101, 7139-7146. 

Key words Sorbitol - cryoprotectant - phosphatidylcholine - micelle neutron scattering - contrast-variation method... 

Figure 7.3 Neutron scattering contrasts of polymer blend, illustrating good and weak contrast. The weak contrast examples illustrate the contrast within typical polymer blends. The good contrast example illustrates how contrast between the A and B-polymers can be...

Figure 1. Scattered intensity from a statistical gel (a semi-dilute solution of polymer volume fraction ([) = 0.1, transformed into a "gel" by random reaction of tie-points between the chains concentration of crosslinking molecules Cx=0.8%, in moles per mole of "monomer unit"). The neutron scattering contrast between the network and the solvent is achieved by swelling the gels with deuterated toluene. The signal from the gel is compared to that of a semi-dilute solution of the same polymer concentration, here for two swelling degrees only left, nearly that of preparation right maximum swelling approximately...

Small angle neutron scattering measurements were carried out with the PACE diffractometer at the Laboratoire Leon Brillouin, (CE Saclay, France). The q range observed was 3.4 lO" to 0.2 A l. Samples were prepared in deuterated instead of ordinary water to achieve a suitable value for the neutron contrast factor. 

The prerequisite for an experimental test of a molecular model by quasi-elastic neutron scattering is the calculation of the dynamic structure factors resulting from it. As outlined in Section 2 two different correlation functions may be determined by means of neutron scattering. In the case of coherent scattering, all partial waves emanating from different scattering centers are capable of interference the Fourier transform of the pair-correlation function is measured Eq. (4a). In contrast, incoherent scattering, where the interferences from partial waves of different scatterers are destructive, measures the self-correlation function [Eq. (4b)]. 

The size and shape of polymer chains joined in a crosslinked matrix can be measured in a small angle neutron scattering (SANS) experiment. This is a-chieved by labelling a small fraction of the prepolymer with deuterium to contrast strongly with the ordinary hydrogenous substance. The deformation of the polymer chains upon swelling or stretching of the network can also be determined and the results compared with predictions from the theory of rubber elasticity. 

Performing neutron scattering not on perdeuterated samples but on a single deuterated chain in a protonated matrix (or vice versa both ways provide the same contrast) gives the single-chain structure factor,... 

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