Scattering contrast

Figure Bl.17.4. Visualization of image contrast fomiation methods (a) scattering contrast and (b) interference contrast (weak phase/weak amplitude contrast).

If the object is embedded into a matrix with the same average scattering properties as the considered jumping unit, then the scattering contrast from the average size of the object is matched by the matrix and the corresponding forward scattering is suppressed. It can be shown [133] that the dynamic structure factor for an object embedded in a matrix, which performs jumps in a two level system, can be obtained as ... 

According to [291] the intensity scaled to the scattering contrast factor Ap may be written as ... 

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... 

Thin films of block copolymer melts, and block copolymers adsorbed at the liquid-liquid interface, have been investigated using specular reflectivity (largely neutron reflectivity due to the ability to vary the scattering contrast). Off-specular reflection is, in principle, a powerful method for determining in-plane structure in block copolymer films but is not yet widely used. 

An additional practical consideration for measurement of RNA using SAXS is the relatively high scattering contrast of RNA molecules relative to that of proteins as a result of the high density of phosphate moieties in the polynucleotide backbone. This means that shorter exposure times or more dilute samples may be used compared to SAXS measurements for proteins. 

The spontaneous mixing of the two polymers will transpire at a rate which reflects the degree of miscibility of the system. As X approaches the critical value for phase separation, "thermodynamic slowing down" of the interdiffusion will occur [12]. The rate of increase of the scattering contrast reflects the proximity of the system to criticality, as well as the strong composition dependence of the glass transition temperature of the blend. Extraction of a value for either the self diffusion constants [13,14] or the interaction parameter is not feasible from the presently available data. 

Figure 5 - Small angle neutron differential scattering cross section (ooo) measured from a sample consisting of sheets of PIP (N = 23000) and deuterated 1,2-PBD (N = 3200) which were in contact for 162 hours at 52°C. The scattering contrast significantly exceeds the incoherent background (—) determined from measurements on the individual polymers, evidencing the thermodynamic miscibility of the blend.

This means that the Flory interaction parameter y can be determined from the low wavevector limit of the scattering function of a single-phase blend of A chains (with monomers) and B chains (with monomers), where o is the volume fraction of A chains. In practice, the concentration fluctuations in the blend provide sufficient scattering contrast for neutron scattering, as long as one of the components is at least partially labelled with deuterium. 

Figure 5.12 compares Eq. (5.75) (l/i>= 1.7) with SANS data on a semidilute solution of polystyrene in carbon disulphide. Since the solvent contains no protons, no deuterium labelling is necessary for good scattering contrast. Fitting Eq. (5.75) with the good solvent value of l/i> = 1.7 to the data yields =5.5nm and provides an excellent description of the data. 

The kinetics of crystallization of PE-containing diblocks have been studied using simultaneous SAXS and WAXS [9,11]. The development of PE crystallites (with an enhanced scattering contrast compared with the initial melt state) was followed via the SAXS invariant using Eq. (2). For PE-PEE diblocks (and PE... 

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