Contrast matching

The ability to contrast match the air with a mixture of water and heavy water makes neutron reflectivity an attractive technique [180,181], Under these contrast conditions the scattering arises from the monolayer alone and combining... 

Hasegawa H., Hashimoto T., Kawai H., Lodge T.P., Amis E.J., Glinka C.J., and Han C. SANS and SAXS studies on molecular conformation of a block copolymer in microdomain space. 2. Contrast matching technique. Macromolecules, 18, 67, 1985. 

The observation of single-chain dynamics in semi-dilute solutions requires contrast matching and labelling. In the case of PDMS this can be achieved using... 

Figure 11.12 SANS of G7(H) in CD3OH, G7(D) in contrast match methanol, and G7(H) in contrast match solvent. Labeled dendrimerin core match solvent shows scattering from labeled terminal generation...

Using contrast matching methods of SANS, Nafion was swollen with various mixtures of H2O and D2O in order to highlight the scattering features of the water swollen ionic domains. Furthermore, quenched samples were used in these studies to eliminate the scattering features attributed to the crystalline do-... 

To further probe the phase behavior of hydrated Nafion, Rollet et al. used a contrast matching method in the SANS analysis of Nafion membranes neutralized with tetramethylammonium ions. With 12 hydrogen atoms per counterion, the N(CH3)4+ ions... 

Small angle X-ray scattering monitoring the distribution of electron density has been used to probe resin morphology [109]. More recently contrast matched small angle neutron scattering has also been employed [110, 111]. These techniques can also be applied to wet resins and tend to probe the very low dimensions of the polymer matrix structure. More studies are needed to identify the real value of these approaches. 

Even the traditional methods discussed in this chapter can be used for concentrated dispersions through contrast matching. For example, silica particles coated with silane coupling agents in a refractive index-matched mixture of ethanol and toluene can be used in combination with visible probe particles to study the dynamics of particles in dense systems. In the case of microemulsions (Chapter 8), selective deuteration of a component (oil, water, or surfactant) can be used in neutron scattering experiments even to measure the curvature of the oil-water interface. 

Fig. 4.25 Experimentally measured SANS patterns for an FCC micellar phase in a dPS-PI diblock (A/ = 55kgmor, 60wt% PS) in core contrast-matched decane/ d-decane mixtures (15wt% polymer) subject to steady shear in a Couette cell at different shear rates (McConnell et al. 1995) (a) y — 0.01 s aligned by inserting the stator (b) y=0.06s 1 (c) y = 0.66s 1 (d) y = 6.60s (e) y = 66.0 s (f) y = 200.0s-1. The wavevectors qv (horizontal) and qe (vertical) for these patterns range from —0.028 to 0.028 A. ...

Mayes et ai. (1994) tested this prediction using SANS on PSPMMA and PMMA-dPMMA diblocks in contrast-matched toluene/d-toluene mixtures in the disordered phase. They did not obtain the scaling (eqn 4.14), instead a best fit to the data yielded q = (p°05 (Fig. 4.34). This slower than expected scaling is presently unexplained. However, the expected concentration dependence of the blob size (Mayes et at. 1994)... 

Fig. 4.45 Structure factors versus wavevector for rfPS-PI diblocks in core-contrast matched decane solutions (Gast 1996 McConnell et al. 1994) (a) dPS,W3PI >o( at cote volume fractions of 0.012 (A), 0.02(+), 0.03( ), 0.04 (A) and 0.05 (o) (b) f/PS Pl at core volume fractions of 0.006 (o), 0.013 ( ) and 0.019 (A). The lines are theoretical fits from the self-consistent field interaction potentials and the Rogers-Young closure to the Ornstein-Zernike equation.

In summary the advantage of using neutrons for catalyst particle-size-distribution function measurements, is that, unlike X-rays, they can be applied to catalysts dispersed on high-electron-density supports such as a-Al203. This is because the technique of contrast matching to mask-out one component of the scattering is much more versatile with neutrons than with X-rays. In part this is due to the ready availability of suitable deuteriated solvents. 

Figure 7. SANS signal from PNIPA in fully deuterated water ( ) at 20 °C and in contrast matched conditions (18% D20 82% H20) with different amounts of deuterated phenol (O 0 mM, 20 mM, and A 40 mM).

SANS experiments were undertaken to confirm the DLS observations. Results obtained with phenol solutions are shown in Figures 7 and 8. In the conditions of contrast matching employed here, where the scattering length density of the water was adjusted to be equal to that of the polymer, clustering... 

Figure 8. Close-up view of contrast-matched signals. The error hars are much larger for the large sample-detector distances d, because the signal intensity decreases as I let. The signal from the phenol is zero within the level of the noise. The phenol is therefore mainly distributed uniformly in the liquid. Symbols are the same as in Figure 7.

An important option of neutron scattering and reflectometry is the possibility of contrast matching, whereby a certain component (for example, the particles) can be made "invisible" by modifying p, just as one can suppress... 

Instead of attempting to contrast match, we chose cobalt as a pore-filling material. The contrast values Ap for alumina/void and alumina/cobalt, fi om Table 1, are of opposite sign but close in magnitude. If the cobalt completely occupies the pore cavities, the intensity profile should therefore have the same shape as that for the empty membrane. 

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

The above study is noteworthy for a few reasons. Firstly, the data were obtained using only one partially deuterated form of the amphiphilic molecules of interest. Secondly, while SANS studies of polymers at a contrast-matched interface are common, the work of Riley et al. is unique owing to the small size of the core particle and the fact that it was the off-contrast match data that provided the more detailed structural information via solvent contrast variation. 

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