Neutron scattering, microemulsion

The structure of microemulsions have been studied by a variety of experimental means. Scattering experiments yield the droplet size or persistence length (3-6 nm) for nonspherical phases. Small-angle neutron scattering (SANS) [123] and x-ray scattering [124] experiments are appropriate however, the isotopic substitution of D2O for H2O... 

K. V. Schubert, R. Strey. Small-angle neutron scattering from microemulsion near the disorder Une in water/formamide-octane-C,E systems. J Chem Phys 95 8532-8545, 1991. 

By small-angle neutron scattering experiments on water/AOT/hydrocarbon microemulsions containing various additives, the change of the radius of the miceUar core with the addition of small quantities of additives has been investigated. The results are consistent with a model in which amphiphilic molecules such as benzyl alcohol and octanol are preferentially adsorbed into the water/surfactant interfacial region, decreasing the micellar radius, whereas toluene remains predominantly in the bulk hydrocarbon phase. The effect of n-alcohols on the stability of microemulsions has also been reported [119],... 

Robinson BH, Toprakcioglu C, Dore JC, Chieux P (1984) Small-Angle Neutron-Scattering Study of Microemulsions Stabilized by Aerosol-Ot.l. Solvent and Concentration Variation. J Chem Soc Faraday Trans 1 80 13-27... 

Water-in-fluorocarbon emulsions, stabilised with fluorinated nonionic surfactants, were investigated by small angle neutron scattering (SANS) spectroscopy [8,99]. The results indicated that the continuous oil phase comprised an inverse micellar solution, or water-in-oil microemulsion, with a water content of 5 to 10%. However, there was no evidence of a liquid crystalline layer at the w/o interface. A subsequent study using small angle x-ray scattering (SAXS) spectroscopy gave similar results [100]. 

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. 

Small-angle neutron scattering (SANS) can be applied to food systems to obtain information on intra- and inter-particle structure, on a length scale of typically 10-1000 A. The systems studied are usually disordered, and so only a limited number of parameters can be determined. Some model systems (e.g., certain microemulsions) are characterized by only a limited number of parameters, and so SANS can describe them fully without complementary techniques. Food systems, however, are often disordered, polydisperse and complex. For these systems, SANS is rarely used alone. Instead, it is used to study systems that have already been well characterized by other methods, viz., light scattering, electron microscopy, NMR, fluorescence, etc. SANS data can then be used to test alternative models, or to derive quantitative parameters for an existing qualitative model. 

Another interesting technique able to investigate the microstructure of dense microemulsions is represented by the small-angle neutron scattering (SANS) (de Campo et al., 2004). 

M. A. Bolzinger-Thevenin, I. L. Grossiord, and M. C. Poelman, Characterization of a sucrose ester microemulsion by freeze fracture electron micrograph and small angle neutron scattering experiments, Langmuir, 15 (1999) 2307-2315. 

Although NMR results provide perhaps the most convincing evidence of the bicontinuous structure of some microemulsions, many other techniques support their existence. These techniques include electrical conductimetry, x-ray and neutron scattering, quasielastic light scattering, and electron... 

C. Micellar and microemulsion shell thickness determination by combination of light scattering and neutron scattering... 

Microemulsions consist of oil, water and an oil-water interfacial Him. DLS and SLS have been used to determine the translational diffusion coefficient and the interaction potential of microemulsions [45—47). The thickness of the inter-facial film and its curvature were measured by the contrast variation method in neutron scattering [48,491. This method is based on changing the scattering strength by changing the relative amount of light and heavy water in the microemulsion. 

Shukla, A. Kiselev, M.A. Hoell, A. Neubert, R.H.H. Characterization of nanoparticles of lidocaine in w/o microemulsions using small-angle neutron scattering and dynamic light scattering. Pramana-Journal of Physics... 

As in binary surfactant-water systems considered previously, two constraints on the geometry of the surfactant interface are active a local constraint, which is due to the surfactant molecular architecture, and a global constraint, set by the composition. These constraints alone are sufficient to determine the microstructure of the microemulsion. They imply that the expected microstructure must vary continuously as a function of the composition of tile microemulsion. Calculations show - and small-angle X-ray and neutron scattering studies confirm - that the DDAB/water/alkane microemulsions consist of a complex network of water tubes within the hydrocarbon matrix. As water is added to the mixture, the Gaussian curvature - and topology -decreases [41]. Thus the connectivity of the water networks drops (Fig. 4.20). 

Now let us emphasize that we want all the conclusions to be drawn exclusively from the experimental results (i.e. the neutron scattering spectra), without making use of any theory on microemulsions. In particular, at a given temperature and for a certain overall composition, the structures must be determined independently of any hypothesis about the (oil) dilution. Quite the contrary, these structural results should be actually used to support the eventual validity of that theory or other, which can be proposed to explain the evolution of the phase diagrams. 

Eastoe J, Cazelles BMH, Ste5Tler DC, Holmes JD, Pitt AR, Wear TJ, Heenan RK. Water-in-C02 microemulsions studied by small-angle neutron scattering. Langmuir 1997 13 6980-6984. 

Lee CT, Johnston KP, Dai HJ, Cochran HD, Melnichenko YB, Wignall GD. Droplet interactions in water-in-carbon dioxide microemulsions near the critical point a small-angle neutron scattering study. J Phys Chem B 2001 105 3540-3548. 

Chen, S.H. (1986) Small angle neutron scattering studies of the structure and interaction in micellar and microemulsions. Ann. Rev. Phys. Chem., 37, 351-399. 

Schubert, K.-V., Strey, R., Kline, S. and Kaler, E.W. (1994) Small-angle neutron scattering near the Lifshitz lines Transition from weakly structured mixtures to microemulsions. /. Chem. 

Gradzielski, M., Langevin, D., Magid, L. and Strey, R. (1995) Small-angle neutron scattering from diffuse interfaces. 2. Polydisperse shells in water n-alkane-C10E4 microemulsions. /. Phys. Chem., 99, 13232-13238. 

Arleth, L. and Pedersen, J.S. (2001) Droplet polydispersity and shape fluctuations in AOT [bis(2-ethylhexyl)sulfosuccinate sodium salt] microemulsions studied by contrast variation small-angle neutron scattering. Phys. Rev. E, 63, 61406-61423. 

Bagger-Jorgensen, H., Olsson, U. and Mortensen, K. (1997) Microstructure in a ternary microemulsion studied by small angle neutron scattering. Langmuir, 13, 1413-1421. 

Sottmann, T., Strey, R. and Chen, S.-H. (1997) A small-angle neutron scattering study of nonionic surfactant molecules at the water-oil interface Area per molecule, microemulsion domain size, rigidity. /. Chem. Phys., 106, 6483-6491. 

In Ref. [42], PEO was embedded in a w/o-droplet microemulsion and studied by small-angle neutron scattering. The authors state that this polymer does not adsorb considerably at the SDS monolayer. The important statement is that both the size polydispersity and the shape fluctuations are increased compared to the reference system without polymer. Larger shape fluctuations are also found for gelatine embedded in w/o-droplet microemulsions (see Fig. 4.10 in [43]). Here, by strong confinement, the elongated shapes... 

Zielinski, R.G., Kline, S.R., Kaler, E.W. and Rosov, N. (1997) A small-angle neutron scattering study of water in carbon dioxide microemulsions. Langmuir, 13, 3934-3937. 

Rananavare, S.B., Ward, A.J.I., Osborne, D.W., Friberg, S.E. and Kaiser, H. (1988) A small-angle neutron-scattering study of a nonaqueous 3-component microemulsion. /. Phys. Chem., 92, 5181-5183. 

Schubert, K.V. and Strey, R. (1991) Small-angle neutron-scattering from microemulsions near the disorder line in water formamide octane QEj systems. /. Chem. Phys., 95, 8532-8545. 

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