Small angle neutron diffusion

Other techniques such as X-ray diffusion or small angle neutron diffusion are also used in attempts to describe the size and form of asphaltenes in crude oil. It is generally believed that asphaltenes have the approximate form of very flat ellipsoids whose thicknesses are on the order of one nanometer and diameters of several dozen nanometers. 

NMR self-diffusion coefficients (Lindman, 1983), small-angle neutron scattering (SANS) (Cebula, 1982 Triolo, 1983 Corti, 1984), freezing point and vapor pressure methods (Herrington, 1986) and fluorescent probes (Atik, 1979) have been used to calculate aggregation numbers of several different types of surfactants (Zana, 1980 Lianos, 1980, 1981, 1982, 1983). Some aggregation numbers of surfactants are listed in Table 3-1. 

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. 

Harrison et al. reported the first w/c microemulsion in 1994 (20). A hybrid surfactant, namely F7H7, made of respectively one hydrocarbon and one fluorocarbon chain attached onto the same sulfate head group, was able to stabilize a w/c microemulsion at 35 and 262 bar. For a surfactant concentration of 1.9 wt %, water up to a w = 32 value ([water]/surfactant]) could be dispersed. A spherical micellar structure was confirmed by small-angle neutron scattering (SANS) experiments (21). This surfactant was later the subject of dynamic molecular simulations (22, 23). The calculations were consistent with the SANS data and high diffusivity was predicted, highlighting this important feature of low-density and low-viscosity supercritical fluids (SCF). 

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