Small contrast variation-SANS

The more recent neutron reflectivity studies have established that flattened surface micelle or fragmented bilayer structure in more detail and with more certainty, using contrast variation in the surfactant and the solvent [24, 31]. However, the extent of the lateral dimension (in the plane of the surface) and the detailed structure in that direction is less certain. From those neutron reflectivity measurements [24, 31] and related SANS data on the adsorption of surfactants onto colloidal particles [5], it is known that the lateral dimension is small compared with the neutron coherence length, such that averaging in the plane is adequate to describe the data. The advent of the AFM technique and its application to surfactant adsorption [15] has provided data that suggest that there is more structure and ordering in the lateral direction than implied from other measurements. This will be discussed in more detail in a later section of the chapter. At the hydrophobic interface, although the thickness of the adsorbed layer is now consistent with a monolayer, the same uncertainties about lateral structure exist. 

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. 

Keywords Block copolymer micelles Contrast variation Equilibrium and nonequilibrium kinetics Morphology Small-angle neutron and X-ray scattering Time-resolved SAXS/SANS... 

Abstract Partial structure functions and mean curvatures of a ternary amphiphilic system consisting of water, n-octane and nonionic amphiphile C12E5 with equal volume fraction of oil and water have been studied by means of small-angle neutron scattering (SANS). Isotopic contrast variation technique was used to obtain suitable scattering contrasts of oil and water. We observed that the cross partial structure functions, that arise from the correlation between water-surfactant or oil-surfactant, change sign when the temperature... 

Small-angle neutron scattering (SANS) is a unique tool to investigate the structure of mesoscopic molecular systems, e.g. polymeric macromolecules in solution or in the melt or mesoscopic aggregates (micelles, etc.) of small or macro-molecules. The substances involved usually contain a considerable amount of hydrogens, thereby allowing the application of the key technique of SANS, contrast variation. 

Small-angle neutron scattering coupled with the contrast variation technique was used by Caponetti et al. [230] to study solutions of sodium perfluo-rooctaonate, sodium dodecanoate, and their mixture. Their data indicated the existence of mixed micelles having the same composition and a narrow size distribution. SANS data obtained by Berr and Jones [231] indicated that sodium perfluorooctanoate forms in water spherical micelles in which the fluorocarbon chains reside in a water-free core. 

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