Small-angle neutron-scattering study of microemulsions stabilised by aerosol-OT. Part 1.—Solvent and concentration variation

Abstract

Small-angle neutron-scattering (SANS) measurements have been made for a series of aerosol-OT (A0T)-stabilised water-in-oil microemulsions. The intensity pattern has been used to extract a value for the radius of the water core, rw, using D,O to provide the required contrast profile. In heptane the radii are found to follow an approximately linear relationship with respect to the [D,O]/[AOT] concentration ratio, R. At 20 OC, and R = 20, the structure of the water-droplet system is dependent on the hydrocarbon chain length of the oil medium. The experimental SANS patterns show increasing discrepancies with a fitted function based on monodisperse spheres as the length of the alkane chain is increased from n-heptane to n-dodecane. This effect is attributed to polydispersity and indicates that the droplet-size distribution within these microemulsion systems is much larger than had previously been thought.Previous studies by photon correlation spectroscopy 2-4 and 13

Recent advances in nanoparticle synthesis with reversed micelles

“…observed in water-in-oil microemulsion systems. 133,134 Unfortunately in many cases, the same effect is not seen. Cason et al 47 and then Kitchens et al 63 found that at any given value of w 0 , the same size nanoparticles can be synthesized, if left for sufficient time for the reaction to go to completion ( Figure 5).…”

Molecular Dynamics Simulations of the Interior of Aqueous Reverse Micelles

“…Aqueous AOT reverse micelles can be characterized over a wide range of water and surfactant concentrations by a single parameter, which is proportional to the micellar radius. 12, 13 These aggregates have been found to be relatively monodisperse in solution and spherical in shape down to very low water concentrations. 14 The spherical aggregates, which are the focus of this study, range in the diameter of the aqueous core from about 0.5 nm to more than 10.0 nm.…”

“…5 Experimental techniques that have been used to characterize the AOT reverse micelles include light scattering, 41,42 photon correlation, 12 IR spectroscopy, 23,[43][44][45][46][47] NMR, 11,22,[48][49][50][51][52] probe fluorescence, 10,21,53-61 calorimetry, 62,63 small-angle neutron scattering (SANS), 13,14,64 and quasi-elastic neutron scattering. 65,66 While many of these techniques provide information about the structure and properties of reverse micelles, a fundamental dispute remains about the structure of water in the micellar interior.…”

“…Experimental studies of these structures with a range of techniques have shown that they consist of tens to hundreds of surfactant and solvent molecules and tend to be spherical in shape at low surfactant and polar solvent concentrations. [9][10][11][12][13][14] The effects of confinement and the strong interactions between the polar solvent molecules and the headgroups, which are frequently ionic, produce a chemical environment that may differ dramatically from that of the bulk solvent. As more polar solvent is added, the interior pools grow in size and tend to recover the properties of the bulk solvent.…”

Formation and properties of dimeric recombinant horseradish peroxidase in a system of reversed micelles

“…Variations in this parameter are accompanied by changes in the size of the inner water cavity of reversed micelles [30,31]. Maximal enzyme catalytic activity in reversed micelles is observed at a particular degree of surfactant hydration, namely when the size of the inner cavity corresponds to that of the entrapped protein (general regularities of the phenomenon are discussed in [17]).…”