Surfactant assemblies

Shioi A and Flarada M 1996 Model for the geometry of surfactant assemblies in the oil-rich phase of Winsor I microemulsions J. Chem. Eng. Japan 29 95... 

Fluorescence Probing of the Surfactant Assemblies in Solutions and at Solid-Liquid Interfaces... 

Because of the hmited solubility in different solvents surfactants form different types of surfactant assemblies in solutions and on solids. These organized assemblies are formed when different proportions of surfactants, oils, cosurfactants and water are mixed together. The types of surfactant aggregate formed depends on its chemical structure and the nature of the medium. 

These fluorescent probes have been successful in reporting the structural parameters of surfactant assemblies such as micelles [103], reverse micelles [104], ternary systems [105], swollen micelles [106], microemulsion [107], vesicles [108], liposomes [109], hemimicelles [110], monolayers [111] and bilayers [111]. 

The settling rate of the dispersions in cyclohexane initially increases with AOT adsorption but later decreases. The initial increase is attributed to the formation of interparticle surfactant aggregates (Fig. 39A). At higher concentrations, the adsorbed molecules aggregate with excess of surfactant in solution rather than with molecules on the particle, so that flocculation ceases to occur and the dispersion is restabilized. The schematic representation of the surfactant assemblies at the interface is as shown in Fig. 39B. 

The polarity within a surfactant assembly will be quite different from that of the bulk solution. It is useful to know the micropolarity of these assem-bhes for such applications where different substrates are compartmentalized inside these surfactants. The micropolarity of the surfactant assembhes can be determined using any fluorescence probe whose emission characteristics change with solvent polarity. The emissions of the probe are measured in solvents of known polarities and the polarity of the surfactant assembhes is determined by comparison. 

The fluidity (nanoviscosity) in an organized surfactant assembly on soUds can be substantially different from that in the bulk aqueous phase and hence, the diffusional resistance experienced by the probe in the micelle will be considerably different from that faced in the bulk solution [ 145]. Measurement of the viscosity or fluidity of the interior of a micelle is based on measurement of fluorescence properties that depend on the mobihty of the probe in the interior. A commonly used method for such studies involves the intramoleciflar... 

Surfactants provide several types of well-organized self-assembhes, which can be used to control the physical parameters of synthesized nanoparticles, such as size, geometry and stability within liquid media. Estabhshed surfactant assembles that are commonly employed for nanoparticie fabrication are aqueous micelles, reversed micelles, microemulsions, vesicles [15,16], polymerized vesicles, monolayers, deposited organized multilayers (Langmuir-Blodgett (LB) films) [17,18] and bilayer Upid membranes [19](Fig. 2). 

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