Optical models, surfactant molecules

Since, however, each model involves some assumptions, the calculation of h2 always renders certain inaccuracy. The most important problem in the three-layer model concerns the position of the plane that divides the hydrophobic and hydrophilic parts of the adsorbed surfactant molecule. In some cases it seems reasonable to have this plane passing through the middle of the hydrophilic head of the molecule, in others the head does not enter into the aqueous core. That is why it is worth comparing film thicknesses determined by the interferometric technique using the three-layer model, to those estimated by other methods. An attempt for such a comparison is presented in [63]. Discussed are phospholipid foam films the thickness of which was determined by two optical techniques the microinterferometric and FT-IR (see Section 2.2.5). The comparison could be proceeded with the results from the X-ray Reflectivity technique that deals not only with the foam film itself but also with the lamellar structures in the solution bulk, the latter being much better studied. Undoubtedly, this would contribute to a more detailed understanding of the foam film structure. 

An optical three-layer model has proved superior to a one-layer model for the interpretation of the ellipsometric data. The refractive indices of the film and surface layers are determined and it is found that the index for the surface is higher than that for the film core. A Lorenz-Lorentz type treatment of NBF reveals that there are approximately seven water molecules per molecule of surfactants in both NaDoS and NaDoBS films. The optical data obtained by the three-layer model for NBF from NaDoS indicate that the thickness of the aqueous core is zero while that of the adsorption monolayers of surfactant molecules with refractive index 1.365 is 1.8 nm, i.e. the thickness of NBF is 3.6 nm. 

Self-assembled monolayers of surfactant molecules constitute model systems that permit incorporation of diverse chemical and physical properties and ease of preparation. Technological areas involving electronic and optical devices, sensors and transducers, protective and lubricating layers, and pattemable materials require ultrathin organic molecular films in which the relationships between structure, forces, and electrical and mechanical properties are continuously under investigation according to their application." ... 

The primary aim is to introduce the current concepts used to interpret the properties of homogeneous, optically transparent, self-assembling aqueous solutions of small molecule surfactants that form into association colloids composed of charged or uncharged surfactants into micelles, miaoemul-sions, vesicles, or other mesophases. Pseudophase models are used to interpret chemical reactivity in surfactant solutions. Large surface-active molecules such as proteins, starches, and polymers are not considered. Much of the information is on surfactant solutions at room temperature and atmospheric pressure because most of the important properties, concepts, and unanswered questions can be developed at ambient conditions. Effects of additives such as salts, alcohols, and oils, and temperature are introduced briefly. Many introductory books include substantial sections on surfactant self-assembly. " Current research on a variety of topics is periodically reviewed in Current Opinion in Colloid and Interface Science. 

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