Amphiphilicity factor

The interpretation of small SANS data from systems of type D20/NaCl- -decane/triolein-CioE4 showed that the order of the microstructure systematically decreases with increasing triolein content (Fig. 11.8(c) and Table 11.3). However, the value of the amphiphilicity factor [49, 50] /a = —0.65 indicates that the pure triolein microemulsion is still a microemulsion in the narrower sense. The bending constants k and i< obtained from phase diagrams and scattering curves furthermore verify that the rigidity of the amphiphilic film decreases with increasing triolein content (Fig. 11.9). 

Table 11.3 Correlation length tS/ periodicity djs and amphiphilicity factor fa of the systems D20/NaCI-n-decane/triolein-CioE4 at tf> = 0.50 and e = 0.001...

This correlation function describes a structure of periodicity d (= In/k), i.e., a measure of the repeat distance between alternately arranged water and oil domains, dampened as a function of the correlation length which characterizes the decay of local order [65] and may also be interpreted [69] as a measure of the dispersion of d. The order parameter coefficients G2, C[, and C2 can be grouped together to define an amphiphilicity factor fa = C 7(4 2These parameters can also be used to express d and (. Figure 3 illustrates the use of this amphiphilicity scale [68]. 

Figure 3 Schematic diagram of observations of microemulsion systems as a function of the amphiphilicity factor. (From Ref. 68.)...

In conclusion, the amphiphilicity factor is important for the understanding of microemulsion structuring. It was also suggested as an additional means of classifying surfactants, together with the packing parameter or the hydrophilic-lipophilic-balance (HLB) scale [84],... 

A third parameter, which can also be defined, is f, the amphiphilicity factor [124,127-129], which relates to the behavior of the correlation function y(r) and reflects the ability of the surfactant to impose order on the microemulsion ... 

Values of the Amphiphilicity Factor for the Water/Sucrose Laurate/Ethoxylated Mono-Di-Glyceride/R (+)-LIM Microemulsion System as a Function of the Water Volume Fraction ( ) along the Dilution Line N60... 

Most characteristics of amphiphilic systems are associated with the alteration of the interfacial stnicture by the amphiphile. Addition of amphiphiles might reduce the free-energy costs by a dramatic factor (up to 10 dyn cm in the oil/water/amphiphile mixture). Adding amphiphiles to a solution or a mixture often leads to the fomiation of a microenuilsion or spatially ordered phases. In many aspects these systems can be conceived as an assembly of internal interfaces. The interfaces might separate oil and water in a ternary mixture or they might be amphiphilic bilayers in... 

Lyotropic LCs can also be described by a simple model. Such molecules usually possess the amphiphilic nature characteristic of surfactant, consisting of a polar head and one or several aliphatic chains. A representative example is sodium stearate (soap), which forms mesophases in aqueous solutions (Figure 8.4a). In lyotropic mesophases, not only does temperature play an important role, but also the solvent, the number of components in the solution and their concentration. Depending on these factors, different types of micelles can be formed. Three representative types of micelles are presented in Figure 8.4b-d. 

Chemistry of micelles is an important area of dendrimer research. A micellar structure depends on numerous factors, such as temperature, concentration, and mainly the molecular framework of the given amphiphiles. Revolutionary research in micellar chemistry is exhibited in the work of Menger et al. [57] and by Shinkai et al. [58]. 

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

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