Dispersions complementarity

Sedimentation and diffusion data allow for the unambiguous determination of particle mass and also allow the suspended particles to be placed on a contour in a plot such as that of Figure 2.9. This is as far as these experiments can take us toward the characterization of the particles. Of course, additional data from other sources, such as the x-ray diffraction results just cited, may lead to still further specification of the system. One such source of information is intrinsic viscosity data for the same dispersion. In Chapter 4 we discuss the complementarity between viscosity data and sedimentation-diffusion results (see Section 4.7b). 

Note that for aqueous systems the contact dissimilarity term favours mixing of the polymer and dispersion medium, apparently in violation of the maxim like dissolves like . This violation is not serious, however, because it is the highly favourable nature of the interaction between the polymer and the water, as witnessed by, say, the formation of hydrogen bonds, that promotes mixing. The dissimilarity should therefore be considered to represent a strong complementarity rather than a true dissimilarity. 

An amphiphilic film at the oil-water interface exists as a duplex film influenced by the properties of the oil and water phases (Schuhnan et al., 1959 Hanagan and Singh, 2(X)6). When oil molecules have the ability to associate with those within the interfacial film, a microemulsion readily forms. For instance, a mixed system consisting of cetyl alcohol, benzene and 2-amino-2-methyl-1-propanol (AMP) oleate does not form microemulsions due to the lack of complementarity between these compounds. However, if benzene is replaced by a straight-chained hydrocarbon chain (7-18 C), a microemulsion readily forms due to the ability of the oil molecules to associate with the alcohol and AMP oleate at the interface (Schulman et al., 1959). It is normally assumed that microemulsion formation requires the presence of a duplex film with differing tensions on either side of the interface, which impart curvature and thus the possibility of forming dispersed domains or bicontinuous structures (Prince, 1969). 

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