Association colloids solubilization

Fig. 1 Association colloids (A) spherical micelle (B) cylindrical micelle (C) flattened disc-shaped micelle (D) microtubular micelle (E) inverted micelle and (F) micelle swollen by the presence of solubilized lipid soluble drug.

It is of interest to note that the focus of research on the self-association of hydrotrope molecules was due, in part, to the early discussions about the fundamental nature of the solubility-enhancing capacity of hydrotrope molecules in aqueous solutions. These early attempts at clarification argued for the phenomena of colloidal solubilization versus molecular dispersion [6-8], This dispute was resolved by the results from traditional surface chemistry analysis of interfacial tension, etc., which favored a colloidal association of molecules at high concentrations [48,49], and from vapor pressure measurements [42],... 

In most reactions it is reasonable to analyze rate data in terms of reactions in water or in the interfacial region of the association colloids. This simplification fails for reactions of very hydrophobic substrates in O/W microemulsions. These substrates may be solubilized in a region of the oil microdroplets that is inaccessible to ionic or polar reactants, and it is then necessary to consider the partitioning of substrates between aqueous, interfacial, and oil regions [110,111]. 

Because of this dual character of its molecules association colloids are of great practical utility. Most of them are surface-active substances. Examples of this class are the soaps and detergents like sodium dodecyl sulphate. While some are excellent solubilizers of various types of organic compounds in water, others are good dispersion stabilizers. 

The existence in the same molecule of two moieties, one of which has affinity for solvent and the other of which is antipathetic to it, is termed amphipathy. This dual nature is responsible for the phenomenon of surface activity, and of micellization and solubilization. As a class these substances, which include soaps and detergents, can be called association colloids, a name indicating their... 

Table 6.16 Maximum solubilization of steroids in association colloid solutions...

It is likely that some and perhaps all the methanol measured corresponds to the presence of lithium methoxide. This must have some influence on the reaction. Experiments show that it in fact accelerates the polymerization when deliberately added even though it does not initiate polymerization under the conditions used. Even more effective are lithium ethoxide and propoxide which are considerably more soluble in toluene. Lithium methoxide itself is virtually insoluble in toluene, but produced in situ is probably solubilized by association with the active polymer chain ends. Some of it, however, might not be in solution and the possibility of some reaction occurring on the surface of colloidally dispersed salt cannot be excluded. It is interesting to note that both initiators (fiuorenyllithium and butyllithium) which produce a high... 

Sample Preparation of Foam and Water Samples and Humic Substances Isolation. All foam and water samples were filtered through 0.45- Lim silver filter using stainless-steel filtration units. Silver filtration of Como Creek and Suwannee River foam samples resulted in build up of a brown extract on the filter paper, which was readily solubilized in 0.1 N sodium hydroxide. This extract was refiltered through silver filters as a sodium hydroxide solution. This fraction was believed to be colloidal in nature and was treated as a separate humic fraction, called the "foam-extract" fraction. A part of the filtered foam was freeze dried directly and considered "raw" foam. Fulvic and humic acids were isolated from foam and stream-water samples via the XAD-8 adsorption technique developed by Thurman and Malcolm (77), freeze dried, and weighed. To obtain a sufficient mass of humic substances, each entire sample was used for one extraction. As multiple samples were not extracted, calculation of the error associated with humic substances isolation cannot be made, and the contributions of humic substances to the DOC content must be regarded as estimates. 

The caseins exist in milk as polydisperse aggregates ranging in size from ca. 40 to 220nm (3), but the size distribution of micelles depends upon the method of measurement. These casein micelles scatter light and are responsible for the whitish, opaque nature of skim milk. The casein micelles are also associated with a colloidal apatite comprised of calcium-phosphate-citrate (CPC) which has a stabilizing influence on the micelle structure. The colloidal CPC is in equilibrium with soluble CPC in the milk serum phase and is solubilized as the pH is reduced. Thus, as the pH is reduced to the isoelectric point of the caseins (4.6), the colloidal CPC solubilizes, and the caseins precipitate (143). This phenomenon should be kept in mind during some of the following discussions. 

---