Association colloids surface activity

Natural surface activity In association with surface-active agents Foam fractionation for example, detergents from aqueous solutions Ion flotation, molecular flotation, adsorbing colloid flotation for example, Sr , Pb , Hg , cyanides Foam flotation for example, microorganisms, proteins Microflotation, colloid flotation, ultraflotation for example, particulates in wastewater, clay, microorganisms Froth flotation of nonpolar minerals for example, sulfiir Froth flotation for example minerals such as silica Precipitate flotation (1st and 2nd kind) for example, ferric hydroxide... 

The surface-active agents (surfactants) responsible for wetting, flotation and detergency exhibit rather special and interesting properties characteristic of what are called association colloids or, in the older literature, colloidal electrolytes. These properties play an important role in determining, at least indirectly, the detergency of a given surfactant and are therefore considered here... 

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

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... 

The structure of the lyotropically mesomorphous lattice is made up of multimolecular units called mesoaggregates. These are surrounded by an intervening liquid. Lyotropic mesomorphism is therefore closely related to the tendency of lipids to accumulate at interfaces. The surface activity is a consequence of the same dualistic polar/non-polar molecular structure that causes the formation of micelles in solutions of association colloids (I, 2, 3, 4, 5, 6). 

Throughout the discussion, the terms surface active agent, surfactant, and detergent are used interchangeably to refer to amphiphilic substances which form association colloids or micelles in solution. Amphiphilic substances or amphiphiles are molecules possessing distinct regions of hydrophobic and hydrophilic character. 

Association colloids are aggregates or associations of amphipathic surface active molecules. These molecules are soluble in the solvent, and their molecular dimensions are below the colloidal size range. When present in solution at concentrations above a certain critical value (the critical micelle concentration), these molecules tend to form association colloids (micelles) (Fig. 1). 

Soaps are metal salts of fatty acids and the alkali salts are the most important members of this group of amphiphiles. Applications of soaps are related to their properties as association colloids and surface-active agents. 

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. 

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 interfacial tension can undergo significant changes if the polarity of the medium is altered, such as in the stability/coagulation transition caused by the addition of water to hydrophobic silica dispersions in propanol or ethanol [44,52,53]. Also, the addition of small additives of various surface-active substances can have a dramatic effect on the structure and properties of disperse systems and the conditions of transitions [14,16,17,26]. The formation and structure of stable micellar systems and various surfactant association colloids, such as microemulsion systems and liquid crystalline phases formed in various multicomponent water/hydrocarbon/surfactant/alcohol systems with varying compositions and temperatures, have been described in numerous publications [14-22,78,79,84-88]. These studies provide a detailed analysis of the phase equilibria under various conditions and cover all kinds of systems with all levels of disperse phase concentration. Special attention is devoted to the role of low and ultralow values of the surface energy at the interfaces. The author s first observations of areas of stable microheterogeneity in two-, three-, and four-component systems were documented in [66-68],... 

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... 

As particles approach the colloidal size range-arbitrarily defined as being between lOOnm and lO m diameter- surfaces tend to become more diffuse as the underlying material becomes hydrated or charged. In addition, other materials such as surface active agents or charged ionic species tend to either adhere to the surface or become closely associated with it, and these associations may, in turn, influence the actual behavior of the dispersed system. This... 

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