Accumulation of surfactants

This transition may j-.e. reducing the specific surface energy, f. The reduction of f to sufficiently small values was accounted for by Ruckenstein (15) in terms of the so called dilution effect". Accumulation of surfactant and cosurfactant at the interface not only causes significant reduction in the interfacial tension, but also results in reduction of the chemical potential of surfactant and cosurfactant in bulk solution. The latter reduction may exceed the positive free energy caused by the total interfacial tension and hence the overall Ag of the system may become negative. Further analysis by Ruckenstein and Krishnan (16) have showed that micelle formation encountered with water soluble surfactants reduces the dilution effect as a result of the association of the the surfactants molecules. However, if a cosurfactant is added, it can reduce the interfacial tension by further adsorption and introduces a dilution effect. The treatment of Ruckenstein and Krishnan (16) also highlighted the role of interfacial tension in the formation of microemulsions. When the contribution of surfactant and cosurfactant adsorption is taken into account, the entropy of the drops becomes negligible and the interfacial tension does not need to attain ultralow values before stable microemulsions form. 

The role of foams and foam films depends significantly on the flotation type. From all methods only the foam adsorptive accumulation of surfactants and their complexes with ions, is based entirely on the regularities of the process of substance accumulation by adsorption in the stable foam. That is why further on the main target will be the analysis of the regularities of the adsorptive accumulation and separation of surfactants in the polyhedral foam. 

The process of foam separation of surfactants is used for solving various problems accumulation of surfactants in a foam that aims their extraction or the purification of a... 

Other factors (pH, temperature, foam dispersity, foam column height, rate of gas and liquid feed, etc.) also affect the accumulation effectiveness (parameter //). Some of these, such as pH, temperature, type and concentration of the collector, are changing the adsorption, others, like dispersity and foam column height, are changing the drainage rate that determines foam stability and expansion ratio. The book of Rusanov et al. [23] summarises the results on the effect of these factors on foam accumulation of surfactants. 

The main characteristics that determine the level of production of particular surfactants, aside from physico-chemical properties, are cost, availability of raw materials and environmental safety. The latter is characterized primarily by biodegradability, which is defined as the time required to reduce the surfactant concentration in the ambient medium by a given factor [26], The synthesis of surfactants with good biodegradability is an important task, as the environmental issues has become of a major concern. For example, the accumulation of surfactants within the adsorption layers formed in natural water reservoirs affects the life of various living organisms... 

If the rate of desorption of surfactants is very much greater than the rate at which the drop traverses through a distance equivalent to its diameter (about 0.02 sec), one may expect (D6) no accumulation of surfactants at the rear end. A quantitative semiempirical expression for the degree of drop circulation as a function of the viscous forces, drop diameter, densities and the compressional modulus of the surface film (surface-tension gradient), as well as the empirical fraction of liquid circulating, has been suggested by Davies (D6). 

Another case that is important in many applications involves the motion of a drop in a liquid containing a surfactant, which can be adsorbed at the drop s surface [2]. The motion of the drop results in that, due to the constant stretching of the surface, the surface density of adsorbed surfactant molecules in the front part of the surface will be smaller than in the case of the drop s equilibrium with the solution. In the rear part of the drop, the surface density will exceed the density at equilibrium. Because, unlike the surface of a solid particle, the surface of a drop is mobile, the motion of the liquid will cause surfactant molecules to drift to the rear part of drop and accumulate there. Accumulation of surfactant results in a decreased surface tension in the rear part of the drop. On the other hand, the increase of surfactant concentration in the rear part leads to the appearance of a surface diffusion flux in the opposite direction - from the rear to the front. This... 

Viscoelastic and viscosimetic measurements have been performed on model systems and on commercial products [29]. Water-in-silicone emulsions have been prepared, in which the oil phase consisted of decamethylcyclopentasiloxane (cyclomethicone, D5) and the surfactant used was a branched type silicone copolymer. The interfacial rheology study of such surfactants revealed that the ability of these eopolymers to effectively stabilize water-in-D5 emulsions is a result of a process involving the nucleation, growth, and accumulation of surfactant-rich particulates at the D5/water interface [55]. 

An initial and important result is that the accumulation of surfactant molecules at the rear stagnation point of a translating droplet imposes a surface stress which opposes the outer flow (see Fig. 2). A direct implication is that for a gas bubble rising in a quiescent liquid, the surface is immobilized and the rise velocity is more similar to the rise of a rigid disc than to an inviscid bubble. 

In the lungs of rats instilled with 0.5 ml of a suspension of 1 mg NiO -1-0.1 mg CdO one week before, the alveolar macrophages appeared smaller than those of control, with numerous lamellar bodies of different sizes. The lamellar bodies consisted of membranous whorls, disintegrating structures, as well as accumulation of surfactant-like material (Murthy and Holovack 1991). In addition, the cytoplasm was filled with multivesicular bodies, degenerating mitochondria, as well as primary and secondary lysosomes. 

Pulmonary alveolar proteinosis (PAP) is a rare disorder characterized by the accumulation of surfactant-like material in the alveolar spaces, with resultant impairment in gas exchange (1-8). Since the sentinel description of PAP by Rosen and colleagues in 1958 (9), fewer than 500 cases have been reported in the literature (5). 

Accumulation of surfactant-like material in alveolar spaces Insidious onset of dyspnea and cough Hypoxemia and intrapulmonary shunting... 

The main problem of measurement for surfactant solutions is that the accumulation of surfactant molecules takes some time. At high concentrations, the equilibrium is established in less than a second, but it may take hours for low concentrations, depending on the surfactant nature. 

Hydrophobization of the surface causes basic changes in the adsorption properties of the soil minerals. Neutral (hydrophobic) molecules may be taken up into the surfactant layer. On the basis of this knowledge, alkyl ammonium montmorillonites are being investigated and recommended for sealing landfill sites [17, 18]. Similar sorption processes may take place in soils and sediments. Probably, the hydrophobic character of soil minerals will increase due to the accumulation of surfactants, thus promoting the adsorption of non polar less water-soluble substances. That would immobilize them and exclude them from further natural transport or degradation processes. 

Figure 5.27 Schematic of an (a) oil recovery system and (b) bubble shape inside the capillary due to accumulation of surfactant...

A number of other diseases or conditions are known to affect surfactant metabolism and, hence, lung function. For example, dust-related industrial diseases such as silicosis lead to a massive accumulation of surfactant (up to 40-times normal amounts) which impairs gas exchange and breathing. In paraquat (a herbicide) poisoning the opposite occurs and the type II cells no longer produce surfactant - leading to particularly painful efforts at breathing by the victim who dies within a few days. 

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