Surfactant films

Derive Eq. XIV-11 from Eq. XIV-10. State the approximations involved. Explain whether the surface elasticity should be small or large for a surfactant film if the bulk surfactant concentration is about its CMC. 

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

For thin surfactant films the integrals in (78) and (79) are restricted to the region of the film, and if ( (r)) const across the film then... 

Coordination of NO to the divalent tetrasulfonated phthalocyanine complex [Co(TSPc)]4 results in a complex formally represented as [(NO )Coin(TSPc)]4 kf= 142M-1s-1, KA 3.0 x 105 M-1). When adsorbed to a glassy carbon electrode, [Co(TSPc)]4- catalyzes the oxidation and reduction of NO with catalytic currents detectable even at nanomolar concentrations. Electrochemistry of the same complex in surfactant films has also been studied.905 Bent nitrosyl complexes of the paramagnetic trivalent tropocoronand complex Co(NO)(TC) ((189), R = NO) have also been reported.849... 

A.E.F. Nassar, W.S. Willis, and J.F. Rusling, Electron transfer from electrodes to myoglobin facilitated in surfactant films and blocked by adsorbed biomacromolecules. Anal. Chem. 67, 2386-2392 (1995). 

D. Mimica, J.H. Zagal, and F. Bedioui, Electroreduction of nitrite by hemin, myoglobin and haemoglobin in surfactant films. J. Electroanal. Chem. 497, 106-113 (2001). 

X.H. Chen, X.S. Peng, J.L. Kong, and J.Q. Deng, Facilitated electron transfer from an electrode to horseradish peroxidase in a biomembrane-like surfactant film. J. Electroanal. Chem. 480, 26-33 (2000). 

The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

The situation is, however, different in the alveolar region of the lung where the respiratory gas exchange takes place. Its thin squamous epithelium is covered by the so-called alveolar surface liquid (ASL). Its outermost surface is covered by a mixture of phospholipids and proteins with a low surface tension, also often referred to as lung surfactant. For this surfactant layer only, Scarpelli et al. [74] reported a thickness between 7 and 70 nm in the human lung. For the thickness of an additional water layer in between the apical surface of alveolar epithelial cells and the surfactant film no conclusive data are available. Hence, the total thickness of the complete ASL layer is actually unknown, but is certainly thinner than 1 gm. 

Monolayer films are usually spread from a dilute solution in an appropriate volatile and highly purified solvent. Small droplets of solution are spotted at 40 or SO points on the clean subphase surface using a micrometer syringe. Adequate time, say 20 min, must be allowed for the surfactant film to spread evenly and also for the solvent to evaporate completely. Since certain solvents are retained in some... 

Enhoming G, Potoschnik R, Possmayer F, et al. 1986. Pulmonary surfactant films affected by solvent vapors. Anesth Analg 65 1275-1280. 

Different surfactants are usually characterised by the solubility behaviour of their hydrophilic and hydrophobic molecule fraction in polar solvents, expressed by the HLB-value (hydrophilic-lipophilic-balance) of the surfactant. The HLB-value of a specific surfactant is often listed by the producer or can be easily calculated from listed increments [67]. If the water in a microemulsion contains electrolytes, the solubility of the surfactant in the water changes. It can be increased or decreased, depending on the kind of electrolyte [68,69]. The effect of electrolytes is explained by the HSAB principle (hard-soft-acid-base). For example, salts of hard acids and hard bases reduce the solubility of the surfactant in water. The solubility is increased by salts of soft acids and hard bases or by salts of hard acids and soft bases. Correspondingly, the solubility of the surfactant in water is increased by sodium alkyl sulfonates and decreased by sodium chloride or sodium sulfate. In the meantime, the physical interactions of the surfactant molecules and other components in microemulsions is well understood and the HSAB-principle was verified. The salts in water mainly influence the curvature of the surfactant film in a microemulsion. The curvature of the surfactant film can be expressed, analogous to the HLB-value, by the packing parameter Sp. The packing parameter is the ratio between the hydrophilic and lipophilic surfactant molecule part [70] ... 

Bubble Coalescence, Foams and Thin Surfactant Films... 

BUBBLE COALESCENCE, FOAMS AND THIN SURFACTANT FILMS... 

Microemulsions are dynamic systems in which droplets continually collide, coalesce, and reform in the nanosecond to millisecond time scale. These droplet interactions result in a continuous exchange of solubilizates. The composition of the microemulsion phase determines the exchange rate through its effect on the elasticity of the surfactant film surrounding the aqueous microdomains. Compared with nonionic surfactant-based microemulsions, AOT reverse micelles have a more rigid... 

Role of Surfactant Film in Restricting Particle Growth... 

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