Interfacial tension solute-solvent

Diffusivity or viscosity Solid-liquid interfacial tension Water/solvent activity Boiling/melting point Solute activity (concentration)... 

The log of the reciprocal of the bulk concentration of surfactant (C in mol/ L) necessary to produce a surface or interfacial pressure of 20 raN/m, log( 1 / On= 20 i e > a 20 mN/m reduction in the surface or interfacial tension, is considered a measure of the efficiency of a surfactant. The effectiveness of surface tension reduction is the maximum effect the surfactant can produce irrespective of concentration, (rccmc = [y]0 - y), where [y]0 is the surface tension of the pure solvent and y is the surface tension of the surfactant solution at its cmc. 

The entropy of formation of the interface was calculated from the temperature coefficient of the interfacial tension.304 The entropy of formation has been found to increase with the nature of the electrolyte in the same sequence as the single cation entropy in DMSO.108, 09,329 The entropy of formation showed a maximum at negative charges. The difference in AS between the maximum and the value at ff=ocan be taken as a measure of the specific ordering of the solvent at the electrode/solution interface. Data 108,109304314 have shown that A(AS) decreases in the sequence NMF > DMSO > DMF > H90 > PC > MeOH. 

Miscible organic solutes modify the solvent properties of the solution to decrease the interfacial tension and give rise to an enhanced solubility of organic chemicals in a phenomenon often called cosolvency . According to theory, a miscible organic chemical such as a short chain alcohol will have the effect of modifying the structure of the water in which it is dissolved. On the macroscopic scale, this will manifest itself as a decrease in the surface tension of the solution [238,246]. 

The integrated DLS device provides an example of a measurement tool tailored to nano-scale structure determination in fluids, e.g., polymers induced to form specific assemblies in selective solvents. There is, however, a critical need to understand the behavior of polymers and other interfacial modifiers at the interface of immiscible fluids, such as surfactants in oil-water mixtures. Typical measurement methods used to determine the interfacial tension in such mixtures tend to be time-consuming and had been described as a major barrier to systematic surveys of variable space in libraries of interfacial modifiers. Critical information relating to the behavior of such mixtures, for example, in the effective removal of soil from clothing, would be available simply by measuring interfacial tension (ILT ) for immiscible solutions with different droplet sizes, a variable not accessible by drop-volume or pendant drop techniques [107]. 

If the original liquids are mutually soluble and the third component is soluble in only one of them, the mutual solubility will be diminished by its addition—according to Nernst s law, at low concentrations. The rise or fall of interfacial tension will thus depend on two superimposed effects, the change of surface tension of the better solvent owing to addition of the solute, and that in each of the two liquids due to diminished concentration of the other. The latter effect tends to increase the tension while the former may work in either direction. 

The most accurately determined example of the third class has already been cited, namely the effect of butyric acid on the interfacial tension benzene-water. Harkins has found the concentration of acid in both layers for each pair of phases in equilibrium, but did not measure that of the second solvent. The mutual solubility must however almost certainly increase with the addition of a body soluble in either, but the interfacial tension is still diminished, adsorption of the solute counterbalancing the greater resemblance of the two phases. Bubanovic has also determined the interfacial tensions of the same solutions against olive oil, obtaining very similar results. He has also examined solutions of chloral hydrate. 

In this equation. Act is taken as the maximum possible surface tension lowering. Hence for a solute-free continuous phase, Aa is the difference between the interfacial tension for the solvent-free system and the equilibrium interfacial tension corresponding to the solute concentration in the dispersed phase. Equation (10-6) indicates a strong effect of the viscosity ratio k on the mass transfer coefficient as found experimentally (LI 1). For the few systems in which measurements are reported (Bll, Lll, 04), estimates from Eq. (10-6) have an average error of about 30% for the first 5-10 seconds of transfer when interfacial turbulence is strongest. 

These assumptions are continuity of stress and velocity across the interfaces since stress discontinuities owing to high interfacial tensions increase the viscosity (3), to explain the unexpected low viscosities we must doubt the validity of the velocity condition at the interfaces. This is supported by the fact that the two polymers are incompatible, which implies a relatively low concentration or even complete absence of entanglements at the interface. A very thin layer of solute-free solvent around the droplets would result. Such a low viscosity layer might be the cause of the anomalous behavior. 

Other attempts at characterizing the deviation from ideal solubility theory have been made. Anderson et al. [50] showed that solubilities that could not be rationalized from the regular solution theory could be rationalized by assuming the formation of speciLc solute-solvent complexes. Yalkowsky et al. [51,52] showed that the deviation from the ideal solubility equation could be expressed in terms of interfacial tension and surface area. In equation form,... 

Surfactants are compounds that exhibit surface activity, or more generally, interfacial activity, and migrate to the interface when placed in solution. This migration results in lowering the solution surface tension (interfacial tension) as compared to the surface tension of the pure solvent. Thermodynamically, adsorption of a surfactant is deLned by the Gibbs adsorption equation ... 

Although solvent samples have been observed for approximately one year without any solids formation, work was completed to define a new solvent composition that was thermodynamically stable with respect to solids formation and to expand the operating temperature with respect to third-phase formation.109 Chemical and physical data as a function of solvent component concentrations were collected. The data included BC6 solubility cesium distribution ratio under extraction, scrub, and strip conditions flowsheet robustness temperature range of third-phase formation dispersion numbers for the solvent against waste simulant, scrub and strip acids, and sodium hydroxide wash solutions solvent density viscosity and surface and interfacial tension. These data were mapped against a set of predefined performance criteria. The composition of 0.007 M BC6, 0.75 M l-(2,2,3,3-tetrafluoropropoxy)-3-(4-.sw-butylphenoxy)-2-propanol, and 0.003 M TOA in the diluent Isopar L provided the best match between the measured properties and the performance criteria. 

Figure 7.12 Trebal correlation for interfacial tension. XAB, mole fraction of raffinate dissolved in solvent XBA, mole fraction of solvent dissolved in raffinate XCA, mole fraction of solute dissolved in raffinate ...

The equilibrium solution surfactant concentration needed to achieve a specified level of adsorption at an interface. Example one such measure of efficiency is the surfactant concentration needed to reduce the surface or interfacial tension by 20 mN/m from the value of the pure solvent(s). This term has a different meaning from surfactant effectiveness. 

A number of experimental techniques by measurements of physical properties (interfacial tension, surface tension, osmotic pressure, conductivity, density change) applicable in aqueous systems suffer frequently from insufficient sensitivity at low CMC values in hydrocarbon solvents. Some surfactants in hydrocarbon solvents do not give an identifiable CMC the conventional properties of the hydrocarbon solvent solutions of surfactant compounds can be interpreted as a continuous aggregation from which the apparent aggregation number can be calculated. Other, quite successful, techniques (light scattering, solubilization, fluorescence indicator) were applied to a number of CMCs, e.g., alkylammonium salts, carboxylates, sulfonates and sodium bis(2-ethylhexyl)succinate (AOT) in hydrocarbon solvents, see Table 3.1 (Eicke, 1980 Kertes, 1977 Kertes and Gutman, 1976 Luisi and Straub, 1984 Preston, 1948). 

Polysaccharides interfaced with water act as adsorbents on which surface accumulations of solute lower the interfacial tension. The polysaccharide-water interface is a dynamic site of competing forces. Water retains heat longer than most other solvents. The rate of accumulation of micromolecules and microions on the solid surface is directly proportional to their solution concentration and inversely proportional to temperature. As adsorbates, micromolecules and microions ordinarily adsorb to an equilibrium concentration in a monolayer (positive adsorption) process they desorb into the outer volume in a negative adsorption process. The adsorption-desorption response to temperature of macromolecules—including polysaccharides —is opposite that of micromolecules and microions. As adsorbate, polysaccharides undergo a nonequilibrium, multilayer accumulation of like macromolecules. 

See also - electrode surface area, -> Gibbs-Lippmann equation, - interfacial tension, -> interface between two liquid solvents, -> interface between two immiscible electrolyte solutions -> Lippmann capillary electrometer, -> Lippmann equation -> surface, -> surface analytical methods, - surface stress. 

The surface tension of a solution of a surfactant is lower than that of the pure solvent. Surface tension is roughly a linear function of ln(surfactant concentration) up to the critical micelle concentration (CMC) (Figure 3). Above the CMC the thermodynamic activity of the surfactant does not increase with the addition of more surfactant, and the surface tension remains constant. Interfacial tension also decreases with the concentration of an emulsifier dissolved in one of the phases. In Figure 4 the decrease in y does not level off, because the emulsifier (PGMS) does not form micelles in the organic solvent phase (heptane). The changes in the slope of the plot are attributed to changes in orientation of emulsifier molecules at the interface (7). 

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