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Micelles interfacial tension

Critical Micelle Concentration. The rate at which the properties of surfactant solutions vary with concentration changes at the concentration where micelle formation starts. Surface and interfacial tension, equivalent conductance (50), dye solubilization (51), iodine solubilization (52), and refractive index (53) are properties commonly used as the basis for methods of CMC determination. [Pg.238]

Finally, some general rules for the amount of surfactant appear to be vaHd (13). For anionic surfactants the average size of droplets is reduced for an increase of surfactant concentration up to the critical micellization concentration, whereas for nonionic surfactants a reduction occurs also for concentrations in excess of this value. The latter case may reflect the solubiHty of the nonionic surfactant in both phases, causing a reduction of interfacial tension at higher concentrations, or may reflect the stabilizing action of the micelles per se. [Pg.197]

This block copolymer acts as an emulsifying agent in the blends leading to a reduction in interfacial tension and improved adhesion. At concentrations higher than the critical value, the copolymer forms micelles in the continuous phase and thereby increases the domain size of the dispersed phase. [Pg.679]

The molecular collective behavior of surfactant molecules has been analyzed using the time courses of capillary wave frequency after injection of surfactant aqueous solution onto the liquid-liquid interface [5,8]. Typical power spectra for capillary waves excited at the water-nitrobenzene interface are shown in Fig. 3 (a) without CTAB (cetyltrimethy-lammonium bromide) molecules, and (b) 10 s after the injection of CTAB solution to the water phase [5]. The peak appearing around 10-13 kHz represents the beat frequency, i.e., the capillary wave frequency. The peak of the capillary wave frequency shifts from 12.5 to 10.0kHz on the injection of CTAB solution. This is due to the decrease in interfacial tension caused by the increased number density of surfactant molecules at the interface. Time courses of capillary wave frequency after the injection of different CTAB concentrations into the aqueous phase are reproduced in Fig. 4. An anomalous temporary decrease in capillary wave frequency is observed when the CTAB solution beyond the CMC (critical micelle concentration) was injected. The capillary wave frequency decreases rapidly on injection, and after attaining its minimum value, it increases... [Pg.243]

Effectiveness of a crude oil demulsifier is correlated with the lowering of shear viscosity and dynamic tension gradient of the oil-water interface. Using the pulsed drop technique, the interfacial dilational modulii with different demulsifiers have been measured. The interfacial tension relaxation occurs faster with an effective demulsifier. Electron spin resonance with labeled demulsifiers indicate that the demulsifiers form reverse micelle like clusters in bulk oil. The slow unclustering of the demulsifier at the interface appears to be the rate determining step in the tension relaxation process. [Pg.366]

At concentrations above their aqueous solubility, the so-called c.m.c., low-molar-mass biosurfactants form micelles in the aqueous phase. Micelles are spherical or lamellar aggregates with a hydrophobic core and a hydrophilic outer surface. They are capable of solubilising nonpolar chemicals in their hydrophobic interior, and can thereby mobilise separate phase (liquid, solid or sorbed) hydrophobic organic compounds. The characteristics for the efficiency of (bio)surfactants are the extent of the reduction of the surface or interfacial tension, the c.m.c. as a measure of the concentration needed to bring about this reduction, and the molar solubilisation ratio MSR, which is the number of moles of a chemical solubilised per mole of surfactant in the form of micelles [96]. [Pg.424]

For crew-cut micelles, Zhulina and Birshtein demonstrated that the dependence of the micellar parameters on Nb disappears and Rc scales as yl/3N /3a and Z yNA, where y is the interfacial tension between the A and B blocks and a is the segment length [209]. [Pg.111]

The impact of salt concentration on the formation of micelles has been reported and is in apparent accord with the interfacial tension model discussed in Sect. 4.1, where the CMC is lowered by the addition of simple electrolytes [ 19,65, 280,282]. The existence of a micellar phase in solution is important not only insofar as it describes the behavior of amphipathic organic chemicals in solution, but the existence of a nonpolar pseudophase can enhance the solubility of other hydrophobic chemicals in solution as they partition into the hydrophobic interior of the micelle. A general expression for the solubility enhancement of a solute by surfactants has been given by Kile and Chiou [253] in terms of the concentrations of monomers and micelles and the corresponding solute partition coefficients, giving... [Pg.145]

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. [Pg.159]

Microemulsions are thermodynamically stable mixtures. The interfacial tension is almost zero. The size of drops is very small, and this makes the microemulsions look clear. It has been suggested that microemulsion may consists of bicontinuous structures, which sounds more plausible in these four-component microemulsion systems. It has also been suggested that microemulsion may be compared to swollen micelles (i.e., if one solubilizes oil in micelles). In such isotropic mixtures, short-range order exists between droplets. As found from extensive experiments, not all mixtures of water-oil-surfactant-cosurfactant produce a microemulsion. This has led to studies that have attempted to predict the molecular relationship. [Pg.183]

In acid solution as far as Ph = 5 the interfacial tension is constant but with increasing alkalinity it falls. In the case of fatty acids the tension becomes vanishingly small when the Ph exceeds 8 and the acid dissolves in the alkali in the form of micelles (see Ch. ix). [Pg.249]

They are emulsions with droplet diameters in the range 0.01 to 0.1 pm. It is formed when the oil-water interfacial tension approaches zero. Micro emulsions represents an intermediate state between micelles and ordinary emulsions. They are usually of low viscosity. [Pg.79]

The effect of increasing only the radius of curvature of the oil drop on the displacement of the contact fine while keeping the interfacial tension constant at 20 dyn/cm, is illustrated in Figs. 9 and 11. Figure 11 shows that for a radius of a curvature of 100 xm, there is virtually no movement of the contact fine from the base case due to the presence of nanoparticles/micelles even at volume fraction 0.25. However, when the radius of curvature is increased to 500 xm (recall Fig. 9), thereby decreasing the capillary pressure, the presence of nanoparticles at the same concentration moves the contact fine by 1 xm. [Pg.136]

In mixed surfactant systems, physical properties such as the critical micelle concentration (cmc) and interfacial tensions are often substantially lower than would be expected based on the properties of the pure components. Such nonideal behavior is of both theoretical interest and industrial importance. For example, mixtures of different classes of surfactants often exhibit synergism (1-3) and this behavior can be utilized in practical applications ( ).In addition, commercial surfactant preparations usually contain mixtures of various species (e.g. different isomers and chain lengths) and often include surface active impurities which affect the critical micelle concentration and other properties. [Pg.102]

C FNa-CioSNa and C-7FNa-Cla5Na systems. These are the mixed anionic-anionic surfactants systems. The surface tension (interfacial tension) - concentration relationships are shomn in Fig, 1 to 3. There are surfactant compositions at which uniform or homogeneous mixed micelle do not exist in these two systems due to the "mutual pho-bicity" between FC- and HC-chains of the surfactants (4,7) Therefore the molecular interaction parameterof the two surfactants in micelles can not be calculated from the Surface tension curves because this cmc has no longer the physical meaning of mixture cmc. However, we can obtain the /3(t values from the surface tension curves by means of equation 13, Table 1 and 2 show the results. [Pg.188]

Octadecanol was recrystallized from hexane after fractionation by vacuum distillation, and its purity was checked by gas-liquid chromatography. Dodecylammonium chloride was recrystallized from a mixture of ethanol and water, and its purity was confirmed by the fact that it had no minimum near the critical micelle concentration on the surface tension vs concentration curve. Hexane was distilled after passing through an activated alumina column. Water was distilled from alkaline permanganate solution of distilled water after refluxing for one day. The purity of hexane and water was confirmed by the value of the interfacial tension between them. [Pg.313]


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