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Interfacial tension gradients

Estimate the interfacial tension gradient formed in alcohol-water mixtures as a function of alcohol content. Determine the minimum alcohol content necessary to form wine tears on a vertical glass wall [174] (experimental veriflcation is possible). [Pg.382]

The effectiveness of a crude oil demulsifier is correlated with the lowering of the shear viscosity and the dynamic tension gradient of the oil-water interface. The interfacial tension relaxation occurs faster with an effective demulsifier [1714]. Short relaxation times imply that interfacial tension gradients at slow film thinning are suppressed. Electron spin resonance experiments with labeled demulsifiers indicate that the demulsifiers form reverse micellelike clusters in the bulk oil [1275]. The slow unclustering of the demulsifier at the interface appears to be the rate-determining step in the tension relaxation process. [Pg.327]

A study on a commonly used demulsifier, namely, a phenol-formaldehyde resin, elucidated how various parameters such as interfacial tension, interfacial shear viscosity, dynamic interfacial-tension gradient, dilatational elasticity, and demulsifier clustering affect the demulsification effectiveness [1275]. [Pg.342]

Our goal is to develop a property-performance relationship for different types of demulsifiers. The important interfacial properties governing water-in-oil emulsion stability are shear viscosity, dynamic tension and dilational elasticity. We have studied the relative importance of these parameters in demulsification. In this paper, some of the results of our study are presented. In particular, we have found that to be effective, a demulsifier must lower the dynamic interfacial tension gradient and its ability to do so depends on the rate of unclustering of the ethylene oxide groups at the oil-water interface. [Pg.367]

Only the difference in oxygen concentration between the Pt/Au junction and the extreme end of the Au part of the rod is needed to compute force resulting from an interfacial tension gradient. [Pg.30]

The mechanism of movement was also confirmed to be similiar. Catchmark was able to control hydrophobicity of the gold through different wet chemistries, thereby demonstrating that a hydrophobic gold surface is necessary for movement to occur. This is in agreement with the interfacial tension gradient concept in that a hydrophobic gold surface is necessary to observe platinum end forward movement. [Pg.32]

J. M. Catchmark, S. Subramanian, and A. Sen, Directed rotational motion of microscale objects using interfacial tension gradients continually generated via catalytic reactions. Small 1,1—5 (2005). [Pg.37]

Interfacial turbulence [60] Due to a nonuniform distribution of surfactant molecules at the interface or to local convection currents close to the interface, interfacial tension gradients lead to a mechanical instability of the interface and therefore to production of small drops. [Pg.10]

All of these disturbances cause a many-fold increase in the rate of transfer of solute across the interface. If a chemical or thermal difference along an interface causes an interfacial tension gradient, violent flow in the direction of low a will result. This action is usually termed the Marangoni effect. [Pg.77]

A recent paper by Schechter and Farley (S3) presented a modification of the Hadamard approach to relate circulation and mass transfer rates to interfacial tension gradients. Limited to creeping flow regimes, their approach appears to be the best to date. [Pg.84]

Another role of the surfactant is to initiate interfacial instability, e.g., by creating turbulence and Raykleigh and Kelvin-Helmholtz instabilities. Turbulence eddies tend to disrupt the interface since they create local pressures. Interfacial instabilities may also occur for cylindrical threads of disperse phase during emulsification. Such cylinders undergo deformation and become unstable under certain conditions. The presence of surfactants will accelerate these instabilities as a result of the interfacial tension gradient. [Pg.512]

Y, will tend to be higher at the points of closest approach than at the more distant parts of the interfaces. The ensuing gradient in y tends to suck aqueous solution between the newly formed droplets forcing them apart and hence providing them with time to stabilize themselves against coalescence after the interfacial tension gradient has vanished 5). [Pg.8]

Our objective in this study is to elucidate the complex phenomena occurring during the process of three phase foam thinning, to identify the interaction mechanisms between the oil droplets, the thinning foam film and the Plateau-Gibbs borders and the role of surface and interfacial tension gradients in foam stability, and to examine the implications upon crude oil displacement by foam in pourous media. [Pg.136]

Marangoni Effects in Foam Stability. To estimate the effect of interfacial tension gradients upon foam stability we used the maximum droplet pressure technique (19). The oil phases chosen were n-octane and n-dodecane and the surfactants used were 16 ... [Pg.152]

These high stability foams correlate directly with the results based upon interfacial tension gradient measurements, confirming the significance of Marangoni phenomena (31) in three phase foam stability. [Pg.152]

Figure 3.35. Creation of cin interfacial tension gradient by an externally applied tangential flow of the adjacent liquid in the x-direction, (a) Schematic picture of the phenomenon (b) creation of a gradient in the interfacial tension (c) the resulting v z) profile somewhere in this gradient. Figure 3.35. Creation of cin interfacial tension gradient by an externally applied tangential flow of the adjacent liquid in the x-direction, (a) Schematic picture of the phenomenon (b) creation of a gradient in the interfacial tension (c) the resulting v z) profile somewhere in this gradient.
A force balance for an interfacial element can be constructed by realizing that forces caused by interfacial tension gradients are compensated by forces due to flow in the fluid above (a) and below (b) the element. Consider first the x -component of the force balance. Its interfacial contribution consists of two peirts, one caused by X -momentum and one by y -momentum transport. The corresponding interfacial stresses are and r , and the ensuing forces 3r / dx and dr /dy, respectively. The bulk contributions contciin only transport of x momentum in the z-direction,... [Pg.305]

On the other hand, if a liquid film experiences interfacial tension gradients, then the balance of tangential stresses at the interface gives rise to the key relationship... [Pg.408]

Numerous studies have shown that mass transfer of solute from one phase to the other can alter the behavior of a liquid-liquid dispersion—because of interfacial tension gradients that form along the surface of a dispersed drop. For example, see Sawistowski and Goltz, Trans. Inst. Chem. Engrs., 41, p. 174 (1963) BaWcer, van Buytenen, and Beek, Chem Eng. Sci., 21(11), pp. 1039-1046 (1966) Rucken-stein and Berbente, Chem. Eng. Sci., 25(3), pp. 475—482 (1970) Lode and Heideger, Chem. Eng. Sci., 25(6), pp. 1081—1090 (1970) and Takeuchi and Numata, Int. Chem. Eng., 17(3), p. 468 (1977). These interfacial tension gradients can induce interfaci turbulence and circulation within drops. These effects, known as Marangoni instabilities, have been shown to enhance mass-transfer rates in certain cases. [Pg.1729]

Apart from their effect on reducing y, surfactants play major roles in the deformation and break-up of droplets, and this is summarised as follows. Surfactants allow the existence of interfacial tension gradients which is cracial for the formation of stable droplets [8]. In the absence of surfactants (clean interface), the interface cannot withstand a tangential stress, and the liquid motion will be continuous (Figure 10.17a). [Pg.179]

If a liquid flows along the interface with surfactants, the latter will be swept downstream, causing an interfacial tension gradient (Figure 10.17b). Thus, a balance of forces will be established. [Pg.179]


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See also in sourсe #XX -- [ Pg.212 ]




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