Interfacial tension variation

The low interfacial tensions between two liquids have been measured for different systems by using the pendant drop method. In the case of the quaternary system Ci2ll25S 3 tNa+H20+n-Butanol+Toluene, the interfacial data as measured by pendant drop method are compared with reported literature data, using other methods (with varying NaCl concentration). In order to understand the role of co-surfactant, ternary systems were also investigated. The pendant drop method was also used for measuring the interfacial tension between surfactant-H20/n-alcohol (with number of carbon atoms in alcohol varying from 4-10). The interfacial tension variation was dependent on both the surfactant and alcohol. 

Some questions remain unanswered about the values of the prefactor measured in our experiments (table III). The value of the prefactor y of the interfacial tension variations is very small ... 

The presence of surfactants in the mass transfer systems presented has been shown to affect the mass transfer process by inducing, reducing or suppressing interfacial convection. Since interfacial convection is caused by interfacial tension variations and the addition of a surfactant to a system alters interfacial tension, an examination of the effect surfactants have on the interfacial tension of the systems is of interest. 

For a single-component liquid-vapor interface, it is not possible to vary temperature and pressure independendy while maintaining the phases in equihbrium. Flowever, measurement of interfacial tension variation with pressure at constant temperature is possible in a binary system. Good (1976) has shown that such data can be used to obtain useful information about interfacial characteristics in this case. 

The interfadal tension y in this equation is that of the initial stagnant layer, with interfacial tension variations providing a second-order correction that is neglected in our linear analysis. With the pressure given by Equations 5.39 and 5.26, z given by and A3, A5, and Ag eliminated by Equations 6.21 through 6.23, Equation 6.24 becomes... 

The coefficient dy/dT of interfacial tension variation with tranpraatuie is assumed to have a constant valne. It is virtually always negative, a typical value being abont -0.1 mN/m K. According to Equation 6.26, developmrait of a temperature gradient along an interface causes flow to arise having shear stresses that balance the lateral force produced by the interfadal tension gradirait. In terms of the coeffidents A, Equation 6.26 becomes... 

Adsorbed monolayers of BSA at the liquid/liquid interface give rise to a phase difference, at certain frequencies, between the sinusoidal area oscillation and the interfacial tension variation. This contrasts sharply with the behavior at the liquid/air interface, where a previous investigation found no phase angle (14) for both spread and adsorbed films. Thus, relaxation processes can be shown to be important at the liquid/liquid interface for adsorbed... 

The effect of a dynamic interfacial tension will be to increase the probability of a moving oil blob being trapped. The overall kinetics of blob entrapment and mobilization which depend on the dynamics of interfacial tension variation will determine whether or not the blobs will aggregate this will be a key factor in formation and stabilization of an oil bank. In addition, any interfacial rheological resistance will reduce the probability of mobilization, and of drop coalescence during oil bank formation. The quantitative assessment of interfacial dynamic properties is therefore of major importance in the development and optimization of chemical FOR systems. 

Many technologies and natural phenomena involve processes of fast expansion or compression of fluid interfaces covered with surfactant adsorption layers. The dynamic system properties depend on the mechanisms and rate of equilibrium restoration after a deformation. At small magnitudes of deformation the mechanical relaxation of an interface can be described by the complex dilational viscoelastic modulus [1,2]. For sinusoidal deformations it is deflned as the ratio of complex amplitudes of interfacial tension variation and the relative surface area variation f (I ty) = dy /din A being a function of frequency. This modulus may include... 

Since nonaggregated surfactant molecules are responsible for interfacial tension effects, any interfacial tension variations will be hindered by self-assembly above CMC. This is pictorially represented in Fignre 15.13 for the particular case of commercial mixture A in 0.5 M NaCl aqneous solutions at 27°C (CMC = 0.2269%). 

Recently, Markin and Volkov have studied the adsorption of ion pairs at ITIES using a generalized Langmuir isotherm that takes into account the limited number of adsorption sites, the final size of molecules, the complex formation at the interface, and the interaction between adsorbed particles, and were able to fit the interfacial tension variation with salt concentrations [65-67]. 

The extensive use of the Young equation (Eq. X-18) reflects its general acceptance. Curiously, however, the equation has never been verified experimentally since surface tensions of solids are rather difficult to measure. While Fowkes and Sawyer [140] claimed verification for liquids on a fluorocarbon polymer, it is not clear that their assumptions are valid. Nucleation studies indicate that the interfacial tension between a solid and its liquid is appreciable (see Section K-3) and may not be ignored. Indirect experimental tests involve comparing the variation of the contact angle with solute concentration with separate adsorption studies [173]. 

Variations include the use of steam and the means of reducing interfacial tension by the use of various solvents. The solvent extraction approach has... 

A typical example of an ideal polarizable interface is the mercury-solution interface [1,2]. From an experimental point of view it is characterized by its electrocapillary curve describing the variation of the interfacial tension 7 with the potential drop across the interface, 0. Using the thermodynamic relation due to Lippmann, we get the charge of the wall a (-a is the charge on the solution side) from the derivative of the electrocapillary curve ... 

This equation may be used for the estimation of the swelling capacity of the activated seed particles with the monomer. A typical graph sketched based on Eq. (11) is given in Fig. 18. This graph shows the variation of the swelling capacity of the seed polymer particles VmIVp) with the ratio of interfacial tension-initial particle radius... 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Phosphoric acid ester was used as a model for the estimation of concentration of a reagent in an adsorbed layer by optical measurements of the intensity of a beam reflecting externally from the liquid-liquid interface. The refractive index of an adsorbed layer between water and organic solution phases was measured through an external reflection method with a polarized incident laser beam to estimate the concentration of a surfactant at the interface. Variation of the interfacial concentration with the bulk concentration estimated on phosphoric acid ester in heptane and water system from the optical method agreed with the results determined from the interfacial tension measurements... 

Eq. (132) states that the interfacial tension has to be balanced by a pressure difference between the two phases. The terms containing derivatives of crin Eqs. (133) and (134) are non-zero only if there are local variations of the interfacial tension, which might be due to differences in concentration or temperature. The flow induced by such an effect is known as Marangoni convection. 

Figure 7 Variation of interfacial tension between Athabasca bitumen and D20 containing Sun Tech IV (2 g/L) as a function of pH and temperature at constant ionic strength of 10 M. The dashed line represents data from reference T211 at 50 C in the absence of added surfactant or brine.

The loss of phase complexity in both systems may be attributed to an increase of the PS/PEO and PI/PEO interaction parameters. Because LiClC is selectively located in the PEO domains, the interaction parameters (/ps-peo and xpi-peo ) must increase, leading to variations in domain type and dimension. As the lithium salt increases the polarity (and presumably the solubility parameters) of the PEO domains, the interfacial tensions between PEO and PI, and PEO and PS are elevated. Thus, a reduction in the overall PEO interfacial area is required, which necessitates additional chain stretching. In consequence, the CSC structure becomes dominant when comparing doped and non-doped samples [171] (Figs. 54 and 55b). 

Figure 22. Variations of the electrical potential and the interfacial tension. The aqueous phases in the inner cylinder are ...

Evidence for an Interfacial Tension Mechanism. The mechanism was later tested with longer Pt/Au rods, various diameters and finally solutions of ethanol/water made up in varying ethanol concentrations. Ethanol was chosen because literature values exist for the interfacial tension of various ethanol/water compositions. Figure 3.3 shows the variation of the product of tension and the oxygen flux with particle speed as evidence in support of a interfacial tension mechanism. 

The second complicating factor is interfacial turbulence (1, 12), very similar to the surface turbulence discussed above. It is readily seen when a solution of 4% acetone dissolved in toluene is quietly placed in contact with water talc particles sprinkled on to the plane oil surface fall to the interface, where they undergo rapid, jerky movements. This effect is related to changes in interfacial tension during mass transfer, and depends quantitatively on the distribution coefficient of the solute (here acetone) between the oil and the water, on the concentration of the solute, and on the variation of the interfacial tension with this concentration. Such spontaneous interfacial turbulence can increase the mass-transfer rate by 10 times 38). 

The variation of interfacial tensions with temperature has been measured by Harkins in the case of a few organic liquids against mercury, and like surface tensions they diminish with rise of temperature. 

For the buffer solution Ph = 5 6 the variation of interfacial tension with the strength does not exceed the experimental error, but in the more alkaline solution we must conclude that either sodium ions or phosphate ions (or both) are positively adsorbed according to the equation... 

Movements in the plane of the interface result from local variations of interfacial tension during the course of mass transfer. These variations may be produced by local variations of any quantity which affects the interfacial tension. Interfaeial motions have been ascribed to variations in interfacial concentration (H6, P6, S33), temperature (A9, P6), and electrical properties (AlO, B19). In ternary systems, variations in concentration are the major factor causing interfacial motion in partially miscible binary systems, interfacial temperature variations due to heat of solution effects are usually the cause. 

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