Octane, interfacial tension

For long-chain alcohol esters it is interesting to see that the interfacial tension between a 0.01 wt % aqueous solution and octane or xylene has a minimum for ester sulfonates with a total 22 carbon atoms in the fatty acid chain and the ester chain [60]. The balance in length between the two chains has only a poor effect. Thus, a-sulfonated fatty acid esters with a total number of 22-26 carbon atoms in the molecule have excellent interfacial activities. To attain the same magnitude in the interfacial tension between linear alkylbenzenesulfonate (LAS) solution and octane, the required concentration of LAS is 0.1 wt %. This is 10 times the concentration needed for a-sulfonated fatty acid esters [60]. 

In n-octane/aqueous systems at 27°C, TRS 10-80 has been shown to form a surfactant-rich third phase, or a thin film of liquid crystals (see Figure 1), with a sharp interfacial tension minimum of about 5x10 mN/m at 15 g/L NaCI concentration f131. Similarly, in this study the bitumen/aqueous tension behavior of TRS 10-80 and Sun Tech IV appeared not to be related to monolayer coverage at the interface (as in the case of Enordet C16 18) but rather was indicative of a surfactant-rich third phase between oil and water. The higher values for minimum interfacial tension observed for a heavy oil compared to a pure n-alkane were probably due to natural surfactants in the crude oil which somewhat hindered the formation of the surfactant-rich phase. This hypothesis needs to be tested, but the effect is not unlike that of the addition of SDS (which does not form liquid crystals) in partially solubilizing the third phase formed by TRS 10-80 or Aerosol OT at the alkane/brine interface Til.121. 

The view that the monomers are confined to the reverse micellar pseudophase is supported by interfacial tension data (67), which demonstrate that in a two-phase octane/water system, partially hydrolyzed TEOS species partition preferentially into the aqueous phase. The interfacial tension determined at the octane/water interface for samples prepared with precursor ethanolic solutions of different water-to-TEOS molar ratios (h - 0, 0.29, and 0.55) are presented in Figure 2.2.14 (67). As can be seen, for TEOS concentrations below about 4 X 10- 1 M, the octane/water interfacial tension is independent of the concentration of TEOS species in the organic phase... 

Fig. 2.2.14 Effect of the water-to-TEOS molar ratio (/i) in the precursor ethanolic solution on the interfacial tension at the octane/water interface [TEOS], referred to the conjugate organic phase. (From Ref. 67.)...

EXAMPLE 6.5 Estimation of Interfacial Tensions Using the Girifalco-Good-Fowkes Equation. The following are the interfacial tensions for the various two-phase surfaces formed by n-octane (O), water (W), and mercury (Hg) for n-octane-water, y = 50.8 mJ m 2 for n-octane-mercury, y = 375 mJ m 2 and for water-mercury, y = 426 mJ m 2. Assuming that only London forces operate between molecules of the hydrocarbon, use Equation (100) to estimate y d for water and mercury. Do the values thus obtained make sense Take y values from Table 6.1 for the interfaces with air of these liquids. 

Table 4.3 shows the surface tensions and the interfacial tensions against water at 20°C. Based on the interfacial tension or surface tension measurement, it is possible to calculate the water-water dispersion and hydrogen bonding forces. The value of the surface tension is the sum of the combined dispersion and the hydrogen bonding forces. For example, for the water-n-octane system,... 

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 ... 

The structure of the liquid- liquid interfadal layer depends on the difference in polarity between the two liquids (Kaeble, 1971). Asymmetric molecules of some liquids display a molecular orientation on the interface which is indicative of their structure. Thus, interfacial tension at the octane-water interlace is SO.S nm/m whereas at the octanol-water interne it is only 8.8 nm/m. Reduction of inter dal tension in the latter case points to the orientation of octanol hydroxyl groups toward water, in other words to the structure and polarity of the interfadal layer. Because of such an orientation, the stimulus for adsorption of other asymmetric molecules on the interface is decreased. A similar pattern is typical of the homologous series of lower attcy] acrylates at the interface with water the carbonyl groups of their asymmetrical molecules are oriented toward water this orientation is more eSective the higher the polarization of the carbonyl, i.e the smaller the alkyl. Interfadal tension decreases in the same order from 27.2 nm/m for hexyl acrylate (Yeliseyeva et at, 1978) to 8 nm/m for methyl acrylate (datum from our laboratory by A, Vasilenko). 

Liquid-liquid interfacial tensions can in principle also be obtained by simulations, but for the time being, the technical problems are prohibitive. Benjamin studied the dynamics of the water-1,2-dichloroethane interface in connection with a study of transfer rates across the interface, but gave no interfacial tensions. In a subsequent study the interface between nonane and water was simulated by MD, with some emphasis on the dynamics. Nonane appears to orient relatively flat towards water. The same trend, but weaker, was found with respect to vapour. Water dipoles adjacent to nonane adsorb about flat, with a broad distribution the ordering is a few molecular layers deep. Fukunishi et al. studied the octane-water Interface, but with a very low number of molecules. Their approach differed somewhat from that taken in the simulations described previously they computed the potential of mean force for transferring a solute molecule to the interface. The interfacial tension was 57 11 mN m", which is in the proper range (experimental value 50.8) but of course not yet discriminative (for all hydrocarbons the interfacial tension with water is very similar). In an earlier study Linse investigated the benzene-water interface by MC Simulation S He found that the water-benzene orientation in the interface was similar to that in dilute solution of benzene in water. At the interface the water dipoles tend to assume a parallel orientation. The author did not compute a x -potential. Obviously, there is much room for further developments. 

Effect of salinity on interfacial tension and partition coefficient for TRS 10-80/n-octane system. 

Figure 14.4 Interfacial tensions of n-octane against water in the presence of various surfactants above the cmc as a function of temperature.

Figure 1.15(a) shows the variation of the interfacial tension aab with the temperature for the system water-n-octane-Ci0E4 [17] and aab as a function of the composition of the amphiphilic film 8Vji (8v,i is the volume fraction and can be calculated by replacing m in Eq. (1.9) with V) in the quaternary system FbO-w-octane-P-QGj-QEo at T = 25°C (Fig. 1.15(b)) [90]. In both cases a log-scale is used for the interfacial tension because of the strong variation over several orders of magnitudes. 

Figure 1.15 Water/oil interfacial tension crab (plotted on log-scale) as function of the relevant tuning parameter, (a) Variation of crab with temperature T, exemplarily shown for the water-n-octane-C- oE4 system [17]. (b) Variation of crab with the composition of the amphiphilic film 8yi in the quaternary system hbO-n-octane-fS-CsG-i-CsEo at T = 25°C [90]. Both systems show that the water/oil interfacial tension runs through a distinct minimum in the middle of the three-phase region. The full line is calculated considering the bending energy difference between a curved amphiphilic film in the microemulsion and the flat film of the macroscopic interface [96].

In Fig. 1.16, the variation of the water/oil interfacial tension with temperature is shown for four representative systems, namely water-n-octane-C6E2, CgEj, Q0E4 and Ci2E5. In... 

Figure 1.16 Temperature dependence of the water/oil interfacial tension

Figure 1.17 shows the scaling of interfacial tension curves for four ternary water-n-octane-QEj systems (see Fig. 1.16) and the quaternary system water-n-octane-(3-C8Gi-C Eo (see Fig. 1.15). As canbe seen, the scaled

Figure 1.23 Variation of the water (shown as hollow symbols) and n-octane (shown as filled symbols) diffusion coefficients DA and Dg [115], the length scale [25], the mean curvature H and the water/oil interfacial tension (jat, as function of the temperature for the system hbO-n-octane-CnEs. Note that at the mean temperature of the three-phase body f the diffusion of water and oil molecules is equal (points to bicontinuity), the length scale runs through a maximum, the curvature change sign and the water/oil interfacial shows an extreme minimum.

The minimum of the interfacial tension for the system E O/NaCl-triolein-CioEs corresponds to (fab = 2.6 10 1 mN m-1 at f = 43.5°C. The variation of aab as a function of T is similar to the n-alkane systems with the curve showing the typical V-shape (Fig. 11.8(b)). The value of the interfacial tension between water and oil is comparable to the inefficient H20-n-octane-C4Ei system [48]. However, compared to the pure water-oil interfacial tension (50 mN m 1), it is still two orders of magnitude lower. 

The results of one of these comparisons for a typical group II surfactant, sulfonated 4( diethylphenyl )nonane, are shown in figure 4. The plots are of interfacial tension vs. alkane carbon number of EACN of the crude. Another comparison is shown in figure 5, this time for a mixture of two group II surfactants, sulfonated 5(p butylphenyl) decane and sulfonated 4(p butylphenyl) octane. 

Figure 6 Interfacial tension between oil and water in the presence of a saturated surfactant monolayer versus temperature. The surfactants are alkyl polyoxyethylene glycol ethers C12E5 with hexane, C10E4 with octane, and CsEi with decane. The vertical bars indicate the transition temperatures between the different Winsor systems. (Data from Ref. 50.)...

Figure 3 Isotherms of interfacial tension and surface excess for acidic chelating extractant at octane/water (O/W) and toluene/ water (T/W) interface.

In the following section the calculated interfacial tensions for some typical components are presented as a function of temperature and compared to experimental data. In Figure la the interfacial tension is shown for octane. It is easy to see that the agreement between experiment and calculation is good. The results found here are similar to those obtained by Carey et al. [7]. 

Some of the computed interfacial tensions have been included in Figures 2a and b (solid lines). In the first figure the results of the calculations for octane are presented. These results do not show a large deviation from the experiments, an effect that has been observed for the PR equation of state as well. This is not very surprising since both the PR equation and APACT are able to describe the thermodynamic properties of the alkanes accurately. 

Pigure 2. The interfacial tensions of octane (a) and water (b). APACT compared to experiments [17]. Dashed line c = c(T), solid line c c(T). 

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