Water-toluene interfacial tension

Fig. 10. Interfacial tensions of toluene Span 85 solutions/water by pendant drop and I.D.T.

Surface tensions of water and methylene iodide measured in our laboratory were 71.8 and 42.8 dyne/cm, respectively. The interfacial tension between these two liquids was 33.2 dyne/cm. The values for surface tension of methylene iodide and the interfacial tension differ from frequently cited literature values, viz. 50.8 and 41.6 dyne/cm, respectively.(33) The difficulties in determining the surface tension of methylene iodide consistently has been alluded to in the literature.(33,34) On the other hand, the DCA instrument we used to determine the surface tension of the liquids is quite reliable. For example, the measured surface tension for toluene, 28.2 dyne/cm, and the interfacial tension between toluene and water, 34.6 dyne/cm, are in good agreement with literature values, 28.5 and 36.1 dyne/cm.(30). With this demonstrated accuracy, the values obtained in our laboratory were used in the calculations described by equations 4-6. 

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). 

As far as water/toluene interfacial tension is measured, it appears that the saturation of the interface is reached more quickly with PTBS (P0)2 star-shaped block copolymers (Table VII) this molecular architecture seems to be more efficient to fill in the interface (3 0 ... 

Figure 7 compares the water/toluene interfacial tensions measured in the presence of various commercial surfactants and P0/PS based diblock (8) and star-shaped copolymers the higher activity of the star-shaped block copolymers over a broad range of concentrations is clearly put in evidence. 

TABLE VII Toluene/Water Interfacial Tension of Diblock and Star-shaped Copolymers at Different Concentrations (20°C)... 

Figure 7. Comparison of the toluene-water interfacial tension obtained from commercial surfactants and polyoxirane-based block copolymers with different...

The use of sc C02 instead of toluene as a solvent leads to some rate enhancement in these two systems, although it is clear that this activity is still not practical for most nonpolar, nonvolatile substrates. Significant improvements to the biphasic water/supercritical C02 system were accomplished by forming H20/C02 emulsions using newly developed surfactants (Jacobson et al., 1999). Three different surfactants were used that form water in C02 (w/c) or C02 in water (c/w) emulsions (1) anionic surfactant perfluoropolyether ammonium carboxylate, (2) cationic Lodyne 106A, and (3) nonionic poly(butylene oxide)-h-poly(ethylene oxide). The low interfacial tension, y, between water and C02 (17 mNm-1 at pressures above 70 bar), which is significantly lower than water/alkane systems (30-60 mNm-1),... 

Figure 3.15 Suspension-air and suspension-toluene surface and interfacial tensions for aqueous suspensions of Na-mont-morillonite. The broken lines show the values measured for pure water. From data reported in Schramm and I—lepler [139].

Carbon tetrachloride/water Toluene/water <)> = 0.00-0.20 [50] y — interfacial tension between the... 

There is little applicability of this mechanism to stabilization by small particles. For instance, using the values exemplified earlier, the energy required to remove a particle with a diameter of 200 nm (approximate actual size of the particles in the above study) and a contact angle of 150° from a water/toluene interface (interfacial tension = 0.036 N/m) is 4927 kT, while a 5 nm particle in the same system has a binding energy of 3 kT. Therefore, a 200 nm particle will be irreversibly bound to the interface, while a 5nm particle should not be held at the interface and if stabilization occurs, it must take place by a different mechanism. 

The variation of the desorption energy with the contact angle is displayed in Fig. 3. Binks and Lumsdon investigated a toluene-water system with constant interfacial tension of 36mN/m by using silica nanoparticles of constant radius of lOnm and various wettabilities [4]. At a contact angle of 90°, a maximum in desorption... 

Fig. 5 Dynamic interfacial tension (y) measurements of a toluene-water interface during adsorption of 6-nm CdSe nanoparticles to a pendant water drop in toluene (CdSe concentration was 1.58 x 10-6 mol/L). The circles mark the time at which TEM samples shown in Fig. 6 were prepared. The inset depicts the data on a logarithmic time scale. Reprinted with permission from Physical Chemistry Chemical Physics [50], Copyright (2007) RSC Publishing...

Figure 8, Water-toluene interfacial tension vs. C mHMHEC concentration. Reproduced with permission from ref. 3. Copyright 1982 Wiley.)...

Interfacial tension is an important property in the process design of liquid-liquid processes. The decrement of interfacial tension between both phases leads to an increased interfacial area [135]. Because the volumetric rate of extraction was found to be dependent on the interfacial area, interfacial tension data are useful in understanding the effect of interfacial area on the volumetric rate of extraction and overall reaction rates for a PT-catalyzed reaction. Dutta and Patil [136] reported that the effect on the interfacial tension of the water/toluene system has been studied in the presence of four PT catalysts, i.e., tricaprylmethyl ammonium chloride, hexadecyltrimethyl ammonium chloride, hexadecy-trimethyl ammonium bromide, and hexadecyltributyl phosphonium bromide. The decrease in interfacial tension by surfactants increases the interfacial contact area, enhancing the volumetric rate of extraction. 

Juang and Liu [74,75] presented that the interfacial tensions between water/ -hexane and water/toluene in the synthesis of ether-ester compounds by PTC could be measured. These two-phase systems contained PT catalyst, an aqueous phase reactant, and/or alkali. The interfacial data could be well described by the Gibbs adsorption equation coupled with the Langmuir monolayer isotherm. 

Figure 9 Interfacial tension at water droplets in toluene containing increasing amounts of bitumen. The solid line on the figure represents toluene — water interfacial tension.

Three systems were selected and their properties published (Misek, 1979). These are water-toluene-acetone, water-methyl isobutyl-ketone (MIBK)-acetic acid and water-butanol-succinic acid, representing systems with high, medium and low interfacial tensions respectively. 

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

Interfacial tension has been deduced from the spectrum of the light scattered by the interface. The results are relative to water-toluene-sodium dodecyl sulfate (SDS)-butanol mixtures either in the two phase, or in the three phase region of the phase diagram. Values down to 10 dynes/cm have been measured. Measurements down to 10 - 10 6 dynes/cm are expected to be achievable with this technique. 

---