Interface water-benzene

The Gibbs equation allows the amount of surfactant adsorbed at the interface to be calculated from the interfacial tension values measured with different concentrations of surfactant, but at constant counterion concentration. The amount adsorbed can be converted to the area of a surfactant molecule. The co-areas at the air-water interface are in the range of 4.4-5.9 nm2/molecule [56,57]. A comparison of these values with those from molecular models indicates that all four surfactants are oriented normally to the interface with the carbon chain outstretched and closely packed. The co-areas at the oil-water interface are greater (heptane-water, 4.9-6.6 nm2/molecule benzene-water, 5.9-7.5 nm2/molecule). This relatively small increase of about 10% for the heptane-water and about 30% for the benzene-water interface means that the orientation at the oil-water interface is the same as at the air-water interface, but the a-sulfo fatty acid ester films are more expanded [56]. 

Supercomputers become more and more useful, and the Insights they can generate become more and more unique, as the complexity of the system modelled Is Increased. Thus Interfaclal phenomena are a very natural field for supercomputation. In addition to the examples In this volume It may be useful to mention the work of Llnse on liquid-liquid benzene-water interfaces, which he studied with 504 H2O molecules, 144 CgHg molecules, and 3700 Interaction sites. He generated over 50 million configurations In 56 hours on a Cray-lA, and he was able to quantitatively assess the sharpness of the Interfaclal density gradient, which Is very hard to probe experimentally. Similarly Spohr and Helnzlnger have studied orientational polarization of H2O molecules at a metallic Interface, which is also hard to probe experimentally. 

To the Grignard solution, 75 g. (71.5 cc., 0.5 mole) of ethyl benzoate (Org. Syn. 10, 51) in 200 cc. of dry benzene (Note 2) is added at such a rate that the mixture refluxes gently. The flask is cooled in a pan of cold water during the addition, which requires about an hour. After the addition is complete, the mixture is refluxed for an hour on a steam bath. The reaction mixture is cooled in an ice-salt bath and then poured slowly, with constant stirring, into a mixture of 1.5 kg. of cracked ice and 50 cc. of concentrated sulfuric acid. The mixture is stirred at intervals until all the solid which separates at the benzene-water interface has dissolved. If necessary, 50 g. of ammonium chloride is added to facilitate the decomposition of the magnesium salt, and additional benzene may be added if the amount present... 

Using 379.5 and 34.0 erg cm-2, respectively, as the values of y for the mercury-water and benzene-water interfaces, compare the observed contact angles with the predictions of Young s equation. Comment on the fact that constant values are used for yHg w and ybeniene.w... 

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. 

Tsionski and coworkers extended the study to the electron transfer through a lipid monolayer at a benzene-water interface [67]. The electron transfer reactions between the oxidized form of zinc porphyrin (ZnPor+) in a benzene phase and the reduced form of a metal complex (R,... 

R= Ru(CN)6 -, Mo(CN)8 -, Fe(CN)6 -, and so forth (Table 2)) in an aqueous phase have been surveyed. At the probe microelectrode surface, ZnPor+ was oxidized to ZuFor" ". When the probe is positioned close to the benzene-water interface, ZnPor+ is reduced back to ZnPor by accepting an electron from R in the aqueous phase at the liquid-liquid interface. In the experiment, the driving force was controlled with two parameters the difference in standard potentials of the redox mediators in benzene and in water (AE ), and the interfacial potential drop (A ), which is controllable by varying the concentration ratio of a base electrolyte such as Cl04 in the two Kquids. The driving force dependence on the electron transfer rate at the liquid-liquid interface has been shown in the literature in the absence and presence of the monolayer. The existence of the monolayer lowers the electron transfer... 

Long before interfacial charge transfer reactions began to be studied systematically. Bell [8] observed a multielectron transfer reaction across a benzene/water interface. This involved permanganate oxidation of benzoyl-o-tol-uidine to benzoylanthranilic acid ... 

Figure 7.7 Orientation of caproic aad molecules across a benzene-water interface...

When measuring the surface pressure isotherms, it is desirable that the values of the interfacial tension are not time-dependent. In this case, in the interfacial region a state is reached close to the equilibrium for the surfactant distribution between the phases [55]." If the surfactant is soluble in both phases, one should be careful in calculating the surface excess in such systems, and the surfactant distribution coefficient should be determined independently. For instance, trioctylmethylammonium chloride (Oct3MeNCl) in the benzene-water system has a distribution coefficient of the order of 10 [57]. The surface pressure isotherms at the benzene-water interface are almost independent of the phase in which Oct3MeNCl is dissolved. It means that in both cases Oct3MeNCl is almost completely located in the benzene phase, i.e. the surfactant distribution equilibrium is reached at the interface. Apparently, the anomalies in the... 

Linse, R, Monte-Carlo simulation of liquid-liquid benzene-water interface, J Ghent Phys, Wol 86, (1987) p. 4177. 

Liquid-liquid interfacial tensions exist for immiscible liquid-liquid systems, e.g. water or glycols with hydrocarbons and water-alcohols. In most cases, the interfacial tension value is between the surface tensions of the two liquids involved, e.g. the value of 51 mN m reported for water-hexane is between the 18 and 72 mN m for hexane and water, respectively. The lower, compared to hexane-water, value for the interfacial tension of benzene-water (35 mN m ) is due to the higher solubility of benzene compared to hexane in water (Figure 3.9). This is due to the weak complexes formed between aromatics and water which exist because of the so-called r -electrons of the aromatic rings. For this reason, the benzene-water interface is much smaller than the hexane-water one and this is why water-benzene has a much lower interfacial tension than the more insoluble water-hexane. 

P. Linse, /. Chem. Phys., 86, 4177 (1987). Monte Carlo Simulation of Liquid-Liquid Benzene-Water Interface. 

The dendrite-like structures were made from highly porous hollow spheres. As the SnOEP became localized at the benzene-water interface, the platinum seeds formed during the photoreduction were able to grow in autocatalytic fashion and form Pt dendrites that eventually became nano foams [60]. 

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