Interface water-hydrocarbon

The behavior of insoluble monolayers at the hydrocarbon-water interface has been studied to some extent. In general, a values for straight-chain acids and alcohols are greater at a given film pressure than if spread at the water-air interface. This is perhaps to be expected since the nonpolar phase should tend to reduce the cohesion between the hydrocarbon tails. See Ref. 91 for early reviews. Takenaka [92] has reported polarized resonance Raman spectra for an azo dye monolayer at the CCl4-water interface some conclusions as to orientation were possible. A mean-held theory based on Lennard-Jones potentials has been used to model an amphiphile at an oil-water interface one conclusion was that the depth of the interfacial region can be relatively large [93]. 

During the past few years, the determination of the interfacial properties of binary mixtures of surfactants has been an area in which there has been considerable activity on the part of a number of investigators, both in industry and in academia. The Interest in this area stems from the fact that mixtures of two different types of surfactants often have interfacial properties that are better than those of the individual surfactants by themselves. For example, mixtures of two different surface-active components sometimes reduce the interfacial tension at the hydrocarbon/water interface to values far lower than that obtained with the individual surfactants, and certain mixtures of surfactants are better foaming agents than the individual components. For the purpose of this discussion we define synergism as existing in a system when a given property of the mixture can reach a more desirable value than that attainable by either surface-active component of the mixture by itself. 

Figure 9.2 Calculation of the surface packing parameter. Via x I, which determines to some extent the form of the aggregate. For V/(a x 1) c. 1, bilayers are preferentially formed when this ratio is less or more than one, spherical aqueous and reverse micelles are formed, respectively. Self-assembly may be described in terms of the curvature that exists at the hydrocarbon-water interface.

Desorption from the hydrocarbon is a critical part of the growth cycle of petroleum-degrading bacteria. Petroleum is a mixture of thousands of different hydrocarbon molecules. Any particular bacterium is only able to use a part of the petroleum. As the bacteria multiply at the hydrocarbon/water interface of a droplet, the relative amount of nonutilizable hydrocarbon continually increases, until the cells can no longer grow. For bacteria to continue to multiply, they must be able to... 

Pines, O. Gutnick, D. L. (1984). Specific binding of a bacterio-phage at a hydrocarbon-water interface. Journal of Bacteriology, 157, 179-83. 

Rosenberg, M. Rosenberg, E. (1985). Bacterial adherence at the hydrocarbon-water interface. Oil and Petrochemical Pollution, 2, 155-62. 

Aqueous surfactants are another class of catalysts. Substantial rate enhancement is seen in the reaction occurring at the micellar hydrocarbon-water interface, which is ascribed to a concentration of the reactant in the micellar pseudo-phase. Chiral p-nitrophenyl esters derived from phenylalanine are hydrolyzed by a histidine-containing dipeptide at a micellar interphase, at which a very high enantiomer discrimination, kR/ks up to 30.4 at 0°C, is observed (49). As shown in Scheme 20, the enantioselectivity is expressed at the stage at which a transient, zwitter-ionic tetrahedral intermediate leading to the acylimidazole is formed,... 

Case A. Transfer of hydrocarbon from water to hydrocarbon. The transfer of a hydrocarbon solute of surface area A from water to hydrocarbon removes the hydrocarbon-water interface (w = — yHc/w) and creates a hydrocarbon-vacuum and a water-vacuum interface (w = yHC + yw) formation of a cavity in the hydrocarbon solvent creates a hydrocarbon-vacuum interface (w = ync) transfer of the hydrocarbon solute to the hydrocarbon, and collapse of the water-vacuum cavity, loses two hydrocarbon-vacuum surfaces and a water-vacuum surface (w = — 2yHC — yw). The free energy of transfer, AGtrans, is given by A X Sw i.e.,... 

Experimentally, a liquid hydrocarbon/water interface has been reported to be rough, so that the local free energy will fluctuate in time [18]. In the present system, analogous fluctuations at the droplet/water interface will induce position- and time-dependent irregularities of the surface structure, and this will relate with adsorption/entrance channels at the interface. 

Figure 3.25 Cyclopentane hydrate formation from a water droplet (a) initial contact, (b) hydrate shell formation around the water droplet, (c) depressions formed on the hydrate shell, (d) conversion of interior water to hydrate, indicated by darkening, (e) almost completely converted hydrate. (From Taylor, C.J., Adhesion Force between Hydrate Particles andMacroscopic Investigation of Hydrate Film Growth at the Hydrocarbon/Water Interface, Master s Thesis, Colorado School of Mines, Golden, CO, (2006). With permission.)...

A conceptual picture of the proposed mechanism for hydrate film growth at the hydrocarbon-water interface based on the above experimental results is given... 

Taylor, C.J., Adhesion Force between Hydrate Particles and Macroscopic Investigation of Hydrate Film Growth at the Hydrocarbon/Water Interface, Masters Thesis, Colorado School of Mines, Golden, CO (2006). 

The contact angle between water and glass is increased considerably by even less than an adsorbed monolayer of greasy material such as fatty acid. Wa is decreased, since some of the glass-water interface is replaced by hydrocarbon-water interface (Figure 6.4a) hence, from the Young-Dupr6 equation, 0 increases. 

It can be seen that for the A/W interface y decreases from the value for water ( 72 mN m-1), reaching about 25-30 mN m-1 near the cmc. For the O/W interface y decreases from 50 mN m-1 (for a pure hydrocarbon-water interface) to l-5 mN m-1. Clearly the rate of reduction of y with log C below the cmc and the limiting y reached at and above the cmc depend on the nature of surfactant and the interface. 

Thoma, M. Mohwald, H. Phospholipid monolayers at hydrocarbon/water interfaces. J. Colloid Interface Sci. 1994,162, 340. 

TABLE 1.1. Comparison of the free energy of adsorption for PNP at the air/water and hydrocarbon/water interfaces. 

Considerable care needs to be taken in extracting the interfacial concentration from the SHG intensities because of the interaction between surface density and surface order on the SHG process [49]. Table 1 shows a comparison of the values of Aaresults obtained at the dodecane/water interface where different isotherms were used to fit the SHG data suggest that the determination of—AadsG° at the heptane/water interface using only a Langmuir isotherm gives a value that is too high and thus this value should be re-examined. 

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